SIP WG J. Peterson
Internet-Draft NeuStar
Expires: March 30, 2005 C. Jennings
Cisco Systems
September 29, 2004
Enhancements for Authenticated Identity Management in the Session
Initiation Protocol (SIP)
draft-ietf-sip-identity-03
Status of this Memo
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance with
RFC 3668.
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 March 30, 2005.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
The existing security mechanisms in the Session Initiation Protocol
are inadequate for cryptographically assuring the identity of the end
users that originate SIP requests, especially in an interdomain
context. This document recommends practices and conventions for
identifying end users in SIP messages, and proposes a way to
distribute cryptographically-secure authenticated identities.
Peterson & Jennings Expires March 30, 2005 [Page 1]
Internet-Draft SIP Identity September 2004
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Overview of Operations . . . . . . . . . . . . . . . . . . . 6
6. Authentication Service Behavior . . . . . . . . . . . . . . 7
7. Verifying Identity . . . . . . . . . . . . . . . . . . . . . 9
8. User Agent Behavior . . . . . . . . . . . . . . . . . . . . 10
9. Proxy Server Behavior . . . . . . . . . . . . . . . . . . . 10
10. Header Syntax . . . . . . . . . . . . . . . . . . . . . . . 11
11. Compliance Tests and Examples . . . . . . . . . . . . . . . 13
11.1 Identity-Info with a Singlepart MIME body . . . . . . . 14
11.2 Identity for a Request with no MIME body or Contact . . 16
12. Identity and the TEL URI Scheme . . . . . . . . . . . . . . 19
13. Privacy Considerations . . . . . . . . . . . . . . . . . . . 20
14. Security Considerations . . . . . . . . . . . . . . . . . . 21
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . 25
15.1 Header Field Names . . . . . . . . . . . . . . . . . . . 25
15.2 Response Code . . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 26
A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 26
B. Bit-exact archive of example messages . . . . . . . . . . . 27
B.1 Encoded Reference Files . . . . . . . . . . . . . . . . . 27
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
16.1 Normative References . . . . . . . . . . . . . . . . . . . 25
16.2 Informative References . . . . . . . . . . . . . . . . . . 26
C. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . 30
Intellectual Property and Copyright Statements . . . . . . . 32
Peterson & Jennings Expires March 30, 2005 [Page 2]
Internet-Draft SIP Identity September 2004
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 address-of-record URI employed to reach a
user (such as 'sip:alice@atlanta.example.com').
RFC3261 enumerates a number of places within a SIP request that a
user can express an identity for themselves, notably the
user-populated From header field. However, the recipient of a SIP
request has no way to verify that the From header field has been
populated accurately, in the absence of some sort of cryptographic
authentication mechanism.
RFC3261 specifies a number of security mechanisms that can be
employed by SIP UAs, including Digest, TLS and S/MIME
(implementations may support other security schemes as well).
However, few SIP user agents today support the end-user certificates
necessary to authenticate themselves via TLS or S/MIME, and
furthermore Digest authentication is limited by the fact that the
originator and destination must share a pre-arranged 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.
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. Background
All RFC3261-compliant SIP user agents 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 (e.g.,
'sip:alice@atlanta.example.com').
The address-of-record URI used for registration is also the URI with
which a UA commonly populates the From header of requests in order to
Peterson & Jennings Expires March 30, 2005 [Page 3]
Internet-Draft SIP Identity September 2004
provide their 'return address' identity to recipients. If you can
prove you are eligible to register in a domain under a particular
address-of-record, you are proving that you are capable of
legitimately receiving requests for that address-of-record, and
accordingly, when you place that address-of-record in the From header
field of a SIP request other than a registration (like an INVITE),
you are providing a 'return address' where you can legitimately be
reached. In other words, if you are authorized to receive requests
for that 'return address', you are also authorized to assert that
'return address' in your From header field.
In the context of registration, users already have a means of proving
their identity to a registrar. However, the credentials with which a
user agent proves their identity to a registrar cannot be validated
by just any user agent or proxy server - these credentials are only
shared between the user agent and their domain administrator. For
the purposes of determining whether or not the 'return address' of a
request can legitimately be asserted in the From header field of a
request, SIP entities that are not operated by the domain
administrator require an assurance that the sender of a message is
capable of authenticating themselves to a registrar in their own
domain.
Ideally, then, SIP user agents should have some way of proving to
recipients of SIP requests that their local domain has authenticated
them. 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 such requests (using the same practices by which
the domain would authenticate REGISTER requests). Once a message has
been authenticated, the local domain then needs some way to
communicate to other SIP entities that the sending user has been
authenticated. This draft addresses how that imprimatur of
authentication can be 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, transitive trust is inherently
weaker than an assertion that can be validated end-to-end. It is
possible for SIP requests to cross multiple intermediaries in
separate administrative domains, in which case transitive trust
becomes even less compelling. It also requires intermediaries to act
as proxies, rather than redirecting requests to their destinations
(redirection lightens loads on SIP intermediaries).
Peterson & Jennings Expires March 30, 2005 [Page 4]
Internet-Draft SIP Identity September 2004
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 [8]. 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.
Accordingly, this document specifies a means of sharing a
cryptographic assurance of end-user SIP identity in an interdomain
context based on the concept of an 'authentication service' and a new
SIP header, the Identity header. Note that the scope of this
document is limited to providing this identity assurance for SIP
requests; solving this problem for SIP responses is more complicated,
and is a subject for future work.
This specification allows either a user agent or a proxy server to
act as an authentication service. To maximize end-to-end security,
it is obviously preferable for end users to hold their own
certificates; if they do, they can act as an authentication service.
However, end-user certificates may be neither practical nor
affordable, given the difficulties of establishing a PKI that extends
to end users, and moreover, given the potentially large number of SIP
user agents (phones, PCs, laptops, PDAs, gaming devices) that may be
employed by a single user. In such environments, synchronizing
certificates across multiple devices may be very complex, and
requires quite a good deal of additional endpoint behavior. Managing
several certificates for the various devices is also quite
problematic and unpopular with users. Accordingly, in the initial
use of this mechanism, it is likely that intermediaries will
instantiate the authentication service role.
4. Requirements
This draft addresses the following requirements:
o The mechanism must allow a UAC to provide a strong cryptographic
identity assurance in a request that can be verified by a proxy
server or UAS.
o User agents that receive identity assurances must be able to
validate these assurances without performing any network lookup.
o User agents that hold certificates on behalf of their user must be
capable of adding this identity assurance to requests.
o Proxy servers that hold certificates on behalf of their domain
must be capable of adding this identity assurance to requests; a
UAC is not required to support the Identity header in order for
identity to be added to a request in this fashion.
Peterson & Jennings Expires March 30, 2005 [Page 5]
Internet-Draft SIP Identity September 2004
o The mechanism must prevent replay of the identity assurance by an
attacker.
o The mechanism must be capable of protecting the integrity of SIP
message bodies (to ensure that media offers and answers are linked
to the signaling identity).
o It must be possible for a user to have multiple AoRs (i.e.
accounts or aliases) under which it is known at a domain, and for
the UAC to assert one identity while authenticating itself as
another, related, identity, as permitted by the local policy of
the domain.
o It must be possible, in cases where a request has been retargeted
to a different AoR than the one designated in the To header field,
for the UAC to ascertain the AoR to which the request has been
sent.
5. Overview of Operations
This section provides an informative (non-normative) high-level
overview of the mechanisms described in this document.
Imagine the case where Alice, who has the home proxy of example.com
and the address-of-record sip:alice@example.com, wants to communicate
with sip:bob@example.org.
Alice generates an INVITE and places her identity in the From header
field of the request. She then sends an INVITE over TLS to an
authentication service proxy for her domain.
The authentication service authenticates Alice (possibly by sending a
Digest authentication challenge) and validates that she is authorized
to populate the value of the From header field (which may be Alice's
AoR, or it may be some other value that the policy of the proxy
server permits her to use). It then computes a hash over some
particular headers, including the From header field and the bodies in
the message. This hash is signed with the certificate for the domain
(example.com, in Alice's case) and inserted in a new header field in
the SIP message, the 'Identity' header.
The proxy, as the holder the private key of its domain, is asserting
that the originator of this request has been authenticated and that
she is authorized to claim the identity (the SIP address-of-record)
which appears in the From header field. The proxy also inserts a
companion header field that tells Bob how to acquire its certificate,
if he doesn't already have it.
When Bob's domain receives the request, it verifies the signature
provided in the Identity header, and thus can authenticate that the
domain indicated by the host portion of the AoR in the From header
Peterson & Jennings Expires March 30, 2005 [Page 6]
Internet-Draft SIP Identity September 2004
field authenticated the user, and permitted them to assert that From
header field value.
6. Authentication Service Behavior
This document defines a new role for SIP entities called an
authentication service. The authentication service role can be
instantiated by a proxy server, redirect server or a user agent. Any
entity that instantiates the authentication service role MUST possess
the private key of a domain certificate, and MUST be capable of
authenticating one or more SIP users that can register in that
domain. Commonly, this role will be instantiated by a proxy server
or redirect server, since these entities are more likely to have a
static hostname, hold a corresponding certificate, and access to SIP
registrar capabilities that allow them to authenticate users in their
domain.
SIP entities that act as an authentication service MUST add a Date
header field to SIP requests if one is not already present.
Similarly, authentication services MUST add a Content-Length header
field to SIP requests if one is not already present; this can help
the verifier to double-check that they are hashing exactly as many
bytes of message-body as the authentication service when they verify
the message.
The authentication service authenticates the identity of the message
sender and validates that the identity given in the message can
legitimately be asserted by the sender. Then it computes a signature
over the canonical form of several headers and all the bodies, and
inserts this signature into the message.
First, an authentication service MUST extract the identity of the
sender from the request. The authentication service takes this value
from the From header field; this AoR will be referred to here as the
'identity field'. If the identity field contains a SIP or SIPS URI,
the authentication service MUST extract the hostname portion of the
identity field and compare it to the domain(s) for which it is
responsible. If the identity field uses the TEL URI scheme, the
policy of the authentication service determines whether or not it is
responsible for this identity; see Section 12 for more information.
If the authentication service is not responsible for the identity in
question, it MAY handle the request normally, but it MUST NOT add an
Identity header; see below for more information on authentication
service handling of an existing Identity header.
Second, the authentication service needs to determine whether or not
the sender of the request is authorized to claim the identity given
in the identity field. In order to do so, the authentication service
Peterson & Jennings Expires March 30, 2005 [Page 7]
Internet-Draft SIP Identity September 2004
MUST authenticate the sender of the message. Some possible ways in
which this authentication might be performed include:
o If the authentication service is instantiated by a SIP
intermediary (proxy or redirect server), it may challenge the
request with a 407 response code using the Digest authentication
scheme (or viewing a Proxy-Authentication header sent in the
request which was sent in anticipation of a challenge using cached
credentials, as described in RFC 3261 Section 22.3).
o If the authentication service is instantiated by a SIP user agent,
a user agent can be said to authenticate its user on the grounds
that the user can provision the user agent with the private key of
the domain, or by preferably by providing a password that unlocks
said private key.
Authorization of the assertion of a particular username in the From
header field of a SIP message is a matter of local policy for the
authorization service which depends greatly on the manner in which
authentication is performed. A RECOMMENDED policy is as follows: the
username asserted during Digest authentication MUST correspond
exactly to the username in the From header field of the SIP message.
However, there are many cases in which a user might manage multiple
accounts in the same administrative domain. Accordingly, provided
the authentication service is aware of the relationships between
these accounts, it might allow a user providing credentials for one
account to assert a username associated with another account
controlled by the user name. Furthermore, if the AoR asserted in the
From header field is anonymous (per RFC3323 [3]), then the proxy
should authenticate that the user is a valid user in the domain and
insert the signature over the From header field as usual.
Note that this check is performed on the addr-spec in the From header
field (e.g., the URI of the sender, like
'sip:alice@atlanta.example.com'); it does not convert the
display-name portion of the From header field (e.g., 'Alice
Atlanta'). Some SIP user agents that receive requests render the
display-name of the caller as the identity of the caller. However,
there are many environments in which legislating the display-name
isn't feasible, judging from experience with email, where users
frequent make slight textual changes to their display-names.
Ultimately, there is more value in focusing on the SIP address of the
sender (which has some meaning in the network and provides a chain of
accountability) than trying to constrain how the display-name is set.
As such, authentication services MAY check the display-name as well,
and compare it to a list of acceptable display-names that may be used
by the sender; if the display-name does not meet policy constraints,
the authentication service MUST return a 403 'Inappropriate
Display-Name' response code. However, in many environments this will
not make sense. For more information on rendering identity in a user
Peterson & Jennings Expires March 30, 2005 [Page 8]
Internet-Draft SIP Identity September 2004
interface, see Section 8.
Third, the authentication service MUST form the identity signature
and add an Identity header to the request containing this signature.
After the Identity header has been added to the request, the
authentication service MUST also add an Identity-Info header. The
Identity-Info header contains a URI from which its certificate can be
acquired. Details are provided in section Section 10.
Finally, the authentication service MUST forward the message
normally.
7. Verifying Identity
When a user agent or proxy server receives a SIP message containing
an Identity header, it can inspect the signature to verify the
identity of the sender of the message. If an Identity header is not
present in a request, and one is required by local policy (for
example, based on a global policy, a per-sending-domain policy, or a
per-sending-user policy), then a 428 'Use Identity Header' response
MUST be sent.
In order to verify the identity of the sender of a message, the user
agent or proxy server MUST first acquire the certificate for the
signing domain. Implementations supporting this specification should
have some means of retaining domain certificates (in accordance with
normal practices for certificate lifetimes and revocation) in order
to prevent themselves from needlessly downloading the same
certificate every time a request from the same domain is received.
Certificates retained in this manner should be indexed by the URI
given in the Identity-Info header field value.
Provided that the domain certificate used to sign this message is not
previously known to the recipient, SIP entities SHOULD discover this
certificate by dereferencing the Identity-Info header, unless they
have some more efficient implementation-specific way of acquiring
certificates for that domain. The client processes this certificate
in the usual ways, including checking that it has not expired, that
the chain is valid back to a trusted CA, and that it does not appear
on revocation lists. Once the certificate is acquired, it MUST be
validated.
Subsequently, the recipient MUST verify the signature in the Identity
header, and compare the identity of the signer (the subjectAltName of
the certificate) with the domain portion of the URI in the From
header field of the request as described in Section 14.
Additionally, the Date, Contact and Call-ID headers MUST be analyzed
in the manner described in Section 14; recipients that wish to verify
Peterson & Jennings Expires March 30, 2005 [Page 9]
Internet-Draft SIP Identity September 2004
Identity signatures MUST support all of the operations described
there. Any discrepancies or violations MUST be reported to the user.
If a verifier determines that the signature on the message does not
correspond to the text of the message, then a 428 'Invalid Identity
Header' response MUST be returned.
Once the identity of the sender of a request has been ascertained,
various policies MAY be used to make authorization decisions about
accepting communications and the like. Such policies are outside the
scope of this document.
8. User Agent Behavior
This mechanism requires one important change to existing user agent
requirements for sending requests: user agents using this mechanism
to send requests to an authentication service MUST support TLS.
Because this mechanism does not provide integrity protection for the
first hop to the authentication service, the UAC MUST send requests
to an authentication service only over a TLS connection.
When a UAC sends a request, it MUST accurately populate the header
field that asserts its identity (for a SIP request, this is the From
header field). In a request it MUST set the URI portion of its From
header to match a SIP, SIPS or TEL URI AoR under which the UAC can
register (including anonymous URIs, as described in RFC 3323 [3]).
In general, UACs SHOULD NOT use the TEL URI form in the From header
field (see Section 12).
The UAC MUST also be capable of sending requests, including mid-call
requests, through an 'outbound' proxy (the authentication service).
The best way to accomplish this is using pre-loaded Route headers and
loose routing. UAC implementations MUST provide a way of
provisioning pre-loaded Route headers in order for this mechanism to
work for mid-call requests in the backwards direction of a dialog.
As a recipient of a request, a user agent that can verify signed
identities should also support an appropriate user interface to
render the validity of identity to a user. User agent
implementations SHOULD differentiate signed From header field values
from unsigned From header field values when rendering to an end user
the identity of the sender of a request.
9. Proxy Server Behavior
Domain policy may require proxy servers to inspect and verify the
identity provided in SIP requests. A proxy server may wish to
ascertain the identity of the sender of the message to provide spam
Peterson & Jennings Expires March 30, 2005 [Page 10]
Internet-Draft SIP Identity September 2004
prevention or call control services. Even if a proxy server does not
act as an authentication service, it MAY verify the existence of an
Identity before it makes a forwarding decision for a request. Proxy
servers MUST NOT remove or modify an existing Identity or
Identity-Info header in a request.
10. Header Syntax
This document specifies two new SIP headers: Identity and
Identity-Info. Each of these headers can appear only once in a SIP
message.
Identity = "Identity" HCOLON signed-identity-digest
signed-identity-digest = LDQUOT 32LHEX RDQUOT
Identity-Info = "Identity-Info" HCOLON ident-info
ident-info = LAQUOT absoluteURI RAQUOT
The signed-identity-digest is a signed hash of a canonical string
generated from certain components of a SIP request. To create the
contents of the signed-identity-digest, the following elements of a
SIP message MUST placed in a bit-exact string in the order specified
here, separated by a colon:
o The AoR of the UA sending the message, or the 'identity field'.
For a request, this is the addr-spec from the From header field.
o The addr-spec component of the To header field, which is the AoR
to which the request is being sent.
o The callid from Call-Id header field.
o The digit (1*DIGIT) and method (method) portions from CSeq header
field, separated by a single space (ABNF SP, or %x20). Note that
the CSeq header field allows LWS rather than SP to separate the
digit and method portions, and thus the CSeq header field may need
to be transformed in order to be canonicalized.
o The Date header field, with exactly one space each for each SP and
the weekday and month items case set as shown in BNF in 3261. The
first letter is upper case and the rest of the letters are lower
case. All requests that use the Identity mechanism MUST contain a
Date header.
o The addr-spec component of the Contact header field value. If the
request does not contain a Contact header, this field MUST be
empty (i.e., there will be no whitespace between the fourth and
fifth colons in the canonical string).
o The body content of the message with the bits exactly as they are
in the Message (in the ABNF for SIP, the message-body). Note that
the message-body does NOT include the CRLF separating the SIP
headers from the message-body, but does include everything that
follows that CRLF. If the message has no body, then message-body
will be empty, and the final colon will not be followed by any
Peterson & Jennings Expires March 30, 2005 [Page 11]
Internet-Draft SIP Identity September 2004
additional characters.
For more information on the security properties of these headers, and
why their inclusion mitigates replay attacks, see Section 14 and [5].
The precise formulation of this digest-string is, therefore
(following the ABNF [6] in RFC3261):
digest-string = addr-spec ":" addr-spec ":" callid ":" 1*DIGIT SP method ":"
SIP-Date ":" [ addr-spec ] ":" message-body
Note again that the first addr-spec MUST be taken from the From
header field value, the second addr-spec MUST be taken from the To
header field value, and the third addr-spec MUST be taken from the
Contact header field value, provided the Contact header is present in
the request.
After the digest-string is formed, it MUST be hashed and signed with
the certificate for the domain, as follows: compute the results of
signing this string with sha1WithRSAEncryption as described in RFC
3370 and base64 encode the results as specified in RFC 3548. Put the
result in the Identity header.
Note on this choice: Assuming a 1024 bit RSA key, the raw signature
will result in about 170 octets of base64 encoded data (without
base64, as an aside, it would be about 130 bytes). For comparison's
sake, a typical HTTP Digest Authorization header (such as those used
in RFC3261) with no cnonce is around 180 octets. From a speed point
of view, a 2.8GHz Intel processor does somewhere in the range of 250
RSA 1024 bits signs per second or 1200 RSA 512 bits signs; verifies
are roughly 10 times faster. Hardware accelerator cards are
available that speed this up.
The Identity-Info header MUST contain either an HTTPS URI or a SIPS
URI. If it contains an HTTPS URI, the URI must dereference to a
resource that contains a single MIME body containing the certificate
of the authentication service. If it is a SIPS URI, then the
authentication service intends for a user agent that wishes to fetch
the certificate to form a TLS connection to that URI, acquire the
certificate during normal TLS negotiation, and close the connection.
This document adds the following entries to Table 2 of [1]:
Header field where proxy ACK BYE CAN INV OPT REG
------------ ----- ----- --- --- --- --- --- ---
Identity R a o o - o o -
SUB NOT REF INF UPD PRA
--- --- --- --- --- ---
Peterson & Jennings Expires March 30, 2005 [Page 12]
Internet-Draft SIP Identity September 2004
o o o o o o
Header field where proxy ACK BYE CAN INV OPT REG
------------ ----- ----- --- --- --- --- --- ---
Identity-Info R a o o - o o -
SUB NOT REF INF UPD PRA
--- --- --- --- --- ---
o o o o o o
Note, in the table above, that this mechanism does not protect the
REGISTER method or the CANCEL method. The CANCEL method cannot be
challenged, because it is hop-by-hop, and accordingly authentication
service behavior for CANCEL would be significantly limited. The
REGISTER method uses Contact header fields in very unusual ways that
complicate its applicability to this mechanism. Accordingly, the
Identity and Identity-Info header MUST NOT appear in REGISTER or
CANCEL.
11. Compliance Tests and Examples
The examples in this section illustrate the use of the Identity
header in the context of a SIP transaction. Implementations MUST
verify their compliance with these examples, i.e.:
o Implementations of the authentication service role MUST generate
identical base64 identity strings to the ones shown in the
Identity headers in these examples when presented with the source
message and utilizing the appropriate supplied private key for the
domain in question.
o Implementations of the verifier role MUST correctly validate the
given messages containing the Identity header when utilizing the
supplied certificates (with the caveat about self-signed
certificates below).
Note that the following examples use self-signed certificates, rather
than certificates issued by a recognized certificate authority. The
use of self-signed certificates for this mechanism is NOT
RECOMMENDED, and appear here only for illustrative purposes.
Therefore, in compliance testing, implementations of verifiers SHOULD
generated appropriate warnings about the use of self-signed
certificates.
Bit-exact reference files for these messages and their various
transformations are supplied in Appendix B.
Peterson & Jennings Expires March 30, 2005 [Page 13]
Internet-Draft SIP Identity September 2004
11.1 Identity-Info with a Singlepart MIME body
Consider the following private key and certificate pair assigned to
'atlanta.example.com'.
-----BEGIN RSA PRIVATE KEY-----
MIICXQIBAAKBgQC8HmM8b9E4WNhb7tZAoBVSkKyV9rAEX3nyQbg4hXte1oW1BxC+
43MQHrG3nk6Kc9afPR6VloKwWoUoAcCnbTJ/zEiZ6dq+C5EsQGIOowYkSgqdO2po
joCnRgzgjgvAl41R2J6CE1kMwOQxNCxPnTco8l8UGdKbNLXIuNdUM1MG8QIDAQAB
AoGAAtPOGAVyNo+XSOJxE+2UBHaqMWLQyHAK7Coys57F+OnufocJqGTQwOhFMYZO
leQh0KjhgcwOUMo7gBtuotWQUbbLHTGKXiBR6Pqbm6CvhwJSuNYv0vONuTb1SMll
Kadg43na4B9kQeytn1y6lfkTkK2oYqkDVZ2AAmLSLrfhl1UCQQDp7VFItgmnybwK
PKwJs8gnF+u+K9j+sac/3vgGgrOvpxVqwoMXl6eWN//pZ/cqshanDLmtr9ahjWCD
DxYVyklrAkEAzd6JLJAhG8cZymVCS5Jf0F7FAVxpx0BgRPHwJliyUg6O4jPY+ASg
cLP6nz9a38wWZQj6rRygffGZHXbBFm+8EwJBAJmZEf5ESSK6+5VdMTlNqubAdjJw
aBMUY1U0+naL66AyfYWUIq+jDI8+RfLkKQ8H0IfvexvokW2SfwSPK1kzcfECQD/O
MQW2xgwt8ThhmeKCQ1/5f2WklsRCl5PGyH+aDeqQyIgjOaPlCzTjE1I3+JpUTryR
w9/Td4qRTrtrCv1BNDECQQCgHIzF8LFtI003w9MAEAoCyDbtHFPEj71b+qG22Yc4
SPFBAbo3JGO+mrB0MX/GwJr+3DfgzMHaUx/tinPr+u1D
-----END RSA PRIVATE KEY-----
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
A user of atlanta.example.com, Alice, wants to send an INVITE to
bob@biloxi.example.org. She therefore creates the following INVITE
request, which she forwards to the atlanta.example.org proxy server
that instantiates the authentication service role:
Peterson & Jennings Expires March 30, 2005 [Page 14]
Internet-Draft SIP Identity September 2004
INVITE sip:bob@biloxi.exmple.org SIP/2.0
Via: SIP/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bKnashds8
To: Bob <sip:bob@biloxi.example.org>
From: Alice <sip:alice@atlanta.example.com>;tag=1928301774
Call-ID: a84b4c76e66710
CSeq: 314159 INVITE
Max-Forwards: 70
Date: Thu, 21 Feb 2002 13:02:03 GMT
Contact: <sip:alice@pc33.atlanta.example.com>
Content-Type: application/sdp
Content-Length: 147
v=0
o=UserA 2890844526 2890844526 IN IP4 pc33.atlanta.example.com
s=Session SDP
c=IN IP4 pc33.atlanta.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
When the authentication service receives the INVITE, in authenticates
Alice by sending a 407 response. As a result, Alice adds an
Authorization header to her request, and resends to the
atlanta.example.com authentication service. Now that the service is
sure of Alice's identity, it calculates an Identity header for the
request. The canonical string over which the identity signature will
be generated is the following (note that the first line wraps because
of RFC editorial conventions):
sip:alice@atlanta.example.com:sip:bob@biloxi.example.org:a84b4c76e66710:314159 INVITE:Thu, 21 Feb 2002 13:02:03 GMT:alice@pc33.atlanta.example.com:v=0
o=UserA 2890844526 2890844526 IN IP4 pc33.atlanta.example.com
s=Session SDP
c=IN IP4 pc33.atlanta.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
The resulting signature (sha1WithRsaEncryption) using the private RSA
key given above, with base64 encoding, is the following:
CyI4+nAkHrH3ntmaxgr01TMxTmtjP7MASwliNRdupRI1vpkXRvZXx1ja9k0nB2sN
3W+v1PDsy32MaqZi0M5WfEkXxbgTnPYW0jIoK8HMyY1VT7egt0kk4XrKFCHYWGCl
sM9CG4hq+YJZTMaSROoMUBhikVIjnQ8ykeD6UXNOyfI=
Accordingly, the atlanta.example.com authentication service will
create an Identity header containing that base64 signature string
(175 bytes). It will also add an HTTPS URL where its certificate is
made available. With those two headers added, the message looks
Peterson & Jennings Expires March 30, 2005 [Page 15]
Internet-Draft SIP Identity September 2004
like:
INVITE sip:bob@biloxi.exmple.org SIP/2.0
Via: SIP/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bKnashds8
To: Bob <sip:bob@biloxi.example.org>
From: Alice <sip:alice@atlanta.example.com>;tag=1928301774
Call-ID: a84b4c76e66710
CSeq: 314159 INVITE
Max-Forwards: 70
Date: Thu, 21 Feb 2002 13:02:03 GMT
Contact: <sip:alice@pc33.atlanta.example.com>
Identity: CyI4+nAkHrH3ntmaxgr01TMxTmtjP7MASwliNRdupRI1vpkXRvZXx1ja9k0nB2sN
3W+v1PDsy32MaqZi0M5WfEkXxbgTnPYW0jIoK8HMyY1VT7egt0kk4XrKFCHYWGCl
sM9CG4hq+YJZTMaSROoMUBhikVIjnQ8ykeD6UXNOyfI=
Identity-Info: https://atlanta.example.com/cert
Content-Type: application/sdp
Content-Length: 147
v=0
o=UserA 2890844526 2890844526 IN IP4 pc33.atlanta.example.com
s=Session SDP
c=IN IP4 pc33.atlanta.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
atlanta.example.com then forwards the request normally. When Bob
receives the request, if he does not already know the certificate of
atlanta.example.com, he de-references the URL the Identity-Info
header to acquire the certificate. Bob then generates the same
canonical string given above, from the same headers of the SIP
request. Using this canonical string, the signed digest in the
Identity header, and the certificate discovered by de-referencing the
Identity-Info header, Bob can verify that the given set of headers
and the message body have not been modified.
11.2 Identity for a Request with no MIME body or Contact
Consider the following private key and certificate pair assigned to
"biloxi.example.org".
Peterson & Jennings Expires March 30, 2005 [Page 16]
Internet-Draft SIP Identity September 2004
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
-----BEGIN CERTIFICATE-----
MIIC7DCCAlWgAwIBAgIBADANBgkqhkiG9w0BAQQFADBUMQswCQYDVQQGEwJVUzEU
MBIGA1UECBMLTWlzc2lzc2lwcGkxDzANBgNVBAcTBkJpbG94aTENMAsGA1UEChME
SUVURjEPMA0GA1UECxMGU0lQIFdHMB4XDTA0MDkxMzEwMzg1NVoXDTA1MDkxMzEw
Mzg1NVowVDELMAkGA1UEBhMCVVMxFDASBgNVBAgTC01pc3Npc3NpcHBpMQ8wDQYD
VQQHEwZCaWxveGkxDTALBgNVBAoTBElFVEYxDzANBgNVBAsTBlNJUCBXRzCBnzAN
BgkqhkiG9w0BAQEFAAOBjQAwgYkCgYEAwyERDCCEvbwQRE9hRR7LNi28K4v5yvgD
KFGe+FE92phv22IA5x/OnlFBIxn1d3H1xKxV0pyPOrFAC6Co48BmAaIlLmjIcnq2
chfg/UrdqZZwXqun6q22j6S+m7yABet+vztvhhT9y0i4+ikuB0MJ7GlAa9mM8pAQ
9OT38Kx9vFUCAwEAAaOBzTCByjAdBgNVHQ4EFgQUlZRLaS3Zm/b0xWcq7TSnQMHM
7w8wfAYDVR0jBHUwc4AUlZRLaS3Zm/b0xWcq7TSnQMHM7w+hWKRWMFQxCzAJBgNV
BAYTAlVTMRQwEgYDVQQIEwtNaXNzaXNzaXBwaTEPMA0GA1UEBxMGQmlsb3hpMQ0w
CwYDVQQKEwRJRVRGMQ8wDQYDVQQLEwZTSVAgV0eCAQAwDAYDVR0TBAUwAwEB/zAd
BgNVHREEFjAUghJiaWxveGkuZXhhbXBsZS5vcmcwDQYJKoZIhvcNAQEEBQADgYEA
SufJHtereahZlkE5ssRRZRd/erLpEe2uUfHnTOydPBKOkvhVG4Vr4aoroPlE7gJK
a/2BF9bohwAUSC5j5q3nvuhUcoK9XZYm2nLkN3IAhCU6oswVBJAxLanGUCjR5sxS
HfGhGsqLmTEQ22HsrtLo68IYiwftXcLZbep50gRVX6c=
-----END CERTIFICATE-----
Bob (bob@biloxi.example.org) now wants to send a BYE request to Alice
at the end of the dialog initiated in the previous example. He
therefore creates the following BYE request which he forwards to the
'biloxi.example.org' proxy server that instantiates the
authentication service role:
BYE sip:alice@pc33.atlanta.example.com SIP/2.0
Via: SIP/2.0/TLS 192.0.2.4;branch=z9hG4bKnashds10
Max-Forwards: 70
From: Bob <sip:bob@biloxi.example.org>;tag=a6c85cf
To: Alice <sip:alice@atlanta.example.com>;tag=1928301774
Call-ID: a84b4c76e66710
CSeq: 231 BYE
Content-Length: 0
Peterson & Jennings Expires March 30, 2005 [Page 17]
Internet-Draft SIP Identity September 2004
When the authentication service receives the BYE, it authenticates
Bob by sending a 407 response. As a result, Bob adds an
Authorization header to his request, and resends to the
biloxi.example.org authentication service. Now that the service is
sure of Bob's identity, it prepares to calculate an Identity header
for the request. Note that this request does not have a Date header
field. Accordingly, the biloxi.example.org will add a Date header to
the request before calcuating the identity signature. If the
Content-Length header were not present, the authentication service
would add it as well. The baseline message is thus:
BYE sip:alice@pc33.atlanta.example.com SIP/2.0
Via: SIP/2.0/TLS 192.0.2.4;branch=z9hG4bKnashds10
Max-Forwards: 70
From: Bob <sip:bob@biloxi.example.org>;tag=a6c85cf
To: Alice <sip:alice@atlanta.example.com>;tag=1928301774
Date: Thu, 21 Feb 2002 14:19:51 GMT
Call-ID: a84b4c76e66710
CSeq: 231 BYE
Content-Length: 0
Also note that this request contains no Contact header field.
Accordingly, biloxi.example.org will place no value in the canonical
string for the addr-spec of the Contact address. Also note that
there is no message body, and accordingly, the signature string will
terminate, in this case, with two colons. The canonical string over
which the identity signature will be generated is the following (note
that the first line wraps because of RFC editorial conventions):
sip:bob@biloxi.example.org:sip:alice@atlanta.example.com:a84b4c76e66710:231 BYE:Thu, 21 Feb 2002 14:19:51 GMT::
The resulting signature (sha1WithRsaEncryption) using the private RSA
key given above for biloxi.example.org, with base64 encoding, is the
following:
A5oh1tSWpbmXTyXJDhaCiHjT2xR2PAwBroi5Y8tdJ+CL3ziY72N3Y+lP8eoiXlrZ
Ouwb0DicF9GGxA5vw2mCTUxc0XG0KJOhpBnzoXnuPNAZdcZEWsVOQAKj/ERsYR9B
fxNPazWmJZjGmDoFDbUNamJRjiEPOKn13uAZIcuf9zM=
Accordingly, the biloxi.example.org authentication service will
create an Identity header containing that base64 signature string.
It will also add an HTTPS URL where its certificate is made
available. With those two headers added, the message looks like:
Peterson & Jennings Expires March 30, 2005 [Page 18]
Internet-Draft SIP Identity September 2004
BYE sip:alice@pc33.atlanta.example.com SIP/2.0
Via: SIP/2.0/TLS 192.0.2.4;branch=z9hG4bKnashds10
Max-Forwards: 70
From: Bob <sip:bob@biloxi.example.org>;tag=a6c85cf
To: Alice <sip:alice@atlanta.example.com>;tag=1928301774
Date: Thu, 21 Feb 2002 14:19:51 GMT
Call-ID: a84b4c76e66710
CSeq: 231 BYE
Identity: A5oh1tSWpbmXTyXJDhaCiHjT2xR2PAwBroi5Y8tdJ+CL3ziY72N3Y+lP8eoiXlrZ
Ouwb0DicF9GGxA5vw2mCTUxc0XG0KJOhpBnzoXnuPNAZdcZEWsVOQAKj/ERsYR9B
fxNPazWmJZjGmDoFDbUNamJRjiEPOKn13uAZIcuf9zM=
Identity-Info: https://biloxi.example.org/cert
Content-Length: 0
biloxi.example.org then forwards the request normally.
12. Identity and the TEL URI Scheme
Since many SIP applications provide a VoIP service, telephone numbers
are commonly used as identities in SIP deployments. In the majority
of cases, this is not problematic for the identity mechanism
described in this document. Telephone numbers commonly appear in the
username portion of a SIP URI (e.g.,
'sip:+17005551008@chicago.example.com'). That username conforms to
the syntax of the TEL URI scheme (RFC2806bis [9]). For this sort of
SIP address-of-record, chicago.example.com is the appropriate
signatory.
It is also possible for a TEL URI to appear in the SIP To or From
header field outside the context of a SIP or SIPS URI (e.g.,
'tel:+17005551008'). In this case, it is much less clear which
signatory is appropriate for the identity. Fortunately for the
identity mechanism, this form of the TEL URI is more common for the
To header field and Request-URI in SIP than in the From header field,
since the UAC has no option but to provide a TEL URI alone when the
remote domain to which a request is sent is unknown. The local
domain, however, is usually known by the UAC, and accordingly it can
form a proper From header field containing a SIP URI with a username
in TEL URI form. Implementations that intend to send their requests
through an authentication service MUST put telephone numbers in the
From header field into SIP or SIPS URIs, if possible.
If the local domain is unknown to a UAC formulating a request, it
most likely will not be able to locate an authentication service for
its request, and therefore the question of providing identity in
these cases is somewhat moot. However, an authentication service MAY
sign a request containing a TEL URI in the From header field in
accordance with its local policies. Verifiers SHOULD NOT accept
Peterson & Jennings Expires March 30, 2005 [Page 19]
Internet-Draft SIP Identity September 2004
signatures over From header TEL URIs in the absence of some
pre-provisioned relationship with the signing domain that authorizes
this usage of TEL URIs.
The guidance in the paragraph above is largely provided for forward
compatibility. In the longer-term, it is possible that ENUM [10] may
provide a way to determine which administrative domain is responsible
for a telephone number, and this may aid in the signing and
verification of SIP identities that contain telephone numbers. This
is a subject for future work.
13. Privacy Considerations
The identity mechanism presented in this draft is compatible with the
standard SIP practices for privacy described in RFC3323 [3]. A SIP
proxy server can act both as a privacy service and as an
authentication service. Since a user agent can provide any From
header field value which the authentication service is willing to
authorize, there is no reason why private SIP URIs (e.g.,
sip:anonymous@example.com) cannot be signed by an authentication
service. The construction of the Identity header is the same for
private URIs as it is for any other sort of URIs.
Note, however, that an authentication service must possess a
certificate corresponding to the host portion of the addr-spec of the
From header field of any request that it signs; accordingly, using
domains like 'invalid.net' may not be possible for privacy services
that also act as authentication services. The assurance offered by
this combination service is "this is a known user in my domain that I
have authenticated, but I am keeping their identity private".
The "header" level of privacy described in RFC3323 requests that a
privacy service to alter the Contact header field value of a SIP
message. Since the Contact header field is protected by the
signature in an Identity header, privacy services cannot be applied
after authentication services without a resulting integrity
violation.
RFC3325 [8] defines the "id" priv-value token which is specific to
the P-Asserted-Identity header. The sort of assertion provided by
the P-Asserted-Identity header is very different from the Identity
header presented in this document. It contains additional
information about the sender of a message that may go beyond what
appears in the From header field; P-Asserted-Identity holds a
definitive identity for the sender which is somehow known to a closed
network of intermediaries that presumably the network will use this
identity for billing or security purposes. The danger of this
network-specific information leaking outside of the closed network
Peterson & Jennings Expires March 30, 2005 [Page 20]
Internet-Draft SIP Identity September 2004
motivated the "id" priv-value token. The "id" priv-value token has
no implications for the Identity header, and privacy services MUST
NOT remove the Identity header when a priv-value of "id" appears in a
Privacy header.
14. Security Considerations
This document describes a mechanism which provides a signature over
the Contact, Date, Call-ID, CSeq To, and From header fields of SIP
messages. While a signature over the From header field would be
sufficient to secure a URI alone, the additional headers provide
replay protection and reference integrity necessary to make sure that
the Identity header will not be used in cut-and-paste attacks. In
general, the considerations related to the security of these headers
are the same as those given in RFC3261 for including headers in
tunneled 'message/sip' MIME bodies (see Section 23 in particular).
The From header field indicates the identity of the sender of the
message, and the SIP address-of-record URI in the From header field
is the identity of a SIP user, for the purposes of this document.
The To header field provides the identity of the SIP user that this
request targets. Providing the To header field in the Identity
signature servers two purposes: first, it prevents replay attacks in
which an Identity header from legitimate request for one user is
cut-and-pasted into a request for a different user; second, it
preserves the starting URI scheme of the request, which helps prevent
downgrade attacks against the use of SIPS.
The Date and Contact headers provide reference integrity and replay
protection, as described in RFC3261 Section 23.4.2. Implementations
of this specification MUST NOT deem valid a request with an outdated
Date header field (the RECOMMENDED interval is that the Date header
must indicate a time within 3600 seconds of the receipt of a
message). Implementations MUST also record Call-IDs received in
valid requests containing an Identity header, and MUST remember those
Call-IDs for at least the duration of a single Date interval (i.e.
commonly 3600 seconds). Accordingly, if an Identity header is
replayed within the Date interval, receivers will recognize that it
is invalid because of a Call-ID duplication; if an Identity header is
replayed after the Date interval, receivers will recognize that it is
invalid because the Date is stale. The CSeq header field contains a
numbered identifier for the transaction, and the name of the method
of the request; without this information, an INVITE request could be
cut-and-pasted by an attacker and transformed into a BYE request
without changing any fields covered by the Identity header, and
moreover requests within a certain transaction could be replayed in
potentially confusing or malicious ways.
Peterson & Jennings Expires March 30, 2005 [Page 21]
Internet-Draft SIP Identity September 2004
The Contact header field is included to tie the Identity header to a
particular device instance that generated the request. Were an
active attacker to intercept a request containing an Identity header,
and cut-and-paste the Identity header field into their own request
(reusing the From, To, Contact, Date and Call-ID fields that appear
in the original message), they would not be eligible to receive SIP
requests from the called user agent, since those requests are routed
to the URI identified in the Contact header field. However, the
Contact header is only included in dialog-forming requests, so it
does not provide this protection in all cases.
It might seem attractive to provide a signature over some of the
information present in the Via header field value(s). For example,
without a signature over the sent-by field of the topmost Via header,
an attacker could remove that Via header and insert their own in a
cut-and-paste attack, which would cause all responses to the request
to be routed to a host of the attacker's choosing. However, a
signature over the topmost Via header does not prevent attacks of
this nature, since the attacker could leave the topmost Via intact
and merely insert a new Via header field directly after it, which
would cause responses to be routed to the attacker's host "on their
way" to the valid host, which has exactly the same end result.
Although it is possible that an intermediary-based authentication
service could guarantee that no Via hops are inserted between the
sending user agent and the authentication service, it could not
prevent an attacker from adding a Via hop after the authentication
service, and accordingly pre-empting responses. It is necessary for
the proper operation of SIP for subsequent intermediaries to be
capable of inserting such Via header fields, and thus it cannot be
prevented. As such, though it is desirable, securing Via is not
possible through the sort of identity mechanism described in this
document; the best known practice for securing Via is the use of
SIPS.
Note that this mechanism does not provide any protection for the
display-name portion of the From header field, and thus users are
free to use any display-name of their choosing, and attackers could
conceivably alter the display-names in a request with impunity. If
an administrative domain wants to control the display-names selected
by users, they could do so with policies outside the scope of this
document (for example, their authentication service could reject
requests from valid users that contain an improper display-name in
the From header field). While there are conceivably attacks that an
adversary could mount against SIP systems that rely too heavily on
the display-name in their user interface, this argues for intelligent
interface design, not changes to the protocol.
This mechanism also provides a signature over the bodies of SIP
Peterson & Jennings Expires March 30, 2005 [Page 22]
Internet-Draft SIP Identity September 2004
requests. The most important reason for doing so is to protect SDP
bodies carried in SIP requests. There is little purpose in
establishing the identity of the user agent that originated a SIP
request if a man-in-the-middle can change the SDP and direct media to
an different IP address. Note however that this is not perfect
end-to-end security. The authentication service itself, when
instantiated at a intermediary, could conceivably change the SDP (and
SIP headers, for that matter) before providing a signature. Thus,
while this mechanism reduces the chance that a man-in-the-middle will
interfere with sessions, it does not eliminate it entirely. Since it
is a foundational assumption of this mechanism that the user trusts
their local domain to vouch for their security, they must also trust
the service not to violate the integrity of their message without
good reason. Note that RFC3261 16.6 states that SIP proxy servers
"MUST NOT add to, modify, or remove the message body."
Users SHOULD NOT provide credentials to an authentication service to
which they cannot initiate a direct connection, preferably one
secured by TLS. If a user does not receive a certificate from the
authentication service over this TLS connection 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.
Ultimately, the worth of an assurance provided by an Identity header
is limited by the security practices of the domain that issues the
assurance. Relying on an Identity header generated by a remote
administrative domain assumes that the issuing domain uses some
trustworthy 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). The value of an Identity header
from such domains is questionable. While there is no magic way for a
verifier to distinguish "good" from "bad" domains by inspecting a SIP
request, it is expected that further work in authorization practices
could be built on top of this identity solution; without such an
identity solution, many promising approaches to authorization policy
are impossible. That much said, it is RECOMMENDED that
authentication services based on proxy servers employ strong
authentication practices such as token-based identifiers.
Since a domain certificate is used by an authentication service
(rather than individual certificates for each identity), certain
Peterson & Jennings Expires March 30, 2005 [Page 23]
Internet-Draft SIP Identity September 2004
problems can arise with name subordination. For example, if an
authentication service holds a common certificate for the hostname
'sip.atlanta.example.com', can it legitimately sign a token
containing an identity of 'sip:alice@atlanta.example.com'? It is
difficult for the recipient of a request to ascertain whether or not
'sip.atlanta.example.com' is authoritative for the
'atlanta.example.com' domain unless the recipient has some
foreknowledge of the administration of 'atlanta.example.com'.
Therefore, it is RECOMMENDED that UASs receiving signed requests
notify end users if there is ANY discrepancy between the
subjectAltName of the signers certificate and the identity within the
authentication token. Minor discrepancies MAY be characterized as a
warning. Additionally, relying parties MAY follow the procedures in
RFC3263 [4] to look up in the DNS the domain portion of the identity
in the From header field, and compare the SIP services listed for
that domain with the subjectAltName of the certificate; this can give
the relying party a better sense of the canonical SIP services for
that domain.
Because the domain 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 authentication services. Some federations of service
providers, for example, might only trust certificates that have been
provided by a certificate authority operated by the federation.
Finally, the Identity and Identity-Info headers cannot protect
themselves. Any attacker could remove these headers from a SIP
request, and modify the request arbitrarily afterwards. Accordingly,
these headers are only truly efficacious if the would-be verifier
knows that they must be included in a request. In the long term,
some sort of identity mechanism along these lines must become
mandatory-to-use for the SIP protocol; that is the only way to
guarantee that this protection can always be expected. In the
interim, however, identity reception policies at a domain level or an
address-book level should be used by verifiers to determine whether
or not identity is expected from a particular source of SIP requests.
Those authorization policies are outside the scope of this document.
Peterson & Jennings Expires March 30, 2005 [Page 24]
Internet-Draft SIP Identity September 2004
15. IANA Considerations
This document requests changes to the header and response-code
sub-registries of the SIP parameters IANA registry.
15.1 Header Field Names
This document specifies two new SIP headers: Identity and
Identity-Info. Their syntax is given in Section 10. These headers
are defined by the following information, which is to be added to the
header sub-registry under
http://www.iana.org/assignments/sip-parameters.
Header Name: Identity
Compact Form: y
Header Name: Identity-Info
Compact Form: (none)
15.2 Response Code
This document registers one new SIP response code which is described
in Section 7. This response codes is defined by the following
information, which is to be added to the method and response-code
sub-registry under http://www.iana.org/assignments/sip-parameters.
Response Code Number: 428
Default Reason Phrase: Use Identity Header
16. References
16.1 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] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
(SIP): Locating SIP Servers", RFC 3263, June 2002.
[5] Peterson, J., "Session Initiation Protocol (SIP) Authenticated
Identity Body (AIB) Format", RFC 3893, September 2004.
[6] Crocker, D., "Augmented BNF for Syntax Specifications: ABNF",
RFC 2234, November 1997.
Peterson & Jennings Expires March 30, 2005 [Page 25]
Internet-Draft SIP Identity September 2004
16.2 Informative References
[7] Kohl, J. and C. Neumann, "The Kerberos Network Authentication
Service (V5)", RFC 1510, September 1993.
[8] 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.
[9] Schulzrinne, H., "The TEL URI for Telephone Numbers",
draft-ietf-iptel-rfc2806bis-09 (work in progress), June 2004.
[10] Faltstrom, P. and M. Mealling, "The E.164 to URI DDDS
Application", RFC 3761, April 2004.
Authors' Addresses
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/
Cullen Jennings
Cisco Systems
170 West Tasman Drive
MS: SJC-21/2
San Jose, CA 95134
USA
Phone: +1 408 902-3341
EMail: fluffy@cisco.com
Appendix A. Acknowledgments
The authors would like to thank Eric Rescorla, Rohan Mahy, Robert
Sparks, Jonathan Rosenberg, Mark Watson, Henry Sinnreich, Alan
Johnston and Patrik Faltstrom for their comments. The bit-archive
presented in Appendix B follows the pioneering example of Robert
Sparks' torture-test draft.
Peterson & Jennings Expires March 30, 2005 [Page 26]
Internet-Draft SIP Identity September 2004
Appendix B. Bit-exact archive of example messages
The following text block is an encoded, gzip compressed TAR archive
of files that represent the transformations performed on the example
messages discussed in Section 11. It includes for each example:
o (foo).message: the original message
o (foo).canonical: the canonical string constructed from that
message
o (foo).sha1: the SHA1 hash of the canonical string (hexadecimal)
o (foo).signed: the RSA-signed SHA1 hash of the canonical string
(binary)
o (foo).signed.enc: the base64 encoding of the RSA-signed SHA1 hash
of the canonical string as it would appear in the request
o (foo).identity: the original message with the Identity and
Identity-Info headers added
Also included in the archive are two public key/certificate pairs,
for atlanta.example.com and biloxi.example.org, respectively,
including:
o (foo).cert: the certificate of the domain
o (foo).privkey: the private key of the domain
o (foo).pubkey: the public key of the domain, extracted from the
cert file for convenience
To recover the compressed archive file intact, the text of this
document may be passed as input to the following Perl script (the
output should be redirected to a file or piped to "tar -xzvf -").
#!/usr/bin/perl
use strict;
my $bdata = "";
use MIME::Base64;
while(<>) {
if (/-- BEGIN MESSAGE ARCHIVE --/ .. /-- END MESSAGE ARCHIVE --/) {
if ( m/^\s*[^\s]+\s*$/) {
$bdata = $bdata . $_;
}
}
}
print decode_base64($bdata);
Alternatively, the base-64 encoded block can be edited by hand to
remove document structure lines and fed as input to any base-64
decoding utility.
B.1 Encoded Reference Files
-- BEGIN MESSAGE ARCHIVE --
Peterson & Jennings Expires March 30, 2005 [Page 27]
Internet-Draft SIP Identity September 2004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 & Jennings Expires March 30, 2005 [Page 28]
Internet-Draft SIP Identity September 2004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 & Jennings Expires March 30, 2005 [Page 29]
Internet-Draft SIP Identity September 2004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-- END MESSAGE ARCHIVE --
Appendix C. Changelog
NOTE TO THE RFC-EDITOR: Please remove this section prior to
publication as an RFC.
Changes from draft-ietf-sip-identity-02:
- Extracted text relating to providing identity in SIP responses;
this text will appear in a separate draft
- Added compliance testing/example section
- Added CSeq to the signature of the Identity header to prevent a
specific cut-and-paste attack; also added addr-spec of the To
header to the signature of the Identity header for similar reasons
- Added text about why neither Via headers nor display-names are
protected by this mechanism
- Added bit-exact reference files for compliance testing
- Added privacy considerations
Changes from draft-ietf-sip-identity-01:
- Completely changed underlying mechanism - instead of using an
AIB, the mechanism now recommends the use of the Identity header
and Identity-Info header
- Numerous other changes resulting from the above
- Various other editorial corrections
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:
Peterson & Jennings Expires March 30, 2005 [Page 30]
Internet-Draft SIP Identity September 2004
- 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
- Various other editorial corrections
Peterson & Jennings Expires March 30, 2005 [Page 31]
Internet-Draft SIP Identity September 2004
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Peterson & Jennings Expires March 30, 2005 [Page 32]
