SIP WG J. Peterson
Internet-Draft NeuStar
Expires: August 2, 2003 February 2003
Enhancements for Authenticated Identity Management in the Session
Initiation Protocol (SIP)
draft-ietf-sip-identity-01
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at http://
www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 2, 2003.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
The existing mechanisms for expressing identity in the Session
Initiation Protocol oftentimes do not permit an administrative domain
to verify securely the identity of the originator of a request. This
document recommends practices and conventions for authenticating end
users, and proposes a way to distribute cryptographically secure
authenticated identities within SIP messages.
Peterson Expires August 2, 2003 [Page 1]
Internet-Draft SIP Identity February 2003
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Using an Authentication Service . . . . . . . . . . . . . . . 5
4. How to Share Verified Identities . . . . . . . . . . . . . . . 5
4.1 Body Added by Client . . . . . . . . . . . . . . . . . . . . . 7
4.2 Body Added by Authentication Service . . . . . . . . . . . . . 8
4.3 Using Content Indirection . . . . . . . . . . . . . . . . . . 8
5. Identity in Responses . . . . . . . . . . . . . . . . . . . . 9
6. Receiving an Authentication Token . . . . . . . . . . . . . . 10
6.1 Authentication Service Handling of Authentication Tokens . . . 10
7. Selective Sharing of Identity . . . . . . . . . . . . . . . . 10
7.1 Requesting Privacy . . . . . . . . . . . . . . . . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 14
A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
Normative References . . . . . . . . . . . . . . . . . . . . . 13
Informative References . . . . . . . . . . . . . . . . . . . . 13
B. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Full Copyright Statement . . . . . . . . . . . . . . . . . . . 16
Peterson Expires August 2, 2003 [Page 2]
Internet-Draft SIP Identity February 2003
1. Introduction
This document provides enhancements to the existing mechanisms for
authenticated identity management in the Session Initiation Protocol
(SIP [1]). An identity, for the purposes of this document, is
defined as a canonical SIP URI employed to reach a user (such as
'sip:alice@atlanta.com').
RFC3261 enumerates a number of places within a SIP request that a
user can express an identity for themselves, notably the From header
field. However, the recipient of a SIP request has no way to verify
that the From header field has been populated appropriately without
some sort of cryptographic authentication mechanism.
Today, RFC3261 specifies a number of security mechanisms that can be
used by SIP UAs, including Digest, TLS and S/MIME (and
implementations may support other security schemes as well).
However, few SIP user agents today can support the end-user
certificates necessary to authenticate themselves via TLS or S/MIME,
and Digest authentication is limited by the fact that the originator
and destination must share a secret. It is desirable for SIP user
agents to be able to send requests to destinations with they have no
previous association - just as in the telephone network today, one
can receive a call from someone with whom one has no previous
association, and still have a reasonable assurance that their
displayed Caller-ID is accurate.
Many SIP user agents today support a means of authenticating
themselves to a SIP registrar - commonly with a shared secret (Digest
authentication, which MUST be supported by SIP user agents, is
typically used for this purpose). Registration allows a user agent
to express that it is the proper entity to which requests should be
sent for a particular address-of-record SIP URI.
Coincidentally, the address-of-record URI of a SIP user is also the
URI with which a SIP UA populates the From header of requests from
that user - in other words, the address-of-record is an identity. So
in this context users already have a means of providing their
identity, which makes good sense: since the contents of a From header
field are essentially a 'return address' for SIP requests, being able
to prove that you are eligible to receive requests for that 'return
address' should be identical to proving that you are authorized to
assert this identity.
However, the credentials with which a user agent proves to a
registrar that they are, for example, an authorized recipient of
requests for 'sip:alice@atlanta.com' will not be accepted by a server
in another domain - these credentials are currently only useful for
Peterson Expires August 2, 2003 [Page 3]
Internet-Draft SIP Identity February 2003
local registration. What other domains really want to know about
your identity is that you are capable of authenticating yourself in
your own domain.
Ideally, then, there should be some way of proving to remote domains
that your local domain has authenticated you. In the absence of end-
user certificates in user agents, it is possible to implement a
mediated authentication architecture for SIP in which requests are
sent to a server in the user's local domain which authenticates them
(using the same practices by which the domain would authenticate
REGISTER requests). Once a request has been authenticated, the local
domain then needs some way to communicate to remote domains that it
has sanctioned the request. This draft addresses how that identity
can could be securely shared.
RFC3261 already describes an architecture very similar to this in
Section 26.3.2.2, in which a user agent authenticates itself to a
local proxy server which in turn authenticates itself to a remote
proxy server via mutual TLS, creating a two-link chain of transitive
authentication between the originator and the remote domain. While
this works well in some architectures, there are a few respects in
which this is impractical. For one, it is possible for SIP requests
to cross multiple intermediaries in separate administrative domains,
in which case transitive trust becomes far less compelling. It also
requires intermediaries to act as proxies, rather than redirecting
requests to their destinations (redirection lightens loads on SIP
intermediaries). Both of these limitations result from the fact that
authentication takes place outside the application, at the transport
layer, rather than within SIP itself.
One solution to this problem is to use 'trusted' SIP intermediaries
that assert an identity for users in the form of a privileged SIP
header. A mechanism for doing so (with the P-Asserted-Identity
header) is given in [6]. However, this solution allows only hop-by-
hop trust between intermediaries, not end-to-end cryptographic
authentication, and it assumes a managed network of nodes with strict
mutual trust relationships, an assumption that is incompatible with
widespread Internet deployment.
The desired mediated authentication architecture has quite a bit in
common with the problem space of Kerberos [5]. Ideally, there should
be a way for a user to authenticate themselves to the local domain,
and receive some kind of token that they can share with recipients of
requests that lets them know that the user has been authenticated by
the local domain. However, Kerberos support in SIP user agents is
not widespread, and moreover SIP uses other means (such as Digest) to
perform key authentication functions already. An ideal solution
would adapt existing SIP security mechanisms to address this problem.
Peterson Expires August 2, 2003 [Page 4]
Internet-Draft SIP Identity February 2003
Therefore, this document defines a new logical role for SIP network
intermediaries called an 'authentication service'. Once an
authentication service has verified the identity of the originator of
a request, as described above, it creates a cryptographic token that
contains the authenticated identity of the user, and which has some
reference integrity with the request itself. This token can then be
added to a SIP request and inspected by recipients of the request who
need a cryptographic guarantee of the identity of the user.
One possible format for such tokens is the Authenticated Identity
Body (AIB) described in [4]. Other token formats are a matter for
further investigation. Throughout this document, the use of AIB
format for the token is considered exclusively. Only tokens that are
suitable to be carried in a MIME body are considered in this
document.
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in RFC2119 [2] and indicate requirement levels for
compliant SIP implementations.
3. Using an Authentication Service
A SIP user agents sends requests to an authentication service in
order to receive an authentication token for the request. How
exactly the association with an authentication service is learned or
configured is an implementation-specific matter for the user agent -
it might be implemented with a pre-loaded Route header. The
guidelines given in RFC3261 Sections 26.3.2.1 and 26.3.2.2 should be
used when connecting to an authentication service; ideally, an
authentication service should be one hop away from a user agent, it
should use a lower-layer security protocol such as TLS or IPSec to
authenticate the authentication service before providing credentials
(especially shared secrets).
This document places no requirements on how an authentication
services authenticates requests. Since Digest authentication MUST be
supported by all SIP entities, the use of Digest for this purpose is
RECOMMENDED for compatibility with the maximum set of user agents.
4. How to Share Verified Identities
When an authentication service has authenticated the user, it must
construct an identity URI for that user that will be contained in the
token. It is RECOMMENDED that these identities take the form of SIP
Peterson Expires August 2, 2003 [Page 5]
Internet-Draft SIP Identity February 2003
address-of-record URI (as opposed to contact addresses), as they are
defined in Section 10 of RFC3261; in other words, URIs of the form
'sip:alice@atlanta.com'.
This identity must be expressed in the authentication token that will
be signed by the authentication service. For example, if the
Authenticated Identity Body (AIB) format described in [4] is used,
then for an INVITE this identity would be stored in the From header
field within a 'message/sip' or 'message/sipfrag' [7] body that will
be signed by the authentication service.
Once the token has been created, the server MUST sign the token. The
subject of the certificate SHOULD be assigned in one of the two
following ways:
An authentication service MAY use a common certificate, such as a
site certificate, for its administrative domain. The
subjectAltName of this certificate MUST correspond with the host
portion of the From header field of the identity in the
authentication token (if the identity were
'sip:alice@atlanta.com', the subjectAltName of the certificate
would be 'atlanta.com'); this should be the same certificate that
the authentication service provides when proving its own identity
(via TLS or some similar protocol).
An authentication service MAY hold a certificate corresponding to
each user in its administrative domain (in other words, a
certificate whose subjectAltName contains a URI equivalent to the
address-of-record URI of the user). In this case, the appropriate
certificate for the authenticated user will be used to sign the
authentication token. Maintaining individual certificates for
each user is RECOMMENDED, since the name subordination rules
involved with the use of a common certificate for the domain can
become complicated.
After the authentication token has been signed, the authentication
token MUST somehow be integrated with any existing MIME bodies in the
request, if necessary by transitioning the outermost MIME body to a
'multipart/mixed' format, before the request can be forwarded. Three
options are considered for ways that an authentication token could be
added to a SIP message: one in which the authentication service
pushes the token back to the client for resubmission, one in which
the authentication service adds the token itself, and one in which
the client anticipates a URI at which the authentication service will
make the token available. Authentication services MUST support the
mechanism in Section 4.1 and MAY support the mechanism in Section
4.2; the mechanism in Section 4.3 is included to illustrate a future
direction.
Peterson Expires August 2, 2003 [Page 6]
Internet-Draft SIP Identity February 2003
4.1 Body Added by Client
In this case, the authentication service returns the authentication
token to the originating user agent, prompting the user agent to
retry the request with the authentication token attached. No
existing SIP mechanism can perform this function. Therefore, this
document defines a 428 "Use Authentication Token" response code.
After a user has been authenticated (in the Digest example, with the
407 response) an authentication service sends a 428 with a MIME body
in order to request that a user agent add the enclosed MIME body to
their request and retry the request. A 428 MUST have at most a
single MIME body. This MIME body MUST be signed by the
authentication service.
The use of 428 without any MIME body is also defined in this
document. It can be sent by any server to reject a request because
the request does not contain an authentication token. A user agent
receiving this rejection SHOULD retry their request through the same
server after acquiring a token from an authentication service.
In order to signal to the authentication services and other
intermediaries that the originating user agent supports the receipt
of the 428 response code, a new option-tag has been defined, the
'auth-id' option-tag. User agents SHOULD supply the 'auth-id'
option-tag in a Supported header whenever they provide credentials to
a server (for example, in Digest authentication, whenever a Proxy-
Authorization header is added to a request).
Using the 428 response code may introduce extra round-trip times for
messages, delaying the setup of requests. However, there are some
circumstances under which extra RTTs may not impede performance. If
the originating user agent possesses a non-stale nonce (assuming
Digest authentication) from the authentication service, it can pre-
emptively include a Proxy-Authorization header, eliminating one RTT
(the one resulting from a 407). With regard to the second RTT, note
that the request needn't necessarily go through the authentication
service again once the authentication token has been added - it could
go directly to its destination, which reduce the impact of the second
RTT.
There are two good reasons to think that the originating user agent
should be the party responsible for adding the authentication token
to the request. Firstly, because this gives the client the
opportunity to inspect the body itself (perhaps only to see whether
or not it is encrypted; see [4]) in order to verify that the
authenticated identity corresponds with the provided credentials and
the user's preferences. Secondly, the client can provide a signature
Peterson Expires August 2, 2003 [Page 7]
Internet-Draft SIP Identity February 2003
over the entire body of the message (either with S/MIME or some
header-based mechanism) so that the final recipient of messages can
be assured that all information in the body is there at the
originator's behest.
4.2 Body Added by Authentication Service
Another possibility is that the authentication service could add the
body to the request itself before forwarding the request. However,
the authentication service role is usually played by entities that
act as proxy servers for most requests, and proxy servers cannot
modify message bodies (see RFC3261 Section 16.6). In order to add an
authentication token, the authentication service needs to act as a
transparent back-to-back user agent, effectively terminating the
request and re-originating it with a new body appended to any
existing MIME bodies (again, transposing to various MIME multipart
forms as necessary).
This mechanism has some potential advantages over pushing the
authentication token back to the originating user agent. For one, it
saves one additional round-trip time that would be used by the 428
response. It also requires no new SIP mechanisms, whereas the 428
response necessitates option-tag support.
However, there are proposed SIP integrity mechanisms that place a
signature over the entire message body in a SIP message header. Were
a server to modify the body of a message that was protected by such
signature, that would be perceived as an integrity violation by
downstream recipients of the message. Presumably, a back-to-back
user agent function would have to sacrifice this end-to-end
integrity. The notion of a transparent back-to-back user agent is
also ill-defined, and it is questionable if any SIP intermediaries
should interfere with SIP message bodies.
4.3 Using Content Indirection
Work is currently underway in the SIP WG to define a content
indirection [8] mechanism for SIP, a mechanism by which a MIME body
in a SIP request can refer, with a URL, to a document that it hosted
somewhere in the network. This raises another interesting
possibility for authentication token transport in SIP.
A SIP user agent could create a content indirection MIME body (using
the RFC2017 [9] URL MIME External-Body Access-Type) that contains a
URL that identities a resource controlled by the authentication
service, anticipating that the authentication service will make the
authentication token available at that URL. This URL could be pushed
by the authentication service to the UAC when the authentication
Peterson Expires August 2, 2003 [Page 8]
Internet-Draft SIP Identity February 2003
service challenges the UAC (as a new header in the 407 response).
Once an authentication service has validated the request, it simply
makes the authentication token available at the anticipated URL;
recipients of the message would then dereference the URL in order to
inspect the token.
This approach could allow user agents to have full control over the
integrity of SIP requests, while still requiring the extra RTT caused
by the use of the 428 response code. It also has numerous advantages
over other ways of handling authentication tokens issued for SIP
response messages (see Section 5).
5. Identity in Responses
Many of the practices described in the preceding sections can be
applied to responses as well as requests, with some important
differences. Primarily, the distinction is that a response cannot be
challenged or resubmitted in the same manner as a request, and
therefore the mechanism in Section 4.1 is not usable. However, when
a user agent registers under a particular identity, and thereby
becomes eligible to receive requests and send responses associated
with that identity, it provides credentials that prove its identity,
and thus if the registrar is co-located with the proxy that receives
requests for the user's administrative domain, is in a reasonable
position to act as an authentication service for responses.
Note that the identity in an authentication token in a response
almost certainly will not correspond with the identity asserted in
the From header field of the response (which is copied from the
request); the identity in the authentication token represents a
different entity. For many requests, the identity in the
authentication token of a response will correspond to the To header
field of the request, but there are numerous legitimate ways that
requests can be retargeted in which this will not be the case.
An authentication service that also acts as a registrar and inbound
proxy can add to a response an authentication token that corresponds
to the identity of the originator of that response in roughly the
same manner described in Section 4.2 - the authentication service
adds the authentication token to a response before it forwards the
response towards the originator of the request. There is no way for
an authentication service to perform a function for responses
comparable to the mechanism described in Section 4.1; however,
content indirection (see Section 4.3 could provide an alternative
that would allow the client to retain end-to-end integrity properties
on responses.
Peterson Expires August 2, 2003 [Page 9]
Internet-Draft SIP Identity February 2003
6. Receiving an Authentication Token
The manner in which an authentication token is handled is dependent
on the nature of the token itself; rules for handling the
Authenticated Identity Body (AIB) format are given [4].
6.1 Authentication Service Handling of Authentication Tokens
SIP intermediaries generally should not attempt to inspect MIME
bodies; following the rules of RFC3261 Section 16.6, MIME bodies may
be encrypted end-to-end or have other properties that make them
unsuitable for consumption by intermediaries. However,
intermediaries that implement the authentication service logical role
MAY inspect MIME bodies in order to find one with a Content-
Disposition of 'auth-id'.
For the most part, the actual value of an authenticated identity is
not likely to be of interest to a proxy server, though it MAY refuse
to process a request that does not contain a valid authentication
token (using the 428 request, as described in Section 4.1). However,
authentication services MAY additionally maintain lists of known
problem users that are banned from making requests to their
administrative domain, for example, and subsequently reject some
requests after comparing their authenticated identities to such
access control lists.
7. Selective Sharing of Identity
Most of the time, there is no need to restrict the propagation of
verified identities in the network. User agents and intermediaries
benefit from receiving verified identities. However, in some cases
intermediaries might want to restrict the distribution of identity
information, for example if
o the authenticated identity body contains an identity that is only
meaningful as an internal identifier within a particular service
provider's network, or,
o the originating user agent has requested privacy, and the
unrestricted distribution of the authenticated identity body would
violate that request.
If it is not appropriate to share an authenticated identity because a
user has requested privacy, an authenticated identity body SHOULD NOT
be created and distributed. However, in some cases there may be
other entities in the administrative domain of the authentication
service that are consumers of the authenticated identity. If, for
example, each of these servers needed to challenge the user
Peterson Expires August 2, 2003 [Page 10]
Internet-Draft SIP Identity February 2003
individually for identity, it might significantly delay the
processing of the request. For that reason, it may be appropriate to
circulate authenticated identity bodies among a controlled set of
entities. For that purpose, an encryption mechanism for
authenticated identities is required.
7.1 Requesting Privacy
When users authenticate themselves to an authentication service, they
MAY explicitly notify the service that they do not wish their
authenticated identity to be circulated. Usually, the user in
question would also be taking other steps to preserve their privacy
(perhaps by including an anonymous From header in the SIP request,
and following other standard privacy practices).
Authentication services MUST support the privacy mechanism described
in RFC3323 [3]. Users requesting privacy should also support the
mechanisms described in that document.
In particular, this document uses an identity-specific priv-value
that can appear in the Privacy header, a value of 'id', which was
registered by RFC3325 [6]. This Privacy value requests that the
results of authentication should not be shared by the authenticating
intermediary. An authentication service SHOULD NOT create an
authentication token for a request when 'id' privacy has been
requested. If such a token is created, it MUST be encrypted or
rendered confidential in the manner most appropriate to the token.
Guidelines for encrypting AIBs are given in [4], and these mechanisms
MUST be supported by any authentication service that uses AIBs.
8. Security Considerations
Users SHOULD NOT provide credentials to an authentication service to
which they cannot initiate a direct connection, preferably one
secured by a network or transport layer security protocol such as
TLS. If a user does not receive a certificate from the
authentication service over this lower-layer protocol that
corresponds to the expected domain (especially when they receive a
challenge via a mechanism such as Digest), then it is possible that a
rogue server is attempting to pose as a authentication service for a
domain that it does not control, possibly in an attempt to collect
shared secrets for that domain. If a user cannot connect directly to
the desired authentication service, the user SHOULD at least use a
SIPS URI to ensure that mutual TLS authentication will be used to
reach the remote server.
Relying on an authentication token generated by a remote
administrative domain assumes that the domain uses some trustworthy
Peterson Expires August 2, 2003 [Page 11]
Internet-Draft SIP Identity February 2003
practice to authenticate its users. However, it is possible that
some domains will implement policies that effectively make users
unaccountable (such as accepting unauthenticated registrations from
arbitrary users). Therefore, it is RECOMMENDED that authentication
tokens contain some indication of the specific practice (for example,
Digest) that was used to authenticate this request as a rough
indicator of credential strength. No manner of describing
authentication practices is specified in this document.
If a common certificate is used by an authentication service (rather
than individual certificates for each identity), certain problems can
arise with name subordination. For example, if an authentication
service holds a common certificate for the hostname
'sip.atlanta.com', can it legitimately sign a token containing an
identity of 'sip:alice@atlanta.com'? It is difficult for the
recipient of a request to ascertain whether or not 'sip.atlanta.com'
is authoritative for the 'atlanta.com' domain unless the recipient
has some foreknowledge of the administration of 'atlanta.com'.
Therefore, it is RECOMMEND that user agent recipients of
authentication tokens notify end users if there is ANY discrepancy
between the subjectAltName of the signers certificate and the
identity within the authentication token.
Authentication tokens MUST have some form of replay protection. The
best protection is to copy the SIP request in its entirety (via the
'message/sip' MIME type) into the authentication token - in that way,
it will be clear that this token has been issued for this request,
since collectively the headers of a SIP request provide a unique
identifier. However, SIP requests can be large, and it is reasonable
to include only a subset of the SIP headers in a request (using the
'message/sipfrag' MIME type) as long as certain critical headers are
provided. For further discussion of this issue, including guidelines
for including particular headers in a sipfrag, see [4].
Because the common certificates that can be used by authentication
services need to assert only the hostname of the authentication
service, existing certificate authorities can provide adequate
certificates for this mechanism. However, not all proxy servers and
user agents will be able support the root certificates of all
certificate authorities, and moreover there are some significant
differences in the policies by which certificate authorities issue
their certificates. This document makes no recommendations for the
usage of particular certificate authorities, nor does it describe any
particular policies that certificate authorities should follow, but
it is anticipated that operational experience will create de facto
standards for the purposes of authentication services. Some
federations of service providers, for example, might only trust
certificates that have been provided by a certificate authority
Peterson Expires August 2, 2003 [Page 12]
Internet-Draft SIP Identity February 2003
operated by the federation.
9. IANA Considerations
This document defines a new SIP status code, '428 Use Authentication
Token'. The use of this status code is further described in Section
4.1.
Normative References
[1] 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.
[2] Bradner, S., "Key words for use in RFCs to indicate requirement
levels", RFC 2119, March 1997.
[3] Peterson, J., "A Privacy Mechanism for the Session Initiation
Protocol (SIP)", RFC 3323, November 2002.
[4] Peterson, J., "SIP Authenticated Identity Body (AIB) Format",
draft-ietf-sip-authid-body-01 (work in progress), October 2002.
Informative References
[5] Kohl, J. and C. Neumann, "The Kerberos Network Authentication
Service (V5)", RFC 1510, September 1993.
[6] Jennings, C., Peterson, J. and M. Watson, "Private Extensions to
the Session Initiation Protocol (SIP) for Asserted Identity
within Trusted Networks", RFC 3325, November 2002.
[7] Sparks, R., "Internet Media Type message/sipfrag", RFC 3420,
November 2002.
[8] Olson, S., "A Mechanism for Content Indirection in SIP
Messages", draft-ietf-sip-content-indirect-mech-01 (work in
progress), August 2002.
[9] Freed, N., "Definition of the URL MIME External-Body Access-
Type", RFC 2017, November 1996.
Peterson Expires August 2, 2003 [Page 13]
Internet-Draft SIP Identity February 2003
Author's Address
Jon Peterson
NeuStar, Inc.
1800 Sutter St
Suite 570
Concord, CA 94520
US
Phone: +1 925/363-8720
EMail: jon.peterson@neustar.biz
URI: http://www.neustar.biz/
Appendix A. Acknowledgments
The authors would like to thank Eric Rescorla, Rohan Mahy, Robert
Sparks, Jonathan Rosenberg, Mark Watson and Patrik Faltstrom for
their comments. Cullen Jennings assisted greatly in the development
of the content indirection mechanism considered in Section 4.3.
Appendix B. Changelog
Changes from draft-peterson-sip-identity-01:
- Split off child draft-ietf-sip-authid-body-00 for defining of
the AIB
- Clarified scope in introduction
- Removed a lot of text that was redundant with RFC3261
(especially about authentication practices)
- Added mention of content indirection mechanism for adding token
to requests and responses
- Improved Security Considerations (added piece about credential
strength)
Changes from draft-peterson-sip-identity-00:
- Added a section on authenticated identities in responses
- Removed hostname convention for authentication services
- Added text about using 'message/sip' or 'message/sipfrag' in
authenticated identity bodies, also RECOMMENDED a few more headers
in sipfrags to increase reference integrity
Peterson Expires August 2, 2003 [Page 14]
Internet-Draft SIP Identity February 2003
- Various other editorial corrections
Peterson Expires August 2, 2003 [Page 15]
Internet-Draft SIP Identity February 2003
Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Peterson Expires August 2, 2003 [Page 16]
