Internet Engineering Task Force (IETF) V. Gurbani
Request for Comments: 5922 Bell Laboratories, Alcatel-Lucent
Updates: 3261 S. Lawrence
Category: Standards Track
ISSN: 2070-1721 A. Jeffrey
Bell Laboratories, Alcatel-Lucent
June 2010
Domain Certificates in the Session Initiation Protocol (SIP)
Abstract
This document describes how to construct and interpret certain
information in a PKIX-compliant (Public Key Infrastructure using
X.509) certificate for use in a Session Initiation Protocol (SIP)
over Transport Layer Security (TLS) connection. More specifically,
this document describes how to encode and extract the identity of a
SIP domain in a certificate and how to use that identity for SIP
domain authentication. As such, this document is relevant both to
implementors of SIP and to issuers of certificates.
Status of This Memo
This is an Internet Standards Track document.
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). Further information on
Internet Standards is available in 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/rfc5922.
Gurbani, et al. Standards Track [Page 1]
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Copyright Notice
Copyright (c) 2010 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
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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
2. Terminology .....................................................3
2.1. Key Words ..................................................3
3. Problem Statement ...............................................3
4. SIP Domain to Host Resolution ...................................5
5. The Need for Mutual Interdomain Authentication ..................6
6. Certificate Usage by a SIP Service Provider .....................7
7. Behavior of SIP Entities ........................................8
7.1. Finding SIP Identities in a Certificate ....................8
7.2. Comparing SIP Identities ...................................9
7.3. Client Behavior ...........................................10
7.4. Server Behavior ...........................................11
7.5. Proxy Behavior ............................................12
7.6. Registrar Behavior ........................................12
7.7. Redirect Server Behavior ..................................12
7.8. Virtual SIP Servers and Certificate Content ...............12
8. Security Considerations ........................................13
8.1. Connection Authentication Using Digest ....................13
9. Acknowledgments ................................................14
10. References ....................................................14
10.1. Normative References .....................................14
10.2. Informative References ...................................15
Appendix A. Editorial Guidance (Non-Normative) ...................16
A.1. Additions .................................................16
A.2. Changes ...................................................16
A.2.1. Changes to Section 26.3.1 .............................16
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1. Introduction
RFC 5246 [5] Transport Layer Security (TLS) is available in an
increasing number of Session Initiation Protocol (SIP) RFC 3261 [2]
implementations. In order to use the authentication capabilities of
TLS, certificates as defined by the Internet X.509 Public Key
Infrastructure, see RFC 5280 [6], are required.
Existing SIP specifications do not sufficiently specify how to use
certificates for domain (as opposed to host) authentication. This
document provides guidance to ensure interoperability and uniform
conventions for the construction and interpretation of certificates
used to identify their holders as being authoritative for the domain.
The discussion in this document is pertinent to an X.509 PKIX-
compliant certificate used for a TLS connection; this document does
not define use of such certificates for any other purpose (such as
Secure/Multipurpose Internet Mail Extensions (S/MIME)).
2. Terminology
2.1. Key Words
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 RFC 2119 [1].
Additional definition(s):
SIP domain identity: An identity (e.g., "sip:example.com") contained
in an X.509 certificate bound to a subject that identifies the
subject as an authoritative SIP server for a domain.
3. Problem Statement
TLS uses RFC 5280 [6] X.509 Public Key Infrastructure to bind an
identity or a set of identities, to the subject of an X.509
certificate. While RFC 3261 provides adequate guidance on the use of
X.509 certificates for S/MIME, it is relatively silent on the use of
such certificates for TLS. With respect to certificates for TLS, RFC
3261 (Section 26.3.1) says:
Proxy servers, redirect servers, and registrars SHOULD possess a
site certificate whose subject corresponds to their canonical
hostname.
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The security properties of TLS and S/MIME as used in SIP are
different: X.509 certificates for S/MIME are generally used for end-
to-end authentication and encryption; thus, they serve to bind the
identity of a user to the certificate and RFC 3261 is sufficiently
clear that in certificates used for S/MIME, the subjectAltName field
will contain the appropriate identity. On the other hand, X.509
certificates used for TLS serve to bind the identities of the per-hop
domain sending or receiving the SIP messages. However, the lack of
guidelines in RFC 3261 on exactly where to put identities -- in the
subjectAltName field or carried as a Common Name (CN) in the Subject
field -- of an X.509 certificate created ambiguities. Following the
accepted practice of the time, legacy X.509 certificates were allowed
to store the identity in the CN field of the certificate instead of
the currently specified subjectAltName extension. Lack of further
guidelines on how to interpret the identities, which identity to
choose if more than one identity is present in the certificate, the
behavior when multiple identities with different schemes were present
in the certificate, etc., lead to ambiguities when attempting to
interpret the certificate in a uniform manner for TLS use.
This document shows how the certificates are to be used for mutual
authentication when both the client and server possess appropriate
certificates, and normative behavior for matching the DNS query
string with an identity stored in the X.509 certificate.
Furthermore, a certificate can contain multiple identities for the
subject in the subjectAltName extension (the "subject" of a
certificate identifies the entity associated with the public key
stored in the public key field). As such, this document specifies
appropriate matching rules to encompass various subject identity
representation options. And finally, this document also provides
guidelines to service providers for assigning certificates to SIP
servers.
The rest of this document is organized as follows: the next section
provides an overview of the most primitive case of a client using DNS
to access a SIP server and the resulting authentication steps.
Section 5 looks at the reason why mutual inter-domain authentication
is desired in SIP, and the lack of normative text and behavior in RFC
3261 for doing so. Section 6 outlines normative guidelines for a
service provider assigning certificates to SIP servers. Section 7
provides normative behavior on the SIP entities (user agent clients,
user agent servers, registrars, redirect servers, and proxies) that
need perform authentication based on X.509 certificates. Section 8
includes the security considerations.
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4. SIP Domain to Host Resolution
Routing in SIP is performed by having the client execute RFC 3263 [8]
procedures on a URI, called the "Application Unique String (AUS)"
(c.f. Section 8 of RFC 3263 [8]). These procedures take as input a
SIP AUS (the SIP URI), extract the domain portion of that URI for use
as a lookup key, and query the Domain Name Service (DNS) to obtain an
ordered set of one or more IP addresses with a port number and
transport corresponding to each IP address in the set (the "Expected
Output"). If the transport indicates the use of TLS, then a TLS
connection is opened to the server on a specific IP address and port.
The server presents an X.509 certificate to the client for
verification as part of the initial TLS handshake.
The client extracts identifiers from the Subject and any
subjectAltName extension in the certificate (see Section 7.1) and
compares these values to the domain part extracted from the original
SIP URI (the AUS). If any identifier match is found, the server is
considered to be authenticated and subsequent signaling can now
proceed over the TLS connection. Matching rules for X.509
certificates and the normative behavior for clients is specified in
Section 7.3.
As an example, consider a request that is to be routed to the SIP
address "sips:alice@example.com". This address requires a secure
connection to the SIP domain "example.com" (the 'sips' scheme
mandates a secure connection). Through a series of DNS
manipulations, the domain name is mapped to a set of host addresses
and transports. The entity attempting to create the connection
selects an address appropriate for use with TLS from this set. When
the connection is established to that server, the server presents a
certificate asserting the identity "sip:example.com". Since the
domain part of the SIP AUS matches the subject of the certificate,
the server is authenticated (see Section 7.2 for the normative rules
that govern this comparison).
Session Initiation Protocol Secure (SIPS) borrows this pattern of
server certificate matching from HTTPS. However, RFC 2818 [7]
prefers that the identity be conveyed as a subjectAltName
extension of type dNSName rather than the common practice of
conveying the identity in the CN field of the Subject field.
Similarly, this document recommends that the SIP domain identity
be conveyed as a subjectAltName extension of type
uniformResourceIdentifier (c.f. Sections 6 and 7.1).
A domain name in an X.509 certificates is properly interpreted
only as a sequence of octets to be compared to the URI used to
reach the host. No inference can be made based on the DNS name
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hierarchy. For example, a valid certificate for "example.com"
does not imply that the owner of that certificate has any
relationship at all to "subname.example.com".
5. The Need for Mutual Interdomain Authentication
Consider the SIP trapezoid shown in Figure 1.
Proxy-A.example.com Proxy-B.example.net
+-------+ +-------+
| Proxy |--------------------| Proxy |
+----+--+ +---+---+
| |
| |
| |
| +---+
0---0 | |
/-\ |___|
+---+ / /
+----+
alice@example.com bob@example.net
Figure 1: SIP Trapezoid
A user, alice@example.com, invites bob@example.net for a multimedia
communication session. Alice's outbound proxy, Proxy-A.example.com,
uses normal RFC 3263 [8] resolution rules to find a proxy -- Proxy-
B.example.net -- in the example.net domain that uses TLS. Proxy-A
actively establishes an interdomain TLS connection with Proxy-B and
each presents a certificate to authenticate that connection.
RFC 3261 [2], Section 26.3.2.2, "Interdomain Requests" states that
when a TLS connection is created between two proxies:
Each side of the connection SHOULD verify and inspect the
certificate of the other, noting the domain name that appears in
the certificate for comparison with the header fields of SIP
messages.
However, RFC 3261 is silent on whether to use the subjectAltName or
CN of the certificate to obtain the domain name, and which takes
precedence when there are multiple names identifying the holder of
the certificate.
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The authentication problem for Proxy-A is straightforward: in the
certificate Proxy-A receives from Proxy-B, Proxy-A looks for an
identity that is a SIP URI ("sip:example.net") or a DNS name
("example.net") that asserts Proxy-B's authority over the example.net
domain. Normative behavior for a TLS client like Proxy-A is
specified in Section 7.3.
The problem for Proxy-B is slightly more complex since it accepts the
TLS request passively. Thus, Proxy-B does not possess an equivalent
AUS that it can use as an anchor in matching identities from
Proxy-A's certificate.
RFC 3261 [2], Section 26.3.2.2, only tells Proxy-B to "compare the
domain asserted by the certificate with the 'domainname' portion
of the From header field in the INVITE request". The difficulty
with that instruction is that the domainname in the From header
field is not always that of the domain from which the request is
received.
The normative behavior for a TLS server like Proxy-B that passively
accepts a TLS connection and requires authentication of the sending
peer domain is provided in Section 7.4.
6. Certificate Usage by a SIP Service Provider
It is possible for service providers to continue the practice of
using existing certificates for SIP usage with the identity conveyed
only in the Subject field, but they should carefully consider the
following advantages of conveying identity in the subjectAltName
extension field:
o The subjectAltName extension can hold multiple values, so the same
certificate can identify multiple servers or sip domains.
o There is no fixed syntax specified for the Subject field, so
issuers vary in how the field content is set. This forces a
recipient to use heuristics to extract the identity, again
increasing opportunities for misinterpretation.
Because of these advantages, service providers are strongly
encouraged to obtain certificates that contain the identity or
identities in the subjectAltName extension field.
When assigning certificates to authoritative servers, a SIP service
provider MUST ensure that the SIP domain used to reach the server
appears as an identity in the subjectAltName field, or for
compatibility with existing certificates, the Subject field of the
certificate. In practice, this means that a service provider
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distributes to its users SIP URIs whose domain portion corresponds to
an identity for which the service provider has been issued a
certificate.
7. Behavior of SIP Entities
This section normatively specifies the behavior of SIP entities when
using X.509 certificates to determine an authenticated SIP domain
identity.
The first two subsections apply to all SIP implementations that use
TLS to authenticate the peer: Section 7.1 describes how to extract a
set of SIP identities from the certificate obtained from a TLS peer,
and Section 7.2 specifies how to compare SIP identities. The
remaining subsections provide context for how and when these rules
are to be applied by entities in different SIP roles.
7.1. Finding SIP Identities in a Certificate
Implementations (both clients and server) MUST determine the validity
of a certificate by following the procedures described in RFC 5280
[6].
As specified by RFC 5280 [6], Section 4.2.1.12, implementations MUST
check for restrictions on certificate usage declared by any
extendedKeyUsage extensions in the certificate. The SIP Extended Key
Usage (EKU) document [12] defines an extendedKeyUsage for SIP.
Given an X.509 certificate that the above checks have found to be
acceptable, the following describes how to determine what SIP domain
identity or identities the certificate contains. A single
certificate can serve more than one purpose -- that is, the
certificate might contain identities not acceptable as SIP, domain
identities and/or might contain one or more identities that are
acceptable for use as SIP domain identities.
1. Examine each value in the subjectAltName field. The
subjectAltName field and the constraints on its values are
defined in Section 4.2.1.6 of RFC 5280 [6]. The subjectAltName
field can be absent or can contain one or more values. Each
value in the subjectAltName has a type; the only types acceptable
for encoding a SIP domain identity SHALL be:
URI If the scheme of the URI is not "sip", then the
implementation MUST NOT accept the value as a SIP domain
identity.
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If the scheme of the URI value is "sip", and the URI value
that contains a userpart (there is an '@'), the
implementation MUST NOT accept the value as a SIP domain
identity (a value with a userpart identifies an individual
user, not a domain).
If the scheme of the URI value is "sip", and there is no
userinfo component in the URI (there is no '@'), then the
implementation MUST accept the hostpart as a SIP domain
identity.
Note: URI scheme tokens are always case insensitive.
DNS An implementation MUST accept a domain name system
identifier as a SIP domain identity if and only if no other
identity is found that matches the "sip" URI type described
above.
2. If and only if the subjectAltName does not appear in the
certificate, the implementation MAY examine the CN field of the
certificate. If a valid DNS name is found there, the
implementation MAY accept this value as a SIP domain identity.
Accepting a DNS name in the CN value is allowed for backward
compatibility, but when constructing new certificates, consider
the advantages of using the subjectAltName extension field (see
Section 6).
The above procedure yields a set containing zero or more identities
from the certificate. A client uses these identities to authenticate
a server (see Section 7.3) and a server uses them to authenticate a
client (see Section 7.4).
7.2. Comparing SIP Identities
When an implementation (either client or server) compares two values
as SIP domain identities:
Implementations MUST compare only the DNS name component of each
SIP domain identifier; an implementation MUST NOT use any scheme
or parameters in the comparison.
Implementations MUST compare the values as DNS names, which means
that the comparison is case insensitive as specified by RFC 4343
[3]. Implementations MUST handle Internationalized Domain Names
(IDNs) in accordance with Section 7.2 of RFC 5280 [6].
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Implementations MUST match the values in their entirety:
Implementations MUST NOT match suffixes. For example,
"foo.example.com" does not match "example.com".
Implementations MUST NOT match any form of wildcard, such as a
leading "." or "*." with any other DNS label or sequence of
labels. For example, "*.example.com" matches only
"*.example.com" but not "foo.example.com". Similarly,
".example.com" matches only ".example.com", and does not match
"foo.example.com".
RFC 2818 [7] (HTTP over TLS) allows the dNSName component to
contain a wildcard; e.g., "DNS:*.example.com". RFC 5280
[6], while not disallowing this explicitly, leaves the
interpretation of wildcards to the individual specification.
RFC 3261 [2] does not provide any guidelines on the presence
of wildcards in certificates. Through the rule above, this
document prohibits such wildcards in certificates for SIP
domains.
7.3. Client Behavior
A client uses the domain portion of the SIP AUS to query a (possibly
untrusted) DNS to obtain a result set, which is one or more SRV and A
records identifying the server for the domain (see Section 4 for an
overview).
The SIP server, when establishing a TLS connection, presents its
certificate to the client for authentication. The client MUST
determine the SIP domain identities in the server certificate using
the procedure in Section 7.1. Then, the client MUST compare the
original domain portion of the SIP AUS used as input to the RFC 3263
[8] server location procedures to the SIP domain identities obtained
from the certificate.
o If there were no identities found in the server certificate, the
server is not authenticated.
o If the domain extracted from the AUS matches any SIP domain
identity obtained from the certificate when compared as described
in Section 7.2, the server is authenticated for the domain.
If the server is not authenticated, the client MUST close the
connection immediately.
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7.4. Server Behavior
When a server accepts a TLS connection, the server presents its own
X.509 certificate to the client. Servers that wish to authenticate
the client will ask the client for a certificate. If the client
possesses a certificate, that certificate is presented to the server.
If the client does not present a certificate, the client MUST NOT be
considered authenticated.
Whether or not to close a connection if the client does not
present a certificate is a matter of local policy, and depends on
the authentication needs of the server for the connection. Some
currently deployed servers use Digest authentication to
authenticate individual requests on the connection, and choose to
treat the connection as authenticated by those requests for some
purposes (but see Section 8.1).
If the local server policy requires client authentication for some
local purpose, then one element of such a local policy might be to
allow the connection only if the client is authenticated. For
example, if the server is an inbound proxy that has peering
relationships with the outbound proxies of other specific domains,
the server might allow only connections authenticated as coming
from those domains.
When authenticating the client, the server MUST obtain the set of SIP
domain identities from the client certificate as described in
Section 7.1. Because the server accepted the TLS connection
passively, unlike a client, the server does not possess an AUS for
comparison. Nonetheless, server policies can use the set of SIP
domain identities gathered from the certificate in Section 7.1 to
make authorization decisions.
For example, a very open policy could be to accept an X.509
certificate and validate the certificate using the procedures in RFC
5280 [6]. If the certificate is valid, the identity set is logged.
Alternatively, the server could have a list of all SIP domains the
server is allowed to accept connections from; when a client presents
its certificate, for each identity in the client certificate, the
server searches for the identity in the list of acceptable domains to
decide whether or not to accept the connection. Other policies that
make finer distinctions are possible.
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The decision of whether or not the authenticated connection to the
client is appropriate for use to route new requests to the client
domain is independent of whether or not the connection is
authenticated; the connect-reuse [10] document discusses this aspect
in more detail.
7.5. Proxy Behavior
A proxy MUST use the procedures defined for a User Agent Server (UAS)
in Section 7.4 when authenticating a connection from a client.
A proxy MUST use the procedures defined for a User Agent Client (UAC)
in Section 7.3 when requesting an authenticated connection to a UAS.
If a proxy adds a Record-Route when forwarding a request with the
expectation that the route is to use secure connections, the proxy
MUST insert into the Record-Route header a URI that corresponds to an
identity for which the proxy has a certificate; if the proxy does not
insert such a URI, then creation of a secure connection using the
value from the Record-Route as the AUS will be impossible.
7.6. Registrar Behavior
A SIP registrar, acting as a server, follows the normative behavior
of Section 7.4. When the SIP registrar accepts a TLS connection from
the client, the SIP registrar presents its certificate. Depending on
the registrar policies, the SIP registrar can challenge the client
with HTTP Digest.
7.7. Redirect Server Behavior
A SIP redirect server follows the normative behavior of a UAS as
specified in Section 7.4.
7.8. Virtual SIP Servers and Certificate Content
In the "virtual hosting" cases where multiple domains are managed by
a single application, a certificate can contain multiple subjects by
having distinct identities in the subjectAltName field as specified
in RFC 4474 [9]. Clients seeking to authenticate a server on such a
virtual host can still follow the directions in Section 7.3 to find
the identity matching the SIP AUS used to query DNS.
Alternatively, if the TLS client hello "server_name" extension as
defined in RFC 4366 [4] is supported, the client SHOULD use that
extension to request a certificate corresponding to the specific
domain (from the SIP AUS) with which the client is seeking to
establish a connection.
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8. Security Considerations
The goals of TLS (when used with X.509 certificates) include the
following security guarantees at the transport layer:
Confidentiality: packets tunneled through TLS can be read only by
the sender and receiver.
Integrity: packets tunneled through TLS cannot be undetectably
modified on the connection between the sender and receiver.
Authentication: each principal is authenticated to the other as
possessing a private key for which a certificate has been issued.
Moreover, this certificate has not been revoked, and is verifiable
by a certificate chain leading to a (locally configured) trust
anchor.
We expect appropriate processing of domain certificates to provide
the following security guarantees at the application level:
Confidentiality: SIPS messages from alice@example.com to
bob@example.net can be read only by alice@example.com,
bob@example.net, and SIP proxies issued with domain certificates
for example.com or example.net.
Integrity: SIPS messages from alice@example.com to bob@example.net
cannot be undetectably modified on the links between
alice@example.com, bob@example.net, and SIP proxies issued with
domain certificates for example.com or example.net.
Authentication: alice@example.com and proxy.example.com are mutually
authenticated; moreover, proxy.example.com is authenticated to
alice@example.com as an authoritative proxy for domain
example.com. Similar mutual authentication guarantees are given
between proxy.example.com and proxy.example.net and between
proxy.example.net and bob@example.net. As a result,
alice@example.com is transitively mutually authenticated to
bob@example.net (assuming trust in the authoritative proxies for
example.com and example.net).
8.1. Connection Authentication Using Digest
Digest authentication in SIP provides for authentication of the
message sender to the challenging UAS. As commonly deployed, digest
authentication provides only very limited integrity protection of the
authenticated message, and has no provision for binding the
authentication to any attribute of the transport. Many existing SIP
deployments have chosen to use the Digest authentication of one or
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more messages on a particular transport connection as a way to
authenticate the connection itself -- by implication, authenticating
other (unauthenticated) messages on that connection. Some even
choose to similarly authenticate a UDP source address and port based
on the digest authentication of another message received from that
address and port. This use of digest goes beyond the assurances that
the Digest Authentication mechanism was designed to provide. A SIP
implementation SHOULD NOT use the Digest Authentication of one
message on a TCP connection or from a UDP peer to infer any
authentication of any other messages on that connection or from that
peer. Authentication of the domain at the other end of a connection
SHOULD be accomplished using TLS and the certificate validation rules
described by this specification instead.
9. Acknowledgments
The following IETF contributors provided substantive input to this
document: Jeroen van Bemmel, Michael Hammer, Cullen Jennings, Paul
Kyzivat, Derek MacDonald, Dave Oran, Jon Peterson, Eric Rescorla,
Jonathan Rosenberg, and Russ Housley. Special acknowledgement goes
to Stephen Kent for extensively reviewing document versions and
suggesting invaluable feedback, edits, and comments.
Paul Hoffman, Eric Rescorla, and Robert Sparks provided many valuable
WGLC comments.
10. References
10.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[3] Eastlake, D., "Domain Name System (DNS) Case Insensitivity
Clarification", RFC 4343, January 2006.
[4] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., and
T. Wright, "Transport Layer Security (TLS) Extensions",
RFC 4366, April 2006.
[5] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
Protocol Version 1.2", RFC 5246, August 2008.
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[6] 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.
10.2. Informative References
[7] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[8] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
(SIP): Locating SIP Servers", RFC 3263, June 2002.
[9] Peterson, J. and C. Jennings, "Enhancements for Authenticated
Identity Management in the Session Initiation Protocol (SIP)",
RFC 4474, August 2006.
[10] Mahy, R., Gurbani, V., and B. Tate, "Connection Reuse in the
Session Initiation Protocol", RFC 5923, June 2010.
[11] Drage, K., "A Process for Handling Essential Corrections to the
Session Initiation Protocol (SIP)", Work in Progress,
July 2008.
[12] Lawrence, S. and V. Gurbani, "Using Extended Key Usage (EKU)
for Session Initiation Protocol (SIP) X.509 Certificates",
RFC 5924, June 2010.
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Appendix A. Editorial Guidance (Non-Normative)
This document is intended to update RFC 3261 in accordance with the
SIP Working Group procedures described in [11] or its successor.
This appendix provides guidance to the editor of the next
comprehensive update to RFC 3261 [2] on how to incorporate the
changes provided by this document.
A.1. Additions
The content of Sections 4 through 7 inclusive can be incorporated as
subsections within a section that describes SIP domain
authentication.
The contents of Section 8.1 can be incorporated into the Security
Considerations section of the new document.
All normative references from this document can be carried forward to
its successor.
A.2. Changes
The following subsections describe changes in specific sections of
RFC 3261 [2] that need to be modified in the successor document to
align them with the content of this document. In each of the
following, the token is a reference to the
section added as described in Appendix A.1.
A.2.1. Changes to Section 26.3.1
The current text says:
Proxy servers, redirect servers and registrars SHOULD possess a
site certificate whose subject corresponds to their canonical
hostname.
The suggested replacement for the above is:
Proxy servers, redirect servers, registrars, and any other server
that is authoritative for some SIP purpose in a given domain
SHOULD possess a certificate whose subjects include the name of
that SIP domain.
Gurbani, et al. Standards Track [Page 16]
RFC 5922 Domain Certs June 2010
Authors' Addresses
Vijay K. Gurbani
Bell Laboratories, Alcatel-Lucent
1960 Lucent Lane
Room 9C-533
Naperville, IL 60566
USA
Phone: +1 630 224-0216
EMail: vkg@alcatel-lucent.com
Scott Lawrence
EMail: scott-ietf@skrb.org
Alan S.A. Jeffrey
Bell Laboratories, Alcatel-Lucent
1960 Lucent Lane
Room 9C-533
Naperville, IL 60566
USA
EMail: ajeffrey@alcatel-lucent.com
Gurbani, et al. Standards Track [Page 17]
RFC, FYI, BCP