Internet Engineering Task Force (IETF) M. Lepinski
Request for Comments: 6480 S. Kent
Category: Informational BBN Technologies
ISSN: 2070-1721 February 2012
An Infrastructure to Support Secure Internet Routing
Abstract
This document describes an architecture for an infrastructure to
support improved security of Internet routing. The foundation of
this architecture is a Resource Public Key Infrastructure (RPKI) that
represents the allocation hierarchy of IP address space and
Autonomous System (AS) numbers; and a distributed repository system
for storing and disseminating the data objects that comprise the
RPKI, as well as other signed objects necessary for improved routing
security. As an initial application of this architecture, the
document describes how a legitimate holder of IP address space can
explicitly and verifiably authorize one or more ASes to originate
routes to that address space. Such verifiable authorizations could
be used, for example, to more securely construct BGP route filters.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6480.
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Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................3
1.1. Terminology ................................................4
2. Public Key Infrastructure for Internet Number Resources .........4
2.1. Role in the Overall Architecture ...........................5
2.2. CA Certificates ............................................6
2.3. End-Entity (EE) Certificates ...............................7
2.4. Trust Anchors ..............................................8
3. Route Origination Authorizations ................................9
3.1. Role in the Overall Architecture ...........................9
3.2. Syntax and Semantics ......................................10
4. Repositories ...................................................11
4.1. Role in the Overall Architecture ..........................12
4.2. Contents and Structure ....................................12
4.3. Access Protocols ..........................................14
4.4. Access Control ............................................15
5. Manifests ......................................................15
5.1. Syntax and Semantics ......................................15
6. Local Cache Maintenance ........................................16
7. Common Operations ..............................................17
7.1. Certificate Issuance ......................................17
7.2. CA Key Rollover ...........................................18
7.3. ROA Management ............................................19
7.3.1. Single-Homed Subscribers ...........................20
7.3.2. Multi-Homed Subscribers ............................20
7.3.3. Provider-Independent Address Space .................21
8. Security Considerations ........................................21
9. IANA Considerations ............................................21
10. Acknowledgments ...............................................22
11. References ....................................................22
11.1. Normative References .....................................22
11.2. Informative References ...................................23
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1. Introduction
This document describes an architecture for an infrastructure to
support improved security for BGP routing [RFC4271] for the Internet.
The architecture encompasses three principle elements:
o Resource Public Key Infrastructure (RPKI)
o digitally signed routing objects to support routing security
o a distributed repository system to hold the PKI objects and the
signed routing objects
The architecture described by this document enables an entity to
verifiably assert that it is the legitimate holder of a set of IP
addresses or a set of Autonomous System (AS) numbers. As an initial
application of this architecture, the document describes how a
legitimate holder of IP address space can explicitly and verifiably
authorize one or more ASes to originate routes to that address space.
Such verifiable authorizations could be used, for example, to more
securely construct BGP route filters. In addition to this initial
application, the infrastructure defined by this architecture also is
intended to provide future support for security protocols such as
Secure BGP [S-BGP] or Secure Origin BGP [soBGP]. This architecture
is applicable to the routing of both IPv4 and IPv6 datagrams. IPv4
and IPv6 are currently the only address families supported by this
architecture. Thus, for example, use of this architecture with MPLS
labels is beyond the scope of this document.
In order to facilitate deployment, the architecture takes advantage
of existing technologies and practices. The structure of the PKI
element of the architecture corresponds to the existing resource
allocation structure. Thus management of this PKI is a natural
extension of the resource-management functions of the organizations
that are already responsible for IP address and AS number resource
allocation. Likewise, existing resource allocation and revocation
practices have well-defined correspondents in this architecture.
Note that while the initial focus of this architecture is routing
security applications, the PKI described in this document could be
used to support other applications that make use of attestations of
IP address or AS number resource holdings.
To ease implementation, existing IETF standards are used wherever
possible; for example, extensive use is made of the X.509 certificate
profile defined by the Public Key Infrastructure using X.509 (PKIX)
[RFC5280] working group and the extensions for IP addresses and AS
numbers representation defined in RFC 3779 [RFC3779]. Also,
Cryptographic Message Syntax (CMS) [RFC5652] is used as the syntax
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for the newly defined signed objects [RFC6488] required by this
infrastructure.
As noted above, the architecture is comprised of three main
components: an X.509 PKI in which certificates attest to holdings of
IP address space and AS numbers; non-certificate signed objects
(including route origination authorizations and manifests) used by
the infrastructure; and a distributed repository system that makes
all of these signed objects available for use by ISPs in making
routing decisions. These three basic components enable several
security functions; most notably the cryptographic validation that an
autonomous system is authorized to originate routes to a given prefix
[RFC6483].
1.1. Terminology
It is assumed that the reader is familiar with the terms and concepts
described in "Internet X.509 Public Key Infrastructure Certificate
and Certificate Revocation List (CRL) Profile" [RFC5280] and "X.509
Extensions for IP Addresses and AS Identifiers" [RFC3779].
Throughout this document, we use the terms "address space holder" or
"holder of IP address space" interchangeably to refer to a legitimate
holder of IP address space who has received this address space
through the standard IP address allocation hierarchy. That is, the
address space holder has either directly received the address space
as an allocation from a Regional Internet Registry (RIR) or IANA; or
else the address space holder has received the address space as a
sub-allocation from a National Internet Registry (NIR) or Local
Internet Registry (LIR). We use the term "resource holder" to refer
to a legitimate holder of either IP address or AS number resources.
Throughout this document, we use the terms "registry" and "ISP" to
refer to an entity that has an IP address space and/or AS number
allocation that it is permitted to sub-allocate.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC
2119 [RFC2119].
2. Public Key Infrastructure for Internet Number Resources
Because the holder of a block of IP address space is entitled to
define the topological destination of IP datagrams whose destinations
fall within that block, decisions about inter-domain routing are
inherently based on knowledge of the allocation of the IP address
space. Thus, a basic function of this architecture is to provide
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cryptographically verifiable attestations as to these allocations.
In current practice, the allocation of IP addresses is hierarchical.
The root of the hierarchy is IANA. Below IANA are five Regional
Internet Registries (RIRs), each of which manages address and AS
number allocation within a defined geopolitical region. In some
regions, the third tier of the hierarchy includes National Internet
Registries (NIRs) as well as Local Internet Registries (LIRs) and
subscribers with so-called provider-independent ("portable")
allocations. (The term "LIR" is used in some regions to refer to
what other regions define as an ISP. Throughout the rest of this
document, we will use the term "LIR/ISP" to simplify references to
these entities.) In other regions, the third tier consists only of
LIRs/ISPs and subscribers with provider-independent allocations.
In general, the holder of a block of IP address space may sub-
allocate portions of that block, either to itself (e.g., to a
particular unit of the same organization), or to another
organization, subject to contractual constraints established by the
registries. Because of this structure, IP address allocations can be
described naturally by a hierarchic public key infrastructure, in
which each certificate attests to an allocation of IP addresses, and
issuance of subordinate certificates corresponds to sub-allocation of
IP addresses. The above reasoning holds true for AS number resources
as well, with the difference that, by convention, AS numbers may not
be sub-allocated except by RIRs or NIRs. Thus, allocations of both
IP addresses and AS numbers can be expressed by the same PKI. Such a
PKI, which is henceforth referred to as the "Resource Public Key
Infrastructure (RPKI)", is a central component of this architecture.
2.1. Role in the Overall Architecture
Certificates in this PKI are called resource certificates, and
conform to the certificate profile for such certificates [RFC6487].
Resource certificates attest to the allocation by the (certificate)
issuer of IP addresses or AS numbers to the subject. They do this by
binding the public key contained in the resource certificate to the
IP addresses or AS numbers included in the certificate's IP Address
Delegation or AS Identifier Delegation extensions, respectively, as
defined in RFC 3779 [RFC3779].
An important property of this PKI is that certificates do not attest
to the identity of the subject. Therefore, the subject names used in
certificates are not intended to be "descriptive". That is, the
resource PKI is intended to provide authorization, but not
authentication. This is in contrast to most PKIs where the issuer
ensures that the descriptive subject name in a certificate is
properly associated with the entity that holds the private key
corresponding to the public key in the certificate. Because issuers
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need not verify the right of an entity to use a subject name in a
certificate, they avoid the costs and liabilities of such
verification. This makes it easier for these entities to take on the
additional role of Certification Authority (CA).
Most of the certificates in the PKI assert the basic facts on which
the rest of the infrastructure operates. CA certificates within the
PKI attest to IP address space and AS number holdings. End-entity
(EE) certificates are issued by resource holder CAs to delegate the
authority attested by their allocation certificates. The primary use
for EE certificates is the validation of Route Origination
Authorizations (ROAs), signed objects which provide an explicit
authorization by an address holder that a given AS is permitted to
originate routes to a set of addresses (see Section 3). End-entity
certificates are also used to verify other signed objects, such as
manifests, which will be used to help ensure the integrity of the
repository system (see Section 5).
2.2. CA Certificates
Any resource holder who is authorized to sub-allocate these resources
must be able to issue resource certificates to correspond to these
sub-allocations. Thus, for example, CA certificates will be
associated with IANA and each of the RIRs, NIRs, and LIRs/ISPs.
Also, a CA certificate is required to enable a resource holder to
issue ROAs, because it must issue the corresponding end-entity
certificate used to validate each ROA. Thus, some entities that do
not sub-allocate their resources also will need to have CA
certificates for their allocations, e.g., a multi-homed subscriber
with a provider-independent allocation, to enable them to issue ROAs.
(A subscriber who is not multi-homed, whose allocation comes from an
LIR/ISP, and who has not moved to a different LIR/ISP, need not be
represented in the PKI. Moreover, a multi-homed subscriber with an
allocation from an LIR/ISP may or may not need to be explicitly
represented, as discussed in Section 7.3.2).
Unlike in most PKIs, the distinguished name of the subject in a CA
certificate is chosen by the certificate issuer. The subject's
distinguished name must not attempt to convey the identity of the
subject in a descriptive fashion. The subject's distinguished name
must include the CommonName attribute and may additionally include
the serial attribute.
In this PKI, the certificate issuer, being an RIR, NIR, or LIR/ISP,
is not in the business of verifying the legal right of the subject to
assert a particular identity. Therefore, selecting a distinguished
name that does not convey the identity of the subject in a
descriptive fashion minimizes the opportunity for the subject to
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misuse the certificate to assert an identity, and thus minimizes the
legal liability of the issuer. Since all CA certificates are issued
to subjects with whom the issuer has an existing relationship, it is
recommended that the issuer select a subject name that enables the
issuer to easily link the certificate to existing database records
associated with the subject. For example, an authority may use
internal database keys or subscriber IDs as the subject's common name
in issued certificates.
Although the subject's common name in a certificate does not convey
identity, it is still the case that the common name must be unique
among all subjects to whom a certification authority issues
certificates. That is, a CA must not issue certificates to two
different entities that use the same common name for the subject.
Each resource certificate attests to an allocation of resources to a
resource holder, so entities that have allocations from multiple
sources will have multiple CA certificates. Note that when an entity
receives multiple certificates from different issuers, the subject
names in these certificates will generally be different. A CA also
may issue distinct certificates for each distinct allocation to the
same entity, if the CA and the resource holder agree that such an
arrangement will facilitate management and use of the certificates.
For example, an LIR/ISP may have several certificates issued to it by
one registry, each describing a distinct set of address blocks,
because the LIR/ISP desires to treat the allocations as separate.
2.3. End-Entity (EE) Certificates
The private key corresponding to a public key contained in an EE
certificate is not used to sign other certificates in a PKI. The
primary function of end-entity certificates in this PKI is the
verification of signed objects that relate to the usage of the
resources described in the certificate, e.g., ROAs and manifests.
For ROAs and manifests, there will be a one-to-one correspondence
between end-entity certificates and signed objects, i.e., the private
key corresponding to each end-entity certificate is used to sign
exactly one object, and each object is signed with only one key.
This property allows the PKI to be used to revoke these signed
objects, rather than creating a new revocation mechanism. When the
end-entity certificate used to sign an object has been revoked, the
signature on that object (and any corresponding assertions) will be
considered invalid, so a signed object can be effectively revoked by
revoking the end-entity certificate used to sign it.
A secondary advantage to this one-to-one correspondence is that the
private key corresponding to the public key in a certificate is used
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exactly once in its lifetime, and thus can be destroyed after it has
been used to sign its one object. This fact should simplify key
management, since there is no requirement to protect these private
keys for an extended period of time.
The EE certificate used to verify a signed object appears in the
Cryptographic Message Syntax (CMS) wrapper (see [RFC6488]) of the
signed object. Therefore, it is not necessary to transmit the EE
certificate separately from the signed object. Likewise, it is not
necessary for the EE certificate to appear in the RPKI repository
system except as part of the corresponding signed object.
Although this document describes only two uses for end-entity
certificates, additional uses will likely be defined in the future.
For example, end-entity certificates could be used as a more general
authorization for their subjects to act on behalf of the specified
resource holder. This could facilitate authentication of inter-ISP
interactions, or authentication of interactions with the repository
system. These additional uses for end-entity certificates may
require retention of the corresponding private keys, even though such
retention is not required for keys used to sign ROAs and manifests.
2.4. Trust Anchors
In any PKI, each relying party (RP) chooses its own set of trust
anchors (TAs). This general property of PKIs applies here as well.
There is an extant IP address space and AS number allocation
hierarchy, and thus IANA and/or the five RIRs are obvious candidates
to be default TAs here. Nonetheless, each RP ultimately chooses the
set of trust anchors it will use for certificate validation.
For example, an RP (e.g., an LIR/ISP) could create a trust anchor to
which all address space and/or all AS numbers are assigned, and for
which the RP knows the corresponding private key. The RP could then
issue certificates under this trust anchor to whatever entities in
the PKI it wishes, with the result that the certification paths
terminating at this locally installed trust anchor will satisfy the
validation requirements specified in RFC 3779. A large ISP that uses
private IP address space (i.e., RFC 1918) and runs BGP internally
will need to create this sort of trust anchor to accommodate a CA to
which all private address space is assigned. The RP could then issue
certificates under this CA that correspond to the RP's internal use
of private address space.
Note that an RP who elects to create and manage its own set of trust
anchors may fail to detect allocation errors that arise under such
circumstances, but the resulting vulnerability is local to the RP.
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It is expected that some parties within the extant IP address space
and AS number allocation hierarchy may wish to publish trust anchor
material for possible use by relying parties. A standard profile for
the publication of trust anchor material for this public key
infrastructure can be found in [RFC6490].
3. Route Origination Authorizations
The information on IP address allocation provided by the PKI is not,
in itself, sufficient to guide routing decisions. In particular, BGP
is based on the assumption that the AS that originates routes for a
particular prefix is authorized to do so by the holder of that prefix
(or an address block encompassing the prefix); the PKI contains no
information about these authorizations. A Route Origination
Authorization (ROA) makes such authorization explicit, allowing a
holder of IP address space to create an object that explicitly and
verifiably asserts that an AS is authorized to originate routes to a
given set of prefixes.
3.1. Role in the Overall Architecture
A ROA is an attestation that the holder of a set of prefixes has
authorized an autonomous system to originate routes for those
prefixes. A ROA is structured according to the format described in
[RFC6482]. The validity of this authorization depends on the signer
of the ROA being the holder of the prefix(es) in the ROA; this fact
is asserted by an end-entity certificate from the PKI, whose
corresponding private key is used to sign the ROA.
ROAs may be used by relying parties to verify that the AS that
originates a route for a given IP address prefix is authorized by the
holder of that prefix to originate such a route. For example, an ISP
might use validated ROAs as inputs to route filter construction for
use by its BGP routers. (See [RFC6483] for information on the use of
ROAs to validate the origination of BGP routes.)
Initially, the repository system will be the primary mechanism for
disseminating ROAs, since these repositories will hold the
certificates and CRLs needed to verify ROAs. In addition, ROAs also
could be distributed in BGP UPDATE messages or via other
communication paths, if needed to meet timeliness requirements.
3.2. Syntax and Semantics
A ROA constitutes an explicit authorization for a single AS to
originate routes to one or more prefixes, and is signed by the holder
of those prefixes. Conceptually, the ROA syntax consists of two
parts, a general CMS template common to all RPKI signed objects
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[RFC6488] and an encapsulated content specific to the ROA that
expresses the authorization [RFC6482].
At a high level, the ROA's content contains (1) an AS number; (2) a
list of IP address prefixes; and, optionally, (3) for each prefix,
the maximum length of more specific (longer) prefixes that the AS is
also authorized to advertise. (This last element facilitates a
compact authorization to advertise, for example, any prefixes of
length 20 to 24 bits contained within a given length 20 prefix.)
Note that a ROA contains only a single AS number. Thus, if an ISP
has multiple AS numbers that will be authorized to originate routes
to the prefix(es) in the ROA, an address space holder will need to
issue multiple ROAs to authorize the ISP to originate routes from any
of these ASes.
A ROA is signed using the private key corresponding to the public key
in an end-entity (EE) certificate in the PKI. In order for a ROA to
be valid, its corresponding end-entity certificate must be valid, and
the IP address prefixes of the ROA must exactly match the IP address
prefix(es) specified in the EE certificate's RFC 3779 extension.
Therefore, the validity interval of the ROA is implicitly the
validity interval of its corresponding certificate. A ROA is revoked
by revoking the corresponding EE certificate. There is no
independent method of revoking a ROA. One might worry that this
revocation model could lead to long CRLs for the CA certification
that is signing the EE certificates. However, routing announcements
on the public Internet are generally quite long lived. Therefore, as
long as the EE certificates used to verify a ROA are given a validity
interval of several months, the likelihood that many ROAs would need
to be revoked within that time is quite low.
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--------- ---------
| RIR | | NIR |
| CA | | CA |
--------- ---------
| |
| |
| |
--------- ---------
| ISP | | ISP |
| CA 1 | | CA 2 |
--------- ---------
| \ |
| ----- |
| \ |
---------- ---------- ----------
| ISP | | ISP | | ISP |
| EE 1a | | EE 1b | | EE 2 |
---------- ---------- ----------
| | |
| | |
| | |
---------- ---------- ----------
| ROA 1a | | ROA 1b | | ROA 2 |
---------- ---------- ----------
Figure 1: This figure illustrates an ISP with allocations from two
sources (an RIR and an NIR). It needs two CA certificates due to the
rules defined in RFC 3779.
Because each ROA is associated with a single end-entity certificate,
the set of IP prefixes contained in a ROA must be drawn from an
allocation by a single source, i.e., a ROA cannot combine allocations
from multiple sources. Address space holders who have allocations
from multiple sources, and who wish to authorize an AS to originate
routes for these allocations, must issue multiple ROAs to the AS.
4. Repositories
Initially, an LIR/ISP will make use of the resource PKI by acquiring
and validating every ROA, to create a table of the prefixes for which
each AS is authorized to originate routes. To validate all ROAs, an
LIR/ISP needs to acquire all the certificates and CRLs. The primary
function of the distributed repository system described here is to
store these signed objects and to make them available for download by
LIRs/ISPs. Note that this repository system provides a mechanism by
which relying parties can pull fresh data at whatever frequency they
deem appropriate. However, it does not provide a mechanism for
pushing fresh data to relying parties (e.g., by including resource
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PKI objects in BGP or other protocol messages) and such a mechanism
is beyond the scope of the current document.
The digital signatures on all objects in the repository ensure that
unauthorized modification of valid objects is detectable by relying
parties. Additionally, the repository system uses manifests (see
Section 5) to ensure that relying parties can detect the deletion of
valid objects and the insertion of out-of-date, valid signed objects.
The repository system is also a point of enforcement for access
controls for the signed objects stored in it, e.g., ensuring that
records related to an allocation of resources can be manipulated only
by authorized parties. The use of access controls prevents denial-
of-service attacks based on deletion of or tampering with repository
objects. Indeed, although relying parties can detect tampering with
objects in the repository, it is preferable that the repository
system prevent such unauthorized modifications to the greatest extent
possible.
4.1. Role in the Overall Architecture
The repository system is the untrusted clearing-house for all signed
objects that must be globally accessible to relying parties. When
certificates and CRLs are created, they are uploaded to this
repository, and then downloaded for use by relying parties (primarily
LIRs/ISPs). ROAs and manifests are additional examples of such
objects, but other types of signed objects may be added to this
architecture in the future. This document briefly describes the way
signed objects (certificates, CRLs, ROAs, and manifests) are managed
in the repository system. As other types of signed objects are added
to the repository system, it will be necessary to modify the
description, but it is anticipated that most of the design principles
will still apply. The repository system is described in detail in
[RFC6481].
4.2. Contents and Structure
Although there is a single repository system that is accessed by
relying parties, it is comprised of multiple databases. These
databases will be distributed among registries (RIRs, NIRs,
LIRs/ISPs). At a minimum, the database operated by each registry
will contain all CA and EE certificates, CRLs, and manifests signed
by the CA(s) associated with that registry. Repositories operated by
LIRs/ISPs also will contain ROAs. Registries are encouraged to
maintain copies of repository data from their customers, and their
customer's customers (etc.), to facilitate retrieval of the whole
repository contents by relying parties. Ideally, each RIR will hold
PKI data from all entities within its geopolitical scope.
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For every certificate in the PKI, there will be a corresponding file
system directory in the repository that is the authoritative
publication point for all objects (certificates, CRLs, ROAs, and
manifests) verifiable via this certificate. A certificate's Subject
Information Access (SIA) extension [RFC5280] contains a URI that
references this directory. Additionally, a certificate's Authority
Information Access (AIA) extension [RFC5280] contains a URI that
references the authoritative location for the CA certificate under
which the given certificate was issued. That is, if certificate A is
used to verify certificate B, then the AIA extension of certificate B
points to certificate A, and the SIA extension of certificate A
points to a directory containing certificate B (see Figure 2).
+--------+
+--------->| Cert A |<----+
| | CRLDP | |
| | AIA | |
| +--------- SIA | |
| | +--------+ |
| | |
| | |
| | |
| | +-------------------|------------------+
| | | | |
| +->| +--------+ | +--------+ |
| | | Cert B | | | Cert C | |
| | | CRLDP ----+ | | CRLDP -+-+ |
+----------- AIA | | +----- AIA | | |
| | SIA | | | SIA | | |
| +--------+ | +--------+ | |
| V | |
| +---------+ | |
| | A's CRL |<-----------+ |
| +---------+ |
| A's Repository Publication Directory |
+--------------------------------------+
Figure 2: Use of SIA and AIA extensions in the RPKI
In Figure 2, certificates B and C are issued by CA A. Therefore, the
AIA extensions of certificates B and C point to (certificate) A, and
the SIA extension of certificate A points to the repository
publication point of CA A's subordinate products, which includes
certificates B and C, as well as the CRL issued by A. The CRL
Distribution Points (CRLDP) extension in certificates B and C both
point to the CRL issued by A.
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If a CA certificate is reissued with the same public key, it should
not be necessary to reissue (with an updated AIA URI) all
certificates signed by the certificate being reissued. Therefore, a
certification authority SHOULD use a persistent URI naming scheme for
issued certificates. That is, reissued certificates should use the
same publication point as previously issued certificates having the
same subject and public key, and should overwrite such certificates.
4.3. Access Protocols
Repository operators will choose one or more access protocols that
relying parties can use to access the repository system. These
protocols will be used by numerous participants in the infrastructure
(e.g., all registries, ISPs, and multi-homed subscribers) to maintain
their respective portions of it. In order to support these
activities, certain basic functionality is required of the suite of
access protocols, as described below. No single access protocol
needs to implement all of these functions (although that may be the
case), but each function MUST be implemented by at least one access
protocol deployed by a repository operator.
Download: Access protocols must support the bulk download of
repository contents and subsequent download of changes to the
downloaded contents, since this will be the most common way in which
relying parties interact with the repository system. Other types of
download interactions (e.g., download of a single object) may also be
supported.
Upload/change/delete: Access protocols must also support mechanisms
for the issuers of certificates, CRLs, and other signed objects to
add them to the repository, and to remove them. Mechanisms for
modifying objects in the repository may also be provided. All access
protocols that allow modification to the repository (through
addition, deletion, or modification of its contents) must support
verification of the authorization of the entity performing the
modification, so that appropriate access controls can be applied (see
Section 4.4).
To ensure all relying parties are able to acquire all RPKI signed
objects, all publication points MUST be accessible via rsync (see
[RFC5781] and [RSYNC]), although other download protocols MAY also be
supported. A repository publication point may provide
update/change/delete functionality via (set of) access protocols that
it desires, provided that the supported protocols are clearly
communicated to all certification authorities publishing data at a
given publication point.
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4.4. Access Control
In order to maintain the integrity of information in the repository,
controls must be put in place to prevent the addition, deletion, or
modification of objects in the repository by unauthorized parties.
The identities of parties attempting to make such changes can be
authenticated through the relevant access protocols. Although
specific access control policies are subject to the local control of
repository operators, it is RECOMMENDED that repositories allow only
the issuers of signed objects to add, delete, or modify them.
Alternatively, it may be advantageous in the future to define a
formal delegation mechanism to allow resource holders to authorize
other parties to act on their behalf, as suggested in Section 2.3.
5. Manifests
A manifest is a signed object listing of all of the signed objects
(except for the manifest itself) issued by an authority responsible
for a publication in the repository system. For each unexpired
certificate, CRL, or ROA issued by the authority, the manifest
contains both the name of the file containing the object, and a hash
of the file content.
As with ROAs, a manifest is signed by a private key, for which the
corresponding public key appears in an end-entity certificate. This
EE certificate, in turn, is signed by the CA in question. Since the
private key in an EE certificate is used to sign only a single
manifest, then the manifest can be revoked by revoking the EE
certificate. In such a case, to avoid needless CRL growth, the EE
certificate used to validate a manifest SHOULD expire at the same
time that the manifest expires.
Manifests may be used by relying parties when constructing a local
cache (see Section 6) to mitigate the risk of an attacker who deletes
files from a repository or replaces current signed objects with stale
versions of the same object. Such protection is needed because,
although all objects in the repository system are signed, the
repository system itself is untrusted.
5.1. Syntax and Semantics
A manifest constitutes a list of (the hashes of) all the files in a
repository point at a particular point in time. A detailed
specification of the manifest's content is provided in [RFC6486] but,
at a high level, a manifest consists of (1) a manifest number; (2)
the time the manifest was issued; (3) the time of the next planned
update; and (4) a list of filename and hash value pairs.
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The manifest number is a sequence number that is incremented each
time a manifest is issued by the authority. An authority is REQUIRED
to issue a new manifest any time it alters any of its items in the
repository, or when the specified time of the next update is reached.
A manifest is thus valid until the specified time of the next update
or until a manifest is issued with a greater manifest number,
whichever comes first. (Note that when an EE certificate is used to
sign only a single manifest, whenever the authority issues the new
manifest, the CA MUST also issue a new CRL that includes the EE
certificate corresponding to the old manifest. The revoked EE
certificate for the old manifest will be removed from the CRL when it
expires; thus, this procedure ought not to result in significant CRL
growth.)
6. Local Cache Maintenance
In order to utilize signed objects issued under this PKI, a relying
party must first obtain a local copy of the valid EE certificates for
the PKI. To do so, the relying party performs the following steps:
1. Query the repository system to obtain a copy of all
certificates, manifests, and CRLs issued under the PKI.
2. For each CA certificate in the PKI, verify the signature on the
corresponding manifest. Additionally, verify that the current
time is earlier than the time indicated in the nextUpdate field
of the manifest.
3. For each manifest, verify that certificates and CRLs issued
under the corresponding CA certificate match the hash values
contained in the manifest. Additionally, verify that no
certificate or manifest listed on the manifest is missing from
the repository. If the hash values do not match, or if any
certificate or CRL is missing, notify the appropriate
repository administrator that the repository data has been
corrupted.
4. Validate each EE certificate by constructing and verifying a
certification path for the certificate (including checking
relevant CRLs) to the locally configured set of TAs. (See
[RFC6487] for more details.)
Note that since relying parties will perform these operations
regularly, it is more efficient for the relying party to request from
the repository system only those objects that have changed since the
relying party last updated its local cache.
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Note also that by checking all issued objects against the appropriate
manifest, the relying party can be certain that it is not missing an
updated version of any object.
7. Common Operations
Creating and maintaining the infrastructure described above will
entail additional operations as "side effects" of normal resource
allocation and routing authorization procedures. For example, a
subscriber with provider-independent ("portable") address space who
enters a relationship with an ISP will need to issue one or more ROAs
identifying that ISP, in addition to conducting any other necessary
technical or business procedures. The current primary use of this
infrastructure is for route filter construction; using ROAs, route
filters can be constructed in an automated fashion with high
assurance that the holder of the advertised prefix has authorized the
origin AS to originate an advertised route.
7.1. Certificate Issuance
There are several operational scenarios that require certificates to
be issued. Any allocation that may be sub-allocated requires a CA
certificate, e.g., so that certificates can be issued as necessary
for the sub-allocations. Holders of provider-independent IP address
space allocations also must have certificates, so that a ROA can be
issued to each ISP that is authorized to originate a route to the
allocation (since the allocation does not come from any ISP).
Additionally, multi-homed subscribers may require certificates for
their allocations if they intend to issue the ROAs for their
allocations (see Section 7.3.2). Other resource holders need not be
issued CA certificates within the PKI.
In the long run, a resource holder will not request resource
certificates, but rather receive a certificate as a side effect of
the allocation process for the resource. However, initial deployment
of the RPKI will entail issuance of certificates to existing resource
holders as an explicit event. Note that in all cases, the authority
issuing a CA certificate will be the entity who allocates resources
to the subject. This differs from most PKIs in which a subject can
request a certificate from any certification authority.
If a resource holder receives multiple allocations over time, it may
accrue a collection of resource certificates to attest to them. If a
resource holder receives multiple allocations from the same source,
the set of resource certificates may be combined into a single
resource certificate, if both the issuer and the resource holder
agree. This is accomplished by consolidating the IP Address
Delegation and AS Identifier Delegation extensions into a single
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extension (of each type) in a new certificate. However, if these
certificates attest to allocations that are valid for different
periods of time, creating a certificate that combines them might
create problems, as the combined certificate can express only a
single validity interval.
If a resource holder's allocations come from different sources, they
will be signed by different CAs and cannot be combined. When a set
of resources is no longer allocated to a resource holder, any
certificates attesting to such an allocation MUST be revoked. A
resource holder SHOULD NOT use the same public key in multiple CA
certificates that are issued by the same or differing authorities, as
reuse of a key pair complicates path construction. Note that since
the subject's distinguished name is chosen by the issuer, a subject
who receives allocations from two sources generally will receive
certificates with different subject names.
7.2. CA Key Rollover
Whenever a certification authority wishes to change the public key
(and corresponding private key) associated with its RPKI CA
certificate, it MUST perform a key rollover procedure. Key rollover
is typically performed on a periodic basis, where the frequency of
key rollovers is specified in the certification practice statement of
the given CA. Additionally, unscheduled rollovers may be required in
the event of suspected key compromises.
Note that rollover is only required when the CA's key actually
changes; it is not required in cases where a new CA certificate is
issued with the same key as the previous certificate for this CA.
For example, a new CA certificate must be issued if the CA gains or
relinquishes a resource, or if the validity period of the resource
allocation is extended. However, in such cases, the new certificate
will generally use the same public (and private) key as the previous
certificate; thus, key rollover is not required.
The document [RFC6489] specifies a conservative key rollover
procedure that should be used by a certification authority when it
changes the public (and private) keys associated with its RPKI CA
certificate. At a high level, the two key properties of the rollover
procedure are as follows. First, as data from RPKI signed objects
may be used in routing operations, the procedure ensures that at any
point in the rollover procedure, a relying party will never reach
incorrect conclusions about the validity of a signed object. Note in
particular, that the CA cannot assume that a relying party will use
any particular algorithm for constructing a certificate path from an
EE certificate to (one of) the relying party's trust anchor(s);
therefore, the key rollover procedure is designed to preserve the
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integrity of the SIA and AIA points within the RPKI hierarchy to the
greatest extent possible. Second, the key rollover procedure is
designed so that the reissuance of all certificates below the CA in
the RPKI hierarchy is not required. Of course, it is necessary to
re-sign all certificates issued directly under the CA whose key is
changing. However, the SIA and AIA pointers within the certificates
are populated so that no further reissuance is required.
7.3. ROA Management
Whenever a holder of IP address space wants to authorize an AS to
originate routes for a prefix within his holdings, he MUST issue an
end-entity certificate containing that prefix in an IP Address
Delegation extension. He then uses the corresponding private key to
sign a ROA containing the designated prefix and the AS number for the
AS. The resource holder MAY include more than one prefix in the EE
certificate and corresponding ROA if desired. As a prerequisite,
then, any address space holder that issues ROAs for a prefix must
have a resource certificate for an allocation containing that prefix.
The standard procedure for issuing a ROA is as follows:
1. Create an end-entity certificate containing the prefix(es) to
be authorized in the ROA.
2. Construct the payload of the ROA, including the prefixes in the
end-entity certificate and the AS number to be authorized.
3. Sign the ROA using the private key corresponding to the end-
entity certificate (the ROA is comprised of the payload
encapsulated in a CMS signed message [RFC5652]).
4. Upload the end-entity certificate and the ROA to the repository
system.
The standard procedure for revoking a ROA is to revoke the
corresponding end-entity certificate by creating an appropriate CRL
and uploading it to the repository system. The revoked ROA and end-
entity certificate SHOULD be removed from the repository system.
Care must be taken when revoking ROAs in that revoking a ROA may
cause a relying party to treat routing advertisements corresponding
to the prefixes and origin AS number in the ROA as unauthorized (and
potentially even change routing behavior to no longer forward packets
based on those advertisements). In particular, resource holders
should adhere to the principle of "make before break" as follows.
Before revoking a ROA corresponding to a prefix that the resource
holder wishes to be routable on the Internet, it is very important
for the resource holder to ensure that there exists another valid
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alternative ROA that lists the same prefix (possibly indicating a
different AS number). Additionally, the resource holder should
ensure that the AS indicated in the valid alternative ROA is actually
originating routing advertisements to the prefixes in question.
Furthermore, a relying party must fetch new ROAs from the repository
system before taking any routing action in response to a ROA
revocation.
7.3.1. Single-Homed Subscribers
In BGP, a single-homed subscriber with Provider Aggregatable (PA)
address space does not need to explicitly authorize routes to be
originated for the prefix(es) it is using, since its ISP will already
advertise a more general prefix and route traffic for the
subscriber's prefix as an internal function. Since no routes are
originated specifically for prefixes held by these subscribers, no
ROAs need to be issued under their allocations; rather, the
subscriber's ISP will issue any necessary ROAs for its more general
prefixes under resource certificates from its own allocation. Thus,
a single-homed subscriber with an IP address allocation from his
service provider is not included in the RPKI, i.e., it does not
receive a CA certificate, nor issue EE certificates or ROAs.
7.3.2. Multi-Homed Subscribers
Here we consider a subscriber who receives Provider Aggregatable (PA)
IP address space from a primary ISP (i.e., the IP addresses used by
the subscriber are a subset of ISP A's IP address space allocation)
and receives redundant upstream connectivity from one or more
secondary ISPs, in addition to the primary ISP. The preferred option
for such a multi-homed subscriber is for the subscriber to obtain an
AS number and run BGP with each of its upstream providers. In such a
case, there are two RECOMMENDED ways for ROA management to be
handled. The first is that the primary ISP issues a CA certificate
to the subscriber, and the subscriber issues a ROA to containing the
subscriber's AS number and the subscriber's IP address prefixes. The
second possibility is that the primary ISP does not issue a CA
certificate to the subscriber, and instead issues a ROA on the
subscriber's behalf that contains the subscriber's AS number and the
subscriber's IP address prefixes.
If the subscriber is unable or unwilling to obtain an AS number and
run BGP, the another option is that the multi-homed subscriber can
request that the primary ISP create a ROA for each secondary ISP that
authorizes the secondary ISP to originate routes to the subscriber's
prefixes. The primary ISP will also create a ROA containing its own
AS number and the subscriber's prefixes, as it is likely in such a
case that the primary ISP wishes to advertise precisely the
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subscriber's prefixes and not an encompassing aggregate. Note that
this approach results in inconsistent origin AS numbers for the
subscriber's prefixes that are considered undesirable on the public
Internet; thus, this approach is NOT RECOMMENDED.
7.3.3. Provider-Independent Address Space
A resource holder is said to have provider-independent (portable)
address space if the resource holder received its allocation directly
from a RIR or NIR. Because the prefixes represented in such
allocations are not taken from an allocation held by an ISP, there is
no ISP that holds and advertises a more general prefix. A holder of
a portable IP address space allocation MUST authorize one or more
ASes to originate routes to these prefixes. Thus, the resource
holder MUST generate one or more EE certificates and associated ROAs
to enable the AS(es) to originate routes for the prefix(es) in
question. This ROA is required because none of the ISP's existing
ROAs authorize it to originate routes to the subscriber's provider-
independent allocation.
8. Security Considerations
The focus of this document is security; hence, security
considerations permeate this specification.
The security mechanisms provided by and enabled by this architecture
depend on the integrity and availability of the infrastructure it
describes. The integrity of objects within the infrastructure is
ensured by appropriate controls on the repository system, as
described in Section 4.4. Likewise, because the repository system is
structured as a distributed database, it should be inherently
resistant to denial-of-service attacks; nonetheless, appropriate
precautions should also be taken, both through replication and backup
of the constituent databases and through the physical security of
database servers.
9. IANA Considerations
Instructions for IANA's participation in the RPKI are provided in
[RFC6491].
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10. Acknowledgments
The architecture described in this document is derived from the
collective ideas and work of a large group of individuals. This work
would not have been possible without the intellectual contributions
of George Michaelson, Robert Loomans, Sanjaya and Geoff Huston of
APNIC, Robert Kisteleki and Henk Uijterwaal of the RIPE NCC, Tim
Christensen and Cathy Murphy of ARIN, Rob Austein of ISC, and Randy
Bush of IIJ.
Although we are indebted to everyone who has contributed to this
architecture, we would like to especially thank Rob Austein for the
concept of a manifest, Geoff Huston for the concept of managing
object validity through single-use EE certificate key pairs, and
Richard Barnes for help in preparing an early version of this
document.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779, June 2004.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271, January
2006.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, September 2009.
[RFC5781] Weiler, S., Ward, D., and R. Housley, "The rsync URI
Scheme", RFC 5781, February 2010.
[RFC6481] Huston, G., Loomans, R., and G. Michaelson, "A Profile for
Resource Certificate Repository Structure", RFC 6481,
February 2012.
[RFC6482] Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
Origin Authorizations (ROAs)", RFC 6482, February 2012.
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[RFC6486] Austein, R., Huston., G., Kent, S., and M. Lepinski,
"Manifests for the Resource Public Key Infrastructure",
RFC 6486, February 2012.
[RFC6487] Huston, G., Michaelson, G., and R. Loomans, "A Profile for
X.509 PKIX Resource Certificates", RFC 6487, February
2012.
[RFC6488] Lepinski, M., Chi, A., and S. Kent, "Signed Object
Template for the Resource Public Key Infrastructure", RFC
6488, February 2012.
[RFC6491] Manderson, T., Vegoda, L., and S. Kent, "Resource Public
Key Infrastructure (RPKI) Objects Issued by IANA", RFC
6491, February 2012.
11.2. Informative References
[RFC6483] Huston, G. and G. Michaelson, "Validation of Route
Origination Using the Resource Certificate Public Key
Infrastructure (PKI) and Route Origin Authorizations
(ROAs)", RFC 6483, February 2012.
[RFC6489] Huston, G., Michaelson, G., and S. Kent, "Certification
Authority (CA) Key Rollover in the Resource Public Key
Infrastructure (RPKI)", BCP 174, RFC 6489, February 2012.
[RFC6490] Huston, G., Weiler, S., Michaelson, G., and S. Kent,
"Resource Public Key Infrastructure (RPKI) Trust Anchor
Locator", RFC 6490, February 2012.
[RSYNC] rsync web pages,
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Authors' Addresses
Matt Lepinski
BBN Technologies
10 Moulton St.
Cambridge, MA 02138
EMail: mlepinski@bbn.com
Stephen Kent
BBN Technologies
10 Moulton St.
Cambridge, MA 02138
EMail: kent@bbn.com
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RFC, FYI, BCP