One document matched: draft-ietf-sip-domain-certs-01.txt
Differences from draft-ietf-sip-domain-certs-00.txt
SIP WG V. Gurbani
Internet-Draft Bell Laboratories, Alcatel-Lucent
Updates: rfc3261 S. Lawrence
(if approved) Bluesocket Inc.
Intended status: Standards Track A. Jeffrey
Expires: January 15, 2009 Bell Laboratories, Alcatel-Lucent
July 14, 2008
Domain Certificates in the Session Initiation Protocol (SIP)
draft-ietf-sip-domain-certs-01
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
This document describes how to interpret certain information in a
X.509 PKIX-compliant certificate used in a Session Initiation
Protocol (SIP) over Transport Layer Security (TLS) connection. More
specifically, it describes how to find the right identity for
authentication in such certificates and how to use it for SIP domain
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authentication.
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Key Words . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem statement . . . . . . . . . . . . . . . . . . . . . . 3
4. SIP domain to host resolution . . . . . . . . . . . . . . . . 5
5. The need for mutual interdomain authentication . . . . . . . . 6
6. Guidelines for a SIP service provider . . . . . . . . . . . . 7
7. Behavior of SIP entities . . . . . . . . . . . . . . . . . . . 7
7.1. Finding SIP Identities in a Certificate . . . . . . . . . 8
7.2. Comparing SIP Identities . . . . . . . . . . . . . . . . . 9
7.3. Client behavior . . . . . . . . . . . . . . . . . . . . . 9
7.4. Server behavior . . . . . . . . . . . . . . . . . . . . . 10
7.5. Proxy behavior . . . . . . . . . . . . . . . . . . . . . . 11
7.6. Registrar behavior . . . . . . . . . . . . . . . . . . . . 11
7.7. Redirect server behavior . . . . . . . . . . . . . . . . . 11
7.8. Virtual SIP Servers and Certificate Content . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8.1. Connection authentication using Digest . . . . . . . . . . 13
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.1. Normative References . . . . . . . . . . . . . . . . . . . 13
11.2. Informative References . . . . . . . . . . . . . . . . . . 14
Appendix A. Editorial guidance (non-normative) . . . . . . . . . 14
A.1. Additions . . . . . . . . . . . . . . . . . . . . . . . . 15
A.2. Changes . . . . . . . . . . . . . . . . . . . . . . . . . 15
A.2.1. 26.3.1 . . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 17
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1. Terminology
1.1. 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.
2. Introduction
Transport Layer Security (TLS) [3] has started to appear in an
increasing number of Session Initiation Protocol (SIP) [2]
implementations. In order to use the authentication capabilities of
TLS, certificates as defined by the Internet X.509 Public Key
Infrastructure RFC 5280 [4] 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; it may not apply to
use of such certificates with S/MIME, for instance.
3. Problem statement
TLS uses X.509 Public Key Infrastructure [4] to bind an identity or a
set of identities, to the subject of a X.509 certificate.
Accordingly, the recommendations of the SIP working group have been
to populate the X.509v3 Subject Alternative Names (subjectAltName, or
SAN) extension with an identity. While RFC3261 provides adequate
guidance on the use of X.509 certificates used for S/MIME, it is
relatively silent on the use of such certificates for TLS. The
concept of what should be contained in a site (or domain) certificate
in RFC3261 is quoted below (Section 26.3.1):
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Proxy servers, redirect servers and registrars SHOULD possess a
site certificate whose subject corresponds to their canonical
hostname.
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 RFC3261 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 RFC3261 on exactly where to put identities -- in the
subjectAltName field or carried as a Common Name (CN) in the Subject
field -- of a X.509 certificates 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. It also contains normative behavior for matching the
DNS query string with an identity stored in the X.509 certificate.
Furthermore, it is permissible for a certificate to 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
RFC3261 for doing so. Section 6 outlines normative guidelines for a
service provider when it is 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 [6]
procedures on a URI, called the "Application Unique String (AUS)
(c.f. Section 8 of RFC 3263 [6]). These procedures take as input a
SIP AUS (the SIP domain) and return an ordered set containing one or
more IP addresses, and a port number and transport corresponding to
each IP address in the set (the "Expected Output") by querying an
Domain Name Service (DNS). 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 should extract identifiers from the Subject and
subjectAltName extension in the certificate (see Section 7.1) and
compare these values to 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", which is taken to be the
SIP AUS value. Through a series of DNS manipulations, the AUS is
mapped to a set of host addresses and transports. From this set, an
address appropriate for use with TLS is selected. A connection is
subsequently established to that server, which presents a certificate
asserting an identity of "sip:example.com". Since the host portion
of the SIP AUS matches the subject of the certificate, the server is
considered to be authenticated.
SIPS borrows this behavior from HTTPS. However, to be pedantic,
RFC 2818 [7] prefers that the identity be conveyed as a
subjectAltName extension of type dNSName instead of the commonly
used 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. Section 6, Section 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 should be made based on the DNS name
hierarchy.
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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
An 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 [6] 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, mutual TLS
authentication should follow whereby
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, RFC3261 is silent on where in the certificate should the
domain name be retrieved from (SAN or CN?) and which name takes
precedence when there are multiple names identifying the holder of
the certificate.
The authentication problem for Proxy-A is straightforward: assuming
a secure DNS infrastructure and no routing attacks, Proxy-A already
knows that Proxy-B is a valid proxy for the example.net domain.
Thus, in the certificate it receives from Proxy-B, Proxy-A should
look for the host name ("Proxy-B.example.net") or an identity
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consisting of a SIP URI ("sip: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 accepted
the TLS request passively. Thus, it 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 exhorts 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 this approach is that it is not always the case that the
domainname in From corresponds to the domain from which the
request is being received.
The normative behavior for a TLS server like Proxy-B that passively
accept TLS connections and requires authentication of the sending
peer is provided in Section 7.4.
6. Guidelines for a SIP service provider
Service providers MAY continue the practice of using existing
certificates for SIP usage with the identity conveyed in the Subject
field; however, such usage is NOT RECOMMENDED for new certificates,
which MUST contain the identity or identities in the subjectAltName
extension field.
When assigning certificates to proxy servers, registrars, and
redirect servers, a SIP service provider MUST ensure that the SIP AUS
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 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.
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7.1. Finding SIP Identities in a Certificate
Procedures for constructing a certificate path and checking
revocation status to determine the validity of a certificate are
described in RFC 5280 [4]; implementations MUST follow checks as
prescribed therein. This document adds additional rules for
interpreting an X.509 certificate for use in SIP.
The SIP Extended Key Usage (EKU) document [5] describes the method to
validate EKU values found in the certificate used for SIP. If a
certificate has a SIP EKU value specified, implementations MUST
perform the checks prescribed by that specification.
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 it contains. Note that a single certificate
MAY serve more than one purpose - that is, it MAY contain identities
not valid for use in SIP, and/or MAY contain one or more identities
that are valid for use in SIP.
1. Examine the values in the subjectAltName field. The contents of
subjectAltName field and the constraints that may be imposed on
them are defined in Section 4.2.1.6 of RFC 5280 [4]. The
subjectAltName field may not be present or it may contain one or
more identities. Each value in the subjectAltName has a type;
the only types acceptable for encoding a SIP domain identity are:
URI If the scheme of the URI value is "sip" (URI scheme tokens
are always case insensitive), and there is no userinfo
component in the URI (there is no '@'), then the hostpart is a
SIP domain identity. A URI value that does contain a userpart
MUST NOT be used as a domain identity (such a certificate
identifies an individual user, not a server for the domain).
If the scheme of the URI is not "sip", then the identity
corresponding to that scheme MUST NOT be used as a SIP domain
identity.
DNS A domain name system identifier MUST be accepted 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 client MAY examine the CN field of the
certificate. If a valid DNS name is found there, the
implementation MAY use this value as a SIP domain identity. The
use of the CN value is allowed for backward compatibility, but is
NOT RECOMMENDED. Service providers who are applying for new
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X.509 certificates to be used with SIP SHOULD follow the
guidelines of 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 comparing two values as SIP domain identities:
Implementations MUST compare only that part of each identifier
(from the procedure defined in Section 7.1) that is a DNS name.
Any scheme or parameters extracted from an identifier MUST NOT be
used in the comparison procedure described below.
The values MUST be compared as DNS names, which means that the
comparison is case insensitive. Internationalized Domain Names
(IDNs) must be handled in accordance with Section 7.2 of RFC 5280
[4].
The match MUST be exact:
A suffix match MUST NOT be considered a match. For example,
"foo.example.com" does not match "example.com".
Any form of wildcard, such as a leading "." or "*.", MUST NOT
be considered a match. For example, "foo.example.com" does not
match ".example.com" or "*.example.com".
RFC 2818 (HTTP over TLS) [7] allows the dNSName component to
contain a wildcard; e.g., "DNS:*.example.com". RFC 5280
[4], 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. This document reflects the
consensus from the working group to not allow such
wildcards.
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
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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 server
location procedures [6] 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 AUS matches any SIP domain identity obtained from the
certificate when compared as described in section Section 7.2, the
server is authenticated for the domain.
If the server is not authenticated, the client MUST close the
connection immediately.
7.4. Server behavior
When a server accepts a TLS connection, it presents its own X.509
certificate to the client. To authenticate the client, the server
asks the client for a certificate. If the client possesses a
certificate, it is presented to the server. If the client does not
present a certificate, it MUST NOT be considered authenticated.
Whether or not to close a connection if the client cannot 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 server requires client authentication for some local
purpose, then it MAY implement a policy of allowing 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, it might only allow
connections authenticated as coming from those domains.
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, it 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 a X.509
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certificate and validate it using the procedures in RFC 5280 [4]. If
the certificate is valid, the identity set is logged. Alternatively,
the server could have a list of all SIP domains it is allowed to
accept connections from; when a client presents its certificate, for
each identity in the client certificate, the server searches for it
in the list of acceptable domains to decide whether or not to accept
the connection. Other policies that make finer distinctions are
possible.
Note that 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] draft 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, it MUST
insert into the Record-Route header a URI that corresponds to an
identity for which it has a certificate; if it does not, then it will
not be possible to create a secure connection using the value from
the Record-Route as the AUS.
7.6. Registrar behavior
A SIP registrar, acting as a server, follows the normative behavior
of Section 7.4. When it accepts a TLS connection from the client, it
present its certificate. Depending on the registrar policies, it may
challenge the client with HTTP Digest.
7.7. Redirect server behavior
A SIP redirect server follows the normative behavior of Section 7.4.
When it accepts a TLS connection from the client, it present its
certificate. Depending on the server policies, it may challenge the
client with HTTP Digest.
7.8. Virtual SIP Servers and Certificate Content
In the "virtual hosting" cases where multiple domains are managed by
a single application, a certificate may contain multiple subjects by
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having distinct identities in the subjectAltName field [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 extension [8] is supported,
the client SHOULD use it to request a certificate corresponding to
the specific domain (the SIP AUS) that the client is seeking to
establish a connection with.
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
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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, it
provides only very limited integrity protection of the authenticated
message. Many existing deployments have chosen to use the Digest
authentication of one or more messages on a particular connection as
a way to authenticate the connection itself - and by implication,
authenticating other (unchallenged) messages on that connection.
Some even choose to similarly authenticate a UDP source address and
port based on the Digest authentication of a message received from
that address and port. This use of Digest goes beyond the assurances
it was designed to provide, and is NOT RECOMMENDED. 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. IANA Considerations
This memo does not contain any considerations for IANA.
10. 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, Russ Housley. Special acknowledgement goes to
Stephen Kent for extensively reviewing draft versions and suggesting
invaluable feedback, edits, and comments.
Paul Hoffman, Eric Rescorla and Robert Sparks provided much valuable
WGLC comments.
11. References
11.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
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Session Initiation Protocol", RFC 3261, June 2002.
[3] Dierks, T. and E. Rescorla, "The TLS Protocol Version 1.1",
RFC 4346, April 2006.
[4] Cooper, D., Santesson, S., Farrell, S., Boyen, S., Housley, R.,
and W. Polk, "Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL) Profile",
RFC 5280, May 2008.
[5] Lawrence, S. and V. Gurbani, "Using Extended Key Usage (EKU)
for Session Initiation Protocol (SIP) X.509 Certificates",
draft-ietf-sip-eku-01.txt (work in progress), February 2008.
11.2. Informative References
[6] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
(SIP): Location SIP Servers", RFC 3263, June 2002.
[7] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[8] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., and
T. Wright, "Transport Layer Security (TLS) Extensions",
RFC 4366, April 2006.
[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",
draft-ietf-sip-connect-reuse-08.txt (work in progress),
October 2007.
[11] Drage, K., "A Process for Handling Essential Corrections to the
Session Initiation Protocol (SIP)",
draft-drage-sip-essential-correction-02.txt (work in progress),
November 2007.
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.
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A.1. Additions
The content of sections Section 4 through Section 7 inclusive can be
incorporated as subsections within a section that describes SIP
domain authentication.
Any normative references from this document should be carried forward
to the successor document.
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 <domain-authentication> is a reference to the
section added as described in Appendix A.1.
A.2.1. 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 subject is expressed as
described in <domain-authentication>.
Authors' Addresses
Vijay K. Gurbani
Bell Laboratories, Alcatel-Lucent
2701 Lucent Lane
Room 9F-546
Lisle, IL 60532
USA
Phone: +1 630 224-0216
Email: vkg@alcatel-lucent.com
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Scott Lawrence
Bluesocket Inc.
10 North Ave.
Burlington, MA 01803
USA
Phone: +1 781 229 0533
Email: slawrence@bluesocket.com
Alan S.A. Jeffrey
Bell Laboratories, Alcatel-Lucent
2701 Lucent Lane
Room 9F-534
Lisle, IL 60532
USA
Email: ajeffrey@alcatel-lucent.com
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