Network Working Group D. Cooper
Request for Comments: 5280 NIST
Obsoletes: 3280, 4325, 4630 S. Santesson
Category: Standards Track Microsoft
S. Farrell
Trinity College Dublin
S. Boeyen
Entrust
R. Housley
Vigil Security
W. Polk
NIST
May 2008
Internet X.509 Public Key Infrastructure Certificate
and Certificate Revocation List (CRL) Profile
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This memo profiles the X.509 v3 certificate and X.509 v2 certificate
revocation list (CRL) for use in the Internet. An overview of this
approach and model is provided as an introduction. The X.509 v3
certificate format is described in detail, with additional
information regarding the format and semantics of Internet name
forms. Standard certificate extensions are described and two
Internet-specific extensions are defined. A set of required
certificate extensions is specified. The X.509 v2 CRL format is
described in detail along with standard and Internet-specific
extensions. An algorithm for X.509 certification path validation is
described. An ASN.1 module and examples are provided in the
appendices.
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RFC 5280 PKIX Certificate and CRL Profile May 2008
Table of Contents
1. Introduction ....................................................4
2. Requirements and Assumptions ....................................6
2.1. Communication and Topology .................................7
2.2. Acceptability Criteria .....................................7
2.3. User Expectations ..........................................7
2.4. Administrator Expectations .................................8
3. Overview of Approach ............................................8
3.1. X.509 Version 3 Certificate ................................9
3.2. Certification Paths and Trust .............................10
3.3. Revocation ................................................13
3.4. Operational Protocols .....................................14
3.5. Management Protocols ......................................14
4. Certificate and Certificate Extensions Profile .................16
4.1. Basic Certificate Fields ..................................16
4.1.1. Certificate Fields .................................17
4.1.1.1. tbsCertificate ............................18
4.1.1.2. signatureAlgorithm ........................18
4.1.1.3. signatureValue ............................18
4.1.2. TBSCertificate .....................................18
4.1.2.1. Version ...................................19
4.1.2.2. Serial Number .............................19
4.1.2.3. Signature .................................19
4.1.2.4. Issuer ....................................20
4.1.2.5. Validity ..................................22
4.1.2.5.1. UTCTime ........................23
4.1.2.5.2. GeneralizedTime ................23
4.1.2.6. Subject ...................................23
4.1.2.7. Subject Public Key Info ...................25
4.1.2.8. Unique Identifiers ........................25
4.1.2.9. Extensions ................................26
4.2. Certificate Extensions ....................................26
4.2.1. Standard Extensions ................................27
4.2.1.1. Authority Key Identifier ..................27
4.2.1.2. Subject Key Identifier ....................28
4.2.1.3. Key Usage .................................29
4.2.1.4. Certificate Policies ......................32
4.2.1.5. Policy Mappings ...........................35
4.2.1.6. Subject Alternative Name ..................35
4.2.1.7. Issuer Alternative Name ...................38
4.2.1.8. Subject Directory Attributes ..............39
4.2.1.9. Basic Constraints .........................39
4.2.1.10. Name Constraints .........................40
4.2.1.11. Policy Constraints .......................43
4.2.1.12. Extended Key Usage .......................44
4.2.1.13. CRL Distribution Points ..................45
4.2.1.14. Inhibit anyPolicy ........................48
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4.2.1.15. Freshest CRL (a.k.a. Delta CRL
Distribution Point) ......................48
4.2.2. Private Internet Extensions ........................49
4.2.2.1. Authority Information Access ..............49
4.2.2.2. Subject Information Access ................51
5. CRL and CRL Extensions Profile .................................54
5.1. CRL Fields ................................................55
5.1.1. CertificateList Fields .............................56
5.1.1.1. tbsCertList ...............................56
5.1.1.2. signatureAlgorithm ........................57
5.1.1.3. signatureValue ............................57
5.1.2. Certificate List "To Be Signed" ....................58
5.1.2.1. Version ...................................58
5.1.2.2. Signature .................................58
5.1.2.3. Issuer Name ...............................58
5.1.2.4. This Update ...............................58
5.1.2.5. Next Update ...............................59
5.1.2.6. Revoked Certificates ......................59
5.1.2.7. Extensions ................................60
5.2. CRL Extensions ............................................60
5.2.1. Authority Key Identifier ...........................60
5.2.2. Issuer Alternative Name ............................60
5.2.3. CRL Number .........................................61
5.2.4. Delta CRL Indicator ................................62
5.2.5. Issuing Distribution Point .........................65
5.2.6. Freshest CRL (a.k.a. Delta CRL Distribution
Point) .............................................67
5.2.7. Authority Information Access .......................67
5.3. CRL Entry Extensions ......................................69
5.3.1. Reason Code ........................................69
5.3.2. Invalidity Date ....................................70
5.3.3. Certificate Issuer .................................70
6. Certification Path Validation ..................................71
6.1. Basic Path Validation .....................................72
6.1.1. Inputs .............................................75
6.1.2. Initialization .....................................77
6.1.3. Basic Certificate Processing .......................80
6.1.4. Preparation for Certificate i+1 ....................84
6.1.5. Wrap-Up Procedure ..................................87
6.1.6. Outputs ............................................89
6.2. Using the Path Validation Algorithm .......................89
6.3. CRL Validation ............................................90
6.3.1. Revocation Inputs ..................................91
6.3.2. Initialization and Revocation State Variables ......91
6.3.3. CRL Processing .....................................92
7. Processing Rules for Internationalized Names ...................95
7.1. Internationalized Names in Distinguished Names ............96
7.2. Internationalized Domain Names in GeneralName .............97
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7.3. Internationalized Domain Names in Distinguished Names .....98
7.4. Internationalized Resource Identifiers ....................98
7.5. Internationalized Electronic Mail Addresses ..............100
8. Security Considerations .......................................100
9. IANA Considerations ...........................................105
10. Acknowledgments ..............................................105
11. References ...................................................105
11.1. Normative References ....................................105
11.2. Informative References ..................................107
Appendix A. Pseudo-ASN.1 Structures and OIDs ....................110
A.1. Explicitly Tagged Module, 1988 Syntax ....................110
A.2. Implicitly Tagged Module, 1988 Syntax ....................125
Appendix B. ASN.1 Notes ..........................................133
Appendix C. Examples .............................................136
C.1. RSA Self-Signed Certificate ..............................137
C.2. End Entity Certificate Using RSA .........................140
C.3. End Entity Certificate Using DSA .........................143
C.4. Certificate Revocation List ..............................147
1. Introduction
This specification is one part of a family of standards for the X.509
Public Key Infrastructure (PKI) for the Internet.
This specification profiles the format and semantics of certificates
and certificate revocation lists (CRLs) for the Internet PKI.
Procedures are described for processing of certification paths in the
Internet environment. Finally, ASN.1 modules are provided in the
appendices for all data structures defined or referenced.
Section 2 describes Internet PKI requirements and the assumptions
that affect the scope of this document. Section 3 presents an
architectural model and describes its relationship to previous IETF
and ISO/IEC/ITU-T standards. In particular, this document's
relationship with the IETF PEM specifications and the ISO/IEC/ITU-T
X.509 documents is described.
Section 4 profiles the X.509 version 3 certificate, and Section 5
profiles the X.509 version 2 CRL. The profiles include the
identification of ISO/IEC/ITU-T and ANSI extensions that may be
useful in the Internet PKI. The profiles are presented in the 1988
Abstract Syntax Notation One (ASN.1) rather than the 1997 ASN.1
syntax used in the most recent ISO/IEC/ITU-T standards.
Section 6 includes certification path validation procedures. These
procedures are based upon the ISO/IEC/ITU-T definition.
Implementations are REQUIRED to derive the same results but are not
required to use the specified procedures.
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Procedures for identification and encoding of public key materials
and digital signatures are defined in [RFC3279], [RFC4055], and
[RFC4491]. Implementations of this specification are not required to
use any particular cryptographic algorithms. However, conforming
implementations that use the algorithms identified in [RFC3279],
[RFC4055], and [RFC4491] MUST identify and encode the public key
materials and digital signatures as described in those
specifications.
Finally, three appendices are provided to aid implementers. Appendix
A contains all ASN.1 structures defined or referenced within this
specification. As above, the material is presented in the 1988
ASN.1. Appendix B contains notes on less familiar features of the
ASN.1 notation used within this specification. Appendix C contains
examples of conforming certificates and a conforming CRL.
This specification obsoletes [RFC3280]. Differences from RFC 3280
are summarized below:
* Enhanced support for internationalized names is specified in
Section 7, with rules for encoding and comparing
Internationalized Domain Names, Internationalized Resource
Identifiers (IRIs), and distinguished names. These rules are
aligned with comparison rules established in current RFCs,
including [RFC3490], [RFC3987], and [RFC4518].
* Sections 4.1.2.4 and 4.1.2.6 incorporate the conditions for
continued use of legacy text encoding schemes that were
specified in [RFC4630]. Where in use by an established PKI,
transition to UTF8String could cause denial of service based on
name chaining failures or incorrect processing of name
constraints.
* Section 4.2.1.4 in RFC 3280, which specified the
privateKeyUsagePeriod certificate extension but deprecated its
use, was removed. Use of this ISO standard extension is neither
deprecated nor recommended for use in the Internet PKI.
* Section 4.2.1.5 recommends marking the policy mappings extension
as critical. RFC 3280 required that the policy mappings
extension be marked as non-critical.
* Section 4.2.1.11 requires marking the policy constraints
extension as critical. RFC 3280 permitted the policy
constraints extension to be marked as critical or non-critical.
* The Authority Information Access (AIA) CRL extension, as
specified in [RFC4325], was added as Section 5.2.7.
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* Sections 5.2 and 5.3 clarify the rules for handling unrecognized
CRL extensions and CRL entry extensions, respectively.
* Section 5.3.2 in RFC 3280, which specified the
holdInstructionCode CRL entry extension, was removed.
* The path validation algorithm specified in Section 6 no longer
tracks the criticality of the certificate policies extensions in
a chain of certificates. In RFC 3280, this information was
returned to a relying party.
* The Security Considerations section addresses the risk of
circular dependencies arising from the use of https or similar
schemes in the CRL distribution points, authority information
access, or subject information access extensions.
* The Security Considerations section addresses risks associated
with name ambiguity.
* The Security Considerations section references RFC 4210 for
procedures to signal changes in CA operations.
The ASN.1 modules in Appendix A are unchanged from RFC 3280, except
that ub-emailaddress-length was changed from 128 to 255 in order to
align with PKCS #9 [RFC2985].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Requirements and Assumptions
The goal of this specification is to develop a profile to facilitate
the use of X.509 certificates within Internet applications for those
communities wishing to make use of X.509 technology. Such
applications may include WWW, electronic mail, user authentication,
and IPsec. In order to relieve some of the obstacles to using X.509
certificates, this document defines a profile to promote the
development of certificate management systems, development of
application tools, and interoperability determined by policy.
Some communities will need to supplement, or possibly replace, this
profile in order to meet the requirements of specialized application
domains or environments with additional authorization, assurance, or
operational requirements. However, for basic applications, common
representations of frequently used attributes are defined so that
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RFC 5280 PKIX Certificate and CRL Profile May 2008
application developers can obtain necessary information without
regard to the issuer of a particular certificate or certificate
revocation list (CRL).
A certificate user should review the certificate policy generated by
the certification authority (CA) before relying on the authentication
or non-repudiation services associated with the public key in a
particular certificate. To this end, this standard does not
prescribe legally binding rules or duties.
As supplemental authorization and attribute management tools emerge,
such as attribute certificates, it may be appropriate to limit the
authenticated attributes that are included in a certificate. These
other management tools may provide more appropriate methods of
conveying many authenticated attributes.
2.1. Communication and Topology
The users of certificates will operate in a wide range of
environments with respect to their communication topology, especially
users of secure electronic mail. This profile supports users without
high bandwidth, real-time IP connectivity, or high connection
availability. In addition, the profile allows for the presence of
firewall or other filtered communication.
This profile does not assume the deployment of an X.500 directory
system [X.500] or a Lightweight Directory Access Protocol (LDAP)
directory system [RFC4510]. The profile does not prohibit the use of
an X.500 directory or an LDAP directory; however, any means of
distributing certificates and certificate revocation lists (CRLs) may
be used.
2.2. Acceptability Criteria
The goal of the Internet Public Key Infrastructure (PKI) is to meet
the needs of deterministic, automated identification, authentication,
access control, and authorization functions. Support for these
services determines the attributes contained in the certificate as
well as the ancillary control information in the certificate such as
policy data and certification path constraints.
2.3. User Expectations
Users of the Internet PKI are people and processes who use client
software and are the subjects named in certificates. These uses
include readers and writers of electronic mail, the clients for WWW
browsers, WWW servers, and the key manager for IPsec within a router.
This profile recognizes the limitations of the platforms these users
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employ and the limitations in sophistication and attentiveness of the
users themselves. This manifests itself in minimal user
configuration responsibility (e.g., trusted CA keys, rules), explicit
platform usage constraints within the certificate, certification path
constraints that shield the user from many malicious actions, and
applications that sensibly automate validation functions.
2.4. Administrator Expectations
As with user expectations, the Internet PKI profile is structured to
support the individuals who generally operate CAs. Providing
administrators with unbounded choices increases the chances that a
subtle CA administrator mistake will result in broad compromise.
Also, unbounded choices greatly complicate the software that process
and validate the certificates created by the CA.
3. Overview of Approach
Following is a simplified view of the architectural model assumed by
the Public-Key Infrastructure using X.509 (PKIX) specifications.
The components in this model are:
end entity: user of PKI certificates and/or end user system that is
the subject of a certificate;
CA: certification authority;
RA: registration authority, i.e., an optional system to which
a CA delegates certain management functions;
CRL issuer: a system that generates and signs CRLs; and
repository: a system or collection of distributed systems that stores
certificates and CRLs and serves as a means of
distributing these certificates and CRLs to end entities.
CAs are responsible for indicating the revocation status of the
certificates that they issue. Revocation status information may be
provided using the Online Certificate Status Protocol (OCSP)
[RFC2560], certificate revocation lists (CRLs), or some other
mechanism. In general, when revocation status information is
provided using CRLs, the CA is also the CRL issuer. However, a CA
may delegate the responsibility for issuing CRLs to a different
entity.
Note that an Attribute Authority (AA) might also choose to delegate
the publication of CRLs to a CRL issuer.
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RFC 5280 PKIX Certificate and CRL Profile May 2008
+---+
| C | +------------+
| e | <-------------------->| End entity |
| r | Operational +------------+
| t | transactions ^
| i | and management | Management
| f | transactions | transactions PKI
| i | | users
| c | v
| a | ======================= +--+------------+ ==============
| t | ^ ^
| e | | | PKI
| | v | management
| & | +------+ | entities
| | <---------------------| RA |<----+ |
| C | Publish certificate +------+ | |
| R | | |
| L | | |
| | v v
| R | +------------+
| e | <------------------------------| CA |
| p | Publish certificate +------------+
| o | Publish CRL ^ ^
| s | | | Management
| i | +------------+ | | transactions
| t | <--------------| CRL Issuer |<----+ |
| o | Publish CRL +------------+ v
| r | +------+
| y | | CA |
+---+ +------+
Figure 1. PKI Entities
3.1. X.509 Version 3 Certificate
Users of a public key require confidence that the associated private
key is owned by the correct remote subject (person or system) with
which an encryption or digital signature mechanism will be used.
This confidence is obtained through the use of public key
certificates, which are data structures that bind public key values
to subjects. The binding is asserted by having a trusted CA
digitally sign each certificate. The CA may base this assertion upon
technical means (a.k.a., proof of possession through a challenge-
response protocol), presentation of the private key, or on an
assertion by the subject. A certificate has a limited valid
lifetime, which is indicated in its signed contents. Because a
certificate's signature and timeliness can be independently checked
by a certificate-using client, certificates can be distributed via
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untrusted communications and server systems, and can be cached in
unsecured storage in certificate-using systems.
ITU-T X.509 (formerly CCITT X.509) or ISO/IEC 9594-8, which was first
published in 1988 as part of the X.500 directory recommendations,
defines a standard certificate format [X.509]. The certificate
format in the 1988 standard is called the version 1 (v1) format.
When X.500 was revised in 1993, two more fields were added, resulting
in the version 2 (v2) format.
The Internet Privacy Enhanced Mail (PEM) RFCs, published in 1993,
include specifications for a public key infrastructure based on X.509
v1 certificates [RFC1422]. The experience gained in attempts to
deploy RFC 1422 made it clear that the v1 and v2 certificate formats
were deficient in several respects. Most importantly, more fields
were needed to carry information that PEM design and implementation
experience had proven necessary. In response to these new
requirements, the ISO/IEC, ITU-T, and ANSI X9 developed the X.509
version 3 (v3) certificate format. The v3 format extends the v2
format by adding provision for additional extension fields.
Particular extension field types may be specified in standards or may
be defined and registered by any organization or community. In June
1996, standardization of the basic v3 format was completed [X.509].
ISO/IEC, ITU-T, and ANSI X9 have also developed standard extensions
for use in the v3 extensions field [X.509][X9.55]. These extensions
can convey such data as additional subject identification
information, key attribute information, policy information, and
certification path constraints.
However, the ISO/IEC, ITU-T, and ANSI X9 standard extensions are very
broad in their applicability. In order to develop interoperable
implementations of X.509 v3 systems for Internet use, it is necessary
to specify a profile for use of the X.509 v3 extensions tailored for
the Internet. It is one goal of this document to specify a profile
for Internet WWW, electronic mail, and IPsec applications.
Environments with additional requirements may build on this profile
or may replace it.
3.2. Certification Paths and Trust
A user of a security service requiring knowledge of a public key
generally needs to obtain and validate a certificate containing the
required public key. If the public key user does not already hold an
assured copy of the public key of the CA that signed the certificate,
the CA's name, and related information (such as the validity period
or name constraints), then it might need an additional certificate to
obtain that public key. In general, a chain of multiple certificates
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may be needed, comprising a certificate of the public key owner (the
end entity) signed by one CA, and zero or more additional
certificates of CAs signed by other CAs. Such chains, called
certification paths, are required because a public key user is only
initialized with a limited number of assured CA public keys.
There are different ways in which CAs might be configured in order
for public key users to be able to find certification paths. For
PEM, RFC 1422 defined a rigid hierarchical structure of CAs. There
are three types of PEM certification authority:
(a) Internet Policy Registration Authority (IPRA): This
authority, operated under the auspices of the Internet
Society, acts as the root of the PEM certification hierarchy
at level 1. It issues certificates only for the next level
of authorities, PCAs. All certification paths start with the
IPRA.
(b) Policy Certification Authorities (PCAs): PCAs are at level 2
of the hierarchy, each PCA being certified by the IPRA. A
PCA shall establish and publish a statement of its policy
with respect to certifying users or subordinate certification
authorities. Distinct PCAs aim to satisfy different user
needs. For example, one PCA (an organizational PCA) might
support the general electronic mail needs of commercial
organizations, and another PCA (a high-assurance PCA) might
have a more stringent policy designed for satisfying legally
binding digital signature requirements.
(c) Certification Authorities (CAs): CAs are at level 3 of the
hierarchy and can also be at lower levels. Those at level 3
are certified by PCAs. CAs represent, for example,
particular organizations, particular organizational units
(e.g., departments, groups, sections), or particular
geographical areas.
RFC 1422 furthermore has a name subordination rule, which requires
that a CA can only issue certificates for entities whose names are
subordinate (in the X.500 naming tree) to the name of the CA itself.
The trust associated with a PEM certification path is implied by the
PCA name. The name subordination rule ensures that CAs below the PCA
are sensibly constrained as to the set of subordinate entities they
can certify (e.g., a CA for an organization can only certify entities
in that organization's name tree). Certificate user systems are able
to mechanically check that the name subordination rule has been
followed.
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RFC 1422 uses the X.509 v1 certificate format. The limitations of
X.509 v1 required imposition of several structural restrictions to
clearly associate policy information or restrict the utility of
certificates. These restrictions included:
(a) a pure top-down hierarchy, with all certification paths
starting from IPRA;
(b) a naming subordination rule restricting the names of a CA's
subjects; and
(c) use of the PCA concept, which requires knowledge of
individual PCAs to be built into certificate chain
verification logic. Knowledge of individual PCAs was
required to determine if a chain could be accepted.
With X.509 v3, most of the requirements addressed by RFC 1422 can be
addressed using certificate extensions, without a need to restrict
the CA structures used. In particular, the certificate extensions
relating to certificate policies obviate the need for PCAs and the
constraint extensions obviate the need for the name subordination
rule. As a result, this document supports a more flexible
architecture, including:
(a) Certification paths start with a public key of a CA in a
user's own domain, or with the public key of the top of a
hierarchy. Starting with the public key of a CA in a user's
own domain has certain advantages. In some environments, the
local domain is the most trusted.
(b) Name constraints may be imposed through explicit inclusion of
a name constraints extension in a certificate, but are not
required.
(c) Policy extensions and policy mappings replace the PCA
concept, which permits a greater degree of automation. The
application can determine if the certification path is
acceptable based on the contents of the certificates instead
of a priori knowledge of PCAs. This permits automation of
certification path processing.
X.509 v3 also includes an extension that identifies the subject of a
certificate as being either a CA or an end entity, reducing the
reliance on out-of-band information demanded in PEM.
This specification covers two classes of certificates: CA
certificates and end entity certificates. CA certificates may be
further divided into three classes: cross-certificates, self-issued
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certificates, and self-signed certificates. Cross-certificates are
CA certificates in which the issuer and subject are different
entities. Cross-certificates describe a trust relationship between
the two CAs. Self-issued certificates are CA certificates in which
the issuer and subject are the same entity. Self-issued certificates
are generated to support changes in policy or operations. Self-
signed certificates are self-issued certificates where the digital
signature may be verified by the public key bound into the
certificate. Self-signed certificates are used to convey a public
key for use to begin certification paths. End entity certificates
are issued to subjects that are not authorized to issue certificates.
3.3. Revocation
When a certificate is issued, it is expected to be in use for its
entire validity period. However, various circumstances may cause a
certificate to become invalid prior to the expiration of the validity
period. Such circumstances include change of name, change of
association between subject and CA (e.g., an employee terminates
employment with an organization), and compromise or suspected
compromise of the corresponding private key. Under such
circumstances, the CA needs to revoke the certificate.
X.509 defines one method of certificate revocation. This method
involves each CA periodically issuing a signed data structure called
a certificate revocation list (CRL). A CRL is a time-stamped list
identifying revoked certificates that is signed by a CA or CRL issuer
and made freely available in a public repository. Each revoked
certificate is identified in a CRL by its certificate serial number.
When a certificate-using system uses a certificate (e.g., for
verifying a remote user's digital signature), that system not only
checks the certificate signature and validity but also acquires a
suitably recent CRL and checks that the certificate serial number is
not on that CRL. The meaning of "suitably recent" may vary with
local policy, but it usually means the most recently issued CRL. A
new CRL is issued on a regular periodic basis (e.g., hourly, daily,
or weekly). An entry is added to the CRL as part of the next update
following notification of revocation. An entry MUST NOT be removed
from the CRL until it appears on one regularly scheduled CRL issued
beyond the revoked certificate's validity period.
An advantage of this revocation method is that CRLs may be
distributed by exactly the same means as certificates themselves,
namely, via untrusted servers and untrusted communications.
One limitation of the CRL revocation method, using untrusted
communications and servers, is that the time granularity of
revocation is limited to the CRL issue period. For example, if a
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RFC 5280 PKIX Certificate and CRL Profile May 2008
revocation is reported now, that revocation will not be reliably
notified to certificate-using systems until all currently issued CRLs
are scheduled to be updated -- this may be up to one hour, one day,
or one week depending on the frequency that CRLs are issued.
As with the X.509 v3 certificate format, in order to facilitate
interoperable implementations from multiple vendors, the X.509 v2 CRL
format needs to be profiled for Internet use. It is one goal of this
document to specify that profile. However, this profile does not
require the issuance of CRLs. Message formats and protocols
supporting on-line revocation notification are defined in other PKIX
specifications. On-line methods of revocation notification may be
applicable in some environments as an alternative to the X.509 CRL.
On-line revocation checking may significantly reduce the latency
between a revocation report and the distribution of the information
to relying parties. Once the CA accepts a revocation report as
authentic and valid, any query to the on-line service will correctly
reflect the certificate validation impacts of the revocation.
However, these methods impose new security requirements: the
certificate validator needs to trust the on-line validation service
while the repository does not need to be trusted.
3.4. Operational Protocols
Operational protocols are required to deliver certificates and CRLs
(or status information) to certificate-using client systems.
Provisions are needed for a variety of different means of certificate
and CRL delivery, including distribution procedures based on LDAP,
HTTP, FTP, and X.500. Operational protocols supporting these
functions are defined in other PKIX specifications. These
specifications may include definitions of message formats and
procedures for supporting all of the above operational environments,
including definitions of or references to appropriate MIME content
types.
3.5. Management Protocols
Management protocols are required to support on-line interactions
between PKI user and management entities. For example, a management
protocol might be used between a CA and a client system with which a
key pair is associated, or between two CAs that cross-certify each
other. The set of functions that potentially need to be supported by
management protocols include:
(a) registration: This is the process whereby a user first makes
itself known to a CA (directly, or through an RA), prior to
that CA issuing a certificate or certificates for that user.
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(b) initialization: Before a client system can operate securely,
it is necessary to install key materials that have the
appropriate relationship with keys stored elsewhere in the
infrastructure. For example, the client needs to be securely
initialized with the public key and other assured information
of the trusted CA(s), to be used in validating certificate
paths.
Furthermore, a client typically needs to be initialized with
its own key pair(s).
(c) certification: This is the process in which a CA issues a
certificate for a user's public key, and returns that
certificate to the user's client system and/or posts that
certificate in a repository.
(d) key pair recovery: As an option, user client key materials
(e.g., a user's private key used for encryption purposes) may
be backed up by a CA or a key backup system. If a user needs
to recover these backed-up key materials (e.g., as a result
of a forgotten password or a lost key chain file), an on-line
protocol exchange may be needed to support such recovery.
(e) key pair update: All key pairs need to be updated regularly,
i.e., replaced with a new key pair, and new certificates
issued.
(f) revocation request: An authorized person advises a CA of an
abnormal situation requiring certificate revocation.
(g) cross-certification: Two CAs exchange information used in
establishing a cross-certificate. A cross-certificate is a
certificate issued by one CA to another CA that contains a CA
signature key used for issuing certificates.
Note that on-line protocols are not the only way of implementing the
above functions. For all functions, there are off-line methods of
achieving the same result, and this specification does not mandate
use of on-line protocols. For example, when hardware tokens are
used, many of the functions may be achieved as part of the physical
token delivery. Furthermore, some of the above functions may be
combined into one protocol exchange. In particular, two or more of
the registration, initialization, and certification functions can be
combined into one protocol exchange.
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The PKIX series of specifications defines a set of standard message
formats supporting the above functions. The protocols for conveying
these messages in different environments (e.g., email, file transfer,
and WWW) are described in those specifications.
4. Certificate and Certificate Extensions Profile
This section presents a profile for public key certificates that will
foster interoperability and a reusable PKI. This section is based
upon the X.509 v3 certificate format and the standard certificate
extensions defined in [X.509]. The ISO/IEC and ITU-T documents use
the 1997 version of ASN.1; while this document uses the 1988 ASN.1
syntax, the encoded certificate and standard extensions are
equivalent. This section also defines private extensions required to
support a PKI for the Internet community.
Certificates may be used in a wide range of applications and
environments covering a broad spectrum of interoperability goals and
a broader spectrum of operational and assurance requirements. The
goal of this document is to establish a common baseline for generic
applications requiring broad interoperability and limited special
purpose requirements. In particular, the emphasis will be on
supporting the use of X.509 v3 certificates for informal Internet
electronic mail, IPsec, and WWW applications.
4.1. Basic Certificate Fields
The X.509 v3 certificate basic syntax is as follows. For signature
calculation, the data that is to be signed is encoded using the ASN.1
distinguished encoding rules (DER) [X.690]. ASN.1 DER encoding is a
tag, length, value encoding system for each element.
Certificate ::= SEQUENCE {
tbsCertificate TBSCertificate,
signatureAlgorithm AlgorithmIdentifier,
signatureValue BIT STRING }
TBSCertificate ::= SEQUENCE {
version [0] EXPLICIT Version DEFAULT v1,
serialNumber CertificateSerialNumber,
signature AlgorithmIdentifier,
issuer Name,
validity Validity,
subject Name,
subjectPublicKeyInfo SubjectPublicKeyInfo,
issuerUniqueID [1] IMPLICIT UniqueIdentifier OPTIONAL,
-- If present, version MUST be v2 or v3
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subjectUniqueID [2] IMPLICIT UniqueIdentifier OPTIONAL,
-- If present, version MUST be v2 or v3
extensions [3] EXPLICIT Extensions OPTIONAL
-- If present, version MUST be v3
}
Version ::= INTEGER { v1(0), v2(1), v3(2) }
CertificateSerialNumber ::= INTEGER
Validity ::= SEQUENCE {
notBefore Time,
notAfter Time }
Time ::= CHOICE {
utcTime UTCTime,
generalTime GeneralizedTime }
UniqueIdentifier ::= BIT STRING
SubjectPublicKeyInfo ::= SEQUENCE {
algorithm AlgorithmIdentifier,
subjectPublicKey BIT STRING }
Extensions ::= SEQUENCE SIZE (1..MAX) OF Extension
Extension ::= SEQUENCE {
extnID OBJECT IDENTIFIER,
critical BOOLEAN DEFAULT FALSE,
extnValue OCTET STRING
-- contains the DER encoding of an ASN.1 value
-- corresponding to the extension type identified
-- by extnID
}
The following items describe the X.509 v3 certificate for use in the
Internet.
4.1.1. Certificate Fields
The Certificate is a SEQUENCE of three required fields. The fields
are described in detail in the following subsections.
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4.1.1.1. tbsCertificate
The field contains the names of the subject and issuer, a public key
associated with the subject, a validity period, and other associated
information. The fields are described in detail in Section 4.1.2;
the tbsCertificate usually includes extensions, which are described
in Section 4.2.
4.1.1.2. signatureAlgorithm
The signatureAlgorithm field contains the identifier for the
cryptographic algorithm used by the CA to sign this certificate.
[RFC3279], [RFC4055], and [RFC4491] list supported signature
algorithms, but other signature algorithms MAY also be supported.
An algorithm identifier is defined by the following ASN.1 structure:
AlgorithmIdentifier ::= SEQUENCE {
algorithm OBJECT IDENTIFIER,
parameters ANY DEFINED BY algorithm OPTIONAL }
The algorithm identifier is used to identify a cryptographic
algorithm. The OBJECT IDENTIFIER component identifies the algorithm
(such as DSA with SHA-1). The contents of the optional parameters
field will vary according to the algorithm identified.
This field MUST contain the same algorithm identifier as the
signature field in the sequence tbsCertificate (Section 4.1.2.3).
4.1.1.3. signatureValue
The signatureValue field contains a digital signature computed upon
the ASN.1 DER encoded tbsCertificate. The ASN.1 DER encoded
tbsCertificate is used as the input to the signature function. This
signature value is encoded as a BIT STRING and included in the
signature field. The details of this process are specified for each
of the algorithms listed in [RFC3279], [RFC4055], and [RFC4491].
By generating this signature, a CA certifies the validity of the
information in the tbsCertificate field. In particular, the CA
certifies the binding between the public key material and the subject
of the certificate.
4.1.2. TBSCertificate
The sequence TBSCertificate contains information associated with the
subject of the certificate and the CA that issued it. Every
TBSCertificate contains the names of the subject and issuer, a public
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key associated with the subject, a validity period, a version number,
and a serial number; some MAY contain optional unique identifier
fields. The remainder of this section describes the syntax and
semantics of these fields. A TBSCertificate usually includes
extensions. Extensions for the Internet PKI are described in Section
4.2.
4.1.2.1. Version
This field describes the version of the encoded certificate. When
extensions are used, as expected in this profile, version MUST be 3
(value is 2). If no extensions are present, but a UniqueIdentifier
is present, the version SHOULD be 2 (value is 1); however, the
version MAY be 3. If only basic fields are present, the version
SHOULD be 1 (the value is omitted from the certificate as the default
value); however, the version MAY be 2 or 3.
Implementations SHOULD be prepared to accept any version certificate.
At a minimum, conforming implementations MUST recognize version 3
certificates.
Generation of version 2 certificates is not expected by
implementations based on this profile.
4.1.2.2. Serial Number
The serial number MUST be a positive integer assigned by the CA to
each certificate. It MUST be unique for each certificate issued by a
given CA (i.e., the issuer name and serial number identify a unique
certificate). CAs MUST force the serialNumber to be a non-negative
integer.
Given the uniqueness requirements above, serial numbers can be
expected to contain long integers. Certificate users MUST be able to
handle serialNumber values up to 20 octets. Conforming CAs MUST NOT
use serialNumber values longer than 20 octets.
Note: Non-conforming CAs may issue certificates with serial numbers
that are negative or zero. Certificate users SHOULD be prepared to
gracefully handle such certificates.
4.1.2.3. Signature
This field contains the algorithm identifier for the algorithm used
by the CA to sign the certificate.
This field MUST contain the same algorithm identifier as the
signatureAlgorithm field in the sequence Certificate (Section
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4.1.1.2). The contents of the optional parameters field will vary
according to the algorithm identified. [RFC3279], [RFC4055], and
[RFC4491] list supported signature algorithms, but other signature
algorithms MAY also be supported.
4.1.2.4. Issuer
The issuer field identifies the entity that has signed and issued the
certificate. The issuer field MUST contain a non-empty distinguished
name (DN). The issuer field is defined as the X.501 type Name
[X.501]. Name is defined by the following ASN.1 structures:
Name ::= CHOICE { -- only one possibility for now --
rdnSequence RDNSequence }
RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
RelativeDistinguishedName ::=
SET SIZE (1..MAX) OF AttributeTypeAndValue
AttributeTypeAndValue ::= SEQUENCE {
type AttributeType,
value AttributeValue }
AttributeType ::= OBJECT IDENTIFIER
AttributeValue ::= ANY -- DEFINED BY AttributeType
DirectoryString ::= CHOICE {
teletexString TeletexString (SIZE (1..MAX)),
printableString PrintableString (SIZE (1..MAX)),
universalString UniversalString (SIZE (1..MAX)),
utf8String UTF8String (SIZE (1..MAX)),
bmpString BMPString (SIZE (1..MAX)) }
The Name describes a hierarchical name composed of attributes, such
as country name, and corresponding values, such as US. The type of
the component AttributeValue is determined by the AttributeType; in
general it will be a DirectoryString.
The DirectoryString type is defined as a choice of PrintableString,
TeletexString, BMPString, UTF8String, and UniversalString. CAs
conforming to this profile MUST use either the PrintableString or
UTF8String encoding of DirectoryString, with two exceptions. When
CAs have previously issued certificates with issuer fields with
attributes encoded using TeletexString, BMPString, or
UniversalString, then the CA MAY continue to use these encodings of
the DirectoryString to preserve backward compatibility. Also, new
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CAs that are added to a domain where existing CAs issue certificates
with issuer fields with attributes encoded using TeletexString,
BMPString, or UniversalString MAY encode attributes that they share
with the existing CAs using the same encodings as the existing CAs
use.
As noted above, distinguished names are composed of attributes. This
specification does not restrict the set of attribute types that may
appear in names. However, conforming implementations MUST be
prepared to receive certificates with issuer names containing the set
of attribute types defined below. This specification RECOMMENDS
support for additional attribute types.
Standard sets of attributes have been defined in the X.500 series of
specifications [X.520]. Implementations of this specification MUST
be prepared to receive the following standard attribute types in
issuer and subject (Section 4.1.2.6) names:
* country,
* organization,
* organizational unit,
* distinguished name qualifier,
* state or province name,
* common name (e.g., "Susan Housley"), and
* serial number.
In addition, implementations of this specification SHOULD be prepared
to receive the following standard attribute types in issuer and
subject names:
* locality,
* title,
* surname,
* given name,
* initials,
* pseudonym, and
* generation qualifier (e.g., "Jr.", "3rd", or "IV").
The syntax and associated object identifiers (OIDs) for these
attribute types are provided in the ASN.1 modules in Appendix A.
In addition, implementations of this specification MUST be prepared
to receive the domainComponent attribute, as defined in [RFC4519].
The Domain Name System (DNS) provides a hierarchical resource
labeling system. This attribute provides a convenient mechanism for
organizations that wish to use DNs that parallel their DNS names.
This is not a replacement for the dNSName component of the
alternative name extensions. Implementations are not required to
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convert such names into DNS names. The syntax and associated OID for
this attribute type are provided in the ASN.1 modules in Appendix A.
Rules for encoding internationalized domain names for use with the
domainComponent attribute type are specified in Section 7.3.
Certificate users MUST be prepared to process the issuer
distinguished name and subject distinguished name (Section 4.1.2.6)
fields to perform name chaining for certification path validation
(Section 6). Name chaining is performed by matching the issuer
distinguished name in one certificate with the subject name in a CA
certificate. Rules for comparing distinguished names are specified
in Section 7.1. If the names in the issuer and subject field in a
certificate match according to the rules specified in Section 7.1,
then the certificate is self-issued.
4.1.2.5. Validity
The certificate validity period is the time interval during which the
CA warrants that it will maintain information about the status of the
certificate. The field is represented as a SEQUENCE of two dates:
the date on which the certificate validity period begins (notBefore)
and the date on which the certificate validity period ends
(notAfter). Both notBefore and notAfter may be encoded as UTCTime or
GeneralizedTime.
CAs conforming to this profile MUST always encode certificate
validity dates through the year 2049 as UTCTime; certificate validity
dates in 2050 or later MUST be encoded as GeneralizedTime.
Conforming applications MUST be able to process validity dates that
are encoded in either UTCTime or GeneralizedTime.
The validity period for a certificate is the period of time from
notBefore through notAfter, inclusive.
In some situations, devices are given certificates for which no good
expiration date can be assigned. For example, a device could be
issued a certificate that binds its model and serial number to its
public key; such a certificate is intended to be used for the entire
lifetime of the device.
To indicate that a certificate has no well-defined expiration date,
the notAfter SHOULD be assigned the GeneralizedTime value of
99991231235959Z.
When the issuer will not be able to maintain status information until
the notAfter date (including when the notAfter date is
99991231235959Z), the issuer MUST ensure that no valid certification
path exists for the certificate after maintenance of status
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information is terminated. This may be accomplished by expiration or
revocation of all CA certificates containing the public key used to
verify the signature on the certificate and discontinuing use of the
public key used to verify the signature on the certificate as a trust
anchor.
4.1.2.5.1. UTCTime
The universal time type, UTCTime, is a standard ASN.1 type intended
for representation of dates and time. UTCTime specifies the year
through the two low-order digits and time is specified to the
precision of one minute or one second. UTCTime includes either Z
(for Zulu, or Greenwich Mean Time) or a time differential.
For the purposes of this profile, UTCTime values MUST be expressed in
Greenwich Mean Time (Zulu) and MUST include seconds (i.e., times are
YYMMDDHHMMSSZ), even where the number of seconds is zero. Conforming
systems MUST interpret the year field (YY) as follows:
Where YY is greater than or equal to 50, the year SHALL be
interpreted as 19YY; and
Where YY is less than 50, the year SHALL be interpreted as 20YY.
4.1.2.5.2. GeneralizedTime
The generalized time type, GeneralizedTime, is a standard ASN.1 type
for variable precision representation of time. Optionally, the
GeneralizedTime field can include a representation of the time
differential between local and Greenwich Mean Time.
For the purposes of this profile, GeneralizedTime values MUST be
expressed in Greenwich Mean Time (Zulu) and MUST include seconds
(i.e., times are YYYYMMDDHHMMSSZ), even where the number of seconds
is zero. GeneralizedTime values MUST NOT include fractional seconds.
4.1.2.6. Subject
The subject field identifies the entity associated with the public
key stored in the subject public key field. The subject name MAY be
carried in the subject field and/or the subjectAltName extension. If
the subject is a CA (e.g., the basic constraints extension, as
discussed in Section 4.2.1.9, is present and the value of cA is
TRUE), then the subject field MUST be populated with a non-empty
distinguished name matching the contents of the issuer field (Section
4.1.2.4) in all certificates issued by the subject CA. If the
subject is a CRL issuer (e.g., the key usage extension, as discussed
in Section 4.2.1.3, is present and the value of cRLSign is TRUE),
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then the subject field MUST be populated with a non-empty
distinguished name matching the contents of the issuer field (Section
5.1.2.3) in all CRLs issued by the subject CRL issuer. If subject
naming information is present only in the subjectAltName extension
(e.g., a key bound only to an email address or URI), then the subject
name MUST be an empty sequence and the subjectAltName extension MUST
be critical.
Where it is non-empty, the subject field MUST contain an X.500
distinguished name (DN). The DN MUST be unique for each subject
entity certified by the one CA as defined by the issuer field. A CA
MAY issue more than one certificate with the same DN to the same
subject entity.
The subject field is defined as the X.501 type Name. Implementation
requirements for this field are those defined for the issuer field
(Section 4.1.2.4). Implementations of this specification MUST be
prepared to receive subject names containing the attribute types
required for the issuer field. Implementations of this specification
SHOULD be prepared to receive subject names containing the
recommended attribute types for the issuer field. The syntax and
associated object identifiers (OIDs) for these attribute types are
provided in the ASN.1 modules in Appendix A. Implementations of this
specification MAY use the comparison rules in Section 7.1 to process
unfamiliar attribute types (i.e., for name chaining) whose attribute
values use one of the encoding options from DirectoryString. Binary
comparison should be used when unfamiliar attribute types include
attribute values with encoding options other than those found in
DirectoryString. This allows implementations to process certificates
with unfamiliar attributes in the subject name.
When encoding attribute values of type DirectoryString, conforming
CAs MUST use PrintableString or UTF8String encoding, with the
following exceptions:
(a) When the subject of the certificate is a CA, the subject
field MUST be encoded in the same way as it is encoded in the
issuer field (Section 4.1.2.4) in all certificates issued by
the subject CA. Thus, if the subject CA encodes attributes
in the issuer fields of certificates that it issues using the
TeletexString, BMPString, or UniversalString encodings, then
the subject field of certificates issued to that CA MUST use
the same encoding.
(b) When the subject of the certificate is a CRL issuer, the
subject field MUST be encoded in the same way as it is
encoded in the issuer field (Section 5.1.2.3) in all CRLs
issued by the subject CRL issuer.
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(c) TeletexString, BMPString, and UniversalString are included
for backward compatibility, and SHOULD NOT be used for
certificates for new subjects. However, these types MAY be
used in certificates where the name was previously
established, including cases in which a new certificate is
being issued to an existing subject or a certificate is being
issued to a new subject where the attributes being encoded
have been previously established in certificates issued to
other subjects. Certificate users SHOULD be prepared to
receive certificates with these types.
Legacy implementations exist where an electronic mail address is
embedded in the subject distinguished name as an emailAddress
attribute [RFC2985]. The attribute value for emailAddress is of type
IA5String to permit inclusion of the character '@', which is not part
of the PrintableString character set. emailAddress attribute values
are not case-sensitive (e.g., "subscriber@example.com" is the same as
"SUBSCRIBER@EXAMPLE.COM").
Conforming implementations generating new certificates with
electronic mail addresses MUST use the rfc822Name in the subject
alternative name extension (Section 4.2.1.6) to describe such
identities. Simultaneous inclusion of the emailAddress attribute in
the subject distinguished name to support legacy implementations is
deprecated but permitted.
4.1.2.7. Subject Public Key Info
This field is used to carry the public key and identify the algorithm
with which the key is used (e.g., RSA, DSA, or Diffie-Hellman). The
algorithm is identified using the AlgorithmIdentifier structure
specified in Section 4.1.1.2. The object identifiers for the
supported algorithms and the methods for encoding the public key
materials (public key and parameters) are specified in [RFC3279],
[RFC4055], and [RFC4491].
4.1.2.8. Unique Identifiers
These fields MUST only appear if the version is 2 or 3 (Section
4.1.2.1). These fields MUST NOT appear if the version is 1. The
subject and issuer unique identifiers are present in the certificate
to handle the possibility of reuse of subject and/or issuer names
over time. This profile RECOMMENDS that names not be reused for
different entities and that Internet certificates not make use of
unique identifiers. CAs conforming to this profile MUST NOT generate
certificates with unique identifiers. Applications conforming to
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this profile SHOULD be capable of parsing certificates that include
unique identifiers, but there are no processing requirements
associated with the unique identifiers.
4.1.2.9. Extensions
This field MUST only appear if the version is 3 (Section 4.1.2.1).
If present, this field is a SEQUENCE of one or more certificate
extensions. The format and content of certificate extensions in the
Internet PKI are defined in Section 4.2.
4.2. Certificate Extensions
The extensions defined for X.509 v3 certificates provide methods for
associating additional attributes with users or public keys and for
managing relationships between CAs. The X.509 v3 certificate format
also allows communities to define private extensions to carry
information unique to those communities. Each extension in a
certificate is designated as either critical or non-critical. A
certificate-using system MUST reject the certificate if it encounters
a critical extension it does not recognize or a critical extension
that contains information that it cannot process. A non-critical
extension MAY be ignored if it is not recognized, but MUST be
processed if it is recognized. The following sections present
recommended extensions used within Internet certificates and standard
locations for information. Communities may elect to use additional
extensions; however, caution ought to be exercised in adopting any
critical extensions in certificates that might prevent use in a
general context.
Each extension includes an OID and an ASN.1 structure. When an
extension appears in a certificate, the OID appears as the field
extnID and the corresponding ASN.1 DER encoded structure is the value
of the octet string extnValue. A certificate MUST NOT include more
than one instance of a particular extension. For example, a
certificate may contain only one authority key identifier extension
(Section 4.2.1.1). An extension includes the boolean critical, with
a default value of FALSE. The text for each extension specifies the
acceptable values for the critical field for CAs conforming to this
profile.
Conforming CAs MUST support key identifiers (Sections 4.2.1.1 and
4.2.1.2), basic constraints (Section 4.2.1.9), key usage (Section
4.2.1.3), and certificate policies (Section 4.2.1.4) extensions. If
the CA issues certificates with an empty sequence for the subject
field, the CA MUST support the subject alternative name extension
(Section 4.2.1.6). Support for the remaining extensions is OPTIONAL.
Conforming CAs MAY support extensions that are not identified within
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this specification; certificate issuers are cautioned that marking
such extensions as critical may inhibit interoperability.
At a minimum, applications conforming to this profile MUST recognize
the following extensions: key usage (Section 4.2.1.3), certificate
policies (Section 4.2.1.4), subject alternative name (Section
4.2.1.6), basic constraints (Section 4.2.1.9), name constraints
(Section 4.2.1.10), policy constraints (Section 4.2.1.11), extended
key usage (Section 4.2.1.12), and inhibit anyPolicy (Section
4.2.1.14).
In addition, applications conforming to this profile SHOULD recognize
the authority and subject key identifier (Sections 4.2.1.1 and
4.2.1.2) and policy mappings (Section 4.2.1.5) extensions.
4.2.1. Standard Extensions
This section identifies standard certificate extensions defined in
[X.509] for use in the Internet PKI. Each extension is associated
with an OID defined in [X.509]. These OIDs are members of the id-ce
arc, which is defined by the following:
id-ce OBJECT IDENTIFIER ::= { joint-iso-ccitt(2) ds(5) 29 }
4.2.1.1. Authority Key Identifier
The authority key identifier extension provides a means of
identifying the public key corresponding to the private key used to
sign a certificate. This extension is used where an issuer has
multiple signing keys (either due to multiple concurrent key pairs or
due to changeover). The identification MAY be based on either the
key identifier (the subject key identifier in the issuer's
certificate) or the issuer name and serial number.
The keyIdentifier field of the authorityKeyIdentifier extension MUST
be included in all certificates generated by conforming CAs to
facilitate certification path construction. There is one exception;
where a CA distributes its public key in the form of a "self-signed"
certificate, the authority key identifier MAY be omitted. The
signature on a self-signed certificate is generated with the private
key associated with the certificate's subject public key. (This
proves that the issuer possesses both the public and private keys.)
In this case, the subject and authority key identifiers would be
identical, but only the subject key identifier is needed for
certification path building.
The value of the keyIdentifier field SHOULD be derived from the
public key used to verify the certificate's signature or a method
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that generates unique values. Two common methods for generating key
identifiers from the public key are described in Section 4.2.1.2.
Where a key identifier has not been previously established, this
specification RECOMMENDS use of one of these methods for generating
keyIdentifiers or use of a similar method that uses a different hash
algorithm. Where a key identifier has been previously established,
the CA SHOULD use the previously established identifier.
This profile RECOMMENDS support for the key identifier method by all
certificate users.
Conforming CAs MUST mark this extension as non-critical.
id-ce-authorityKeyIdentifier OBJECT IDENTIFIER ::= { id-ce 35 }
AuthorityKeyIdentifier ::= SEQUENCE {
keyIdentifier [0] KeyIdentifier OPTIONAL,
authorityCertIssuer [1] GeneralNames OPTIONAL,
authorityCertSerialNumber [2] CertificateSerialNumber OPTIONAL }
KeyIdentifier ::= OCTET STRING
4.2.1.2. Subject Key Identifier
The subject key identifier extension provides a means of identifying
certificates that contain a particular public key.
To facilitate certification path construction, this extension MUST
appear in all conforming CA certificates, that is, all certificates
including the basic constraints extension (Section 4.2.1.9) where the
value of cA is TRUE. In conforming CA certificates, the value of the
subject key identifier MUST be the value placed in the key identifier
field of the authority key identifier extension (Section 4.2.1.1) of
certificates issued by the subject of this certificate. Applications
are not required to verify that key identifiers match when performing
certification path validation.
For CA certificates, subject key identifiers SHOULD be derived from
the public key or a method that generates unique values. Two common
methods for generating key identifiers from the public key are:
(1) The keyIdentifier is composed of the 160-bit SHA-1 hash of the
value of the BIT STRING subjectPublicKey (excluding the tag,
length, and number of unused bits).
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(2) The keyIdentifier is composed of a four-bit type field with
the value 0100 followed by the least significant 60 bits of
the SHA-1 hash of the value of the BIT STRING
subjectPublicKey (excluding the tag, length, and number of
unused bits).
Other methods of generating unique numbers are also acceptable.
For end entity certificates, the subject key identifier extension
provides a means for identifying certificates containing the
particular public key used in an application. Where an end entity
has obtained multiple certificates, especially from multiple CAs, the
subject key identifier provides a means to quickly identify the set
of certificates containing a particular public key. To assist
applications in identifying the appropriate end entity certificate,
this extension SHOULD be included in all end entity certificates.
For end entity certificates, subject key identifiers SHOULD be
derived from the public key. Two common methods for generating key
identifiers from the public key are identified above.
Where a key identifier has not been previously established, this
specification RECOMMENDS use of one of these methods for generating
keyIdentifiers or use of a similar method that uses a different hash
algorithm. Where a key identifier has been previously established,
the CA SHOULD use the previously established identifier.
Conforming CAs MUST mark this extension as non-critical.
id-ce-subjectKeyIdentifier OBJECT IDENTIFIER ::= { id-ce 14 }
SubjectKeyIdentifier ::= KeyIdentifier
4.2.1.3. Key Usage
The key usage extension defines the purpose (e.g., encipherment,
signature, certificate signing) of the key contained in the
certificate. The usage restriction might be employed when a key that
could be used for more than one operation is to be restricted. For
example, when an RSA key should be used only to verify signatures on
objects other than public key certificates and CRLs, the
digitalSignature and/or nonRepudiation bits would be asserted.
Likewise, when an RSA key should be used only for key management, the
keyEncipherment bit would be asserted.
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Conforming CAs MUST include this extension in certificates that
contain public keys that are used to validate digital signatures on
other public key certificates or CRLs. When present, conforming CAs
SHOULD mark this extension as critical.
id-ce-keyUsage OBJECT IDENTIFIER ::= { id-ce 15 }
KeyUsage ::= BIT STRING {
digitalSignature (0),
nonRepudiation (1), -- recent editions of X.509 have
-- renamed this bit to contentCommitment
keyEncipherment (2),
dataEncipherment (3),
keyAgreement (4),
keyCertSign (5),
cRLSign (6),
encipherOnly (7),
decipherOnly (8) }
Bits in the KeyUsage type are used as follows:
The digitalSignature bit is asserted when the subject public key
is used for verifying digital signatures, other than signatures on
certificates (bit 5) and CRLs (bit 6), such as those used in an
entity authentication service, a data origin authentication
service, and/or an integrity service.
The nonRepudiation bit is asserted when the subject public key is
used to verify digital signatures, other than signatures on
certificates (bit 5) and CRLs (bit 6), used to provide a non-
repudiation service that protects against the signing entity
falsely denying some action. In the case of later conflict, a
reliable third party may determine the authenticity of the signed
data. (Note that recent editions of X.509 have renamed the
nonRepudiation bit to contentCommitment.)
The keyEncipherment bit is asserted when the subject public key is
used for enciphering private or secret keys, i.e., for key
transport. For example, this bit shall be set when an RSA public
key is to be used for encrypting a symmetric content-decryption
key or an asymmetric private key.
The dataEncipherment bit is asserted when the subject public key
is used for directly enciphering raw user data without the use of
an intermediate symmetric cipher. Note that the use of this bit
is extremely uncommon; almost all applications use key transport
or key agreement to establish a symmetric key.
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The keyAgreement bit is asserted when the subject public key is
used for key agreement. For example, when a Diffie-Hellman key is
to be used for key management, then this bit is set.
The keyCertSign bit is asserted when the subject public key is
used for verifying signatures on public key certificates. If the
keyCertSign bit is asserted, then the cA bit in the basic
constraints extension (Section 4.2.1.9) MUST also be asserted.
The cRLSign bit is asserted when the subject public key is used
for verifying signatures on certificate revocation lists (e.g.,
CRLs, delta CRLs, or ARLs).
The meaning of the encipherOnly bit is undefined in the absence of
the keyAgreement bit. When the encipherOnly bit is asserted and
the keyAgreement bit is also set, the subject public key may be
used only for enciphering data while performing key agreement.
The meaning of the decipherOnly bit is undefined in the absence of
the keyAgreement bit. When the decipherOnly bit is asserted and
the keyAgreement bit is also set, the subject public key may be
used only for deciphering data while performing key agreement.
If the keyUsage extension is present, then the subject public key
MUST NOT be used to verify signatures on certificates or CRLs unless
the corresponding keyCertSign or cRLSign bit is set. If the subject
public key is only to be used for verifying signatures on
certificates and/or CRLs, then the digitalSignature and
nonRepudiation bits SHOULD NOT be set. However, the digitalSignature
and/or nonRepudiation bits MAY be set in addition to the keyCertSign
and/or cRLSign bits if the subject public key is to be used to verify
signatures on certificates and/or CRLs as well as other objects.
Combining the nonRepudiation bit in the keyUsage certificate
extension with other keyUsage bits may have security implications
depending on the context in which the certificate is to be used.
Further distinctions between the digitalSignature and nonRepudiation
bits may be provided in specific certificate policies.
This profile does not restrict the combinations of bits that may be
set in an instantiation of the keyUsage extension. However,
appropriate values for keyUsage extensions for particular algorithms
are specified in [RFC3279], [RFC4055], and [RFC4491]. When the
keyUsage extension appears in a certificate, at least one of the bits
MUST be set to 1.
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4.2.1.4. Certificate Policies
The certificate policies extension contains a sequence of one or more
policy information terms, each of which consists of an object
identifier (OID) and optional qualifiers. Optional qualifiers, which
MAY be present, are not expected to change the definition of the
policy. A certificate policy OID MUST NOT appear more than once in a
certificate policies extension.
In an end entity certificate, these policy information terms indicate
the policy under which the certificate has been issued and the
purposes for which the certificate may be used. In a CA certificate,
these policy information terms limit the set of policies for
certification paths that include this certificate. When a CA does
not wish to limit the set of policies for certification paths that
include this certificate, it MAY assert the special policy anyPolicy,
with a value of { 2 5 29 32 0 }.
Applications with specific policy requirements are expected to have a
list of those policies that they will accept and to compare the
policy OIDs in the certificate to that list. If this extension is
critical, the path validation software MUST be able to interpret this
extension (including the optional qualifier), or MUST reject the
certificate.
To promote interoperability, this profile RECOMMENDS that policy
information terms consist of only an OID. Where an OID alone is
insufficient, this profile strongly recommends that the use of
qualifiers be limited to those identified in this section. When
qualifiers are used with the special policy anyPolicy, they MUST be
limited to the qualifiers identified in this section. Only those
qualifiers returned as a result of path validation are considered.
This specification defines two policy qualifier types for use by
certificate policy writers and certificate issuers. The qualifier
types are the CPS Pointer and User Notice qualifiers.
The CPS Pointer qualifier contains a pointer to a Certification
Practice Statement (CPS) published by the CA. The pointer is in the
form of a URI. Processing requirements for this qualifier are a
local matter. No action is mandated by this specification regardless
of the criticality value asserted for the extension.
User notice is intended for display to a relying party when a
certificate is used. Only user notices returned as a result of path
validation are intended for display to the user. If a notice is
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duplicated, only one copy need be displayed. To prevent such
duplication, this qualifier SHOULD only be present in end entity
certificates and CA certificates issued to other organizations.
The user notice has two optional fields: the noticeRef field and the
explicitText field. Conforming CAs SHOULD NOT use the noticeRef
option.
The noticeRef field, if used, names an organization and
identifies, by number, a particular textual statement prepared by
that organization. For example, it might identify the
organization "CertsRUs" and notice number 1. In a typical
implementation, the application software will have a notice file
containing the current set of notices for CertsRUs; the
application will extract the notice text from the file and display
it. Messages MAY be multilingual, allowing the software to select
the particular language message for its own environment.
An explicitText field includes the textual statement directly in
the certificate. The explicitText field is a string with a
maximum size of 200 characters. Conforming CAs SHOULD use the
UTF8String encoding for explicitText, but MAY use IA5String.
Conforming CAs MUST NOT encode explicitText as VisibleString or
BMPString. The explicitText string SHOULD NOT include any control
characters (e.g., U+0000 to U+001F and U+007F to U+009F). When
the UTF8String encoding is used, all character sequences SHOULD be
normalized according to Unicode normalization form C (NFC) [NFC].
If both the noticeRef and explicitText options are included in the
one qualifier and if the application software can locate the notice
text indicated by the noticeRef option, then that text SHOULD be
displayed; otherwise, the explicitText string SHOULD be displayed.
Note: While the explicitText has a maximum size of 200 characters,
some non-conforming CAs exceed this limit. Therefore, certificate
users SHOULD gracefully handle explicitText with more than 200
characters.
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id-ce-certificatePolicies OBJECT IDENTIFIER ::= { id-ce 32 }
anyPolicy OBJECT IDENTIFIER ::= { id-ce-certificatePolicies 0 }
certificatePolicies ::= SEQUENCE SIZE (1..MAX) OF PolicyInformation
PolicyInformation ::= SEQUENCE {
policyIdentifier CertPolicyId,
policyQualifiers SEQUENCE SIZE (1..MAX) OF
PolicyQualifierInfo OPTIONAL }
CertPolicyId ::= OBJECT IDENTIFIER
PolicyQualifierInfo ::= SEQUENCE {
policyQualifierId PolicyQualifierId,
qualifier ANY DEFINED BY policyQualifierId }
-- policyQualifierIds for Internet policy qualifiers
id-qt OBJECT IDENTIFIER ::= { id-pkix 2 }
id-qt-cps OBJECT IDENTIFIER ::= { id-qt 1 }
id-qt-unotice OBJECT IDENTIFIER ::= { id-qt 2 }
PolicyQualifierId ::= OBJECT IDENTIFIER ( id-qt-cps | id-qt-unotice )
Qualifier ::= CHOICE {
cPSuri CPSuri,
userNotice UserNotice }
CPSuri ::= IA5String
UserNotice ::= SEQUENCE {
noticeRef NoticeReference OPTIONAL,
explicitText DisplayText OPTIONAL }
NoticeReference ::= SEQUENCE {
organization DisplayText,
noticeNumbers SEQUENCE OF INTEGER }
DisplayText ::= CHOICE {
ia5String IA5String (SIZE (1..200)),
visibleString VisibleString (SIZE (1..200)),
bmpString BMPString (SIZE (1..200)),
utf8String UTF8String (SIZE (1..200)) }
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4.2.1.5. Policy Mappings
This extension is used in CA certificates. It lists one or more
pairs of OIDs; each pair includes an issuerDomainPolicy and a
subjectDomainPolicy. The pairing indicates the issuing CA considers
its issuerDomainPolicy equivalent to the subject CA's
subjectDomainPolicy.
The issuing CA's users might accept an issuerDomainPolicy for certain
applications. The policy mapping defines the list of policies
associated with the subject CA that may be accepted as comparable to
the issuerDomainPolicy.
Each issuerDomainPolicy named in the policy mappings extension SHOULD
also be asserted in a certificate policies extension in the same
certificate. Policies MUST NOT be mapped either to or from the
special value anyPolicy (Section 4.2.1.4).
In general, certificate policies that appear in the
issuerDomainPolicy field of the policy mappings extension are not
considered acceptable policies for inclusion in subsequent
certificates in the certification path. In some circumstances, a CA
may wish to map from one policy (p1) to another (p2), but still wants
the issuerDomainPolicy (p1) to be considered acceptable for inclusion
in subsequent certificates. This may occur, for example, if the CA
is in the process of transitioning from the use of policy p1 to the
use of policy p2 and has valid certificates that were issued under
each of the policies. A CA may indicate this by including two policy
mappings in the CA certificates that it issues. Each policy mapping
would have an issuerDomainPolicy of p1; one policy mapping would have
a subjectDomainPolicy of p1 and the other would have a
subjectDomainPolicy of p2.
This extension MAY be supported by CAs and/or applications.
Conforming CAs SHOULD mark this extension as critical.
id-ce-policyMappings OBJECT IDENTIFIER ::= { id-ce 33 }
PolicyMappings ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {
issuerDomainPolicy CertPolicyId,
subjectDomainPolicy CertPolicyId }
4.2.1.6. Subject Alternative Name
The subject alternative name extension allows identities to be bound
to the subject of the certificate. These identities may be included
in addition to or in place of the identity in the subject field of
the certificate. Defined options include an Internet electronic mail
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address, a DNS name, an IP address, and a Uniform Resource Identifier
(URI). Other options exist, including completely local definitions.
Multiple name forms, and multiple instances of each name form, MAY be
included. Whenever such identities are to be bound into a
certificate, the subject alternative name (or issuer alternative
name) extension MUST be used; however, a DNS name MAY also be
represented in the subject field using the domainComponent attribute
as described in Section 4.1.2.4. Note that where such names are
represented in the subject field implementations are not required to
convert them into DNS names.
Because the subject alternative name is considered to be definitively
bound to the public key, all parts of the subject alternative name
MUST be verified by the CA.
Further, if the only subject identity included in the certificate is
an alternative name form (e.g., an electronic mail address), then the
subject distinguished name MUST be empty (an empty sequence), and the
subjectAltName extension MUST be present. If the subject field
contains an empty sequence, then the issuing CA MUST include a
subjectAltName extension that is marked as critical. When including
the subjectAltName extension in a certificate that has a non-empty
subject distinguished name, conforming CAs SHOULD mark the
subjectAltName extension as non-critical.
When the subjectAltName extension contains an Internet mail address,
the address MUST be stored in the rfc822Name. The format of an
rfc822Name is a "Mailbox" as defined in Section 4.1.2 of [RFC2821].
A Mailbox has the form "Local-part@Domain". Note that a Mailbox has
no phrase (such as a common name) before it, has no comment (text
surrounded in parentheses) after it, and is not surrounded by "<" and
">". Rules for encoding Internet mail addresses that include
internationalized domain names are specified in Section 7.5.
When the subjectAltName extension contains an iPAddress, the address
MUST be stored in the octet string in "network byte order", as
specified in [RFC791]. The least significant bit (LSB) of each octet
is the LSB of the corresponding byte in the network address. For IP
version 4, as specified in [RFC791], the octet string MUST contain
exactly four octets. For IP version 6, as specified in
[RFC2460], the octet string MUST contain exactly sixteen octets.
When the subjectAltName extension contains a domain name system
label, the domain name MUST be stored in the dNSName (an IA5String).
The name MUST be in the "preferred name syntax", as specified by
Section 3.5 of [RFC1034] and as modified by Section 2.1 of
[RFC1123]. Note that while uppercase and lowercase letters are
allowed in domain names, no significance is attached to the case. In
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RFC 5280 PKIX Certificate and CRL Profile May 2008
addition, while the string " " is a legal domain name, subjectAltName
extensions with a dNSName of " " MUST NOT be used. Finally, the use
of the DNS representation for Internet mail addresses
(subscriber.example.com instead of subscriber@example.com) MUST NOT
be used; such identities are to be encoded as rfc822Name. Rules for
encoding internationalized domain names are specified in Section 7.2.
When the subjectAltName extension contains a URI, the name MUST be
stored in the uniformResourceIdentifier (an IA5String). The name
MUST NOT be a relative URI, and it MUST follow the URI syntax and
encoding rules specified in [RFC3986]. The name MUST include both a
scheme (e.g., "http" or "ftp") and a scheme-specific-part. URIs that
include an authority ([RFC3986], Section 3.2) MUST include a fully
qualified domain name or IP address as the host. Rules for encoding
Internationalized Resource Identifiers (IRIs) are specified in
Section 7.4.
As specified in [RFC3986], the scheme name is not case-sensitive
(e.g., "http" is equivalent to "HTTP"). The host part, if present,
is also not case-sensitive, but other components of the scheme-
specific-part may be case-sensitive. Rules for comparing URIs are
specified in Section 7.4.
When the subjectAltName extension contains a DN in the directoryName,
the encoding rules are the same as those specified for the issuer
field in Section 4.1.2.4. The DN MUST be unique for each subject
entity certified by the one CA as defined by the issuer field. A CA
MAY issue more than one certificate with the same DN to the same
subject entity.
The subjectAltName MAY carry additional name types through the use of
the otherName field. The format and semantics of the name are
indicated through the OBJECT IDENTIFIER in the type-id field. The
name itself is conveyed as value field in otherName. For example,
Kerberos [RFC4120] format names can be encoded into the otherName,
using a Kerberos 5 principal name OID and a SEQUENCE of the Realm and
the PrincipalName.
Subject alternative names MAY be constrained in the same manner as
subject distinguished names using the name constraints extension as
described in Section 4.2.1.10.
If the subjectAltName extension is present, the sequence MUST contain
at least one entry. Unlike the subject field, conforming CAs MUST
NOT issue certificates with subjectAltNames containing empty
GeneralName fields. For example, an rfc822Name is represented as an
IA5String. While an empty string is a valid IA5String, such an
rfc822Name is not permitted by this profile. The behavior of clients
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RFC 5280 PKIX Certificate and CRL Profile May 2008
that encounter such a certificate when processing a certification
path is not defined by this profile.
Finally, the semantics of subject alternative names that include
wildcard characters (e.g., as a placeholder for a set of names) are
not addressed by this specification. Applications with specific
requirements MAY use such names, but they must define the semantics.
id-ce-subjectAltName OBJECT IDENTIFIER ::= { id-ce 17 }
SubjectAltName ::= GeneralNames
GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName
GeneralName ::= CHOICE {
otherName [0] OtherName,
rfc822Name [1] IA5String,
dNSName [2] IA5String,
x400Address [3] ORAddress,
directoryName [4] Name,
ediPartyName [5] EDIPartyName,
uniformResourceIdentifier [6] IA5String,
iPAddress [7] OCTET STRING,
registeredID [8] OBJECT IDENTIFIER }
OtherName ::= SEQUENCE {
type-id OBJECT IDENTIFIER,
value [0] EXPLICIT ANY DEFINED BY type-id }
EDIPartyName ::= SEQUENCE {
nameAssigner [0] DirectoryString OPTIONAL,
partyName [1] DirectoryString }
4.2.1.7. Issuer Alternative Name
As with Section 4.2.1.6, this extension is used to associate Internet
style identities with the certificate issuer. Issuer alternative
name MUST be encoded as in 4.2.1.6. Issuer alternative names are not
processed as part of the certification path validation algorithm in
Section 6. (That is, issuer alternative names are not used in name
chaining and name constraints are not enforced.)
Where present, conforming CAs SHOULD mark this extension as non-
critical.
id-ce-issuerAltName OBJECT IDENTIFIER ::= { id-ce 18 }
IssuerAltName ::= GeneralNames
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4.2.1.8. Subject Directory Attributes
The subject directory attributes extension is used to convey
identification attributes (e.g., nationality) of the subject. The
extension is defined as a sequence of one or more attributes.
Conforming CAs MUST mark this extension as non-critical.
id-ce-subjectDirectoryAttributes OBJECT IDENTIFIER ::= { id-ce 9 }
SubjectDirectoryAttributes ::= SEQUENCE SIZE (1..MAX) OF Attribute
4.2.1.9. Basic Constraints
The basic constraints extension identifies whether the subject of the
certificate is a CA and the maximum depth of valid certification
paths that include this certificate.
The cA boolean indicates whether the certified public key may be used
to verify certificate signatures. If the cA boolean is not asserted,
then the keyCertSign bit in the key usage extension MUST NOT be
asserted. If the basic constraints extension is not present in a
version 3 certificate, or the extension is present but the cA boolean
is not asserted, then the certified public key MUST NOT be used to
verify certificate signatures.
The pathLenConstraint field is meaningful only if the cA boolean is
asserted and the key usage extension, if present, asserts the
keyCertSign bit (Section 4.2.1.3). In this case, it gives the
maximum number of non-self-issued intermediate certificates that may
follow this certificate in a valid certification path. (Note: The
last certificate in the certification path is not an intermediate
certificate, and is not included in this limit. Usually, the last
certificate is an end entity certificate, but it can be a CA
certificate.) A pathLenConstraint of zero indicates that no non-
self-issued intermediate CA certificates may follow in a valid
certification path. Where it appears, the pathLenConstraint field
MUST be greater than or equal to zero. Where pathLenConstraint does
not appear, no limit is imposed.
Conforming CAs MUST include this extension in all CA certificates
that contain public keys used to validate digital signatures on
certificates and MUST mark the extension as critical in such
certificates. This extension MAY appear as a critical or non-
critical extension in CA certificates that contain public keys used
exclusively for purposes other than validating digital signatures on
certificates. Such CA certificates include ones that contain public
keys used exclusively for validating digital signatures on CRLs and
ones that contain key management public keys used with certificate
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RFC 5280 PKIX Certificate and CRL Profile May 2008
enrollment protocols. This extension MAY appear as a critical or
non-critical extension in end entity certificates.
CAs MUST NOT include the pathLenConstraint field unless the cA
boolean is asserted and the key usage extension asserts the
keyCertSign bit.
id-ce-basicConstraints OBJECT IDENTIFIER ::= { id-ce 19 }
BasicConstraints ::= SEQUENCE {
cA BOOLEAN DEFAULT FALSE,
pathLenConstraint INTEGER (0..MAX) OPTIONAL }
4.2.1.10. Name Constraints
The name constraints extension, which MUST be used only in a CA
certificate, indicates a name space within which all subject names in
subsequent certificates in a certification path MUST be located.
Restrictions apply to the subject distinguished name and apply to
subject alternative names. Restrictions apply only when the
specified name form is present. If no name of the type is in the
certificate, the certificate is acceptable.
Name constraints are not applied to self-issued certificates (unless
the certificate is the final certificate in the path). (This could
prevent CAs that use name constraints from employing self-issued
certificates to implement key rollover.)
Restrictions are defined in terms of permitted or excluded name
subtrees. Any name matching a restriction in the excludedSubtrees
field is invalid regardless of information appearing in the
permittedSubtrees. Conforming CAs MUST mark this extension as
critical and SHOULD NOT impose name constraints on the x400Address,
ediPartyName, or registeredID name forms. Conforming CAs MUST NOT
issue certificates where name constraints is an empty sequence. That
is, either the permittedSubtrees field or the excludedSubtrees MUST
be present.
Applications conforming to this profile MUST be able to process name
constraints that are imposed on the directoryName name form and
SHOULD be able to process name constraints that are imposed on the
rfc822Name, uniformResourceIdentifier, dNSName, and iPAddress name
forms. If a name constraints extension that is marked as critical
imposes constraints on a particular name form, and an instance of
that name form appears in the subject field or subjectAltName
extension of a subsequent certificate, then the application MUST
either process the constraint or reject the certificate.
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Within this profile, the minimum and maximum fields are not used with
any name forms, thus, the minimum MUST be zero, and maximum MUST be
absent. However, if an application encounters a critical name
constraints extension that specifies other values for minimum or
maximum for a name form that appears in a subsequent certificate, the
application MUST either process these fields or reject the
certificate.
For URIs, the constraint applies to the host part of the name. The
constraint MUST be specified as a fully qualified domain name and MAY
specify a host or a domain. Examples would be "host.example.com" and
".example.com". When the constraint begins with a period, it MAY be
expanded with one or more labels. That is, the constraint
".example.com" is satisfied by both host.example.com and
my.host.example.com. However, the constraint ".example.com" is not
satisfied by "example.com". When the constraint does not begin with
a period, it specifies a host. If a constraint is applied to the
uniformResourceIdentifier name form and a subsequent certificate
includes a subjectAltName extension with a uniformResourceIdentifier
that does not include an authority component with a host name
specified as a fully qualified domain name (e.g., if the URI either
does not include an authority component or includes an authority
component in which the host name is specified as an IP address), then
the application MUST reject the certificate.
A name constraint for Internet mail addresses MAY specify a
particular mailbox, all addresses at a particular host, or all
mailboxes in a domain. To indicate a particular mailbox, the
constraint is the complete mail address. For example,
"root@example.com" indicates the root mailbox on the host
"example.com". To indicate all Internet mail addresses on a
particular host, the constraint is specified as the host name. For
example, the constraint "example.com" is satisfied by any mail
address at the host "example.com". To specify any address within a
domain, the constraint is specified with a leading period (as with
URIs). For example, ".example.com" indicates all the Internet mail
addresses in the domain "example.com", but not Internet mail
addresses on the host "example.com".
DNS name restrictions are expressed as host.example.com. Any DNS
name that can be constructed by simply adding zero or more labels to
the left-hand side of the name satisfies the name constraint. For
example, www.host.example.com would satisfy the constraint but
host1.example.com would not.
Legacy implementations exist where an electronic mail address is
embedded in the subject distinguished name in an attribute of type
emailAddress (Section 4.1.2.6). When constraints are imposed on the
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RFC 5280 PKIX Certificate and CRL Profile May 2008
rfc822Name name form, but the certificate does not include a subject
alternative name, the rfc822Name constraint MUST be applied to the
attribute of type emailAddress in the subject distinguished name.
The ASN.1 syntax for emailAddress and the corresponding OID are
supplied in Appendix A.
Restrictions of the form directoryName MUST be applied to the subject
field in the certificate (when the certificate includes a non-empty
subject field) and to any names of type directoryName in the
subjectAltName extension. Restrictions of the form x400Address MUST
be applied to any names of type x400Address in the subjectAltName
extension.
When applying restrictions of the form directoryName, an
implementation MUST compare DN attributes. At a minimum,
implementations MUST perform the DN comparison rules specified in
Section 7.1. CAs issuing certificates with a restriction of the form
directoryName SHOULD NOT rely on implementation of the full ISO DN
name comparison algorithm. This implies name restrictions MUST be
stated identically to the encoding used in the subject field or
subjectAltName extension.
The syntax of iPAddress MUST be as described in Section 4.2.1.6 with
the following additions specifically for name constraints. For IPv4
addresses, the iPAddress field of GeneralName MUST contain eight (8)
octets, encoded in the style of RFC 4632 (CIDR) to represent an
address range [RFC4632]. For IPv6 addresses, the iPAddress field
MUST contain 32 octets similarly encoded. For example, a name
constraint for "class C" subnet 192.0.2.0 is represented as the
octets C0 00 02 00 FF FF FF 00, representing the CIDR notation
192.0.2.0/24 (mask 255.255.255.0).
Additional rules for encoding and processing name constraints are
specified in Section 7.
The syntax and semantics for name constraints for otherName,
ediPartyName, and registeredID are not defined by this specification,
however, syntax and semantics for name constraints for other name
forms may be specified in other documents.
id-ce-nameConstraints OBJECT IDENTIFIER ::= { id-ce 30 }
NameConstraints ::= SEQUENCE {
permittedSubtrees [0] GeneralSubtrees OPTIONAL,
excludedSubtrees [1] GeneralSubtrees OPTIONAL }
GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree
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GeneralSubtree ::= SEQUENCE {
base GeneralName,
minimum [0] BaseDistance DEFAULT 0,
maximum [1] BaseDistance OPTIONAL }
BaseDistance ::= INTEGER (0..MAX)
4.2.1.11. Policy Constraints
The policy constraints extension can be used in certificates issued
to CAs. The policy constraints extension constrains path validation
in two ways. It can be used to prohibit policy mapping or require
that each certificate in a path contain an acceptable policy
identifier.
If the inhibitPolicyMapping field is present, the value indicates the
number of additional certificates that may appear in the path before
policy mapping is no longer permitted. For example, a value of one
indicates that policy mapping may be processed in certificates issued
by the subject of this certificate, but not in additional
certificates in the path.
If the requireExplicitPolicy field is present, the value of
requireExplicitPolicy indicates the number of additional certificates
that may appear in the path before an explicit policy is required for
the entire path. When an explicit policy is required, it is
necessary for all certificates in the path to contain an acceptable
policy identifier in the certificate policies extension. An
acceptable policy identifier is the identifier of a policy required
by the user of the certification path or the identifier of a policy
that has been declared equivalent through policy mapping.
Conforming applications MUST be able to process the
requireExplicitPolicy field and SHOULD be able to process the
inhibitPolicyMapping field. Applications that support the
inhibitPolicyMapping field MUST also implement support for the
policyMappings extension. If the policyConstraints extension is
marked as critical and the inhibitPolicyMapping field is present,
applications that do not implement support for the
inhibitPolicyMapping field MUST reject the certificate.
Conforming CAs MUST NOT issue certificates where policy constraints
is an empty sequence. That is, either the inhibitPolicyMapping field
or the requireExplicitPolicy field MUST be present. The behavior of
clients that encounter an empty policy constraints field is not
addressed in this profile.
Conforming CAs MUST mark this extension as critical.
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id-ce-policyConstraints OBJECT IDENTIFIER ::= { id-ce 36 }
PolicyConstraints ::= SEQUENCE {
requireExplicitPolicy [0] SkipCerts OPTIONAL,
inhibitPolicyMapping [1] SkipCerts OPTIONAL }
SkipCerts ::= INTEGER (0..MAX)
4.2.1.12. Extended Key Usage
This extension indicates one or more purposes for which the certified
public key may be used, in addition to or in place of the basic
purposes indicated in the key usage extension. In general, this
extension will appear only in end entity certificates. This
extension is defined as follows:
id-ce-extKeyUsage OBJECT IDENTIFIER ::= { id-ce 37 }
ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId
KeyPurposeId ::= OBJECT IDENTIFIER
Key purposes may be defined by any organization with a need. Object
identifiers used to identify key purposes MUST be assigned in
accordance with IANA or ITU-T Recommendation X.660 [X.660].
This extension MAY, at the option of the certificate issuer, be
either critical or non-critical.
If the extension is present, then the certificate MUST only be used
for one of the purposes indicated. If multiple purposes are
indicated the application need not recognize all purposes indicated,
as long as the intended purpose is present. Certificate using
applications MAY require that the extended key usage extension be
present and that a particular purpose be indicated in order for the
certificate to be acceptable to that application.
If a CA includes extended key usages to satisfy such applications,
but does not wish to restrict usages of the key, the CA can include
the special KeyPurposeId anyExtendedKeyUsage in addition to the
particular key purposes required by the applications. Conforming CAs
SHOULD NOT mark this extension as critical if the anyExtendedKeyUsage
KeyPurposeId is present. Applications that require the presence of a
particular purpose MAY reject certificates that include the
anyExtendedKeyUsage OID but not the particular OID expected for the
application.
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If a certificate contains both a key usage extension and an extended
key usage extension, then both extensions MUST be processed
independently and the certificate MUST only be used for a purpose
consistent with both extensions. If there is no purpose consistent
with both extensions, then the certificate MUST NOT be used for any
purpose.
The following key usage purposes are defined:
anyExtendedKeyUsage OBJECT IDENTIFIER ::= { id-ce-extKeyUsage 0 }
id-kp OBJECT IDENTIFIER ::= { id-pkix 3 }
id-kp-serverAuth OBJECT IDENTIFIER ::= { id-kp 1 }
-- TLS WWW server authentication
-- Key usage bits that may be consistent: digitalSignature,
-- keyEncipherment or keyAgreement
id-kp-clientAuth OBJECT IDENTIFIER ::= { id-kp 2 }
-- TLS WWW client authentication
-- Key usage bits that may be consistent: digitalSignature
-- and/or keyAgreement
id-kp-codeSigning OBJECT IDENTIFIER ::= { id-kp 3 }
-- Signing of downloadable executable code
-- Key usage bits that may be consistent: digitalSignature
id-kp-emailProtection OBJECT IDENTIFIER ::= { id-kp 4 }
-- Email protection
-- Key usage bits that may be consistent: digitalSignature,
-- nonRepudiation, and/or (keyEncipherment or keyAgreement)
id-kp-timeStamping OBJECT IDENTIFIER ::= { id-kp 8 }
-- Binding the hash of an object to a time
-- Key usage bits that may be consistent: digitalSignature
-- and/or nonRepudiation
id-kp-OCSPSigning OBJECT IDENTIFIER ::= { id-kp 9 }
-- Signing OCSP responses
-- Key usage bits that may be consistent: digitalSignature
-- and/or nonRepudiation
4.2.1.13. CRL Distribution Points
The CRL distribution points extension identifies how CRL information
is obtained. The extension SHOULD be non-critical, but this profile
RECOMMENDS support for this extension by CAs and applications.
Further discussion of CRL management is contained in Section 5.
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The cRLDistributionPoints extension is a SEQUENCE of
DistributionPoint. A DistributionPoint consists of three fields,
each of which is optional: distributionPoint, reasons, and cRLIssuer.
While each of these fields is optional, a DistributionPoint MUST NOT
consist of only the reasons field; either distributionPoint or
cRLIssuer MUST be present. If the certificate issuer is not the CRL
issuer, then the cRLIssuer field MUST be present and contain the Name
of the CRL issuer. If the certificate issuer is also the CRL issuer,
then conforming CAs MUST omit the cRLIssuer field and MUST include
the distributionPoint field.
When the distributionPoint field is present, it contains either a
SEQUENCE of general names or a single value, nameRelativeToCRLIssuer.
If the DistributionPointName contains multiple values, each name
describes a different mechanism to obtain the same CRL. For example,
the same CRL could be available for retrieval through both LDAP and
HTTP.
If the distributionPoint field contains a directoryName, the entry
for that directoryName contains the current CRL for the associated
reasons and the CRL is issued by the associated cRLIssuer. The CRL
may be stored in either the certificateRevocationList or
authorityRevocationList attribute. The CRL is to be obtained by the
application from whatever directory server is locally configured.
The protocol the application uses to access the directory (e.g., DAP
or LDAP) is a local matter.
If the DistributionPointName contains a general name of type URI, the
following semantics MUST be assumed: the URI is a pointer to the
current CRL for the associated reasons and will be issued by the
associated cRLIssuer. When the HTTP or FTP URI scheme is used, the
URI MUST point to a single DER encoded CRL as specified in
[RFC2585]. HTTP server implementations accessed via the URI SHOULD
specify the media type application/pkix-crl in the content-type
header field of the response. When the LDAP URI scheme [RFC4516] is
used, the URI MUST include a field containing the distinguished
name of the entry holding the CRL, MUST include a single
that contains an appropriate attribute description for the attribute
that holds the CRL [RFC4523], and SHOULD include a
(e.g., ). Omitting the (e.g.,
) has
the effect of relying on whatever a priori knowledge the client might
have to contact an appropriate server. When present,
DistributionPointName SHOULD include at least one LDAP or HTTP URI.
If the DistributionPointName contains the single value
nameRelativeToCRLIssuer, the value provides a distinguished name
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fragment. The fragment is appended to the X.500 distinguished name
of the CRL issuer to obtain the distribution point name. If the
cRLIssuer field in the DistributionPoint is present, then the name
fragment is appended to the distinguished name that it contains;
otherwise, the name fragment is appended to the certificate issuer
distinguished name. Conforming CAs SHOULD NOT use
nameRelativeToCRLIssuer to specify distribution point names. The
DistributionPointName MUST NOT use the nameRelativeToCRLIssuer
alternative when cRLIssuer contains more than one distinguished name.
If the DistributionPoint omits the reasons field, the CRL MUST
include revocation information for all reasons. This profile
RECOMMENDS against segmenting CRLs by reason code. When a conforming
CA includes a cRLDistributionPoints extension in a certificate, it
MUST include at least one DistributionPoint that points to a CRL that
covers the certificate for all reasons.
The cRLIssuer identifies the entity that signs and issues the CRL.
If present, the cRLIssuer MUST only contain the distinguished name
(DN) from the issuer field of the CRL to which the DistributionPoint
is pointing. The encoding of the name in the cRLIssuer field MUST be
exactly the same as the encoding in issuer field of the CRL. If the
cRLIssuer field is included and the DN in that field does not
correspond to an X.500 or LDAP directory entry where CRL is located,
then conforming CAs MUST include the distributionPoint field.
id-ce-cRLDistributionPoints OBJECT IDENTIFIER ::= { id-ce 31 }
CRLDistributionPoints ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint
DistributionPoint ::= SEQUENCE {
distributionPoint [0] DistributionPointName OPTIONAL,
reasons [1] ReasonFlags OPTIONAL,
cRLIssuer [2] GeneralNames OPTIONAL }
DistributionPointName ::= CHOICE {
fullName [0] GeneralNames,
nameRelativeToCRLIssuer [1] RelativeDistinguishedName }
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ReasonFlags ::= BIT STRING {
unused (0),
keyCompromise (1),
cACompromise (2),
affiliationChanged (3),
superseded (4),
cessationOfOperation (5),
certificateHold (6),
privilegeWithdrawn (7),
aACompromise (8) }
4.2.1.14. Inhibit anyPolicy
The inhibit anyPolicy extension can be used in certificates issued to
CAs. The inhibit anyPolicy extension indicates that the special
anyPolicy OID, with the value { 2 5 29 32 0 }, is not considered an
explicit match for other certificate policies except when it appears
in an intermediate self-issued CA certificate. The value indicates
the number of additional non-self-issued certificates that may appear
in the path before anyPolicy is no longer permitted. For example, a
value of one indicates that anyPolicy may be processed in
certificates issued by the subject of this certificate, but not in
additional certificates in the path.
Conforming CAs MUST mark this extension as critical.
id-ce-inhibitAnyPolicy OBJECT IDENTIFIER ::= { id-ce 54 }
InhibitAnyPolicy ::= SkipCerts
SkipCerts ::= INTEGER (0..MAX)
4.2.1.15. Freshest CRL (a.k.a. Delta CRL Distribution Point)
The freshest CRL extension identifies how delta CRL information is
obtained. The extension MUST be marked as non-critical by conforming
CAs. Further discussion of CRL management is contained in Section 5.
The same syntax is used for this extension and the
cRLDistributionPoints extension, and is described in Section
4.2.1.13. The same conventions apply to both extensions.
id-ce-freshestCRL OBJECT IDENTIFIER ::= { id-ce 46 }
FreshestCRL ::= CRLDistributionPoints
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4.2.2. Private Internet Extensions
This section defines two extensions for use in the Internet Public
Key Infrastructure. These extensions may be used to direct
applications to on-line information about the issuer or the subject.
Each extension contains a sequence of access methods and access
locations. The access method is an object identifier that indicates
the type of information that is available. The access location is a
GeneralName that implicitly specifies the location and format of the
information and the method for obtaining the information.
Object identifiers are defined for the private extensions. The
object identifiers associated with the private extensions are defined
under the arc id-pe within the arc id-pkix. Any future extensions
defined for the Internet PKI are also expected to be defined under
the arc id-pe.
id-pkix OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) }
id-pe OBJECT IDENTIFIER ::= { id-pkix 1 }
4.2.2.1. Authority Information Access
The authority information access extension indicates how to access
information and services for the issuer of the certificate in which
the extension appears. Information and services may include on-line
validation services and CA policy data. (The location of CRLs is not
specified in this extension; that information is provided by the
cRLDistributionPoints extension.) This extension may be included in
end entity or CA certificates. Conforming CAs MUST mark this
extension as non-critical.
id-pe-authorityInfoAccess OBJECT IDENTIFIER ::= { id-pe 1 }
AuthorityInfoAccessSyntax ::=
SEQUENCE SIZE (1..MAX) OF AccessDescription
AccessDescription ::= SEQUENCE {
accessMethod OBJECT IDENTIFIER,
accessLocation GeneralName }
id-ad OBJECT IDENTIFIER ::= { id-pkix 48 }
id-ad-caIssuers OBJECT IDENTIFIER ::= { id-ad 2 }
id-ad-ocsp OBJECT IDENTIFIER ::= { id-ad 1 }
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Each entry in the sequence AuthorityInfoAccessSyntax describes the
format and location of additional information provided by the issuer
of the certificate in which this extension appears. The type and
format of the information are specified by the accessMethod field;
the accessLocation field specifies the location of the information.
The retrieval mechanism may be implied by the accessMethod or
specified by accessLocation.
This profile defines two accessMethod OIDs: id-ad-caIssuers and
id-ad-ocsp.
In a public key certificate, the id-ad-caIssuers OID is used when the
additional information lists certificates that were issued to the CA
that issued the certificate containing this extension. The
referenced CA issuers description is intended to aid certificate
users in the selection of a certification path that terminates at a
point trusted by the certificate user.
When id-ad-caIssuers appears as accessMethod, the accessLocation
field describes the referenced description server and the access
protocol to obtain the referenced description. The accessLocation
field is defined as a GeneralName, which can take several forms.
When the accessLocation is a directoryName, the information is to be
obtained by the application from whatever directory server is locally
configured. The entry for the directoryName contains CA certificates
in the crossCertificatePair and/or cACertificate attributes as
specified in [RFC4523]. The protocol that application uses to access
the directory (e.g., DAP or LDAP) is a local matter.
Where the information is available via LDAP, the accessLocation
SHOULD be a uniformResourceIdentifier. The LDAP URI [RFC4516] MUST
include a field containing the distinguished name of the entry
holding the certificates, MUST include an field that
lists appropriate attribute descriptions for the attributes that hold
the DER encoded certificates or cross-certificate pairs [RFC4523],
and SHOULD include a (e.g., ).
Omitting the (e.g., ) has the effect of relying on whatever a priori
knowledge the client might have to contact an appropriate server.
Where the information is available via HTTP or FTP, accessLocation
MUST be a uniformResourceIdentifier and the URI MUST point to either
a single DER encoded certificate as specified in [RFC2585] or a
collection of certificates in a BER or DER encoded "certs-only" CMS
message as specified in [RFC2797].
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Conforming applications that support HTTP or FTP for accessing
certificates MUST be able to accept individual DER encoded
certificates and SHOULD be able to accept "certs-only" CMS messages.
HTTP server implementations accessed via the URI SHOULD specify the
media type application/pkix-cert [RFC2585] in the content-type header
field of the response for a single DER encoded certificate and SHOULD
specify the media type application/pkcs7-mime [RFC2797] in the
content-type header field of the response for "certs-only" CMS
messages. For FTP, the name of a file that contains a single DER
encoded certificate SHOULD have a suffix of ".cer" [RFC2585] and the
name of a file that contains a "certs-only" CMS message SHOULD have a
suffix of ".p7c" [RFC2797]. Consuming clients may use the media type
or file extension as a hint to the content, but should not depend
solely on the presence of the correct media type or file extension in
the server response.
The semantics of other id-ad-caIssuers accessLocation name forms are
not defined.
An authorityInfoAccess extension may include multiple instances of
the id-ad-caIssuers accessMethod. The different instances may
specify different methods for accessing the same information or may
point to different information. When the id-ad-caIssuers
accessMethod is used, at least one instance SHOULD specify an
accessLocation that is an HTTP [RFC2616] or LDAP [RFC4516] URI.
The id-ad-ocsp OID is used when revocation information for the
certificate containing this extension is available using the Online
Certificate Status Protocol (OCSP) [RFC2560].
When id-ad-ocsp appears as accessMethod, the accessLocation field is
the location of the OCSP responder, using the conventions defined in
[RFC2560].
Additional access descriptors may be defined in other PKIX
specifications.
4.2.2.2. Subject Information Access
The subject information access extension indicates how to access
information and services for the subject of the certificate in which
the extension appears. When the subject is a CA, information and
services may include certificate validation services and CA policy
data. When the subject is an end entity, the information describes
the type of services offered and how to access them. In this case,
the contents of this extension are defined in the protocol
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specifications for the supported services. This extension may be
included in end entity or CA certificates. Conforming CAs MUST mark
this extension as non-critical.
id-pe-subjectInfoAccess OBJECT IDENTIFIER ::= { id-pe 11 }
SubjectInfoAccessSyntax ::=
SEQUENCE SIZE (1..MAX) OF AccessDescription
AccessDescription ::= SEQUENCE {
accessMethod OBJECT IDENTIFIER,
accessLocation GeneralName }
Each entry in the sequence SubjectInfoAccessSyntax describes the
format and location of additional information provided by the subject
of the certificate in which this extension appears. The type and
format of the information are specified by the accessMethod field;
the accessLocation field specifies the location of the information.
The retrieval mechanism may be implied by the accessMethod or
specified by accessLocation.
This profile defines one access method to be used when the subject is
a CA and one access method to be used when the subject is an end
entity. Additional access methods may be defined in the future in
the protocol specifications for other services.
The id-ad-caRepository OID is used when the subject is a CA that
publishes certificates it issues in a repository. The accessLocation
field is defined as a GeneralName, which can take several forms.
When the accessLocation is a directoryName, the information is to be
obtained by the application from whatever directory server is locally
configured. When the extension is used to point to CA certificates,
the entry for the directoryName contains CA certificates in the
crossCertificatePair and/or cACertificate attributes as specified in
[RFC4523]. The protocol the application uses to access the directory
(e.g., DAP or LDAP) is a local matter.
Where the information is available via LDAP, the accessLocation
SHOULD be a uniformResourceIdentifier. The LDAP URI [RFC4516] MUST
include a field containing the distinguished name of the entry
holding the certificates, MUST include an field that
lists appropriate attribute descriptions for the attributes that hold
the DER encoded certificates or cross-certificate pairs [RFC4523],
and SHOULD include a (e.g., ).
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Omitting the (e.g., ) has the effect of relying on whatever a priori
knowledge the client might have to contact an appropriate server.
Where the information is available via HTTP or FTP, accessLocation
MUST be a uniformResourceIdentifier and the URI MUST point to either
a single DER encoded certificate as specified in [RFC2585] or a
collection of certificates in a BER or DER encoded "certs-only" CMS
message as specified in [RFC2797].
Conforming applications that support HTTP or FTP for accessing
certificates MUST be able to accept individual DER encoded
certificates and SHOULD be able to accept "certs-only" CMS messages.
HTTP server implementations accessed via the URI SHOULD specify the
media type application/pkix-cert [RFC2585] in the content-type header
field of the response for a single DER encoded certificate and SHOULD
specify the media type application/pkcs7-mime [RFC2797] in the
content-type header field of the response for "certs-only" CMS
messages. For FTP, the name of a file that contains a single DER
encoded certificate SHOULD have a suffix of ".cer" [RFC2585] and the
name of a file that contains a "certs-only" CMS message SHOULD have a
suffix of ".p7c" [RFC2797]. Consuming clients may use the media type
or file extension as a hint to the content, but should not depend
solely on the presence of the correct media type or file extension in
the server response.
The semantics of other id-ad-caRepository accessLocation name forms
are not defined.
A subjectInfoAccess extension may include multiple instances of the
id-ad-caRepository accessMethod. The different instances may specify
different methods for accessing the same information or may point to
different information. When the id-ad-caRepository accessMethod is
used, at least one instance SHOULD specify an accessLocation that is
an HTTP [RFC2616] or LDAP [RFC4516] URI.
The id-ad-timeStamping OID is used when the subject offers
timestamping services using the Time Stamp Protocol defined in
[RFC3161]. Where the timestamping services are available via HTTP or
FTP, accessLocation MUST be a uniformResourceIdentifier. Where the
timestamping services are available via electronic mail,
accessLocation MUST be an rfc822Name. Where timestamping services
are available using TCP/IP, the dNSName or iPAddress name forms may
be used. The semantics of other name forms of accessLocation (when
accessMethod is id-ad-timeStamping) are not defined by this
specification.
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Additional access descriptors may be defined in other PKIX
specifications.
id-ad OBJECT IDENTIFIER ::= { id-pkix 48 }
id-ad-caRepository OBJECT IDENTIFIER ::= { id-ad 5 }
id-ad-timeStamping OBJECT IDENTIFIER ::= { id-ad 3 }
5. CRL and CRL Extensions Profile
As discussed above, one goal of this X.509 v2 CRL profile is to
foster the creation of an interoperable and reusable Internet PKI.
To achieve this goal, guidelines for the use of extensions are
specified, and some assumptions are made about the nature of
information included in the CRL.
CRLs may be used in a wide range of applications and environments
covering a broad spectrum of interoperability goals and an even
broader spectrum of operational and assurance requirements. This
profile establishes a common baseline for generic applications
requiring broad interoperability. The profile defines a set of
information that can be expected in every CRL. Also, the profile
defines common locations within the CRL for frequently used
attributes as well as common representations for these attributes.
CRL issuers issue CRLs. The CRL issuer is either the CA or an entity
that has been authorized by the CA to issue CRLs. CAs publish CRLs
to provide status information about the certificates they issued.
However, a CA may delegate this responsibility to another trusted
authority.
Each CRL has a particular scope. The CRL scope is the set of
certificates that could appear on a given CRL. For example, the
scope could be "all certificates issued by CA X", "all CA
certificates issued by CA X", "all certificates issued by CA X that
have been revoked for reasons of key compromise and CA compromise",
or a set of certificates based on arbitrary local information, such
as "all certificates issued to the NIST employees located in
Boulder".
A complete CRL lists all unexpired certificates, within its scope,
that have been revoked for one of the revocation reasons covered by
the CRL scope. A full and complete CRL lists all unexpired
certificates issued by a CA that have been revoked for any reason.
(Note that since CAs and CRL issuers are identified by name, the
scope of a CRL is not affected by the key used to sign the CRL or the
key(s) used to sign certificates.)
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If the scope of the CRL includes one or more certificates issued by
an entity other than the CRL issuer, then it is an indirect CRL. The
scope of an indirect CRL may be limited to certificates issued by a
single CA or may include certificates issued by multiple CAs. If the
issuer of the indirect CRL is a CA, then the scope of the indirect
CRL MAY also include certificates issued by the issuer of the CRL.
The CRL issuer MAY also generate delta CRLs. A delta CRL only lists
those certificates, within its scope, whose revocation status has
changed since the issuance of a referenced complete CRL. The
referenced complete CRL is referred to as a base CRL. The scope of a
delta CRL MUST be the same as the base CRL that it references.
This profile defines one private Internet CRL extension but does not
define any private CRL entry extensions.
Environments with additional or special purpose requirements may
build on this profile or may replace it.
Conforming CAs are not required to issue CRLs if other revocation or
certificate status mechanisms are provided. When CRLs are issued,
the CRLs MUST be version 2 CRLs, include the date by which the next
CRL will be issued in the nextUpdate field (Section 5.1.2.5), include
the CRL number extension (Section 5.2.3), and include the authority
key identifier extension (Section 5.2.1). Conforming applications
that support CRLs are REQUIRED to process both version 1 and version
2 complete CRLs that provide revocation information for all
certificates issued by one CA. Conforming applications are not
required to support processing of delta CRLs, indirect CRLs, or CRLs
with a scope other than all certificates issued by one CA.
5.1. CRL Fields
The X.509 v2 CRL syntax is as follows. For signature calculation,
the data that is to be signed is ASN.1 DER encoded. ASN.1 DER
encoding is a tag, length, value encoding system for each element.
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CertificateList ::= SEQUENCE {
tbsCertList TBSCertList,
signatureAlgorithm AlgorithmIdentifier,
signatureValue BIT STRING }
TBSCertList ::= SEQUENCE {
version Version OPTIONAL,
-- if present, MUST be v2
signature AlgorithmIdentifier,
issuer Name,
thisUpdate Time,
nextUpdate Time OPTIONAL,
revokedCertificates SEQUENCE OF SEQUENCE {
userCertificate CertificateSerialNumber,
revocationDate Time,
crlEntryExtensions Extensions OPTIONAL
-- if present, version MUST be v2
} OPTIONAL,
crlExtensions [0] EXPLICIT Extensions OPTIONAL
-- if present, version MUST be v2
}
-- Version, Time, CertificateSerialNumber, and Extensions
-- are all defined in the ASN.1 in Section 4.1
-- AlgorithmIdentifier is defined in Section 4.1.1.2
The following items describe the use of the X.509 v2 CRL in the
Internet PKI.
5.1.1. CertificateList Fields
The CertificateList is a SEQUENCE of three required fields. The
fields are described in detail in the following subsections.
5.1.1.1. tbsCertList
The first field in the sequence is the tbsCertList. This field is
itself a sequence containing the name of the issuer, issue date,
issue date of the next list, the optional list of revoked
certificates, and optional CRL extensions. When there are no revoked
certificates, the revoked certificates list is absent. When one or
more certificates are revoked, each entry on the revoked certificate
list is defined by a sequence of user certificate serial number,
revocation date, and optional CRL entry extensions.
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5.1.1.2. signatureAlgorithm
The signatureAlgorithm field contains the algorithm identifier for
the algorithm used by the CRL issuer to sign the CertificateList.
The field is of type AlgorithmIdentifier, which is defined in Section
4.1.1.2. [RFC3279], [RFC4055], and [RFC4491] list supported
algorithms for this specification, but other signature algorithms MAY
also be supported.
This field MUST contain the same algorithm identifier as the
signature field in the sequence tbsCertList (Section 5.1.2.2).
5.1.1.3. signatureValue
The signatureValue field contains a digital signature computed upon
the ASN.1 DER encoded tbsCertList. The ASN.1 DER encoded tbsCertList
is used as the input to the signature function. This signature value
is encoded as a BIT STRING and included in the CRL signatureValue
field. The details of this process are specified for each of the
supported algorithms in [RFC3279], [RFC4055], and [RFC4491].
CAs that are also CRL issuers MAY use one private key to digitally
sign certificates and CRLs, or MAY use separate private keys to
digitally sign certificates and CRLs. When separate private keys are
employed, each of the public keys associated with these private keys
is placed in a separate certificate, one with the keyCertSign bit set
in the key usage extension, and one with the cRLSign bit set in the
key usage extension (Section 4.2.1.3). When separate private keys
are employed, certificates issued by the CA contain one authority key
identifier, and the corresponding CRLs contain a different authority
key identifier. The use of separate CA certificates for validation
of certificate signatures and CRL signatures can offer improved
security characteristics; however, it imposes a burden on
applications, and it might limit interoperability. Many applications
construct a certification path, and then validate the certification
path (Section 6). CRL checking in turn requires a separate
certification path to be constructed and validated for the CA's CRL
signature validation certificate. Applications that perform CRL
checking MUST support certification path validation when certificates
and CRLs are digitally signed with the same CA private key. These
applications SHOULD support certification path validation when
certificates and CRLs are digitally signed with different CA private
keys.
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5.1.2. Certificate List "To Be Signed"
The certificate list to be signed, or TBSCertList, is a sequence of
required and optional fields. The required fields identify the CRL
issuer, the algorithm used to sign the CRL, and the date and time the
CRL was issued.
Optional fields include the date and time by which the CRL issuer
will issue the next CRL, lists of revoked certificates, and CRL
extensions. The revoked certificate list is optional to support the
case where a CA has not revoked any unexpired certificates that it
has issued. This profile requires conforming CRL issuers to include
the nextUpdate field and the CRL number and authority key identifier
CRL extensions in all CRLs issued.
5.1.2.1. Version
This optional field describes the version of the encoded CRL. When
extensions are used, as required by this profile, this field MUST be
present and MUST specify version 2 (the integer value is 1).
5.1.2.2. Signature
This field contains the algorithm identifier for the algorithm used
to sign the CRL. [RFC3279], [RFC4055], and [RFC4491] list OIDs for
the most popular signature algorithms used in the Internet PKI.
This field MUST contain the same algorithm identifier as the
signatureAlgorithm field in the sequence CertificateList (Section
5.1.1.2).
5.1.2.3. Issuer Name
The issuer name identifies the entity that has signed and issued the
CRL. The issuer identity is carried in the issuer field.
Alternative name forms may also appear in the issuerAltName extension
(Section 5.2.2). The issuer field MUST contain a non-empty X.500
distinguished name (DN). The issuer field is defined as the X.501
type Name, and MUST follow the encoding rules for the issuer name
field in the certificate (Section 4.1.2.4).
5.1.2.4. This Update
This field indicates the issue date of this CRL. thisUpdate may be
encoded as UTCTime or GeneralizedTime.
CRL issuers conforming to this profile MUST encode thisUpdate as
UTCTime for dates through the year 2049. CRL issuers conforming to
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this profile MUST encode thisUpdate as GeneralizedTime for dates in
the year 2050 or later. Conforming applications MUST be able to
process dates that are encoded in either UTCTime or GeneralizedTime.
Where encoded as UTCTime, thisUpdate MUST be specified and
interpreted as defined in Section 4.1.2.5.1. Where encoded as
GeneralizedTime, thisUpdate MUST be specified and interpreted as
defined in Section 4.1.2.5.2.
5.1.2.5. Next Update
This field indicates the date by which the next CRL will be issued.
The next CRL could be issued before the indicated date, but it will
not be issued any later than the indicated date. CRL issuers SHOULD
issue CRLs with a nextUpdate time equal to or later than all previous
CRLs. nextUpdate may be encoded as UTCTime or GeneralizedTime.
Conforming CRL issuers MUST include the nextUpdate field in all CRLs.
Note that the ASN.1 syntax of TBSCertList describes this field as
OPTIONAL, which is consistent with the ASN.1 structure defined in
[X.509]. The behavior of clients processing CRLs that omit
nextUpdate is not specified by this profile.
CRL issuers conforming to this profile MUST encode nextUpdate as
UTCTime for dates through the year 2049. CRL issuers conforming to
this profile MUST encode nextUpdate as GeneralizedTime for dates in
the year 2050 or later. Conforming applications MUST be able to
process dates that are encoded in either UTCTime or GeneralizedTime.
Where encoded as UTCTime, nextUpdate MUST be specified and
interpreted as defined in Section 4.1.2.5.1. Where encoded as
GeneralizedTime, nextUpdate MUST be specified and interpreted as
defined in Section 4.1.2.5.2.
5.1.2.6. Revoked Certificates
When there are no revoked certificates, the revoked certificates list
MUST be absent. Otherwise, revoked certificates are listed by their
serial numbers. Certificates revoked by the CA are uniquely
identified by the certificate serial number. The date on which the
revocation occurred is specified. The time for revocationDate MUST
be expressed as described in Section 5.1.2.4. Additional information
may be supplied in CRL entry extensions; CRL entry extensions are
discussed in Section 5.3.
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5.1.2.7. Extensions
This field may only appear if the version is 2 (Section 5.1.2.1). If
present, this field is a sequence of one or more CRL extensions. CRL
extensions are discussed in Section 5.2.
5.2. CRL Extensions
The extensions defined by ANSI X9, ISO/IEC, and ITU-T for X.509 v2
CRLs [X.509] [X9.55] provide methods for associating additional
attributes with CRLs. The X.509 v2 CRL format also allows
communities to define private extensions to carry information unique
to those communities. Each extension in a CRL may be designated as
critical or non-critical. If a CRL contains a critical extension
that the application cannot process, then the application MUST NOT
use that CRL to determine the status of certificates. However,
applications may ignore unrecognized non-critical extensions. The
following subsections present those extensions used within Internet
CRLs. Communities may elect to include extensions in CRLs that are
not defined in this specification. However, caution should be
exercised in adopting any critical extensions in CRLs that might be
used in a general context.
Conforming CRL issuers are REQUIRED to include the authority key
identifier (Section 5.2.1) and the CRL number (Section 5.2.3)
extensions in all CRLs issued.
5.2.1. Authority Key Identifier
The authority key identifier extension provides a means of
identifying the public key corresponding to the private key used to
sign a CRL. The identification can be based on either the key
identifier (the subject key identifier in the CRL signer's
certificate) or the issuer name and serial number. This extension is
especially useful where an issuer has more than one signing key,
either due to multiple concurrent key pairs or due to changeover.
Conforming CRL issuers MUST use the key identifier method, and MUST
include this extension in all CRLs issued.
The syntax for this CRL extension is defined in Section 4.2.1.1.
5.2.2. Issuer Alternative Name
The issuer alternative name extension allows additional identities to
be associated with the issuer of the CRL. Defined options include an
electronic mail address (rfc822Name), a DNS name, an IP address, and
a URI. Multiple instances of a name form and multiple name forms may
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RFC 5280 PKIX Certificate and CRL Profile May 2008
be included. Whenever such identities are used, the issuer
alternative name extension MUST be used; however, a DNS name MAY be
represented in the issuer field using the domainComponent attribute
as described in Section 4.1.2.4.
Conforming CRL issuers SHOULD mark the issuerAltName extension as
non-critical.
The OID and syntax for this CRL extension are defined in Section
4.2.1.7.
5.2.3. CRL Number
The CRL number is a non-critical CRL extension that conveys a
monotonically increasing sequence number for a given CRL scope and
CRL issuer. This extension allows users to easily determine when a
particular CRL supersedes another CRL. CRL numbers also support the
identification of complementary complete CRLs and delta CRLs. CRL
issuers conforming to this profile MUST include this extension in all
CRLs and MUST mark this extension as non-critical.
If a CRL issuer generates delta CRLs in addition to complete CRLs for
a given scope, the complete CRLs and delta CRLs MUST share one
numbering sequence. If a delta CRL and a complete CRL that cover the
same scope are issued at the same time, they MUST have the same CRL
number and provide the same revocation information. That is, the
combination of the delta CRL and an acceptable complete CRL MUST
provide the same revocation information as the simultaneously issued
complete CRL.
If a CRL issuer generates two CRLs (two complete CRLs, two delta
CRLs, or a complete CRL and a delta CRL) for the same scope at
different times, the two CRLs MUST NOT have the same CRL number.
That is, if the this update field (Section 5.1.2.4) in the two CRLs
are not identical, the CRL numbers MUST be different.
Given the requirements above, CRL numbers can be expected to contain
long integers. CRL verifiers MUST be able to handle CRLNumber values
up to 20 octets. Conforming CRL issuers MUST NOT use CRLNumber
values longer than 20 octets.
id-ce-cRLNumber OBJECT IDENTIFIER ::= { id-ce 20 }
CRLNumber ::= INTEGER (0..MAX)
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5.2.4. Delta CRL Indicator
The delta CRL indicator is a critical CRL extension that identifies a
CRL as being a delta CRL. Delta CRLs contain updates to revocation
information previously distributed, rather than all the information
that would appear in a complete CRL. The use of delta CRLs can
significantly reduce network load and processing time in some
environments. Delta CRLs are generally smaller than the CRLs they
update, so applications that obtain delta CRLs consume less network
bandwidth than applications that obtain the corresponding complete
CRLs. Applications that store revocation information in a format
other than the CRL structure can add new revocation information to
the local database without reprocessing information.
The delta CRL indicator extension contains the single value of type
BaseCRLNumber. The CRL number identifies the CRL, complete for a
given scope, that was used as the starting point in the generation of
this delta CRL. A conforming CRL issuer MUST publish the referenced
base CRL as a complete CRL. The delta CRL contains all updates to
the revocation status for that same scope. The combination of a
delta CRL plus the referenced base CRL is equivalent to a complete
CRL, for the applicable scope, at the time of publication of the
delta CRL.
When a conforming CRL issuer generates a delta CRL, the delta CRL
MUST include a critical delta CRL indicator extension.
When a delta CRL is issued, it MUST cover the same set of reasons and
the same set of certificates that were covered by the base CRL it
references. That is, the scope of the delta CRL MUST be the same as
the scope of the complete CRL referenced as the base. The referenced
base CRL and the delta CRL MUST omit the issuing distribution point
extension or contain identical issuing distribution point extensions.
Further, the CRL issuer MUST use the same private key to sign the
delta CRL and any complete CRL that it can be used to update.
An application that supports delta CRLs can construct a CRL that is
complete for a given scope by combining a delta CRL for that scope
with either an issued CRL that is complete for that scope or a
locally constructed CRL that is complete for that scope.
When a delta CRL is combined with a complete CRL or a locally
constructed CRL, the resulting locally constructed CRL has the CRL
number specified in the CRL number extension found in the delta CRL
used in its construction. In addition, the resulting locally
constructed CRL has the thisUpdate and nextUpdate times specified in
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the corresponding fields of the delta CRL used in its construction.
In addition, the locally constructed CRL inherits the issuing
distribution point from the delta CRL.
A complete CRL and a delta CRL MAY be combined if the following four
conditions are satisfied:
(a) The complete CRL and delta CRL have the same issuer.
(b) The complete CRL and delta CRL have the same scope. The two
CRLs have the same scope if either of the following
conditions are met:
(1) The issuingDistributionPoint extension is omitted from
both the complete CRL and the delta CRL.
(2) The issuingDistributionPoint extension is present in both
the complete CRL and the delta CRL, and the values for
each of the fields in the extensions are the same in both
CRLs.
(c) The CRL number of the complete CRL is equal to or greater
than the BaseCRLNumber specified in the delta CRL. That is,
the complete CRL contains (at a minimum) all the revocation
information held by the referenced base CRL.
(d) The CRL number of the complete CRL is less than the CRL
number of the delta CRL. That is, the delta CRL follows the
complete CRL in the numbering sequence.
CRL issuers MUST ensure that the combination of a delta CRL and any
appropriate complete CRL accurately reflects the current revocation
status. The CRL issuer MUST include an entry in the delta CRL for
each certificate within the scope of the delta CRL whose status has
changed since the generation of the referenced base CRL:
(a) If the certificate is revoked for a reason included in the
scope of the CRL, list the certificate as revoked.
(b) If the certificate is valid and was listed on the referenced
base CRL or any subsequent CRL with reason code
certificateHold, and the reason code certificateHold is
included in the scope of the CRL, list the certificate with
the reason code removeFromCRL.
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(c) If the certificate is revoked for a reason outside the scope
of the CRL, but the certificate was listed on the referenced
base CRL or any subsequent CRL with a reason code included in
the scope of this CRL, list the certificate as revoked but
omit the reason code.
(d) If the certificate is revoked for a reason outside the scope
of the CRL and the certificate was neither listed on the
referenced base CRL nor any subsequent CRL with a reason code
included in the scope of this CRL, do not list the
certificate on this CRL.
The status of a certificate is considered to have changed if it is
revoked (for any revocation reason, including certificateHold), if it
is released from hold, or if its revocation reason changes.
It is appropriate to list a certificate with reason code
removeFromCRL on a delta CRL even if the certificate was not on hold
in the referenced base CRL. If the certificate was placed on hold in
any CRL issued after the base but before this delta CRL and then
released from hold, it MUST be listed on the delta CRL with
revocation reason removeFromCRL.
A CRL issuer MAY optionally list a certificate on a delta CRL with
reason code removeFromCRL if the notAfter time specified in the
certificate precedes the thisUpdate time specified in the delta CRL
and the certificate was listed on the referenced base CRL or in any
CRL issued after the base but before this delta CRL.
If a certificate revocation notice first appears on a delta CRL, then
it is possible for the certificate validity period to expire before
the next complete CRL for the same scope is issued. In this case,
the revocation notice MUST be included in all subsequent delta CRLs
until the revocation notice is included on at least one explicitly
issued complete CRL for this scope.
An application that supports delta CRLs MUST be able to construct a
current complete CRL by combining a previously issued complete CRL
and the most current delta CRL. An application that supports delta
CRLs MAY also be able to construct a current complete CRL by
combining a previously locally constructed complete CRL and the
current delta CRL. A delta CRL is considered to be the current one
if the current time is between the times contained in the thisUpdate
and nextUpdate fields. Under some circumstances, the CRL issuer may
publish one or more delta CRLs before the time indicated by the
nextUpdate field. If more than one current delta CRL for a given
scope is encountered, the application SHOULD consider the one with
the latest value in thisUpdate to be the most current one.
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id-ce-deltaCRLIndicator OBJECT IDENTIFIER ::= { id-ce 27 }
BaseCRLNumber ::= CRLNumber
5.2.5. Issuing Distribution Point
The issuing distribution point is a critical CRL extension that
identifies the CRL distribution point and scope for a particular CRL,
and it indicates whether the CRL covers revocation for end entity
certificates only, CA certificates only, attribute certificates only,
or a limited set of reason codes. Although the extension is
critical, conforming implementations are not required to support this
extension. However, implementations that do not support this
extension MUST either treat the status of any certificate not listed
on this CRL as unknown or locate another CRL that does not contain
any unrecognized critical extensions.
The CRL is signed using the CRL issuer's private key. CRL
distribution points do not have their own key pairs. If the CRL is
stored in the X.500 directory, it is stored in the directory entry
corresponding to the CRL distribution point, which may be different
from the directory entry of the CRL issuer.
The reason codes associated with a distribution point MUST be
specified in onlySomeReasons. If onlySomeReasons does not appear,
the distribution point MUST contain revocations for all reason codes.
CAs may use CRL distribution points to partition the CRL on the basis
of compromise and routine revocation. In this case, the revocations
with reason code keyCompromise (1), cACompromise (2), and
aACompromise (8) appear in one distribution point, and the
revocations with other reason codes appear in another distribution
point.
If a CRL includes an issuingDistributionPoint extension with
onlySomeReasons present, then every certificate in the scope of the
CRL that is revoked MUST be assigned a revocation reason other than
unspecified. The assigned revocation reason is used to determine on
which CRL(s) to list the revoked certificate, however, there is no
requirement to include the reasonCode CRL entry extension in the
corresponding CRL entry.
The syntax and semantics for the distributionPoint field are the same
as for the distributionPoint field in the cRLDistributionPoints
extension (Section 4.2.1.13). If the distributionPoint field is
present, then it MUST include at least one of names from the
corresponding distributionPoint field of the cRLDistributionPoints
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extension of every certificate that is within the scope of this CRL.
The identical encoding MUST be used in the distributionPoint fields
of the certificate and the CRL.
If the distributionPoint field is absent, the CRL MUST contain
entries for all revoked unexpired certificates issued by the CRL
issuer, if any, within the scope of the CRL.
If the scope of the CRL only includes certificates issued by the CRL
issuer, then the indirectCRL boolean MUST be set to FALSE.
Otherwise, if the scope of the CRL includes certificates issued by
one or more authorities other than the CRL issuer, the indirectCRL
boolean MUST be set to TRUE. The authority responsible for each
entry is indicated by the certificate issuer CRL entry extension
(Section 5.3.3).
If the scope of the CRL only includes end entity public key
certificates, then onlyContainsUserCerts MUST be set to TRUE. If the
scope of the CRL only includes CA certificates, then
onlyContainsCACerts MUST be set to TRUE. If either
onlyContainsUserCerts or onlyContainsCACerts is set to TRUE, then the
scope of the CRL MUST NOT include any version 1 or version 2
certificates. Conforming CRLs issuers MUST set the
onlyContainsAttributeCerts boolean to FALSE.
Conforming CRLs issuers MUST NOT issue CRLs where the DER encoding of
the issuing distribution point extension is an empty sequence. That
is, if onlyContainsUserCerts, onlyContainsCACerts, indirectCRL, and
onlyContainsAttributeCerts are all FALSE, then either the
distributionPoint field or the onlySomeReasons field MUST be present.
id-ce-issuingDistributionPoint OBJECT IDENTIFIER ::= { id-ce 28 }
IssuingDistributionPoint ::= SEQUENCE {
distributionPoint [0] DistributionPointName OPTIONAL,
onlyContainsUserCerts [1] BOOLEAN DEFAULT FALSE,
onlyContainsCACerts [2] BOOLEAN DEFAULT FALSE,
onlySomeReasons [3] ReasonFlags OPTIONAL,
indirectCRL [4] BOOLEAN DEFAULT FALSE,
onlyContainsAttributeCerts [5] BOOLEAN DEFAULT FALSE }
-- at most one of onlyContainsUserCerts, onlyContainsCACerts,
-- and onlyContainsAttributeCerts may be set to TRUE.
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5.2.6. Freshest CRL (a.k.a. Delta CRL Distribution Point)
The freshest CRL extension identifies how delta CRL information for
this complete CRL is obtained. Conforming CRL issuers MUST mark this
extension as non-critical. This extension MUST NOT appear in delta
CRLs.
The same syntax is used for this extension as the
cRLDistributionPoints certificate extension, and is described in
Section 4.2.1.13. However, only the distribution point field is
meaningful in this context. The reasons and cRLIssuer fields MUST be
omitted from this CRL extension.
Each distribution point name provides the location at which a delta
CRL for this complete CRL can be found. The scope of these delta
CRLs MUST be the same as the scope of this complete CRL. The
contents of this CRL extension are only used to locate delta CRLs;
the contents are not used to validate the CRL or the referenced delta
CRLs. The encoding conventions defined for distribution points in
Section 4.2.1.13 apply to this extension.
id-ce-freshestCRL OBJECT IDENTIFIER ::= { id-ce 46 }
FreshestCRL ::= CRLDistributionPoints
5.2.7. Authority Information Access
This section defines the use of the Authority Information Access
extension in a CRL. The syntax and semantics defined in Section
4.2.2.1 for the certificate extension are also used for the CRL
extension.
This CRL extension MUST be marked as non-critical.
When present in a CRL, this extension MUST include at least one
AccessDescription specifying id-ad-caIssuers as the accessMethod.
The id-ad-caIssuers OID is used when the information available lists
certificates that can be used to verify the signature on the CRL
(i.e., certificates that have a subject name that matches the issuer
name on the CRL and that have a subject public key that corresponds
to the private key used to sign the CRL). Access method types other
than id-ad-caIssuers MUST NOT be included. At least one instance of
AccessDescription SHOULD specify an accessLocation that is an HTTP
[RFC2616] or LDAP [RFC4516] URI.
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Where the information is available via HTTP or FTP, accessLocation
MUST be a uniformResourceIdentifier and the URI MUST point to either
a single DER encoded certificate as specified in [RFC2585] or a
collection of certificates in a BER or DER encoded "certs-only" CMS
message as specified in [RFC2797].
Conforming applications that support HTTP or FTP for accessing
certificates MUST be able to accept individual DER encoded
certificates and SHOULD be able to accept "certs-only" CMS messages.
HTTP server implementations accessed via the URI SHOULD specify the
media type application/pkix-cert [RFC2585] in the content-type header
field of the response for a single DER encoded certificate and SHOULD
specify the media type application/pkcs7-mime [RFC2797] in the
content-type header field of the response for "certs-only" CMS
messages. For FTP, the name of a file that contains a single DER
encoded certificate SHOULD have a suffix of ".cer" [RFC2585] and the
name of a file that contains a "certs-only" CMS message SHOULD have a
suffix of ".p7c" [RFC2797]. Consuming clients may use the media type
or file extension as a hint to the content, but should not depend
solely on the presence of the correct media type or file extension in
the server response.
When the accessLocation is a directoryName, the information is to be
obtained by the application from whatever directory server is locally
configured. When one CA public key is used to validate signatures on
certificates and CRLs, the desired CA certificate is stored in the
crossCertificatePair and/or cACertificate attributes as specified in
[RFC4523]. When different public keys are used to validate
signatures on certificates and CRLs, the desired certificate is
stored in the userCertificate attribute as specified in [RFC4523].
Thus, implementations that support the directoryName form of
accessLocation MUST be prepared to find the needed certificate in any
of these three attributes. The protocol that an application uses to
access the directory (e.g., DAP or LDAP) is a local matter.
Where the information is available via LDAP, the accessLocation
SHOULD be a uniformResourceIdentifier. The LDAP URI [RFC4516] MUST
include a field containing the distinguished name of the entry
holding the certificates, MUST include an field that
lists appropriate attribute descriptions for the attributes that hold
the DER encoded certificates or cross-certificate pairs [RFC4523],
and SHOULD include a (e.g., ).
Omitting the (e.g., ) has the effect of relying on whatever a priori
knowledge the client might have to contact an appropriate server.
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5.3. CRL Entry Extensions
The CRL entry extensions defined by ISO/IEC, ITU-T, and ANSI X9 for
X.509 v2 CRLs provide methods for associating additional attributes
with CRL entries [X.509] [X9.55]. The X.509 v2 CRL format also
allows communities to define private CRL entry extensions to carry
information unique to those communities. Each extension in a CRL
entry may be designated as critical or non-critical. If a CRL
contains a critical CRL entry extension that the application cannot
process, then the application MUST NOT use that CRL to determine the
status of any certificates. However, applications may ignore
unrecognized non-critical CRL entry extensions.
The following subsections present recommended extensions used within
Internet CRL entries and standard locations for information.
Communities may elect to use additional CRL entry extensions;
however, caution should be exercised in adopting any critical CRL
entry extensions in CRLs that might be used in a general context.
Support for the CRL entry extensions defined in this specification is
optional for conforming CRL issuers and applications. However, CRL
issuers SHOULD include reason codes (Section 5.3.1) and invalidity
dates (Section 5.3.2) whenever this information is available.
5.3.1. Reason Code
The reasonCode is a non-critical CRL entry extension that identifies
the reason for the certificate revocation. CRL issuers are strongly
encouraged to include meaningful reason codes in CRL entries;
however, the reason code CRL entry extension SHOULD be absent instead
of using the unspecified (0) reasonCode value.
The removeFromCRL (8) reasonCode value may only appear in delta CRLs
and indicates that a certificate is to be removed from a CRL because
either the certificate expired or was removed from hold. All other
reason codes may appear in any CRL and indicate that the specified
certificate should be considered revoked.
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id-ce-cRLReasons OBJECT IDENTIFIER ::= { id-ce 21 }
-- reasonCode ::= { CRLReason }
CRLReason ::= ENUMERATED {
unspecified (0),
keyCompromise (1),
cACompromise (2),
affiliationChanged (3),
superseded (4),
cessationOfOperation (5),
certificateHold (6),
-- value 7 is not used
removeFromCRL (8),
privilegeWithdrawn (9),
aACompromise (10) }
5.3.2. Invalidity Date
The invalidity date is a non-critical CRL entry extension that
provides the date on which it is known or suspected that the private
key was compromised or that the certificate otherwise became invalid.
This date may be earlier than the revocation date in the CRL entry,
which is the date at which the CA processed the revocation. When a
revocation is first posted by a CRL issuer in a CRL, the invalidity
date may precede the date of issue of earlier CRLs, but the
revocation date SHOULD NOT precede the date of issue of earlier CRLs.
Whenever this information is available, CRL issuers are strongly
encouraged to share it with CRL users.
The GeneralizedTime values included in this field MUST be expressed
in Greenwich Mean Time (Zulu), and MUST be specified and interpreted
as defined in Section 4.1.2.5.2.
id-ce-invalidityDate OBJECT IDENTIFIER ::= { id-ce 24 }
InvalidityDate ::= GeneralizedTime
5.3.3. Certificate Issuer
This CRL entry extension identifies the certificate issuer associated
with an entry in an indirect CRL, that is, a CRL that has the
indirectCRL indicator set in its issuing distribution point
extension. When present, the certificate issuer CRL entry extension
includes one or more names from the issuer field and/or issuer
alternative name extension of the certificate that corresponds to the
CRL entry. If this extension is not present on the first entry in an
indirect CRL, the certificate issuer defaults to the CRL issuer. On
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subsequent entries in an indirect CRL, if this extension is not
present, the certificate issuer for the entry is the same as that for
the preceding entry. This field is defined as follows:
id-ce-certificateIssuer OBJECT IDENTIFIER ::= { id-ce 29 }
CertificateIssuer ::= GeneralNames
Conforming CRL issuers MUST include in this extension the
distinguished name (DN) from the issuer field of the certificate that
corresponds to this CRL entry. The encoding of the DN MUST be
identical to the encoding used in the certificate.
CRL issuers MUST mark this extension as critical since an
implementation that ignored this extension could not correctly
attribute CRL entries to certificates. This specification RECOMMENDS
that implementations recognize this extension.
6. Certification Path Validation
Certification path validation procedures for the Internet PKI are
based on the algorithm supplied in [X.509]. Certification path
processing verifies the binding between the subject distinguished
name and/or subject alternative name and subject public key. The
binding is limited by constraints that are specified in the
certificates that comprise the path and inputs that are specified by
the relying party. The basic constraints and policy constraints
extensions allow the certification path processing logic to automate
the decision making process.
This section describes an algorithm for validating certification
paths. Conforming implementations of this specification are not
required to implement this algorithm, but MUST provide functionality
equivalent to the external behavior resulting from this procedure.
Any algorithm may be used by a particular implementation so long as
it derives the correct result.
In Section 6.1, the text describes basic path validation. Valid
paths begin with certificates issued by a trust anchor. The
algorithm requires the public key of the CA, the CA's name, and any
constraints upon the set of paths that may be validated using this
key.
The selection of a trust anchor is a matter of policy: it could be
the top CA in a hierarchical PKI, the CA that issued the verifier's
own certificate(s), or any other CA in a network PKI. The path
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validation procedure is the same regardless of the choice of trust
anchor. In addition, different applications may rely on different
trust anchors, or may accept paths that begin with any of a set of
trust anchors.
Section 6.2 describes methods for using the path validation algorithm
in specific implementations.
Section 6.3 describes the steps necessary to determine if a
certificate is revoked when CRLs are the revocation mechanism used by
the certificate issuer.
6.1. Basic Path Validation
This text describes an algorithm for X.509 path processing. A
conforming implementation MUST include an X.509 path processing
procedure that is functionally equivalent to the external behavior of
this algorithm. However, support for some of the certificate
extensions processed in this algorithm are OPTIONAL for compliant
implementations. Clients that do not support these extensions MAY
omit the corresponding steps in the path validation algorithm.
For example, clients are not required to support the policy mappings
extension. Clients that do not support this extension MAY omit the
path validation steps where policy mappings are processed. Note that
clients MUST reject the certificate if it contains an unsupported
critical extension.
While the certificate and CRL profiles specified in Sections 4 and 5
of this document specify values for certificate and CRL fields and
extensions that are considered to be appropriate for the Internet
PKI, the algorithm presented in this section is not limited to
accepting certificates and CRLs that conform to these profiles.
Therefore, the algorithm only includes checks to verify that the
certification path is valid according to X.509 and does not include
checks to verify that the certificates and CRLs conform to this
profile. While the algorithm could be extended to include checks for
conformance to the profiles in Sections 4 and 5, this profile
RECOMMENDS against including such checks.
The algorithm presented in this section validates the certificate
with respect to the current date and time. A conforming
implementation MAY also support validation with respect to some point
in the past. Note that mechanisms are not available for validating a
certificate with respect to a time outside the certificate validity
period.
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The trust anchor is an input to the algorithm. There is no
requirement that the same trust anchor be used to validate all
certification paths. Different trust anchors MAY be used to validate
different paths, as discussed further in Section 6.2.
The primary goal of path validation is to verify the binding between
a subject distinguished name or a subject alternative name and
subject public key, as represented in the target certificate, based
on the public key of the trust anchor. In most cases, the target
certificate will be an end entity certificate, but the target
certificate may be a CA certificate as long as the subject public key
is to be used for a purpose other than verifying the signature on a
public key certificate. Verifying the binding between the name and
subject public key requires obtaining a sequence of certificates that
support that binding. The procedure performed to obtain this
sequence of certificates is outside the scope of this specification.
To meet this goal, the path validation process verifies, among other
things, that a prospective certification path (a sequence of n
certificates) satisfies the following conditions:
(a) for all x in {1, ..., n-1}, the subject of certificate x is
the issuer of certificate x+1;
(b) certificate 1 is issued by the trust anchor;
(c) certificate n is the certificate to be validated (i.e., the
target certificate); and
(d) for all x in {1, ..., n}, the certificate was valid at the
time in question.
A certificate MUST NOT appear more than once in a prospective
certification path.
When the trust anchor is provided in the form of a self-signed
certificate, this self-signed certificate is not included as part of
the prospective certification path. Information about trust anchors
is provided as inputs to the certification path validation algorithm
(Section 6.1.1).
A particular certification path may not, however, be appropriate for
all applications. Therefore, an application MAY augment this
algorithm to further limit the set of valid paths. The path
validation process also determines the set of certificate policies
that are valid for this path, based on the certificate policies
extension, policy mappings extension, policy constraints extension,
and inhibit anyPolicy extension. To achieve this, the path
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validation algorithm constructs a valid policy tree. If the set of
certificate policies that are valid for this path is not empty, then
the result will be a valid policy tree of depth n, otherwise the
result will be a null valid policy tree.
A certificate is self-issued if the same DN appears in the subject
and issuer fields (the two DNs are the same if they match according
to the rules specified in Section 7.1). In general, the issuer and
subject of the certificates that make up a path are different for
each certificate. However, a CA may issue a certificate to itself to
support key rollover or changes in certificate policies. These
self-issued certificates are not counted when evaluating path length
or name constraints.
This section presents the algorithm in four basic steps: (1)
initialization, (2) basic certificate processing, (3) preparation for
the next certificate, and (4) wrap-up. Steps (1) and (4) are
performed exactly once. Step (2) is performed for all certificates
in the path. Step (3) is performed for all certificates in the path
except the final certificate. Figure 2 provides a high-level
flowchart of this algorithm.
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+-------+
| START |
+-------+
|
V
+----------------+
| Initialization |
+----------------+
|
+<--------------------+
| |
V |
+----------------+ |
| Process Cert | |
+----------------+ |
| |
V |
+================+ |
| IF Last Cert | |
| in Path | |
+================+ |
| | |
THEN | | ELSE |
V V |
+----------------+ +----------------+ |
| Wrap up | | Prepare for | |
+----------------+ | Next Cert | |
| +----------------+ |
V | |
+-------+ +--------------+
| STOP |
+-------+
Figure 2. Certification Path Processing Flowchart
6.1.1. Inputs
This algorithm assumes that the following nine inputs are provided to
the path processing logic:
(a) a prospective certification path of length n.
(b) the current date/time.
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(c) user-initial-policy-set: A set of certificate policy
identifiers naming the policies that are acceptable to the
certificate user. The user-initial-policy-set contains the
special value any-policy if the user is not concerned about
certificate policy.
(d) trust anchor information, describing a CA that serves as a
trust anchor for the certification path. The trust anchor
information includes:
(1) the trusted issuer name,
(2) the trusted public key algorithm,
(3) the trusted public key, and
(4) optionally, the trusted public key parameters associated
with the public key.
The trust anchor information may be provided to the path
processing procedure in the form of a self-signed certificate.
When the trust anchor information is provided in the form of a
certificate, the name in the subject field is used as the trusted
issuer name and the contents of the subjectPublicKeyInfo field is
used as the source of the trusted public key algorithm and the
trusted public key. The trust anchor information is trusted
because it was delivered to the path processing procedure by some
trustworthy out-of-band procedure. If the trusted public key
algorithm requires parameters, then the parameters are provided
along with the trusted public key.
(e) initial-policy-mapping-inhibit, which indicates if policy
mapping is allowed in the certification path.
(f) initial-explicit-policy, which indicates if the path must be
valid for at least one of the certificate policies in the
user-initial-policy-set.
(g) initial-any-policy-inhibit, which indicates whether the
anyPolicy OID should be processed if it is included in a
certificate.
(h) initial-permitted-subtrees, which indicates for each name
type (e.g., X.500 distinguished names, email addresses, or IP
addresses) a set of subtrees within which all subject names
in every certificate in the certification path MUST fall.
The initial-permitted-subtrees input includes a set for each
name type. For each name type, the set may consist of a
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single subtree that includes all names of that name type or
one or more subtrees that each specifies a subset of the
names of that name type, or the set may be empty. If the set
for a name type is empty, then the certification path will be
considered invalid if any certificate in the certification
path includes a name of that name type.
(i) initial-excluded-subtrees, which indicates for each name type
(e.g., X.500 distinguished names, email addresses, or IP
addresses) a set of subtrees within which no subject name in
any certificate in the certification path may fall. The
initial-excluded-subtrees input includes a set for each name
type. For each name type, the set may be empty or may
consist of one or more subtrees that each specifies a subset
of the names of that name type. If the set for a name type
is empty, then no names of that name type are excluded.
Conforming implementations are not required to support the setting of
all of these inputs. For example, a conforming implementation may be
designed to validate all certification paths using a value of FALSE
for initial-any-policy-inhibit.
6.1.2. Initialization
This initialization phase establishes eleven state variables based
upon the nine inputs:
(a) valid_policy_tree: A tree of certificate policies with their
optional qualifiers; each of the leaves of the tree
represents a valid policy at this stage in the certification
path validation. If valid policies exist at this stage in
the certification path validation, the depth of the tree is
equal to the number of certificates in the chain that have
been processed. If valid policies do not exist at this stage
in the certification path validation, the tree is set to
NULL. Once the tree is set to NULL, policy processing
ceases.
Each node in the valid_policy_tree includes three data
objects: the valid policy, a set of associated policy
qualifiers, and a set of one or more expected policy values.
If the node is at depth x, the components of the node have
the following semantics:
(1) The valid_policy is a single policy OID representing a
valid policy for the path of length x.
Cooper, et al. Standards Track [Page 77]
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(2) The qualifier_set is a set of policy qualifiers associated
with the valid policy in certificate x.
(3) The expected_policy_set contains one or more policy OIDs
that would satisfy this policy in the certificate x+1.
The initial value of the valid_policy_tree is a single node with
valid_policy anyPolicy, an empty qualifier_set, and an
expected_policy_set with the single value anyPolicy. This node is
considered to be at depth zero.
Figure 3 is a graphic representation of the initial state of the
valid_policy_tree. Additional figures will use this format to
describe changes in the valid_policy_tree during path processing.
+----------------+
| anyPolicy | <---- valid_policy
+----------------+
| {} | <---- qualifier_set
+----------------+
| {anyPolicy} | <---- expected_policy_set
+----------------+
Figure 3. Initial Value of the valid_policy_tree State Variable
(b) permitted_subtrees: a set of root names for each name type
(e.g., X.500 distinguished names, email addresses, or IP
addresses) defining a set of subtrees within which all
subject names in subsequent certificates in the certification
path MUST fall. This variable includes a set for each name
type, and the initial value is initial-permitted-subtrees.
(c) excluded_subtrees: a set of root names for each name type
(e.g., X.500 distinguished names, email addresses, or IP
addresses) defining a set of subtrees within which no subject
name in subsequent certificates in the certification path may
fall. This variable includes a set for each name type, and
the initial value is initial-excluded-subtrees.
(d) explicit_policy: an integer that indicates if a non-NULL
valid_policy_tree is required. The integer indicates the
number of non-self-issued certificates to be processed before
this requirement is imposed. Once set, this variable may be
decreased, but may not be increased. That is, if a
certificate in the path requires a non-NULL
valid_policy_tree, a later certificate cannot remove this
requirement. If initial-explicit-policy is set, then the
initial value is 0, otherwise the initial value is n+1.
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(e) inhibit_anyPolicy: an integer that indicates whether the
anyPolicy policy identifier is considered a match. The
integer indicates the number of non-self-issued certificates
to be processed before the anyPolicy OID, if asserted in a
certificate other than an intermediate self-issued
certificate, is ignored. Once set, this variable may be
decreased, but may not be increased. That is, if a
certificate in the path inhibits processing of anyPolicy, a
later certificate cannot permit it. If initial-any-policy-
inhibit is set, then the initial value is 0, otherwise the
initial value is n+1.
(f) policy_mapping: an integer that indicates if policy mapping
is permitted. The integer indicates the number of non-self-
issued certificates to be processed before policy mapping is
inhibited. Once set, this variable may be decreased, but may
not be increased. That is, if a certificate in the path
specifies that policy mapping is not permitted, it cannot be
overridden by a later certificate. If initial-policy-
mapping-inhibit is set, then the initial value is 0,
otherwise the initial value is n+1.
(g) working_public_key_algorithm: the digital signature
algorithm used to verify the signature of a certificate. The
working_public_key_algorithm is initialized from the trusted
public key algorithm provided in the trust anchor
information.
(h) working_public_key: the public key used to verify the
signature of a certificate. The working_public_key is
initialized from the trusted public key provided in the trust
anchor information.
(i) working_public_key_parameters: parameters associated with
the current public key that may be required to verify a
signature (depending upon the algorithm). The
working_public_key_parameters variable is initialized from
the trusted public key parameters provided in the trust
anchor information.
(j) working_issuer_name: the issuer distinguished name expected
in the next certificate in the chain. The
working_issuer_name is initialized to the trusted issuer name
provided in the trust anchor information.
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RFC 5280 PKIX Certificate and CRL Profile May 2008
(k) max_path_length: this integer is initialized to n, is
decremented for each non-self-issued certificate in the path,
and may be reduced to the value in the path length constraint
field within the basic constraints extension of a CA
certificate.
Upon completion of the initialization steps, perform the basic
certificate processing steps specified in 6.1.3.
6.1.3. Basic Certificate Processing
The basic path processing actions to be performed for certificate i
(for all i in [1..n]) are listed below.
(a) Verify the basic certificate information. The certificate
MUST satisfy each of the following:
(1) The signature on the certificate can be verified using
working_public_key_algorithm, the working_public_key, and
the working_public_key_parameters.
(2) The certificate validity period includes the current time.
(3) At the current time, the certificate is not revoked. This
may be determined by obtaining the appropriate CRL
(Section 6.3), by status information, or by out-of-band
mechanisms.
(4) The certificate issuer name is the working_issuer_name.
(b) If certificate i is self-issued and it is not the final
certificate in the path, skip this step for certificate i.
Otherwise, verify that the subject name is within one of the
permitted_subtrees for X.500 distinguished names, and verify
that each of the alternative names in the subjectAltName
extension (critical or non-critical) is within one of the
permitted_subtrees for that name type.
(c) If certificate i is self-issued and it is not the final
certificate in the path, skip this step for certificate i.
Otherwise, verify that the subject name is not within any of
the excluded_subtrees for X.500 distinguished names, and
verify that each of the alternative names in the
subjectAltName extension (critical or non-critical) is not
within any of the excluded_subtrees for that name type.
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RFC 5280 PKIX Certificate and CRL Profile May 2008
(d) If the certificate policies extension is present in the
certificate and the valid_policy_tree is not NULL, process
the policy information by performing the following steps in
order:
(1) For each policy P not equal to anyPolicy in the
certificate policies extension, let P-OID denote the OID
for policy P and P-Q denote the qualifier set for policy
P. Perform the following steps in order:
(i) For each node of depth i-1 in the valid_policy_tree
where P-OID is in the expected_policy_set, create a
child node as follows: set the valid_policy to P-OID,
set the qualifier_set to P-Q, and set the
expected_policy_set to
{P-OID}.
For example, consider a valid_policy_tree with a node
of depth i-1 where the expected_policy_set is {Gold,
White}. Assume the certificate policies Gold and
Silver appear in the certificate policies extension of
certificate i. The Gold policy is matched, but the
Silver policy is not. This rule will generate a child
node of depth i for the Gold policy. The result is
shown as Figure 4.
+-----------------+
| Red |
+-----------------+
| {} |
+-----------------+ node of depth i-1
| {Gold, White} |
+-----------------+
|
|
|
V
+-----------------+
| Gold |
+-----------------+
| {} |
+-----------------+ node of depth i
| {Gold} |
+-----------------+
Figure 4. Processing an Exact Match
Cooper, et al. Standards Track [Page 81]
RFC 5280 PKIX Certificate and CRL Profile May 2008
(ii) If there was no match in step (i) and the
valid_policy_tree includes a node of depth i-1 with
the valid_policy anyPolicy, generate a child node with
the following values: set the valid_policy to P-OID,
set the qualifier_set to P-Q, and set the
expected_policy_set to {P-OID}.
For example, consider a valid_policy_tree with a node
of depth i-1 where the valid_policy is anyPolicy.
Assume the certificate policies Gold and Silver appear
in the certificate policies extension of certificate
i. The Gold policy does not have a qualifier, but the
Silver policy has the qualifier Q-Silver. If Gold and
Silver were not matched in (i) above, this rule will
generate two child nodes of depth i, one for each
policy. The result is shown as Figure 5.
+-----------------+
| anyPolicy |
+-----------------+
| {} |
+-----------------+ node of depth i-1
| {anyPolicy} |
+-----------------+
/ \
/ \
/ \
/ \
+-----------------+ +-----------------+
| Gold | | Silver |
+-----------------+ +-----------------+
| {} | | {Q-Silver} |
+-----------------+ nodes of +-----------------+
| {Gold} | depth i | {Silver} |
+-----------------+ +-----------------+
Figure 5. Processing Unmatched Policies when a
Leaf Node Specifies anyPolicy
(2) If the certificate policies extension includes the policy
anyPolicy with the qualifier set AP-Q and either (a)
inhibit_anyPolicy is greater than 0 or (b) i.
The binaries for the certificates and CRLs are available at
http://csrc.nist.gov/groups/ST/crypto_apps_infra/documents/pkixtools.
Cooper, et al. Standards Track [Page 136]
RFC 5280 PKIX Certificate and CRL Profile May 2008
In places in this appendix where a distinguished name is specified
using a string representation, the strings are formatted using the
rules specified in [RFC4514].
C.1. RSA Self-Signed Certificate
This appendix contains an annotated hex dump of a 578 byte version 3
certificate. The certificate contains the following information:
(a) the serial number is 17;
(b) the certificate is signed with RSA and the SHA-1 hash algorithm;
(c) the issuer's distinguished name is
cn=Example CA,dc=example,dc=com;
(d) the subject's distinguished name is
cn=Example CA,dc=example,dc=com;
(e) the certificate was issued on April 30, 2004 and expired on
April 30, 2005;
(f) the certificate contains a 1024-bit RSA public key;
(g) the certificate contains a subject key identifier extension
generated using method (1) of Section 4.2.1.2; and
(h) the certificate is a CA certificate (as indicated through the
basic constraints extension).
0 574: SEQUENCE {
4 423: SEQUENCE {
8 3: [0] {
10 1: INTEGER 2
: }
13 1: INTEGER 17
16 13: SEQUENCE {
18 9: OBJECT IDENTIFIER
: sha1withRSAEncryption (1 2 840 113549 1 1 5)
29 0: NULL
: }
31 67: SEQUENCE {
33 19: SET {
35 17: SEQUENCE {
37 10: OBJECT IDENTIFIER
: domainComponent (0 9 2342 19200300 100 1 25)
49 3: IA5String 'com'
: }
: }
54 23: SET {
56 21: SEQUENCE {
58 10: OBJECT IDENTIFIER
: domainComponent (0 9 2342 19200300 100 1 25)
70 7: IA5String 'example'
: }
Cooper, et al. Standards Track [Page 137]
RFC 5280 PKIX Certificate and CRL Profile May 2008
: }
79 19: SET {
81 17: SEQUENCE {
83 3: OBJECT IDENTIFIER commonName (2 5 4 3)
88 10: PrintableString 'Example CA'
: }
: }
: }
100 30: SEQUENCE {
102 13: UTCTime 30/04/2004 14:25:34 GMT
117 13: UTCTime 30/04/2005 14:25:34 GMT
: }
132 67: SEQUENCE {
134 19: SET {
136 17: SEQUENCE {
138 10: OBJECT IDENTIFIER
: domainComponent (0 9 2342 19200300 100 1 25)
150 3: IA5String 'com'
: }
: }
155 23: SET {
157 21: SEQUENCE {
159 10: OBJECT IDENTIFIER
: domainComponent (0 9 2342 19200300 100 1 25)
171 7: IA5String 'example'
: }
: }
180 19: SET {
182 17: SEQUENCE {
184 3: OBJECT IDENTIFIER commonName (2 5 4 3)
189 10: PrintableString 'Example CA'
: }
: }
: }
201 159: SEQUENCE {
204 13: SEQUENCE {
206 9: OBJECT IDENTIFIER
: rsaEncryption (1 2 840 113549 1 1 1)
217 0: NULL
: }
219 141: BIT STRING, encapsulates {
223 137: SEQUENCE {
226 129: INTEGER
: 00 C2 D7 97 6D 28 70 AA 5B CF 23 2E 80 70 39 EE
: DB 6F D5 2D D5 6A 4F 7A 34 2D F9 22 72 47 70 1D
: EF 80 E9 CA 30 8C 00 C4 9A 6E 5B 45 B4 6E A5 E6
: 6C 94 0D FA 91 E9 40 FC 25 9D C7 B7 68 19 56 8F
: 11 70 6A D7 F1 C9 11 4F 3A 7E 3F 99 8D 6E 76 A5
Cooper, et al. Standards Track [Page 138]
RFC 5280 PKIX Certificate and CRL Profile May 2008
: 74 5F 5E A4 55 53 E5 C7 68 36 53 C7 1D 3B 12 A6
: 85 FE BD 6E A1 CA DF 35 50 AC 08 D7 B9 B4 7E 5C
: FE E2 A3 2C D1 23 84 AA 98 C0 9B 66 18 9A 68 47
: E9
358 3: INTEGER 65537
: }
: }
: }
363 66: [3] {
365 64: SEQUENCE {
367 29: SEQUENCE {
369 3: OBJECT IDENTIFIER subjectKeyIdentifier (2 5 29 14)
374 22: OCTET STRING, encapsulates {
376 20: OCTET STRING
: 08 68 AF 85 33 C8 39 4A 7A F8 82 93 8E 70 6A 4A
: 20 84 2C 32
: }
: }
398 14: SEQUENCE {
400 3: OBJECT IDENTIFIER keyUsage (2 5 29 15)
405 1: BOOLEAN TRUE
408 4: OCTET STRING, encapsulates {
410 2: BIT STRING 1 unused bits
: '0000011'B
: }
: }
414 15: SEQUENCE {
416 3: OBJECT IDENTIFIER basicConstraints (2 5 29 19)
421 1: BOOLEAN TRUE
424 5: OCTET STRING, encapsulates {
426 3: SEQUENCE {
428 1: BOOLEAN TRUE
: }
: }
: }
: }
: }
: }
431 13: SEQUENCE {
433 9: OBJECT IDENTIFIER
: sha1withRSAEncryption (1 2 840 113549 1 1 5)
444 0: NULL
: }
446 129: BIT STRING
: 6C F8 02 74 A6 61 E2 64 04 A6 54 0C 6C 72 13 AD
: 3C 47 FB F6 65 13 A9 85 90 33 EA 76 A3 26 D9 FC
: D1 0E 15 5F 28 B7 EF 93 BF 3C F3 E2 3E 7C B9 52
: FC 16 6E 29 AA E1 F4 7A 6F D5 7F EF B3 95 CA F3
Cooper, et al. Standards Track [Page 139]
RFC 5280 PKIX Certificate and CRL Profile May 2008
: 66 88 83 4E A1 35 45 84 CB BC 9B B8 C8 AD C5 5E
: 46 D9 0B 0E 8D 80 E1 33 2B DC BE 2B 92 7E 4A 43
: A9 6A EF 8A 63 61 B3 6E 47 38 BE E8 0D A3 67 5D
: F3 FA 91 81 3C 92 BB C5 5F 25 25 EB 7C E7 D8 A1
: }
C.2. End Entity Certificate Using RSA
This appendix contains an annotated hex dump of a 629-byte version 3
certificate. The certificate contains the following information:
(a) the serial number is 18;
(b) the certificate is signed with RSA and the SHA-1 hash algorithm;
(c) the issuer's distinguished name is
cn=Example CA,dc=example,dc=com;
(d) the subject's distinguished name is
cn=End Entity,dc=example,dc=com;
(e) the certificate was valid from September 15, 2004 through March
15, 2005;
(f) the certificate contains a 1024-bit RSA public key;
(g) the certificate is an end entity certificate, as the basic
constraints extension is not present;
(h) the certificate contains an authority key identifier extension
matching the subject key identifier of the certificate in
appendix C.1; and
(i) the certificate includes one alternative name -- an electronic
mail address (rfc822Name) of "end.entity@example.com".
0 625: SEQUENCE {
4 474: SEQUENCE {
8 3: [0] {
10 1: INTEGER 2
: }
13 1: INTEGER 18
16 13: SEQUENCE {
18 9: OBJECT IDENTIFIER
: sha1withRSAEncryption (1 2 840 113549 1 1 5)
29 0: NULL
: }
31 67: SEQUENCE {
33 19: SET {
35 17: SEQUENCE {
37 10: OBJECT IDENTIFIER
: domainComponent (0 9 2342 19200300 100 1 25)
49 3: IA5String 'com'
: }
: }
54 23: SET {
Cooper, et al. Standards Track [Page 140]
RFC 5280 PKIX Certificate and CRL Profile May 2008
56 21: SEQUENCE {
58 10: OBJECT IDENTIFIER
: domainComponent (0 9 2342 19200300 100 1 25)
70 7: IA5String 'example'
: }
: }
79 19: SET {
81 17: SEQUENCE {
83 3: OBJECT IDENTIFIER commonName (2 5 4 3)
88 10: PrintableString 'Example CA'
: }
: }
: }
100 30: SEQUENCE {
102 13: UTCTime 15/09/2004 11:48:21 GMT
117 13: UTCTime 15/03/2005 11:48:21 GMT
: }
132 67: SEQUENCE {
134 19: SET {
136 17: SEQUENCE {
138 10: OBJECT IDENTIFIER
: domainComponent (0 9 2342 19200300 100 1 25)
150 3: IA5String 'com'
: }
: }
155 23: SET {
157 21: SEQUENCE {
159 10: OBJECT IDENTIFIER
: domainComponent (0 9 2342 19200300 100 1 25)
171 7: IA5String 'example'
: }
: }
180 19: SET {
182 17: SEQUENCE {
184 3: OBJECT IDENTIFIER commonName (2 5 4 3)
189 10: PrintableString 'End Entity'
: }
: }
: }
201 159: SEQUENCE {
204 13: SEQUENCE {
206 9: OBJECT IDENTIFIER
: rsaEncryption (1 2 840 113549 1 1 1)
217 0: NULL
: }
219 141: BIT STRING, encapsulates {
223 137: SEQUENCE {
226 129: INTEGER
Cooper, et al. Standards Track [Page 141]
RFC 5280 PKIX Certificate and CRL Profile May 2008
: 00 E1 6A E4 03 30 97 02 3C F4 10 F3 B5 1E 4D 7F
: 14 7B F6 F5 D0 78 E9 A4 8A F0 A3 75 EC ED B6 56
: 96 7F 88 99 85 9A F2 3E 68 77 87 EB 9E D1 9F C0
: B4 17 DC AB 89 23 A4 1D 7E 16 23 4C 4F A8 4D F5
: 31 B8 7C AA E3 1A 49 09 F4 4B 26 DB 27 67 30 82
: 12 01 4A E9 1A B6 C1 0C 53 8B 6C FC 2F 7A 43 EC
: 33 36 7E 32 B2 7B D5 AA CF 01 14 C6 12 EC 13 F2
: 2D 14 7A 8B 21 58 14 13 4C 46 A3 9A F2 16 95 FF
: 23
358 3: INTEGER 65537
: }
: }
: }
363 117: [3] {
365 115: SEQUENCE {
367 33: SEQUENCE {
369 3: OBJECT IDENTIFIER subjectAltName (2 5 29 17)
374 26: OCTET STRING, encapsulates {
376 24: SEQUENCE {
378 22: [1] 'end.entity@example.com'
: }
: }
: }
402 29: SEQUENCE {
404 3: OBJECT IDENTIFIER subjectKeyIdentifier (2 5 29 14)
409 22: OCTET STRING, encapsulates {
411 20: OCTET STRING
: 17 7B 92 30 FF 44 D6 66 E1 90 10 22 6C 16 4F C0
: 8E 41 DD 6D
: }
: }
433 31: SEQUENCE {
435 3: OBJECT IDENTIFIER
: authorityKeyIdentifier (2 5 29 35)
440 24: OCTET STRING, encapsulates {
442 22: SEQUENCE {
444 20: [0]
: 08 68 AF 85 33 C8 39 4A 7A F8 82 93 8E 70 6A
: 4A 20 84 2C 32
: }
: }
: }
466 14: SEQUENCE {
468 3: OBJECT IDENTIFIER keyUsage (2 5 29 15)
473 1: BOOLEAN TRUE
476 4: OCTET STRING, encapsulates {
478 2: BIT STRING 6 unused bits
: '11'B
Cooper, et al. Standards Track [Page 142]
RFC 5280 PKIX Certificate and CRL Profile May 2008
: }
: }
: }
: }
: }
482 13: SEQUENCE {
484 9: OBJECT IDENTIFIER
: sha1withRSAEncryption (1 2 840 113549 1 1 5)
495 0: NULL
: }
497 129: BIT STRING
: 00 20 28 34 5B 68 32 01 BB 0A 36 0E AD 71 C5 95
: 1A E1 04 CF AE AD C7 62 14 A4 1B 36 31 C0 E2 0C
: 3D D9 1E C0 00 DC 10 A0 BA 85 6F 41 CB 62 7A B7
: 4C 63 81 26 5E D2 80 45 5E 33 E7 70 45 3B 39 3B
: 26 4A 9C 3B F2 26 36 69 08 79 BB FB 96 43 77 4B
: 61 8B A1 AB 91 64 E0 F3 37 61 3C 1A A3 A4 C9 8A
: B2 BF 73 D4 4D E4 58 E4 62 EA BC 20 74 92 86 0E
: CE 84 60 76 E9 73 BB C7 85 D3 91 45 EA 62 5D CD
: }
C.3. End Entity Certificate Using DSA
This appendix contains an annotated hex dump of a 914-byte version 3
certificate. The certificate contains the following information:
(a) the serial number is 256;
(b) the certificate is signed with DSA and the SHA-1 hash algorithm;
(c) the issuer's distinguished name is cn=Example DSA
CA,dc=example,dc=com;
(d) the subject's distinguished name is cn=DSA End
Entity,dc=example,dc=com;
(e) the certificate was issued on May 2, 2004 and expired on May 2,
2005;
(f) the certificate contains a 1024-bit DSA public key with
parameters;
(g) the certificate is an end entity certificate (not a CA
certificate);
(h) the certificate includes a subject alternative name of
"" and an issuer
alternative name of "" -- both are URLs;
Cooper, et al. Standards Track [Page 143]
RFC 5280 PKIX Certificate and CRL Profile May 2008
(i) the certificate includes an authority key identifier extension
and a certificate policies extension specifying the policy OID
2.16.840.1.101.3.2.1.48.9; and
(j) the certificate includes a critical key usage extension
specifying that the public key is intended for verification of
digital signatures.
0 910: SEQUENCE {
4 846: SEQUENCE {
8 3: [0] {
10 1: INTEGER 2
: }
13 2: INTEGER 256
17 9: SEQUENCE {
19 7: OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)
: }
28 71: SEQUENCE {
30 19: SET {
32 17: SEQUENCE {
34 10: OBJECT IDENTIFIER
: domainComponent (0 9 2342 19200300 100 1 25)
46 3: IA5String 'com'
: }
: }
51 23: SET {
53 21: SEQUENCE {
55 10: OBJECT IDENTIFIER
: domainComponent (0 9 2342 19200300 100 1 25)
67 7: IA5String 'example'
: }
: }
76 23: SET {
78 21: SEQUENCE {
80 3: OBJECT IDENTIFIER commonName (2 5 4 3)
85 14: PrintableString 'Example DSA CA'
: }
: }
: }
101 30: SEQUENCE {
103 13: UTCTime 02/05/2004 16:47:38 GMT
118 13: UTCTime 02/05/2005 16:47:38 GMT
: }
133 71: SEQUENCE {
135 19: SET {
137 17: SEQUENCE {
139 10: OBJECT IDENTIFIER
: domainComponent (0 9 2342 19200300 100 1 25)
Cooper, et al. Standards Track [Page 144]
RFC 5280 PKIX Certificate and CRL Profile May 2008
151 3: IA5String 'com'
: }
: }
156 23: SET {
158 21: SEQUENCE {
160 10: OBJECT IDENTIFIER
: domainComponent (0 9 2342 19200300 100 1 25)
172 7: IA5String 'example'
: }
: }
181 23: SET {
183 21: SEQUENCE {
185 3: OBJECT IDENTIFIER commonName (2 5 4 3)
190 14: PrintableString 'DSA End Entity'
: }
: }
: }
206 439: SEQUENCE {
210 300: SEQUENCE {
214 7: OBJECT IDENTIFIER dsa (1 2 840 10040 4 1)
223 287: SEQUENCE {
227 129: INTEGER
: 00 B6 8B 0F 94 2B 9A CE A5 25 C6 F2 ED FC FB 95
: 32 AC 01 12 33 B9 E0 1C AD 90 9B BC 48 54 9E F3
: 94 77 3C 2C 71 35 55 E6 FE 4F 22 CB D5 D8 3E 89
: 93 33 4D FC BD 4F 41 64 3E A2 98 70 EC 31 B4 50
: DE EB F1 98 28 0A C9 3E 44 B3 FD 22 97 96 83 D0
: 18 A3 E3 BD 35 5B FF EE A3 21 72 6A 7B 96 DA B9
: 3F 1E 5A 90 AF 24 D6 20 F0 0D 21 A7 D4 02 B9 1A
: FC AC 21 FB 9E 94 9E 4B 42 45 9E 6A B2 48 63 FE
: 43
359 21: INTEGER
: 00 B2 0D B0 B1 01 DF 0C 66 24 FC 13 92 BA 55 F7
: 7D 57 74 81 E5
382 129: INTEGER
: 00 9A BF 46 B1 F5 3F 44 3D C9 A5 65 FB 91 C0 8E
: 47 F1 0A C3 01 47 C2 44 42 36 A9 92 81 DE 57 C5
: E0 68 86 58 00 7B 1F F9 9B 77 A1 C5 10 A5 80 91
: 78 51 51 3C F6 FC FC CC 46 C6 81 78 92 84 3D F4
: 93 3D 0C 38 7E 1A 5B 99 4E AB 14 64 F6 0C 21 22
: 4E 28 08 9C 92 B9 66 9F 40 E8 95 F6 D5 31 2A EF
: 39 A2 62 C7 B2 6D 9E 58 C4 3A A8 11 81 84 6D AF
: F8 B4 19 B4 C2 11 AE D0 22 3B AA 20 7F EE 1E 57
: 18
: }
: }
514 132: BIT STRING, encapsulates {
518 128: INTEGER
Cooper, et al. Standards Track [Page 145]
RFC 5280 PKIX Certificate and CRL Profile May 2008
: 30 B6 75 F7 7C 20 31 AE 38 BB 7E 0D 2B AB A0 9C
: 4B DF 20 D5 24 13 3C CD 98 E5 5F 6C B7 C1 BA 4A
: BA A9 95 80 53 F0 0D 72 DC 33 37 F4 01 0B F5 04
: 1F 9D 2E 1F 62 D8 84 3A 9B 25 09 5A 2D C8 46 8E
: 2B D4 F5 0D 3B C7 2D C6 6C B9 98 C1 25 3A 44 4E
: 8E CA 95 61 35 7C CE 15 31 5C 23 13 1E A2 05 D1
: 7A 24 1C CB D3 72 09 90 FF 9B 9D 28 C0 A1 0A EC
: 46 9F 0D B8 D0 DC D0 18 A6 2B 5E F9 8F B5 95 BE
: }
: }
649 202: [3] {
652 199: SEQUENCE {
655 57: SEQUENCE {
657 3: OBJECT IDENTIFIER subjectAltName (2 5 29 17)
662 50: OCTET STRING, encapsulates {
664 48: SEQUENCE {
666 46: [6]
: 'http://www.example.com/users/DSAendentity.'
: 'html'
: }
: }
: }
714 33: SEQUENCE {
716 3: OBJECT IDENTIFIER issuerAltName (2 5 29 18)
721 26: OCTET STRING, encapsulates {
723 24: SEQUENCE {
725 22: [6] 'http://www.example.com'
: }
: }
: }
749 29: SEQUENCE {
751 3: OBJECT IDENTIFIER subjectKeyIdentifier (2 5 29 14)
756 22: OCTET STRING, encapsulates {
758 20: OCTET STRING
: DD 25 66 96 43 AB 78 11 43 44 FE 95 16 F9 D9 B6
: B7 02 66 8D
: }
: }
780 31: SEQUENCE {
782 3: OBJECT IDENTIFIER
: authorityKeyIdentifier (2 5 29 35)
787 24: OCTET STRING, encapsulates {
789 22: SEQUENCE {
791 20: [0]
: 86 CA A5 22 81 62 EF AD 0A 89 BC AD 72 41 2C
: 29 49 F4 86 56
: }
: }
Cooper, et al. Standards Track [Page 146]
RFC 5280 PKIX Certificate and CRL Profile May 2008
: }
813 23: SEQUENCE {
815 3: OBJECT IDENTIFIER certificatePolicies (2 5 29 32)
820 16: OCTET STRING, encapsulates {
822 14: SEQUENCE {
824 12: SEQUENCE {
826 10: OBJECT IDENTIFIER '2 16 840 1 101 3 2 1 48 9'
: }
: }
: }
: }
838 14: SEQUENCE {
840 3: OBJECT IDENTIFIER keyUsage (2 5 29 15)
845 1: BOOLEAN TRUE
848 4: OCTET STRING, encapsulates {
850 2: BIT STRING 7 unused bits
: '1'B (bit 0)
: }
: }
: }
: }
: }
854 9: SEQUENCE {
856 7: OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)
: }
865 47: BIT STRING, encapsulates {
868 44: SEQUENCE {
870 20: INTEGER
: 65 57 07 34 DD DC CA CC 5E F4 02 F4 56 42 2C 5E
: E1 B3 3B 80
892 20: INTEGER
: 60 F4 31 17 CA F4 CF FF EE F4 08 A7 D9 B2 61 BE
: B1 C3 DA BF
: }
: }
: }
C.4. Certificate Revocation List
This appendix contains an annotated hex dump of a version 2 CRL with
two extensions (cRLNumber and authorityKeyIdentifier). The CRL was
issued by cn=Example CA,dc=example,dc=com on February 5, 2005; the
next scheduled issuance was February 6, 2005. The CRL includes one
revoked certificate: serial number 18, which was revoked on November
19, 2004 due to keyCompromise. The CRL itself is number 12, and it
was signed with RSA and SHA-1.
Cooper, et al. Standards Track [Page 147]
RFC 5280 PKIX Certificate and CRL Profile May 2008
0 352: SEQUENCE {
4 202: SEQUENCE {
7 1: INTEGER 1
10 13: SEQUENCE {
12 9: OBJECT IDENTIFIER
: sha1withRSAEncryption (1 2 840 113549 1 1 5)
23 0: NULL
: }
25 67: SEQUENCE {
27 19: SET {
29 17: SEQUENCE {
31 10: OBJECT IDENTIFIER
: domainComponent (0 9 2342 19200300 100 1 25)
43 3: IA5String 'com'
: }
: }
48 23: SET {
50 21: SEQUENCE {
52 10: OBJECT IDENTIFIER
: domainComponent (0 9 2342 19200300 100 1 25)
64 7: IA5String 'example'
: }
: }
73 19: SET {
75 17: SEQUENCE {
77 3: OBJECT IDENTIFIER commonName (2 5 4 3)
82 10: PrintableString 'Example CA'
: }
: }
: }
94 13: UTCTime 05/02/2005 12:00:00 GMT
109 13: UTCTime 06/02/2005 12:00:00 GMT
124 34: SEQUENCE {
126 32: SEQUENCE {
128 1: INTEGER 18
131 13: UTCTime 19/11/2004 15:57:03 GMT
146 12: SEQUENCE {
148 10: SEQUENCE {
150 3: OBJECT IDENTIFIER cRLReason (2 5 29 21)
155 3: OCTET STRING, encapsulates {
157 1: ENUMERATED 1
: }
: }
: }
: }
: }
160 47: [0] {
162 45: SEQUENCE {
Cooper, et al. Standards Track [Page 148]
RFC 5280 PKIX Certificate and CRL Profile May 2008
164 31: SEQUENCE {
166 3: OBJECT IDENTIFIER
: authorityKeyIdentifier (2 5 29 35)
171 24: OCTET STRING, encapsulates {
173 22: SEQUENCE {
175 20: [0]
: 08 68 AF 85 33 C8 39 4A 7A F8 82 93 8E 70 6A
: 4A 20 84 2C 32
: }
: }
: }
197 10: SEQUENCE {
199 3: OBJECT IDENTIFIER cRLNumber (2 5 29 20)
204 3: OCTET STRING, encapsulates {
206 1: INTEGER 12
: }
: }
: }
: }
: }
209 13: SEQUENCE {
211 9: OBJECT IDENTIFIER
: sha1withRSAEncryption (1 2 840 113549 1 1 5)
222 0: NULL
: }
224 129: BIT STRING
: 22 DC 18 7D F7 08 CE CC 75 D0 D0 6A 9B AD 10 F4
: 76 23 B4 81 6E B5 6D BE 0E FB 15 14 6C C8 17 6D
: 1F EE 90 17 A2 6F 60 E4 BD AA 8C 55 DE 8E 84 6F
: 92 F8 9F 10 12 27 AF 4A D4 2F 85 E2 36 44 7D AA
: A3 4C 25 38 15 FF 00 FD 3E 7E EE 3D 26 12 EB D8
: E7 2B 62 E2 2B C3 46 80 EF 78 82 D1 15 C6 D0 9C
: 72 6A CB CE 7A ED 67 99 8B 6E 70 81 7D 43 42 74
: C1 A6 AF C1 55 17 A2 33 4C D6 06 98 2B A4 FC 2E
: }
Cooper, et al. Standards Track [Page 149]
RFC 5280 PKIX Certificate and CRL Profile May 2008
Authors' Addresses
David Cooper
National Institute of Standards and Technology
100 Bureau Drive, Mail Stop 8930
Gaithersburg, MD 20899-8930
USA
EMail: david.cooper@nist.gov
Stefan Santesson
Microsoft
One Microsoft Way
Redmond, WA 98052
USA
EMail: stefans@microsoft.com
Stephen Farrell
Distributed Systems Group
Computer Science Department
Trinity College Dublin
Ireland
EMail: stephen.farrell@cs.tcd.ie
Sharon Boeyen
Entrust
1000 Innovation Drive
Ottawa, Ontario
Canada K2K 3E7
EMail: sharon.boeyen@entrust.com
Russell Housley
Vigil Security, LLC
918 Spring Knoll Drive
Herndon, VA 20170
USA
EMail: housley@vigilsec.com
Tim Polk
National Institute of Standards and Technology
100 Bureau Drive, Mail Stop 8930
Gaithersburg, MD 20899-8930
USA
EMail: wpolk@nist.gov
Cooper, et al. Standards Track [Page 150]
RFC 5280 PKIX Certificate and CRL Profile May 2008
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Cooper, et al. Standards Track [Page 151]
RFC, FYI, BCP