draft-ietf-sip-identity-05.txt   draft-ietf-sip-identity-06.txt 
SIP WG J. Peterson SIP WG J. Peterson
Internet-Draft NeuStar Internet-Draft NeuStar
Expires: September 2, 2005 C. Jennings Expires: April 27, 2006 C. Jennings
Cisco Systems Cisco Systems
March 2005 October 24, 2005
Enhancements for Authenticated Identity Management in the Session Enhancements for Authenticated Identity Management in the Session
Initiation Protocol (SIP) Initiation Protocol (SIP)
draft-ietf-sip-identity-05 draft-ietf-sip-identity-06
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2005).
Abstract Abstract
The existing security mechanisms in the Session Initiation Protocol The existing security mechanisms in the Session Initiation Protocol
are inadequate for cryptographically assuring the identity of the end are inadequate for cryptographically assuring the identity of the end
users that originate SIP requests, especially in an interdomain users that originate SIP requests, especially in an interdomain
context. This document defines a mechanism for securely identifying context. This document defines a mechanism for securely identifying
originators of SIP messages. It does so by defining two new SIP originators of SIP messages. It does so by defining two new SIP
header fields, Identity, for conveying a signature used for header fields, Identity, for conveying a signature used for
validating the identity, and Identity-Info, for conveying a reference validating the identity, and Identity-Info, for conveying a reference
to the certificate of the signer. to the certificate of the signer.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Overview of Operations . . . . . . . . . . . . . . . . . . . . 6
5. Overview of Operations . . . . . . . . . . . . . . . . . . . 6 5. Authentication Service Behavior . . . . . . . . . . . . . . . 7
6. Authentication Service Behavior . . . . . . . . . . . . . . 7 5.1. Identity within a Dialog and Retargeting . . . . . . . . . 9
6.1 Identity within a Dialog and Retargeting . . . . . . . . . 10 6. Verifier Behavior . . . . . . . . . . . . . . . . . . . . . . 10
7. Verifier Behavior . . . . . . . . . . . . . . . . . . . . . 10 7. Considerations for User Agent . . . . . . . . . . . . . . . . 11
8. Considerations for User Agent . . . . . . . . . . . . . . . 12 8. Considerations for Proxy Servers . . . . . . . . . . . . . . . 12
9. Considerations for Proxy Server . . . . . . . . . . . . . . 13 9. Header Syntax . . . . . . . . . . . . . . . . . . . . . . . . 13
10. Header Syntax . . . . . . . . . . . . . . . . . . . . . . . 13 10. Compliance Tests and Examples . . . . . . . . . . . . . . . . 15
11. Compliance Tests and Examples . . . . . . . . . . . . . . . 16 10.1. Identity-Info with a Singlepart MIME body . . . . . . . . 16
11.1 Identity-Info with a Singlepart MIME body . . . . . . . 16 10.2. Identity for a Request with no MIME body or Contact . . . 19
11.2 Identity for a Request with no MIME body or Contact . . 19 11. Identity and the TEL URI Scheme . . . . . . . . . . . . . . . 22
12. Identity and the TEL URI Scheme . . . . . . . . . . . . . . 22 12. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 23
13. Privacy Considerations . . . . . . . . . . . . . . . . . . . 23 13. Security Considerations . . . . . . . . . . . . . . . . . . . 24
14. Security Considerations . . . . . . . . . . . . . . . . . . 24 13.1. Handling of digest-string Elements . . . . . . . . . . . . 24
14.1 Handling of digest-string Elements . . . . . . . . . . . 24 13.2. Display Names and Identity . . . . . . . . . . . . . . . . 27
14.2 Display Names and Identity . . . . . . . . . . . . . . . 26 13.3. Securing the Connection to the Authentication Service . . 28
14.3 Securing the Connection to the Authentication Service . 27 13.4. Domain Names and Subordination . . . . . . . . . . . . . . 28
14.4 Domain Names and Subordination . . . . . . . . . . . . . 28 13.5. Authorization and Transitional Strategies . . . . . . . . 30
14.5 Authorization and Transitional Strategies . . . . . . . 30 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . 31 14.1. Header Field Names . . . . . . . . . . . . . . . . . . . . 31
15.1 Header Field Names . . . . . . . . . . . . . . . . . . . 31 14.2. 428 'Use Identity Header' Response Code . . . . . . . . . 31
15.2 428 'Use Identity Header' Response Code . . . . . . . . 31 14.3. 436 'Bad Identity-Info' Response Code . . . . . . . . . . 31
15.3 436 'Bad Identity-Info' Response Code . . . . . . . . . 31 14.4. 437 'Unsupported Certificate' Response Code . . . . . . . 32
15.4 437 'Unsupported Certificate' Response Code . . . . . . 32 14.5. 438 'Invalid Identity Header' Response Code . . . . . . . 32
15.5 Identity-Info Parameters . . . . . . . . . . . . . . . . 32 14.6. Identity-Info Parameters . . . . . . . . . . . . . . . . . 32
15.6 Identity-Info Algorithm Parameter Values . . . . . . . . 32 14.7. Identity-Info Algorithm Parameter Values . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 34 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 33
A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 34 Appendix B. Bit-exact archive of example messages . . . . . . . . 33
B. Bit-exact archive of example messages . . . . . . . . . . . 34 B.1. Encoded Reference Files . . . . . . . . . . . . . . . . . 34
B.1 Encoded Reference Files . . . . . . . . . . . . . . . . . 35 Appendix C. Original Requirements . . . . . . . . . . . . . . . . 36
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 33 Appendix D. Changelog . . . . . . . . . . . . . . . . . . . . . . 37
16.1 Normative References . . . . . . . . . . . . . . . . . . 33 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39
16.2 Informative References . . . . . . . . . . . . . . . . . 33 15.1. Normative References . . . . . . . . . . . . . . . . . . . 39
C. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . 37 15.2. Informative References . . . . . . . . . . . . . . . . . . 39
Intellectual Property and Copyright Statements . . . . . . . 40 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41
Intellectual Property and Copyright Statements . . . . . . . . . . 42
1. Introduction 1. Introduction
This document provides enhancements to the existing mechanisms for This document provides enhancements to the existing mechanisms for
authenticated identity management in the Session Initiation Protocol authenticated identity management in the Session Initiation Protocol
(SIP [1]). An identity, for the purposes of this document, is (SIP, RFC 3261 [1]). An identity, for the purposes of this document,
defined as a SIP URI, commonly a canonical AoR employed to reach a is defined as a SIP URI, commonly a canonical address-of-record (AoR)
user (such as 'sip:alice@atlanta.example.com'). employed to reach a user (such as 'sip:alice@atlanta.example.com').
RFC3261 stipulates several places within a SIP request where a user RFC3261 stipulates several places within a SIP request where a user
can express an identity for themselves, notably the user-populated can express an identity for themselves, notably the user-populated
From header field. However, the recipient of a SIP request has no From header field. However, the recipient of a SIP request has no
way to verify that the From header field has been populated way to verify that the From header field has been populated
appropriately, in the absence of some sort of cryptographic appropriately, in the absence of some sort of cryptographic
authentication mechanism. authentication mechanism.
RFC3261 specifies a number of security mechanisms that can be RFC3261 specifies a number of security mechanisms that can be
employed by SIP UAs, including Digest, TLS and S/MIME employed by SIP UAs, including Digest, TLS and S/MIME
(implementations may support other security schemes as well). (implementations may support other security schemes as well).
However, few SIP user agents today support the end-user certificates However, few SIP user agents today support the end-user certificates
necessary to authenticate themselves (via S/MIME, for example), and necessary to authenticate themselves (via S/MIME, for example), and
furthermore Digest authentication is limited by the fact that the furthermore Digest authentication is limited by the fact that the
originator and destination must share a pre-arranged secret. It is originator and destination must share a pre-arranged secret. It is
desirable for SIP user agents to be able to send requests to desirable for SIP user agents to be able to send requests to
destinations with which they have no previous association - just as destinations with which they have no previous association - just as
in the telephone network today, one can receive a call from someone in the telephone network today, one can receive a call from someone
with whom one has no previous association, and still have a with whom one has no previous association, and still have a
reasonable assurance that their displayed Caller-ID is accurate. reasonable assurance that their displayed Caller-ID is accurate. A
cryptographic approach, like the one described in this document, can
probably provide a much stronger and less-spoofable assurance of
identity than the telephone network provides today.
2. Terminology 2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in RFC2119 [2] and indicate requirement levels for described in RFC2119 [2] and indicate requirement levels for
compliant SIP implementations. compliant SIP implementations.
3. Background 3. Background
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a SIP request, the From header field, can be populated arbitrarily by a SIP request, the From header field, can be populated arbitrarily by
the controller of a user agent, impersonation is very simple today. the controller of a user agent, impersonation is very simple today.
The mechanism described in this document aspires to provide a strong The mechanism described in this document aspires to provide a strong
identity system for SIP in which authorization policies cannot be identity system for SIP in which authorization policies cannot be
circumvented by impersonation. circumvented by impersonation.
All RFC3261 compliant user agents support Digest authentication, All RFC3261 compliant user agents support Digest authentication,
which utilizes a shared secret, as a means for authenticating which utilizes a shared secret, as a means for authenticating
themselves to a SIP registrar. Registration allows a user agent to themselves to a SIP registrar. Registration allows a user agent to
express that it is an appropriate entity to which requests should be express that it is an appropriate entity to which requests should be
sent for a particular address-of-record SIP URI (e.g., sent for a particular SIP AoR URI (e.g.,
'sip:alice@atlanta.example.com'). 'sip:alice@atlanta.example.com').
By the definition of identity used in this document, registration is By the definition of identity used in this document, registration is
a proof of the identity of the user to a registrar. However, the a proof of the identity of the user to a registrar. However, the
credentials with which a user agent proves their identity to a credentials with which a user agent proves its identity to a
registrar cannot be validated by just any user agent or proxy server registrar cannot be validated by just any user agent or proxy server
- these credentials are only shared between the user agent and their - these credentials are only shared between the user agent and their
domain administrator. So this shared secret does not immediately domain administrator. So this shared secret does not immediately
help a user to authenticate to a wide range of recipients. help a user to authenticate to a wide range of recipients.
Recipients require a means of determining whether or not the 'return Recipients require a means of determining whether or not the 'return
address' identity of a non-REGISTER request (i.e., the From header address' identity of a non-REGISTER request (i.e., the From header
field value) has legitimately been asserted. field value) has legitimately been asserted.
The address-of-record URI used for registration is also the URI with The AoR URI used for registration is also the URI with which a UA
which a UA commonly populates the From header field of requests in commonly populates the From header field of requests in order to
order to provide a 'return address' identity to recipients. From an provide a 'return address' identity to recipients. From an
authorization perspective, if you are can prove you are eligible to authorization perspective, if you can prove you are eligible to
register in a domain under a particular address-of-record, you can register in a domain under a particular AoR, you can prove you can
prove you can legitimately receive requests for that address-of- legitimately receive requests for that AoR, and accordingly, when you
record, and accordingly, when you place that address-of-record in the place that AoR in the From header field of a SIP request other than a
From header field of a SIP request other than a registration (like an registration (like an INVITE), you are providing a 'return address'
INVITE), you are providing a 'return address' where you can where you can legitimately be reached. In other words, if you are
legitimately be reached. In other words, if you are authorized to authorized to receive requests for that 'return address', logically,
receive requests for that 'return address', logically, it follows it follows that you are also authorized to assert that 'return
that you are also authorized to assert that 'return address' in your address' in your From header field. This is of course only one
From header field. This is of course only one manner in which a manner in which a domain might determine how a particular user is
domain might determine how a particular user is authorized to authorized to populate the From header field; as an aside, for other
populate the From header field; as an aside, for other sorts of URIs sorts of URIs in the From (like anonymous URIs), other authorization
in the From (like anonymous URIs), other authorization policies would policies would apply.
apply.
Ideally, then, SIP user agents should have some way of proving to Ideally, then, SIP user agents should have some way of proving to
recipients of SIP requests that their local domain has authenticated recipients of SIP requests that their local domain has authenticated
them and authorized the population of the From header field. This them and authorized the population of the From header field. This
document proposes a mediated authentication architecture for SIP in document proposes a mediated authentication architecture for SIP in
which requests are sent to a server in the user's local domain, which which requests are sent to a server in the user's local domain, which
authenticates such requests (using the same practices by which the authenticates such requests (using the same practices by which the
domain would authenticate REGISTER requests). Once a message has domain would authenticate REGISTER requests). Once a message has
been authenticated, the local domain then needs some way to been authenticated, the local domain then needs some way to
communicate to other SIP entities that the sending user has been communicate to other SIP entities that the sending user has been
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this works well in some architectures, there are a few respects in this works well in some architectures, there are a few respects in
which this is impractical. For one, transitive trust is inherently which this is impractical. For one, transitive trust is inherently
weaker than an assertion that can be validated end-to-end. It is weaker than an assertion that can be validated end-to-end. It is
possible for SIP requests to cross multiple intermediaries in possible for SIP requests to cross multiple intermediaries in
separate administrative domains, in which case transitive trust separate administrative domains, in which case transitive trust
becomes even less compelling. becomes even less compelling.
One solution to this problem is to use 'trusted' SIP intermediaries One solution to this problem is to use 'trusted' SIP intermediaries
that assert an identity for users in the form of a privileged SIP 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. A mechanism for doing so (with the P-Asserted-Identity
header) is given in [10]. However, this solution allows only hop-by- header) is given in [12]. However, this solution allows only hop-by-
hop trust between intermediaries, not end-to-end cryptographic hop trust between intermediaries, not end-to-end cryptographic
authentication, and it assumes a managed network of nodes with strict authentication, and it assumes a managed network of nodes with strict
mutual trust relationships, an assumption that is incompatible with mutual trust relationships, an assumption that is incompatible with
widespread Internet deployment. widespread Internet deployment.
Accordingly, this document specifies a means of sharing a Accordingly, this document specifies a means of sharing a
cryptographic assurance of end-user SIP identity in an interdomain or cryptographic assurance of end-user SIP identity in an interdomain or
intradomain context which is based on the concept of an intradomain context which is based on the concept of an
'authentication service' and a new SIP header, the Identity header. 'authentication service' and a new SIP header, the Identity header.
Note that the scope of this document is limited to providing this Note that the scope of this document is limited to providing this
identity assurance for SIP requests; solving this problem for SIP identity assurance for SIP requests; solving this problem for SIP
responses is more complicated, and is a subject for future work. responses is more complicated, and is a subject for future work.
This specification allows either a user agent or a proxy server to This specification allows either a user agent or a proxy server to
provide identity services and to verify identities. To maximize end- provide identity services and to verify identities. To maximize end-
to-end security, it is obviously preferable for end users to hold to-end security, it is obviously preferable for end users to acquire
their own certificates; if they do, they can act as an authentication their own certificates and corresponding private keys; if they do,
service. However, end-user certificates may be neither practical nor they can act as an authentication service. However, end-user
affordable, given the difficulties of establishing a PKI that extends certificates may be neither practical nor affordable, given the
to end users, and moreover, given the potentially large number of SIP difficulties of establishing a PKI that extends to end users, and
user agents (phones, PCs, laptops, PDAs, gaming devices) that may be moreover, given the potentially large number of SIP user agents
employed by a single user. In such environments, synchronizing (phones, PCs, laptops, PDAs, gaming devices) that may be employed by
certificates across multiple devices may be very complex, and a single user. In such environments, synchronizing keying material
requires quite a good deal of additional endpoint behavior. Managing across multiple devices may be very complex, and requires quite a
several certificates for the various devices is also quite good deal of additional endpoint behavior. Managing several
problematic and unpopular with users. Accordingly, in the initial certificates for the various devices is also quite problematic and
use of this mechanism, it is likely that intermediaries will unpopular with users. Accordingly, in the initial use of this
instantiate the authentication service role. 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 or a proxy server 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 this mechanism in order for an
identity assurance to be added to a request in this fashion.
o The mechanism must prevent replay of the identity assurance by an
attacker.
o In order to provide full replay protection, 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) which it is authorized to use within 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.
5. Overview of Operations 4. Overview of Operations
This section provides an informative (non-normative) high-level This section provides an informative (non-normative) high-level
overview of the mechanisms described in this document. overview of the mechanisms described in this document.
Imagine the case where Alice, who has the home proxy of example.com 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 and the address-of-record sip:alice@example.com, wants to communicate
with sip:bob@example.org. with sip:bob@example.org.
Alice generates an INVITE and places her identity in the From header 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 field of the request. She then sends an INVITE over TLS to an
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Digest authentication challenge) and validates that she is authorized Digest authentication challenge) and validates that she is authorized
to assert the identity which is populated in the From header field. to assert the identity which is populated in the From header field.
This value may be Alice's AoR, or it may be some other value that the This value 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 policy of the proxy server permits her to use. It then computes a
hash over some particular headers, including the From header field hash over some particular headers, including the From header field
and the bodies in the message. This hash is signed with the and the bodies in the message. This hash is signed with the
certificate for the domain (example.com, in Alice's case) and certificate for the domain (example.com, in Alice's case) and
inserted in a new header field in the SIP message, the 'Identity' inserted in a new header field in the SIP message, the 'Identity'
header. header.
The proxy, as the holder the private key of its domain, is asserting The proxy, as the holder of the private key of its domain, is
that the originator of this request has been authenticated and that asserting that the originator of this request has been authenticated
she is authorized to claim the identity (the SIP address-of-record) and that she is authorized to claim the identity (the SIP address-of-
which appears in the From header field. The proxy also inserts a record) which appears in the From header field. The proxy also
companion header field, Identity-Info, that tells Bob how to acquire inserts a companion header field, Identity-Info, that tells Bob how
its certificate, if he doesn't already have it. to acquire its certificate, if he doesn't already have it.
When Bob's domain receives the request, it verifies the signature When Bob's domain receives the request, it verifies the signature
provided in the Identity header, and thus can validates that the provided in the Identity header, and thus can validates that the
domain indicated by the host portion of the AoR in the From header domain indicated by the host portion of the AoR in the From header
field authenticated the user, and permitted them to assert that From field authenticated the user, and permitted them to assert that From
header field value. This same validation operation may be performed header field value. This same validation operation may be performed
by Bob's UAS. by Bob's UAS.
6. Authentication Service Behavior 5. Authentication Service Behavior
This document defines a new role for SIP entities called an This document defines a new role for SIP entities called an
authentication service. The authentication service role can be authentication service. The authentication service role can be
instantiated by a proxy server or a user agent. Any entity that instantiated by a proxy server or a user agent. Any entity that
instantiates the authentication service role MUST possess the private instantiates the authentication service role MUST possess the private
key of a domain certificate, and MUST be capable of authenticating key of a domain certificate, and MUST be capable of authenticating
one or more SIP users that can register in that domain. Commonly, one or more SIP users that can register in that domain. Commonly,
this role will be instantiated by a proxy server, since these this role will be instantiated by a proxy server, since these
entities are more likely to have a static hostname, hold a entities are more likely to have a static hostname, hold a
corresponding certificate, and have access to SIP registrar corresponding certificate, and have access to SIP registrar
capabilities that allow them to authenticate users in their domain. capabilities that allow them to authenticate users in their domain.
It is also possible that the authentication service role might be It is also possible that the authentication service role might be
instantiated by an entity that acts redirect server, but that is left instantiated by an entity that acts as a redirect server, but that is
as a topic for future work. left as a topic for future work.
SIP entities that act as an authentication service MUST add a Date SIP entities that act as an authentication service MUST add a Date
header field to SIP requests if one is not already present. header field to SIP requests if one is not already present (see
Similarly, authentication services MUST add a Content-Length header Section 9 for information on how the Date header field assist
field to SIP requests if one is not already present; this can help verifiers). Similarly, authentication services MUST add a Content-
the verifier to double-check that they are hashing exactly as many Length header field to SIP requests if one is not already present;
bytes of message-body as the authentication service when they verify this can help the verifier to double-check that they are hashing
the message. exactly as many bytes of message-body as the authentication service
when they verify the message.
Entities instantiating the authentication service role performs the Entities instantiating the authentication service role performs the
following steps, in order, to generate an Identity header for a SIP following steps, in order, to generate an Identity header for a SIP
request: request:
Step 1: The authentication service MUST extract the identity of the Step 1: The authentication service MUST extract the identity of the
sender from the request. The authentication service takes this value sender from the request. The authentication service takes this value
from the From header field; this AoR will be referred to here as the 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, 'identity field'. If the identity field contains a SIP or SIPS URI,
the authentication service MUST extract the hostname portion of the the authentication service MUST extract the hostname portion of the
identity field and compare it to the domain(s) for which it is identity field and compare it to the domain(s) for which it is
responsible. If the identity field uses the TEL URI scheme, the responsible (following the procedures in RFC3261 16.4 used by a proxy
policy of the authentication service determines whether or not it is server to determine the domain(s) for which it is responsible). If
responsible for this identity; see Section 12 for more information. the identity field uses the TEL URI scheme, the policy of the
If the authentication service is not responsible for the identity in authentication service determines whether or not it is responsible
for this identity; see Section 11 for more information. If the
authentication service is not responsible for the identity in
question, it SHOULD process and forward the request normally, but it question, it SHOULD process and forward the request normally, but it
MUST NOT add an Identity header; see below for more information on MUST NOT add an Identity header; see below for more information on
authentication service handling of an existing Identity header. authentication service handling of an existing Identity header.
Step 2: The authentication service MUST determine whether or not the Step 2: The authentication service MUST determine whether or not the
sender of the request is authorized to claim the identity given in sender of the request is authorized to claim the identity given in
the identity field. In order to do so, the authentication service the identity field. In order to do so, the authentication service
MUST authenticate the sender of the message. Some possible ways in MUST authenticate the sender of the message. Some possible ways in
which this authentication might be performed include: which this authentication might be performed include:
If the authentication service is instantiated by a SIP If the authentication service is instantiated by a SIP
skipping to change at page 8, line 38 skipping to change at page 8, line 20
was sent in anticipation of a challenge using cached credentials, was sent in anticipation of a challenge using cached credentials,
as described in RFC 3261 Section 22.3). Note that if that proxy as described in RFC 3261 Section 22.3). Note that if that proxy
server is maintaining a TLS connection with the client over which server is maintaining a TLS connection with the client over which
the client had previously authenticated itself using Digest the client had previously authenticated itself using Digest
authentication, the identity value obtained from that previous authentication, the identity value obtained from that previous
authentication step can be reused without an additional Digest authentication step can be reused without an additional Digest
challenge. challenge.
If the authentication service is instantiated by a SIP user agent, If the authentication service is instantiated by a SIP user agent,
a user agent can be said to authenticate its user on the grounds 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 that the user can provision the user agent with the private key of
the domain, or by preferably by providing a password that unlocks the domain, or preferably by providing a password that unlocks
said private key. said private key.
Authorization of the use of a particular username in the From header Authorization of the use of a particular username in the From header
field is a matter of local policy for the authentication service, one field is a matter of local policy for the authentication service, one
which depends greatly on the manner in which authentication is which depends greatly on the manner in which authentication is
performed. For example, one policy might be as follows: the username performed. For example, one policy might be as follows: the username
given in the 'username' parameter of the Proxy-Authorization header given in the 'username' parameter of the Proxy-Authorization header
MUST correspond exactly to the username in the From header field of MUST correspond exactly to the username in the From header field of
the SIP message. However, there are many cases in which this is too the SIP message. However, there are many cases in which this is too
limiting or inappropriate; a realm might use 'username' parameters in limiting or inappropriate; a realm might use 'username' parameters in
skipping to change at page 9, line 29 skipping to change at page 9, line 12
field (e.g., the URI of the sender, like field (e.g., the URI of the sender, like
'sip:alice@atlanta.example.com'); it does not convert the display- 'sip:alice@atlanta.example.com'); it does not convert the display-
name portion of the From header field (e.g., 'Alice Atlanta'). name portion of the From header field (e.g., 'Alice Atlanta').
Authentication services MAY check and validate the display-name as Authentication services MAY check and validate the display-name as
well, and compare it to a list of acceptable display-names that may 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 be used by the sender; if the display-name does not meet policy
constraints, the authentication service MUST return a 403 response constraints, the authentication service MUST return a 403 response
code with the reason phrase "Inappropriate Display-Name". However, code with the reason phrase "Inappropriate Display-Name". However,
the display-name is not always present, and in many environments the the display-name is not always present, and in many environments the
requisite operational procedures for display-name validation may not requisite operational procedures for display-name validation may not
exist. For more information, see Section 14.2. exist. For more information, see Section 13.2.
Step 3: The authentication service SHOULD ensure that any pre- Step 3: The authentication service SHOULD ensure that any pre-
existing Date header in the request is accurate. Local policy can existing Date header in the request is accurate. Local policy can
dictate precisely how accurate the Date must be, a RECOMMENDED dictate precisely how accurate the Date must be, a RECOMMENDED
maximum discrepancy of ten minutes will ensure that the request is maximum discrepancy of ten minutes will ensure that the request is
unlikely to upset any verifiers. If the Date header contains a time unlikely to upset any verifiers. If the Date header contains a time
different by more than ten minutes from the current time noted by the different by more than ten minutes from the current time noted by the
authentication service, the authentication service SHOULD reject the authentication service, the authentication service SHOULD reject the
request. This behavior is not mandatory because a user agent client request. This behavior is not mandatory because a user agent client
could only exploit the Date header in order to cause a request to could only exploit the Date header in order to cause a request to
fail verification; the Identity header is not intended to provide a fail verification; the Identity header is not intended to provide a
source of non-repudiation or a perfect record of when messages are source of non-repudiation or a perfect record of when messages are
processed. processed. Finally, the authentication service MUST verify that the
Date header falls within the validity period of its certificate. For
more information on the security properties associated with the Date
header field value, see Section 9.
Step 4: The authentication service MUST form the identity signature Step 4: The authentication service MUST form the identity signature
and add an Identity header to the request containing this signature. and add an Identity header to the request containing this signature.
After the Identity header has been added to the request, the After the Identity header has been added to the request, the
authentication service MUST also add an Identity-Info header. The authentication service MUST also add an Identity-Info header. The
Identity-Info header contains a URI from which its certificate can be Identity-Info header contains a URI from which its certificate can be
acquired. Details on the generation of both of these headers are acquired. Details on the generation of both of these headers are
provided in section Section 10. provided in section Section 9.
Finally, the authentication service MUST forward the message Finally, the authentication service MUST forward the message
normally. normally.
6.1 Identity within a Dialog and Retargeting 5.1. Identity within a Dialog and Retargeting
Retargeting is defined as the alteration of the Request-URI by Retargeting is broadly defined as the alteration of the Request-URI
intermediaries in order to point to another URI that corresponds to a by intermediaries. More specifically, retargeting supplants the
user that cannot authenticate itself with the identity originally original target URI with one that corresponds to a different user, a
present in the Request-URI. By this definition, retargeting excludes user that is not authorized to register under the original target
translation of the Request-URI to a registered contact of an endpoint URI. By this definition, retargeting does not include translation of
that has authenticated itself as that user. the Request-URI to a contact address of an endpoint that has
registered under the original target URI, for example.
When a dialog-forming request is retargeted, this can cause a few When a dialog-forming request is retargeted, this can cause a few
wrinkles for the Identity mechanism when it is applied to requests wrinkles for the Identity mechanism when it is applied to requests
sent in the backwards direction within a dialog. This section sent in the backwards direction within a dialog. This section
provides some non-normative considerations related to this case. provides some non-normative considerations related to this case.
When a request is retargeted, it may reach a SIP endpoint whose user When a request is retargeted, it may reach a SIP endpoint whose user
is not identified by the URI designated in the To header field value. is not identified by the URI designated in the To header field value.
The value in the To header field of a dialog-forming request is used The value in the To header field of a dialog-forming request is used
as the From header field of requests sent in the backwards direction as the From header field of requests sent in the backwards direction
during the dialog, and is accordingly the header that would be signed during the dialog, and is accordingly the header that would be signed
by an authentication service for requests sent in the backwards by an authentication service for requests sent in the backwards
direction. In retargeting cases, if the URI in the From header does direction. In retargeting cases, if the URI in the From header does
not identify the sender of the request in the backwards direction, not identify the sender of the request in the backwards direction,
then clearly it would be inappropriate to provide an Identity then clearly it would be inappropriate to provide an Identity
signature over that From header. As specified above, if the signature over that From header. As specified above, if the
authentication service is not responsible for the domain in the From authentication service is not responsible for the domain in the From
header field of the request, it must not add an Identity header to header field of the request, it MUST NOT add an Identity header to
the request, and should process/forward the request normally. the request, and should process/forward the request normally.
Any means of anticipating retargeting and so on is outside the scope Any means of anticipating retargeting and so on is outside the scope
of this document, and likely to have equal applicability to response of this document, and likely to have equal applicability to response
identity as it does to requests in the backwards direction within a identity as it does to requests in the backwards direction within a
dialog. Consequently, no special guidance is given for implementers dialog. Consequently, no special guidance is given for implementers
here regarding the 'connected party' problem; authentication service here regarding the 'connected party' problem; authentication service
behavior is unchanged if retargeting has occurred for a dialog- behavior is unchanged if retargeting has occurred for a dialog-
forming request. Ultimately, the authentication service provides an forming request. Ultimately, the authentication service provides an
Identity header for requests in the backwards dialog when the user is Identity header for requests in the backwards dialog when the user is
authorized to assert the identity given in the From header field, and authorized to assert the identity given in the From header field, and
if they are not, an Identity header is not provided. if they are not, an Identity header is not provided.
For further information on the problems of response identity and the For further information on the problems of response identity and the
potential solution spaces, see [14]. potential solution spaces, see [15].
7. Verifier Behavior 6. Verifier Behavior
This document introduces a new logical role for SIP entities called a This document introduces a new logical role for SIP entities called a
'verifier', which may be instantiated by a user agent or proxy 'verifier', which may be instantiated by a user agent or proxy
server. When a verifier receives a SIP message containing an server. When a verifier receives a SIP message containing an
Identity header, it may inspect the signature to verify the identity Identity header, it may inspect the signature to verify the identity
of the sender of the message. Typically, the results of a of the sender of the message. Typically, the results of a
verification are provided as input to an authorization process which verification are provided as input to an authorization process which
is outside the scope of this document. If an Identity header is not is outside the scope of this document. If an Identity header is not
present in a request, and one is required by local policy (for present in a request, and one is required by local policy (for
example, based on a per-sending-domain policy, or a per-sending-user example, based on a per-sending-domain policy, or a per-sending-user
skipping to change at page 11, line 37 skipping to change at page 11, line 25
Provided that the domain certificate used to sign this message is not Provided that the domain certificate used to sign this message is not
previously known to the recipient, SIP entities SHOULD discover this previously known to the recipient, SIP entities SHOULD discover this
certificate by dereferencing the Identity-Info header, unless they certificate by dereferencing the Identity-Info header, unless they
have some more efficient implementation-specific way of acquiring have some more efficient implementation-specific way of acquiring
certificates for that domain. If the URI scheme in the Identity-Info certificates for that domain. If the URI scheme in the Identity-Info
header cannot be dereferenced, then a 436 'Bad Identity-Info' header cannot be dereferenced, then a 436 'Bad Identity-Info'
response MUST be returned. The client processes this certificate in response MUST be returned. The client processes this certificate in
the usual ways, including checking that it has not expired, that the 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 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 revocation lists. Once the certificate is acquired, it MUST be
validated. If the certificate cannot be validated (it is self-signed validated following the procedures in RFC3280 [9]. If the
and untrusted, or signed by an untrusted or unknown certificate certificate cannot be validated (it is self-signed and untrusted, or
authority, expired, or revoked), the verifier MUST send a 437 signed by an untrusted or unknown certificate authority, expired, or
'Unsupported Certificate' response. revoked), the verifier MUST send a 437 'Unsupported Certificate'
response.
Step 2: The verifier MUST compare the identity of the signer with the Step 2: The verifier MUST follow the process described in
domain portion of the URI in the From header field. The verifier Section 13.4 to determine if the signer is authoritative for the URI
MUST follow the process described in Section 14.4 to determine if the in the From header field.
signer is authoritative for the URI in the From header field.
Step 3: The verifier MUST verify the signature in the Identity header Step 3: The verifier MUST verify the signature in the Identity header
field, following the procedures for generating the hashed digest- field, following the procedures for generating the hashed digest-
string described in Section 10. If a verifier determines that the string described in Section 9. If a verifier determines that the
signature on the message does not correspond to the reconstructed signature on the message does not correspond to the reconstructed
digest-string, then a 428 'Invalid Identity Header' response MUST be digest-string, then a 438 'Invalid Identity Header' response MUST be
returned. returned.
Step 4: The verifier MUST validate the Date, Contact and Call-ID Step 4: The verifier MUST validate the Date, Contact and Call-ID
headers the manner described in Section 14.1; recipients that wish to headers in the manner described in Section 13.1; recipients that wish
verify Identity signatures MUST support all of the operations to verify Identity signatures MUST support all of the operations
described there. described there. It must furthermore ensure that the value of the
Date header falls within the validity period of the certificate whose
8. Considerations for User Agent corresponding private key was used to sign the Identity header.
7. Considerations for User Agent
This mechanism can be applied opportunistically to existing SIP This mechanism can be applied opportunistically to existing SIP
deployments; accordingly, it requires no change to SIP user agent deployments; accordingly, it requires no change to SIP user agent
behavior in order for it to be effective. However, because this behavior in order for it to be effective. However, because this
mechanism does not provide integrity protection between the UAC and mechanism does not provide integrity protection between the UAC and
the authentication service, a UAC SHOULD implement some means of the authentication service, a UAC SHOULD implement some means of
providing this integrity. TLS would be one such mechanism, which is providing this integrity. TLS would be one such mechanism, which is
attractive because it MUST be supported by SIP proxy servers, but is attractive because it MUST be supported by SIP proxy servers, but is
potentially problematic because it is a hop-by-hop mechanism. See potentially problematic because it is a hop-by-hop mechanism. See
Section 14.3 for more information about securing the channel between Section 13.3 for more information about securing the channel between
the UAC and the authentication service. the UAC and the authentication service.
When a UAC sends a request, it MUST accurately populate the From When a UAC sends a request, it MUST accurately populate the From
header field with a value corresponding to an identity that it header field with a value corresponding to an identity that it
believes it is authorized to claim. In a request it MUST set the URI believes it is authorized to claim. In a request it MUST set the URI
portion of its From header to match a SIP, SIPS or TEL URI AoR which portion of its From header to match a SIP, SIPS or TEL URI AoR which
it is authorized to use in the domain (including anonymous URIs, as it is authorized to use in the domain (including anonymous URIs, as
described in RFC 3323 [3]). In general, UACs SHOULD NOT use the TEL described in RFC 3323 [3]). In general, UACs SHOULD NOT use the TEL
URI form in the From header field (see Section 12). URI form in the From header field (see Section 11).
Note that this document defines a number of new 4xx response codes. Note that this document defines a number of new 4xx response codes.
If user agents support these response codes, they will be able to If user agents support these response codes, they will be able to
respond intelligently to Identity-based error conditions. respond intelligently to Identity-based error conditions.
The UAC MUST also be capable of sending requests, including mid-call The UAC MUST also be capable of sending requests, including mid-call
requests, through an 'outbound' proxy (the authentication service). requests, through an 'outbound' proxy (the authentication service).
The best way to accomplish this is using pre-loaded Route headers and The best way to accomplish this is using pre-loaded Route headers and
loose routing. For a given domain, if an entity that can instantiate loose routing. For a given domain, if an entity that can instantiate
the authentication service role is not in the path of dialog-forming the authentication service role is not in the path of dialog-forming
requests, identity for mid-dialog requests in the backwards direction requests, identity for mid-dialog requests in the backwards direction
cannot be provided. cannot be provided.
As a recipient of a request, a user agent that can verify signed As a recipient of a request, a user agent that can verify signed
identities should also support an appropriate user interface to identities should also support an appropriate user interface to
render the validity of identity to a user. User agent render the validity of identity to a user. User agent
implementations SHOULD differentiate signed From header field values implementations SHOULD differentiate signed From header field values
from unsigned From header field values when rendering to an end user from unsigned From header field values when rendering to an end user
the identity of the sender of a request. the identity of the sender of a request.
9. Considerations for Proxy Server 8. Considerations for Proxy Servers
Domain policy may require proxy servers to inspect and verify the Domain policy may require proxy servers to inspect and verify the
identity provided in SIP requests. A proxy server may wish to identity provided in SIP requests. A proxy server may wish to
ascertain the identity of the sender of the message to provide spam ascertain the identity of the sender of the message to provide spam
prevention or call control services. Even if a proxy server does not prevention or call control services. Even if a proxy server does not
act as an authentication service, it MAY validate the Identity header act as an authentication service, it MAY validate the Identity header
before it makes a forwarding decision for a request. Proxy servers before it makes a forwarding decision for a request. Proxy servers
MUST NOT remove or modify an existing Identity or Identity-Info MUST NOT remove or modify an existing Identity or Identity-Info
header in a request. header in a request.
10. Header Syntax 9. Header Syntax
This document specifies two new SIP headers: Identity and Identity- This document specifies two new SIP headers: Identity and Identity-
Info. Each of these headers can appear only once in a SIP message. Info. Each of these headers can appear only once in a SIP message.
The grammar for these two headers is: The grammar for these two headers is (following the ABNF [6] in s):
(following the ABNF [6] in RFC3261 [1]):
Identity = "Identity" HCOLON signed-identity-digest Identity = "Identity" HCOLON signed-identity-digest
signed-identity-digest = LDQUOT 32LHEX RDQUOT signed-identity-digest = LDQUOT 32LHEX RDQUOT
Identity-Info = "Identity-Info" HCOLON ident-info (* SEMI identi-info-params ) Identity-Info = "Identity-Info" HCOLON ident-info *( SEMI ident-info-params )
ident-info = LAQUOT absoluteURI RAQUOT ident-info = LAQUOT absoluteURI RAQUOT
ident-info-params = ident-info-alg / ident-info-extension ident-info-params = ident-info-alg / ident-info-extension
ident-info-alg = "alg" EQUAL token ident-info-alg = "alg" EQUAL token
ident-info-extension = generic-param ident-info-extension = generic-param
The signed-identity-digest is a signed hash of a canonical string The signed-identity-digest is a signed hash of a canonical string
generated from certain components of a SIP request. To create the generated from certain components of a SIP request. To create the
contents of the signed-identity-digest, the following elements of a contents of the signed-identity-digest, the following elements of a
SIP message MUST placed in a bit-exact string in the order specified SIP message MUST be placed in a bit-exact string in the order
here, separated by a vertical line, "|" or %x7C, character: specified here, separated by a vertical line, "|" or %x7C, character:
o The AoR of the UA sending the message, or addr-spec of the From o The AoR of the UA sending the message, or addr-spec of the From
header field (referred to occasionally here as the 'identity header field (referred to occasionally here as the 'identity
field'). field').
o The addr-spec component of the To header field, which is the AoR o The addr-spec component of the To header field, which is the AoR
to which the request is being sent. to which the request is being sent.
o The callid from Call-Id header field. o The callid from Call-Id header field.
o The digit (1*DIGIT) and method (method) portions from CSeq header o The digit (1*DIGIT) and method (method) portions from CSeq header
field, separated by a single space (ABNF SP, or %x20). Note that field, separated by a single space (ABNF SP, or %x20). Note that
the CSeq header field allows LWS rather than SP to separate the the CSeq header field allows LWS rather than SP to separate the
digit and method portions, and thus the CSeq header field may need digit and method portions, and thus the CSeq header field may need
to be transformed in order to be canonicalized. The to be transformed in order to be canonicalized. The
authentication service MUST strip leading zeros from the 'digit' authentication service MUST strip leading zeros from the 'digit'
portion of the Cseq before generating the digest-string. portion of the Cseq before generating the digest-string.
o The Date header field, with exactly one space each for each SP and 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. RFC the weekday and month items case set as shown in BNF in 3261. RFC
3261 specifies that the BNF for weekday and month are a choice 3261 specifies that the BNF for weekday and month are a choice
amongst a set of tokens. The RFC 2234 rules for the BNF specify amongst a set of tokens. The RFC 2234 rules for the BNF specify
that tokens are case sensitive. However, when used to construct that tokens are case sensitive. However, when used to construct
the canonical string defined here, the first letter of each week the canonical string defined here, the first letter of each week
and month MUST be capitalized, and the remaining two letter must and month MUST be capitalized, and the remaining two letters must
be lowercase. This matches the capitalization provided in the be lowercase. This matches the capitalization provided in the
definition of each token. All requests that use the Identity definition of each token. All requests that use the Identity
mechanism MUST contain a Date header. mechanism MUST contain a Date header.
o The addr-spec component of the Contact header field value. If the o The addr-spec component of the Contact header field value. If the
request does not contain a Contact header, this field MUST be request does not contain a Contact header, this field MUST be
empty (i.e., there will be no whitespace between the fourth and empty (i.e., there will be no whitespace between the fourth and
fifth "|" characters in the canonical string). fifth "|" characters in the canonical string).
o The body content of the message with the bits exactly as they are 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). This in the Message (in the ABNF for SIP, the message-body). This
includes all components of multipart message bodies. Note that includes all components of multipart message bodies. Note that
the message-body does NOT include the CRLF separating the SIP the message-body does NOT include the CRLF separating the SIP
headers from the message-body, but does include everything that headers from the message-body, but does include everything that
follows that CRLF. If the message has no body, then message-body follows that CRLF. If the message has no body, then message-body
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o The body content of the message with the bits exactly as they are 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). This in the Message (in the ABNF for SIP, the message-body). This
includes all components of multipart message bodies. Note that includes all components of multipart message bodies. Note that
the message-body does NOT include the CRLF separating the SIP the message-body does NOT include the CRLF separating the SIP
headers from the message-body, but does include everything that headers from the message-body, but does include everything that
follows that CRLF. If the message has no body, then message-body follows that CRLF. If the message has no body, then message-body
will be empty, and the final "|" will not be followed by any will be empty, and the final "|" will not be followed by any
additional characters. additional characters.
For more information on the security properties of these headers, and For more information on the security properties of these headers, and
why their inclusion mitigates replay attacks, see Section 14 and [5]. why their inclusion mitigates replay attacks, see Section 13 and [5].
The precise formulation of this digest-string is, therefore The precise formulation of this digest-string is, therefore
(following the ABNF [6] in RFC3261): (following the ABNF [6] in RFC3261):
digest-string = addr-spec "|" addr-spec "|" callid "|" 1*DIGIT SP method "|" digest-string = addr-spec "|" addr-spec "|" callid "|" 1*DIGIT SP Method "|"
SIP-Date "|" [ addr-spec ] "|" message-body SIP-date "|" [ addr-spec ] "|" message-body
Note again that the first addr-spec MUST be taken from the From 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, the second addr-spec MUST be taken from the To
header field value, and the third addr-spec MUST be taken from the header field value, and the third addr-spec MUST be taken from the
Contact header field value, provided the Contact header is present in Contact header field value, provided the Contact header is present in
the request. the request.
After the digest-string is formed, it MUST be hashed and signed with After the digest-string is formed, it MUST be hashed and signed with
the certificate for the domain. The hashing and signing algorithm is the certificate for the domain. The hashing and signing algorithm is
specified by the 'alg' parameter of the Identity-Info header (see specified by the 'alg' parameter of the Identity-Info header (see
below for more information on Identity-Info header parameters). This below for more information on Identity-Info header parameters). This
document defines only one value for the 'alg' parameter: 'rsa-sha1'; document defines only one value for the 'alg' parameter: 'rsa-sha1';
further values MUST be defined in a Standards Track RFC, see further values MUST be defined in a Standards Track RFC, see
Section 15.6 for more information. It is MANDATORY for all Section 14.7 for more information. All implementations of this
implementations of this specification to support 'rsa-sha1'. When specification MUST support 'rsa-sha1'. When the 'rsa-sha1' algorithm
the 'rsa-sha1' algorithm is specified in the 'alg' parameter of is specified in the 'alg' parameter of Identity-Info, the hash and
Identity-Info, the hash and signature MUST be generated as follows: signature MUST be generated as follows: compute the results of
compute the results of signing this string with sha1WithRSAEncryption signing this string with sha1WithRSAEncryption as described in RFC
as described in RFC 3370 [7] and base64 encode the results as 3370 [7] and base64 encode the results as specified in RFC 3548 [8].
specified in RFC 3548 [8]. A 1024 bit or longer RSA key MUST be A 1024 bit or longer RSA key MUST be used. The result is placed in
used. The result in placed int the Identity header field. For the Identity header field. For detailed examples of the usage of
detailed examples of the usage of this algorithm, see Section 11. this algorithm, see Section 10.
Note on the use of 'rsa-sha1': 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 'absoluteURI' portion of the Identity-Info header MUST contain The 'absoluteURI' portion of the Identity-Info header MUST contain
either an HTTP or HTTPS URI which dereferences to a resource that either an HTTP or HTTPS URI which dereferences to a resource that
contains a single MIME body containing the certificate of the contains a single MIME body containing the certificate of the
authentication service. These URIs MUST follow the conventions of authentication service. These URIs MUST follow the conventions of
RFC2585 [11] and the indicated resource MUST be of the form RFC2585 [10] and the indicated resource MUST be of the form
'application/pkix-cert' described in that specification. Note that 'application/pkix-cert' described in that specification. Note that
this introduces key lifecycle management concerns; were a domain to this introduces key lifecycle management concerns; were a domain to
change the key available at the Identity-Info URI before a verifier change the key available at the Identity-Info URI before a verifier
evaluates a request signed by an authentication service, this would evaluates a request signed by an authentication service, this would
cause obvious verifier failures. When a rollover occurs, cause obvious verifier failures. When a rollover occurs,
authentication services SHOULD thus provide new Identity-Info URIs authentication services SHOULD thus provide new Identity-Info URIs
for each new certificate, and SHOULD continue to make older key for each new certificate, and SHOULD continue to make older key
acquisition URIs available for a duration longer than the plausible acquisition URIs available for a duration longer than the plausible
lifetime of a SIP message (an hour would most likely suffice). lifetime of a SIP message (an hour would most likely suffice).
The Identity-Info header field MUST contain an 'alg' parameter. No The Identity-Info header field MUST contain an 'alg' parameter. No
other parameters are defined for the Identity-Info header in this other parameters are defined for the Identity-Info header in this
document. Future Standards Track RFCs may define additional document. Future Standards Track RFCs may define additional
Identity-Info header parameters. Identity-Info header parameters.
This document adds the following entries to Table 2 of [1]: This document adds the following entries to Table 2 of RFC 3261 [1]:
Header field where proxy ACK BYE CAN INV OPT REG Header field where proxy ACK BYE CAN INV OPT REG
------------ ----- ----- --- --- --- --- --- --- ------------ ----- ----- --- --- --- --- --- ---
Identity R a o o - o o o Identity R a o o - o o o
SUB NOT REF INF UPD PRA SUB NOT REF INF UPD PRA
--- --- --- --- --- --- --- --- --- --- --- ---
o o o o o o o o o o o o
Header field where proxy ACK BYE CAN INV OPT REG Header field where proxy ACK BYE CAN INV OPT REG
skipping to change at page 16, line 15 skipping to change at page 15, line 48
CANCEL method. The CANCEL method cannot be challenged, because it is CANCEL method. The CANCEL method cannot be challenged, because it is
hop-by-hop, and accordingly authentication service behavior for hop-by-hop, and accordingly authentication service behavior for
CANCEL would be significantly limited. Note as well that the CANCEL would be significantly limited. Note as well that the
REGISTER method uses Contact header fields in very unusual ways that REGISTER method uses Contact header fields in very unusual ways that
complicate its applicability to this mechanism, and the use of complicate its applicability to this mechanism, and the use of
Identity with REGISTER is consequently a subject for future study, Identity with REGISTER is consequently a subject for future study,
although it is left as optional here for forward-compatibility although it is left as optional here for forward-compatibility
reasons. The Identity and Identity-Info header MUST NOT appear in reasons. The Identity and Identity-Info header MUST NOT appear in
CANCEL. CANCEL.
11. Compliance Tests and Examples 10. Compliance Tests and Examples
The examples in this section illustrate the use of the Identity The examples in this section illustrate the use of the Identity
header in the context of a SIP transaction. Implementers are advised header in the context of a SIP transaction. Implementers are advised
to verify their compliance with the specification against the to verify their compliance with the specification against the
following criteria: following criteria:
o Implementations of the authentication service role MUST generate o Implementations of the authentication service role MUST generate
identical base64 identity strings to the ones shown in the identical base64 identity strings to the ones shown in the
Identity headers in these examples when presented with the source Identity headers in these examples when presented with the source
message and utilizing the appropriate supplied private key for the message and utilizing the appropriate supplied private key for the
domain in question. domain in question.
o Implementations of the verifier role MUST correctly validate the o Implementations of the verifier role MUST correctly validate the
given messages containing the Identity header when utilizing the given messages containing the Identity header when utilizing the
supplied certificates (with the caveat about self-signed supplied certificates (with the caveat about self-signed
certificates below). certificates below).
Note that the following examples use self-signed certificates, rather Note that the following examples use self-signed certificates, rather
than certificates issued by a recognized certificate authority. The than certificates issued by a recognized certificate authority. The
use of self-signed certificates for this mechanism is NOT use of self-signed certificates for this mechanism is NOT
RECOMMENDED, and it appears here only for illustrative purposes. RECOMMENDED, and it appears here only for illustrative purposes.
Therefore, in compliance testing, implementations of verifiers SHOULD Therefore, in compliance testing, implementations of verifiers SHOULD
generated appropriate warnings about the use of self-signed generate appropriate warnings about the use of self-signed
certificates. Also, the example certificates in this section have certificates. Also, the example certificates in this section have
placed their domain name subject in the subjectAltName field; in placed their domain name subject in the subjectAltName field; in
practice, certificate authorities may place domain names in other practice, certificate authorities may place domain names in other
locations in the certificate (see Section 14.4 for more information). locations in the certificate (see Section 13.4 for more information).
Note that all examples in this section use the 'rsa-sha1' algorithm. Note that all examples in this section use the 'rsa-sha1' algorithm.
Bit-exact reference files for these messages and their various Bit-exact reference files for these messages and their various
transformations are supplied in Appendix B. transformations are supplied in Appendix B.
11.1 Identity-Info with a Singlepart MIME body 10.1. Identity-Info with a Singlepart MIME body
Consider the following private key and certificate pair assigned to Consider the following private key and certificate pair assigned to
'atlanta.example.com'. 'atlanta.example.com' (rendered in OpenSSL format).
-----BEGIN RSA PRIVATE KEY----- -----BEGIN RSA PRIVATE KEY-----
MIICXQIBAAKBgQC8HmM8b9E4WNhb7tZAoBVSkKyV9rAEX3nyQbg4hXte1oW1BxC+ MIICXQIBAAKBgQDPPMBtHVoPkXV+Z6jq1LsgfTELVWpy2BVUffJMPH06LL0cJSQO
43MQHrG3nk6Kc9afPR6VloKwWoUoAcCnbTJ/zEiZ6dq+C5EsQGIOowYkSgqdO2po aIeVzIojzWtpauB7IylZKlAjB5f429tRuoUiedCwMLKblWAqZt6eHWpCNZJ7lONc
joCnRgzgjgvAl41R2J6CE1kMwOQxNCxPnTco8l8UGdKbNLXIuNdUM1MG8QIDAQAB IEwnmh2nAccKk83Lp/VH3tgAS/43DQoX2sndnYh+g8522Pzwg7EGWspzzwIDAQAB
AoGAAtPOGAVyNo+XSOJxE+2UBHaqMWLQyHAK7Coys57F+OnufocJqGTQwOhFMYZO AoGBAK0W3tnEFD7AjVQAnJNXDtx59Aa1Vu2JEXe6oi+OrkFysJjbZJwsLmKtrgtt
leQh0KjhgcwOUMo7gBtuotWQUbbLHTGKXiBR6Pqbm6CvhwJSuNYv0vONuTb1SMll PXOU8t2mZpi0wK4hX4tZhntiwGKkUPC3h9Bjp+GerifP341RMyMO+6fPgjqOzUDw
Kadg43na4B9kQeytn1y6lfkTkK2oYqkDVZ2AAmLSLrfhl1UCQQDp7VFItgmnybwK +rPjjMpwD7AkcEcqDgbTrZnWv/QnCSaaF3xkUGfFkLx5OKcRAkEA7UxnsE8XaT30
PKwJs8gnF+u+K9j+sac/3vgGgrOvpxVqwoMXl6eWN//pZ/cqshanDLmtr9ahjWCD tP/UUc51gNk2KGKgxQQTHopBcew9yfeCRFhvdL7jpaGatEi5iZwGGQQDVOVHUN1H
DxYVyklrAkEAzd6JLJAhG8cZymVCS5Jf0F7FAVxpx0BgRPHwJliyUg6O4jPY+ASg 0YLpHQjRowJBAN+R2bvA/Nimq464ZgnelEDPqaEAZWaD3kOfhS9+vL7oqES+u5E0
cLP6nz9a38wWZQj6rRygffGZHXbBFm+8EwJBAJmZEf5ESSK6+5VdMTlNqubAdjJw J7kXb7ZkiSVUg9XU/8PxMKx/DAz0dUmOL+UCQH8C9ETUMI2uEbqHbBdVUGNk364C
aBMUY1U0+naL66AyfYWUIq+jDI8+RfLkKQ8H0IfvexvokW2SfwSPK1kzcfECQD/O DFcndSxVh+34KqJdjiYSx6VPPv26X9m7S0OydTkSgs3/4ooPxo8HaMqXm80CQB+r
MQW2xgwt8ThhmeKCQ1/5f2WklsRCl5PGyH+aDeqQyIgjOaPlCzTjE1I3+JpUTryR xbB3UlpOohcBwFK9mTrlMB6Cs9ql66KgwnlL9ukEhHHYozGatdXeoBCyhUsogdSU
w9/Td4qRTrtrCv1BNDECQQCgHIzF8LFtI003w9MAEAoCyDbtHFPEj71b+qG22Yc4 6/aSAFcvWEGtj7/vyJECQQCCS1lKgEXoNQPqONalvYhyyMZRXFLdD4gbwRPK1uXK
SPFBAbo3JGO+mrB0MX/GwJr+3DfgzMHaUx/tinPr+u1D Ypk3CkfFzOyfjeLcGPxXzq2qzuHzGTDxZ9PAepwX4RSk
-----END RSA PRIVATE KEY----- -----END RSA PRIVATE KEY-----
-----BEGIN CERTIFICATE----- -----BEGIN CERTIFICATE-----
MIIC/TCCAmagAwIBAgIBADANBgkqhkiG9w0BAQQFADBZMQswCQYDVQQGEwJVUzEQ MIIC3TCCAkagAwIBAgIBADANBgkqhkiG9w0BAQUFADBZMQswCQYDVQQGEwJVUzEL
MA4GA1UECBMHR2VvcmdpYTESMBAGA1UEBxQJQXRsYXQIbnRhMQ0wCwYDVQQKEwRJ MAkGA1UECAwCR0ExEDAOBgNVBAcMB0F0bGFudGExDTALBgNVBAoMBElFVEYxHDAa
RVRGMRUwEwYDVQQLFAxTT0lQCAgISVAgV0cwHhcNMDQwOTEzMTAxMzAzWhcNMDUw BgNVBAMME2F0bGFudGEuZXhhbXBsZS5jb20wHhcNMDUxMDI0MDYzNjA2WhcNMDYx
OTEzMTAxMzAzWjBZMQswCQYDVQQGEwJVUzEQMA4GA1UECBMHR2VvcmdpYTESMBAG MDI0MDYzNjA2WjBZMQswCQYDVQQGEwJVUzELMAkGA1UECAwCR0ExEDAOBgNVBAcM
A1UEBxQJQXRsYXQIbnRhMQ0wCwYDVQQKEwRJRVRGMRUwEwYDVQQLFAxTT0lQCAgI B0F0bGFudGExDTALBgNVBAoMBElFVEYxHDAaBgNVBAMME2F0bGFudGEuZXhhbXBs
SVAgV0cwgZ8wDQYJKoZIhvcNAQEBBQADgY0AMIGJAoGBALweYzxv0ThY2Fvu1kCg ZS5jb20wgZ8wDQYJKoZIhvcNAQEBBQADgY0AMIGJAoGBAM88wG0dWg+RdX5nqOrU
FVKQrJX2sARfefJBuDiFe17WhbUHEL7jcxAesbeeTopz1p89HpWWgrBahSgBwKdt uyB9MQtVanLYFVR98kw8fTosvRwlJA5oh5XMiiPNa2lq4HsjKVkqUCMHl/jb21G6
Mn/MSJnp2r4LkSxAYg6jBiRKCp07amiOgKdGDOCOC8CXjVHYnoITWQzA5DE0LE+d hSJ50LAwspuVYCpm3p4dakI1knuU41wgTCeaHacBxwqTzcun9Ufe2ABL/jcNChfa
NyjyXxQZ0ps0tci411QzUwbxAgMBAAGjgdQwgdEwHQYDVR0OBBYEFGfCU7cNxqSK yd2diH6DznbY/PCDsQZaynPPAgMBAAGjgbQwgbEwHQYDVR0OBBYEFNmU/MrbVYcE
NurvFqz8gj5px8uoMIGBBgNVHSMEejB4gBRnwlO3Dcakijbq7xas/II+acfLqKFd KDr/20WISrG1j1rNMIGBBgNVHSMEejB4gBTZlPzK21WHBCg6/9tFiEqxtY9azaFd
pFswWTELMAkGA1UEBhMCVVMxEDAOBgNVBAgTB0dlb3JnaWExEjAQBgNVBAcUCUF0 pFswWTELMAkGA1UEBhMCVVMxCzAJBgNVBAgMAkdBMRAwDgYDVQQHDAdBdGxhbnRh
bGF0CG50YTENMAsGA1UEChMESUVURjEVMBMGA1UECxQMU09JUAgICElQIFdHggEA MQ0wCwYDVQQKDARJRVRGMRwwGgYDVQQDDBNhdGxhbnRhLmV4YW1wbGUuY29tggEA
MAwGA1UdEwQFMAMBAf8wHgYDVR0RBBcwFYITYXRsYW50YS5leGFtcGxlLmNvbTAN MAwGA1UdEwQFMAMBAf8wDQYJKoZIhvcNAQEFBQADgYEADdQYtswBDmTSTq0mt211
BgkqhkiG9w0BAQQFAAOBgQAc0a/5hU6yqRTxwqoBuRk/iSqDnJD/B0QQnSFLqdjy 7alm/XGFrb2zdbU0vorxRdOZ04qMyrIpXG1LEmnEOgcocyrXRBvq5p6WbZAcEQk0
QV/Pm+aluA05aLRDWq6w/ufwX2HPLOvXYubpnNzjpaWCx3OLr4b5NwnsfNSxtKBJ DsE3Ve0Nc8x9nmvljW7GsMGFCnCuo4ODTf/1lGdVr9DeCzcj10YUQ3MRemDMXhY2
vI9PWwhSW6VMo/cT2llhNudCmN+LXPd/SLy3gnGvXtwcrWAT8MVYmkCUQTRvbWaR CtDisLWl7SXOORcZAi1oU9w=
fQ==
-----END CERTIFICATE----- -----END CERTIFICATE-----
A user of atlanta.example.com, Alice, wants to send an INVITE to A user of atlanta.example.com, Alice, wants to send an INVITE to
bob@biloxi.example.org. She therefore creates the following INVITE bob@biloxi.example.org. She therefore creates the following INVITE
request, which she forwards to the atlanta.example.org proxy server request, which she forwards to the atlanta.example.org proxy server
that instantiates the authentication service role: that instantiates the authentication service role:
INVITE sip:bob@biloxi.exmple.org SIP/2.0 INVITE sip:bob@biloxi.example.org SIP/2.0
Via: SIP/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bKnashds8 Via: SIP/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bKnashds8
To: Bob <sip:bob@biloxi.example.org> To: Bob <sip:bob@biloxi.example.org>
From: Alice <sip:alice@atlanta.example.com>;tag=1928301774 From: Alice <sip:alice@atlanta.example.com>;tag=1928301774
Call-ID: a84b4c76e66710 Call-ID: a84b4c76e66710
CSeq: 314159 INVITE CSeq: 314159 INVITE
Max-Forwards: 70 Max-Forwards: 70
Date: Thu, 21 Feb 2002 13:02:03 GMT Date: Thu, 21 Feb 2002 13:02:03 GMT
Contact: <sip:alice@pc33.atlanta.example.com> Contact: <sip:alice@pc33.atlanta.example.com>
Content-Type: application/sdp Content-Type: application/sdp
Content-Length: 147 Content-Length: 147
v=0 v=0
o=UserA 2890844526 2890844526 IN IP4 pc33.atlanta.example.com o=UserA 2890844526 2890844526 IN IP4 pc33.atlanta.example.com
s=Session SDP s=Session SDP
c=IN IP4 pc33.atlanta.example.com c=IN IP4 pc33.atlanta.example.com
t=0 0 t=0 0
m=audio 49172 RTP/AVP 0 m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000 a=rtpmap:0 PCMU/8000
When the authentication service receives the INVITE, in authenticates When the authentication service receives the INVITE, it authenticates
Alice by sending a 407 response. As a result, Alice adds an Alice by sending a 407 response. As a result, Alice adds an
Authorization header to her request, and resends to the Authorization header to her request, and resends to the
atlanta.example.com authentication service. Now that the service is atlanta.example.com authentication service. Now that the service is
sure of Alice's identity, it calculates an Identity header for the sure of Alice's identity, it calculates an Identity header for the
request. The canonical string over which the identity signature will request. The canonical string over which the identity signature will
be generated is the following (note that the first line wraps because be generated is the following (note that the first line wraps because
of RFC editorial conventions): 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 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 o=UserA 2890844526 2890844526 IN IP4 pc33.atlanta.example.com
s=Session SDP s=Session SDP
c=IN IP4 pc33.atlanta.example.com c=IN IP4 pc33.atlanta.example.com
t=0 0 t=0 0
m=audio 49172 RTP/AVP 0 m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000 a=rtpmap:0 PCMU/8000
The resulting signature (sha1WithRsaEncryption) using the private RSA The resulting signature (sha1WithRsaEncryption) using the private RSA
key given above, with base64 encoding, is the following: key given above, with base64 encoding, is the following:
NJguAbpmYXjnlxFmlOkumMI+MZXjB2iV/NW5xsFQqzD/p4yiovrJBqhd3TZkegns kjOP4YVZXmF0X3/4RUfAG6ffwbVQepNGRBz58b3dJq3prEV4h5GnS4F6udDRCI4/
moHryzk9gTBH7Gj/erixEFIf82o3Anmb+CIbrgdl03gGaD6ICvkpVqoMXZZjdvSp rSK9cl+TFv45nu0Qu2d/0WPPOvvc3JWwuUmHrCwGwC+tW7fOWnC07QKgQn40uwg5
ycyHOhh1cmUx3b9Vr3pZuEh+cB01pbMQ8B1ch++iMjw= 7WaXixQev5N0JfoLXnO3UDoum89JRhXPAIp2vffJbD4=
Accordingly, the atlanta.example.com authentication service will Accordingly, the atlanta.example.com authentication service will
create an Identity header containing that base64 signature string create an Identity header containing that base64 signature string
(175 bytes). It will also add an HTTPS URL where its certificate is (175 bytes). It will also add an HTTPS URL where its certificate is
made available. With those two headers added, the message looks made available. With those two headers added, the message looks
like: like:
INVITE sip:bob@biloxi.exmple.org SIP/2.0 INVITE sip:bob@biloxi.exmple.org SIP/2.0
Via: SIP/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bKnashds8 Via: SIP/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bKnashds8
To: Bob <sip:bob@biloxi.example.org> To: Bob <sip:bob@biloxi.example.org>
From: Alice <sip:alice@atlanta.example.com>;tag=1928301774 From: Alice <sip:alice@atlanta.example.com>;tag=1928301774
Call-ID: a84b4c76e66710 Call-ID: a84b4c76e66710
CSeq: 314159 INVITE CSeq: 314159 INVITE
Max-Forwards: 70 Max-Forwards: 70
Date: Thu, 21 Feb 2002 13:02:03 GMT Date: Thu, 21 Feb 2002 13:02:03 GMT
Contact: <sip:alice@pc33.atlanta.example.com> Contact: <sip:alice@pc33.atlanta.example.com>
Identity:"NJguAbpmYXjnlxFmlOkumMI+MZXjB2iV/NW5xsFQqzD/p4yiovrJBqhd3TZkegn Identity:"kjOP4YVZXmF0X3/4RUfAG6ffwbVQepNGRBz58b3dJq3prEV4h5GnS4F6udDRCI4/
smoHryzk9gTBH7Gj/erixEFIf82o3Anmb+CIbrgdl03gGaD6ICvkpVqoMXZZjdvS rSK9cl+TFv45nu0Qu2d/0WPPOvvc3JWwuUmHrCwGwC+tW7fOWnC07QKgQn40uwg5
pycyHOhh1cmUx3b9Vr3pZuEh+cB01pbMQ8B1ch++iMjw=" 7WaXixQev5N0JfoLXnO3UDoum89JRhXPAIp2vffJbD4="
Identity-Info: <https://atlanta.example.com/cert>;alg=rsa-sha1 Identity-Info: <https://atlanta.example.com/atlanta.cer>;alg=rsa-sha1
Content-Type: application/sdp Content-Type: application/sdp
Content-Length: 147 Content-Length: 147
v=0 v=0
o=UserA 2890844526 2890844526 IN IP4 pc33.atlanta.example.com o=UserA 2890844526 2890844526 IN IP4 pc33.atlanta.example.com
s=Session SDP s=Session SDP
c=IN IP4 pc33.atlanta.example.com c=IN IP4 pc33.atlanta.example.com
t=0 0 t=0 0
m=audio 49172 RTP/AVP 0 m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000 a=rtpmap:0 PCMU/8000
atlanta.example.com then forwards the request normally. When Bob atlanta.example.com then forwards the request normally. When Bob
receives the request, if he does not already know the certificate of receives the request, if he does not already know the certificate of
atlanta.example.com, he de-references the URL the Identity-Info atlanta.example.com, he de-references the URL in the Identity-Info
header to acquire the certificate. Bob then generates the same header to acquire the certificate. Bob then generates the same
canonical string given above, from the same headers of the SIP canonical string given above, from the same headers of the SIP
request. Using this canonical string, the signed digest in the request. Using this canonical string, the signed digest in the
Identity header, and the certificate discovered by de-referencing the Identity header, and the certificate discovered by de-referencing the
Identity-Info header, Bob can verify that the given set of headers Identity-Info header, Bob can verify that the given set of headers
and the message body have not been modified. and the message body have not been modified.
11.2 Identity for a Request with no MIME body or Contact 10.2. Identity for a Request with no MIME body or Contact
Consider the following private key and certificate pair assigned to Consider the following private key and certificate pair assigned to
"biloxi.example.org". "biloxi.example.org".
-----BEGIN RSA PRIVATE KEY----- -----BEGIN RSA PRIVATE KEY-----
MIICXQIBAAKBgQDDIREMIIS9vBBET2FFHss2Lbwri/nK+AMoUZ74UT3amG/bYgDn MIICXgIBAAKBgQC/obBYLRMPjskrAqWOiGPAUxI3/m2ti7ix4caqCTAuFX5cLegQ
H86eUUEjGfV3cfXErFXSnI86sUALoKjjwGYBoiUuaMhyerZyF+D9St2plnBeq6fq 7nmquLOHfIhxVIqT2f06UA0lOo2NVofK9G7MTkVbVNiyAlLYUDEj7XWLDICf3ZHL
rbaPpL6bvIAF636/O2+GFP3LSLj6KS4HQwnsaUBr2YzykBD05PfwrH28VQIDAQAB 6Fr/+CF7wrQ9r4kv7XiJKxodVCCd/DhCT9Gp+VDoe8HymqOW/KsneriyIwIDAQAB
AoGAZLRJFwglWcKYZpjNK54T5HdAGP1Zwo2zG3jcYW2UTZ/EguWWb7HzsbNfuZzp AoGBAJ7fsFIKXKkjWgj8ksGOthS3Sn19xPSCyEdBxfEm2Pj7/Nzzeli/PcOaic0k
GWcgHwuOE28nYHQgCKA26avfOGuebFHz2WLAFC3TCOVjMzJEWawtxIc7oX9vziTF JALBcnqN2fHEeIGK/9xUBxTufgQYVJqvyHERs6rXX/iT4Ynm9t1905EiQ9ZpHsrI
1Uk2K4ccK2zdJlPI46fHjJrI2xXKZWkxVNkZ8LeMspckUqECQQDqhD0SoLXoRGks /AMMUYA1QrGgAIHvZLVLzq+9KLDEZ+HQbuCLJXF+6bl0Eb5BAkEA636oMANp0Qa3
h7byNZAMR5PfZTpHli7uFg9O+GoLtxQNE/rW6JPVcVkpCvs8oPPUu+1D7dHnyFiO mYWEQ2utmGsYxkXSfyBb18TCOwCty0ndBR24zyOJF2NbZS98Lz+Ga25hfIGw/JHK
heyme35tAkEA1QEiny94KRtTuP/WEyyYUkRfltYjrAX1BC73Xu395cNwjvnNw7qI nD9bOE88UwJBANBRSpd4bmS+m48R/13tRESAtHqydNinX0kS/RhwHr7mkHTU3k/M
f2dFUm5akGijk9UtL1qNxg+akBgJXkbkiQJAXbUHXkkfRrcHO4bjIDcs3us++BXP FxQtx34I3GKzaZxMn0A66KS9v/SHdnF+ePECQQCGe7QshyZ8uitLPtZDclCWhEKH
yskE6Zeg+FIktZerCGrCYVs/rxsCoHbF2v0JUSjibrE5nZ8dW53B6OgRpQJBAKfr qAQHmUEZvUF2VHLrbukLLOgHUrHNa24cILv4d3yaCVUetymNcuyTwhKj24wFAkAO
9zFrqN0vT/eeqVQAai0g/gLZ2tF4+MpNhHLwSKNkSk5NHSxa19UowvvTR85kz+Bx z/jx1EplN3hwL+NsllZoWI58uvu7/Aq2c3czqaVGBbb317sHCYgKk0bAG3kwO3mi
xOd6Ch7EmmNSr8AFP5ECQQDOXmjIecxNI51of9u6g4T2ITRcHTYyCqWLO6VqAWlD 93/LXWT1cdiYVpmBcHDBAkEAmpgkFj+xZu5gWASY5ujv+FCMP0WwaH5hTnXu+tKe
G6ej+6/h+8DQyfJKMNbfMCGjZ7xZC3isNMmFibGQTLZD PJ3d2IJZKxGnl6itKRN7GeRh9PSK0kZSqGFeVrvsJ4Nopg==
-----END RSA PRIVATE KEY----- -----END RSA PRIVATE KEY-----
-----BEGIN CERTIFICATE----- -----BEGIN CERTIFICATE-----
MIIC7DCCAlWgAwIBAgIBADANBgkqhkiG9w0BAQQFADBUMQswCQYDVQQGEwJVUzEU MIIC1jCCAj+gAwIBAgIBADANBgkqhkiG9w0BAQUFADBXMQswCQYDVQQGEwJVUzEL
MBIGA1UECBMLTWlzc2lzc2lwcGkxDzANBgNVBAcTBkJpbG94aTENMAsGA1UEChME MAkGA1UECAwCTVMxDzANBgNVBAcMBkJpbG94aTENMAsGA1UECgwESUVURjEbMBkG
SUVURjEPMA0GA1UECxMGU0lQIFdHMB4XDTA0MDkxMzEwMzg1NVoXDTA1MDkxMzEw A1UEAwwSYmlsb3hpLmV4YW1wbGUuY29tMB4XDTA1MTAyNDA2NDAyNloXDTA2MTAy
Mzg1NVowVDELMAkGA1UEBhMCVVMxFDASBgNVBAgTC01pc3Npc3NpcHBpMQ8wDQYD NDA2NDAyNlowVzELMAkGA1UEBhMCVVMxCzAJBgNVBAgMAk1TMQ8wDQYDVQQHDAZC
VQQHEwZCaWxveGkxDTALBgNVBAoTBElFVEYxDzANBgNVBAsTBlNJUCBXRzCBnzAN aWxveGkxDTALBgNVBAoMBElFVEYxGzAZBgNVBAMMEmJpbG94aS5leGFtcGxlLmNv
BgkqhkiG9w0BAQEFAAOBjQAwgYkCgYEAwyERDCCEvbwQRE9hRR7LNi28K4v5yvgD bTCBnzANBgkqhkiG9w0BAQEFAAOBjQAwgYkCgYEAv6GwWC0TD47JKwKljohjwFMS
KFGe+FE92phv22IA5x/OnlFBIxn1d3H1xKxV0pyPOrFAC6Co48BmAaIlLmjIcnq2 N/5trYu4seHGqgkwLhV+XC3oEO55qrizh3yIcVSKk9n9OlANJTqNjVaHyvRuzE5F
chfg/UrdqZZwXqun6q22j6S+m7yABet+vztvhhT9y0i4+ikuB0MJ7GlAa9mM8pAQ W1TYsgJS2FAxI+11iwyAn92Ry+ha//ghe8K0Pa+JL+14iSsaHVQgnfw4Qk/RqflQ
9OT38Kx9vFUCAwEAAaOBzTCByjAdBgNVHQ4EFgQUlZRLaS3Zm/b0xWcq7TSnQMHM 6HvB8pqjlvyrJ3q4siMCAwEAAaOBsTCBrjAdBgNVHQ4EFgQU0Z+RL47W/APDtc5B
7w8wfAYDVR0jBHUwc4AUlZRLaS3Zm/b0xWcq7TSnQMHM7w+hWKRWMFQxCzAJBgNV fSoQXuEFE/wwfwYDVR0jBHgwdoAU0Z+RL47W/APDtc5BfSoQXuEFE/yhW6RZMFcx
BAYTAlVTMRQwEgYDVQQIEwtNaXNzaXNzaXBwaTEPMA0GA1UEBxMGQmlsb3hpMQ0w CzAJBgNVBAYTAlVTMQswCQYDVQQIDAJNUzEPMA0GA1UEBwwGQmlsb3hpMQ0wCwYD
CwYDVQQKEwRJRVRGMQ8wDQYDVQQLEwZTSVAgV0eCAQAwDAYDVR0TBAUwAwEB/zAd VQQKDARJRVRGMRswGQYDVQQDDBJiaWxveGkuZXhhbXBsZS5jb22CAQAwDAYDVR0T
BgNVHREEFjAUghJiaWxveGkuZXhhbXBsZS5vcmcwDQYJKoZIhvcNAQEEBQADgYEA BAUwAwEB/zANBgkqhkiG9w0BAQUFAAOBgQBiyKHIt8TXfGNfpnJXi5jCizOxmY8Y
SufJHtereahZlkE5ssRRZRd/erLpEe2uUfHnTOydPBKOkvhVG4Vr4aoroPlE7gJK gln8tyPFaeyq95TGcvTCWzdoBLVpBD+fpRWrX/II5sE6VHbbAPjjVmKbZwzQAtpp
a/2BF9bohwAUSC5j5q3nvuhUcoK9XZYm2nLkN3IAhCU6oswVBJAxLanGUCjR5sxS P2Fauj28t94ZeDHN2vqzjfnHjCO24kG3Juf2T80ilp9YHcDwxjUFrt86UnlC+yid
HfGhGsqLmTEQ22HsrtLo68IYiwftXcLZbep50gRVX6c= yaTeusW5Gu7v1g==
-----END CERTIFICATE----- -----END CERTIFICATE-----
Bob (bob@biloxi.example.org) now wants to send a BYE request to Alice 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 at the end of the dialog initiated in the previous example. He
therefore creates the following BYE request which he forwards to the therefore creates the following BYE request which he forwards to the
'biloxi.example.org' proxy server that instantiates the 'biloxi.example.org' proxy server that instantiates the
authentication service role: authentication service role:
BYE sip:alice@pc33.atlanta.example.com SIP/2.0 BYE sip:alice@pc33.atlanta.example.com SIP/2.0
Via: SIP/2.0/TLS 192.0.2.4;branch=z9hG4bKnashds10 Via: SIP/2.0/TLS 192.0.2.4;branch=z9hG4bKnashds10
skipping to change at page 21, line 29 skipping to change at page 21, line 29
To: Alice <sip:alice@atlanta.example.com>;tag=1928301774 To: Alice <sip:alice@atlanta.example.com>;tag=1928301774
Date: Thu, 21 Feb 2002 14:19:51 GMT Date: Thu, 21 Feb 2002 14:19:51 GMT
Call-ID: a84b4c76e66710 Call-ID: a84b4c76e66710
CSeq: 231 BYE CSeq: 231 BYE
Content-Length: 0 Content-Length: 0
Also note that this request contains no Contact header field. Also note that this request contains no Contact header field.
Accordingly, biloxi.example.org will place no value in the canonical Accordingly, biloxi.example.org will place no value in the canonical
string for the addr-spec of the Contact address. Also note that string for the addr-spec of the Contact address. Also note that
there is no message body, and accordingly, the signature string will there is no message body, and accordingly, the signature string will
terminate, in this case, with two colons. The canonical string over terminate, in this case, with two vertical bars. The canonical
which the identity signature will be generated is the following (note string over which the identity signature will be generated is the
that the first line wraps because of RFC editorial conventions): 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|| 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 The resulting signature (sha1WithRsaEncryption) using the private RSA
key given above for biloxi.example.org, with base64 encoding, is the key given above for biloxi.example.org, with base64 encoding, is the
following: following:
kJl0ILrbzGtQX4zW4GlPo5DELq1hYXgfvI77xeQ1H7mXblNJBf6cLE0JAnRiDMp+ vvXEPaukq60Jd1M7Ag0CeCiI0cGfgV0uAyJA7UdpkT82E1TkWFJhc8DTDV5xnafv
tbwSi9tj7JoknqeZAXtj5czqAKskj7axdYfe40basFy34HhNVc3WH2c3TwAlqbrm wKtekBNpfc0sbW2gfK7i/FRMNLuYOIk9aH9Oc+GhvR5J+m1uw1e2WBSYXH3FQJKM
kspEbEWUnBnIRXjnihQ3Pi5rHwUVkKPdogI26IqRgQE= p94gYvRM3hD0P081WBGgxXlaN5LFplIKE25n4FzLhBc=
Accordingly, the biloxi.example.org authentication service will Accordingly, the biloxi.example.org authentication service will
create an Identity header containing that base64 signature string. create an Identity header containing that base64 signature string.
It will also add an HTTPS URL where its certificate is made It will also add an HTTPS URL where its certificate is made
available. With those two headers added, the message looks like: available. With those two headers added, the message looks like:
BYE sip:alice@pc33.atlanta.example.com SIP/2.0 BYE sip:alice@pc33.atlanta.example.com SIP/2.0
Via: SIP/2.0/TLS 192.0.2.4;branch=z9hG4bKnashds10 Via: SIP/2.0/TLS 192.0.2.4;branch=z9hG4bKnashds10
Max-Forwards: 70 Max-Forwards: 70
From: Bob <sip:bob@biloxi.example.org>;tag=a6c85cf From: Bob <sip:bob@biloxi.example.org>;tag=a6c85cf
To: Alice <sip:alice@atlanta.example.com>;tag=1928301774 To: Alice <sip:alice@atlanta.example.com>;tag=1928301774
Date: Thu, 21 Feb 2002 14:19:51 GMT Date: Thu, 21 Feb 2002 14:19:51 GMT
Call-ID: a84b4c76e66710 Call-ID: a84b4c76e66710
CSeq: 231 BYE CSeq: 231 BYE
Identity: "kJl0ILrbzGtQX4zW4GlPo5DELq1hYXgfvI77xeQ1H7mXblNJBf6cLE0JAnRiDMp Identity: "vvXEPaukq60Jd1M7Ag0CeCiI0cGfgV0uAyJA7UdpkT82E1TkWFJhc8DTDV5xnafv
+tbwSi9tj7JoknqeZAXtj5czqAKskj7axdYfe40basFy34HhNVc3WH2c3TwAlqbr wKtekBNpfc0sbW2gfK7i/FRMNLuYOIk9aH9Oc+GhvR5J+m1uw1e2WBSYXH3FQJKM
mkspEbEWUnBnIRXjnihQ3Pi5rHwUVkKPdogI26IqRgQE=" p94gYvRM3hD0P081WBGgxXlaN5LFplIKE25n4FzLhBc="
Identity-Info: <https://biloxi.example.org/cert>;alg=rsa-sha1 Identity-Info: <https://biloxi.example.org/biloxi.cer>;alg=rsa-sha1
Content-Length: 0 Content-Length: 0
biloxi.example.org then forwards the request normally. biloxi.example.org then forwards the request normally.
12. Identity and the TEL URI Scheme 11. Identity and the TEL URI Scheme
Since many SIP applications provide a VoIP service, telephone numbers Since many SIP applications provide a VoIP service, telephone numbers
are commonly used as identities in SIP deployments. In the majority are commonly used as identities in SIP deployments. In the majority
of cases, this is not problematic for the identity mechanism of cases, this is not problematic for the identity mechanism
described in this document. Telephone numbers commonly appear in the described in this document. Telephone numbers commonly appear in the
username portion of a SIP URI (e.g., username portion of a SIP URI (e.g.,
'sip:+17005551008@chicago.example.com;user=phone'). That username 'sip:+17005551008@chicago.example.com;user=phone'). That username
conforms to the syntax of the TEL URI scheme (RFC3966 [12]). For conforms to the syntax of the TEL URI scheme (RFC3966 [13]). For
this sort of SIP address-of-record, chicago.example.com is the this sort of SIP address-of-record, chicago.example.com is the
appropriate signatory. appropriate signatory.
It is also possible for a TEL URI to appear in the SIP To or From 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., header field outside the context of a SIP or SIPS URI (e.g.,
'tel:+17005551008'). In this case, it is much less clear which 'tel:+17005551008'). In this case, it is much less clear which
signatory is appropriate for the identity. Fortunately for the signatory is appropriate for the identity. Fortunately for the
identity mechanism, this form of the TEL URI is more common 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, 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 since the UAC has no option but to provide a TEL URI alone when the
skipping to change at page 23, line 4 skipping to change at page 23, line 5
in TEL URI form. Implementations that intend to send their requests in TEL URI form. Implementations that intend to send their requests
through an authentication service SHOULD put telephone numbers in the through an authentication service SHOULD put telephone numbers in the
From header field into SIP or SIPS URIs whenever possible. From header field into SIP or SIPS URIs whenever possible.
If the local domain is unknown to a UAC formulating a request, it 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 most likely will not be able to locate an authentication service for
its request, and therefore the question of providing identity in its request, and therefore the question of providing identity in
these cases is somewhat moot. However, an authentication service MAY these cases is somewhat moot. However, an authentication service MAY
sign a request containing a TEL URI in the From header field. This sign a request containing a TEL URI in the From header field. This
is permitted in this specification strictly for forward compatibility is permitted in this specification strictly for forward compatibility
purposes. In the longer-term, it is possible that ENUM [13] may purposes. In the longer-term, it is possible that ENUM [14] may
provide a way to determine which administrative domain is responsible provide a way to determine which administrative domain is responsible
for a telephone number, and this may aid in the signing and for a telephone number, and this may aid in the signing and
verification of SIP identities that contain telephone numbers. This verification of SIP identities that contain telephone numbers. This
is a subject for future work. is a subject for future work.
13. Privacy Considerations 12. Privacy Considerations
The identity mechanism presented in this draft is compatible with the The identity mechanism presented in this draft is compatible with the
standard SIP practices for privacy described in RFC3323 [3]. A SIP standard SIP practices for privacy described in RFC3323 [3]. A SIP
proxy server can act both as a privacy service and as an proxy server can act both as a privacy service and as an
authentication service. Since a user agent can provide any From authentication service. Since a user agent can provide any From
header field value which the authentication service is willing to header field value which the authentication service is willing to
authorize, there is no reason why private SIP URIs which contain authorize, there is no reason why private SIP URIs which contain
legitimate domains (e.g., sip:anonymous@example.com) cannot be signed legitimate domains (e.g., sip:anonymous@example.com) cannot be signed
by an authentication service. The construction of the Identity by an authentication service. The construction of the Identity
header is the same for private URIs as it is for any other sort of header is the same for private URIs as it is for any other sort of
URIs. URIs.
Note, however, that an authentication service must possess a Note, however, that an authentication service must possess a
certificate corresponding to the host portion of the addr-spec of the certificate corresponding to the host portion of the addr-spec of the
From header field of any request that it signs; accordingly, using From header field of any request that it signs; accordingly, using
domains like 'invalid.net' will not be possible for privacy services domains like 'anonymous.invalid' will not be possible for privacy
that also act as authentication services. The assurance offered by services that also act as authentication services. The assurance
the usage of anonymous URIs with a valid domain portion is "this is a offered by the usage of anonymous URIs with a valid domain portion is
known user in my domain that I have authenticated, but I am keeping "this is a known user in my domain that I have authenticated, but I
their identity private". The use of the domain 'invalid.net' implies am keeping their identity private". The use of the domain
that no corresponding authority for the domain can exist, and as a 'anonymous.invalid' entails that no corresponding authority for the
consequence, authentication service functions are meaningless. domain can exist, and as a consequence, authentication service
functions are meaningless.
The "header" level of privacy described in RFC3323 requests that a The "header" level of privacy described in RFC3323 requests that a
privacy service to alter the Contact header field value of a SIP privacy service to alter the Contact header field value of a SIP
message. Since the Contact header field is protected by the message. Since the Contact header field is protected by the
signature in an Identity header, privacy services cannot be applied signature in an Identity header, privacy services cannot be applied
after authentication services without a resulting integrity after authentication services without a resulting integrity
violation. violation.
RFC3325 [10] defines the "id" priv-value token which is specific to RFC3325 [12] 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. The sort of assertion provided by
the P-Asserted-Identity header is very different from the Identity the P-Asserted-Identity header is very different from the Identity
header presented in this document. It contains additional header presented in this document. It contains additional
information about the sender of a message that may go beyond what information about the sender of a message that may go beyond what
appears in the From header field; P-Asserted-Identity holds a appears in the From header field; P-Asserted-Identity holds a
definitive identity for the sender which is somehow known to a closed definitive identity for the sender which is somehow known to a closed
network of intermediaries that presumably the network will use this network of intermediaries that presumably the network will use this
identity for billing or security purposes. The danger of this identity for billing or security purposes. The danger of this
network-specific information leaking outside of the closed network network-specific information leaking outside of the closed network
motivated the "id" priv-value token. The "id" priv-value token has motivated the "id" priv-value token. The "id" priv-value token has
no implications for the Identity header, and privacy services MUST no implications for the Identity header, and privacy services MUST
NOT remove the Identity header when a priv-value of "id" appears in a NOT remove the Identity header when a priv-value of "id" appears in a
Privacy header. Privacy header.
Finally, note that unlike RFC3325, the mechanism described in this Finally, note that unlike RFC3325, the mechanism described in this
specification adds no information to SIP requests that has privacy specification adds no information to SIP requests that has privacy
implications. implications.
14. Security Considerations 13. Security Considerations
14.1 Handling of digest-string Elements 13.1. Handling of digest-string Elements
This document describes a mechanism which provides a signature over This document describes a mechanism which provides a signature over
the Contact, Date, Call-ID, CSeq, To, and From header fields of SIP the Contact, Date, Call-ID, CSeq, To, and From header fields of SIP
requests. While a signature over the From header field would be requests. While a signature over the From header field would be
sufficient to secure a URI alone, the additional headers provide sufficient to secure a URI alone, the additional headers provide
replay protection and reference integrity necessary to make sure that replay protection and reference integrity necessary to make sure that
the Identity header will not be used in cut-and-paste attacks. In the Identity header will not be used in cut-and-paste attacks. In
general, the considerations related to the security of these headers general, the considerations related to the security of these headers
are the same as those given in RFC3261 for including headers in are the same as those given in RFC3261 for including headers in
tunneled 'message/sip' MIME bodies (see Section 23 in particular). tunneled 'message/sip' MIME bodies (see Section 23 in particular).
The following section details the individual security properties
obtained by including each of these header fields within the
signature; collectively, this set of header fields provides the
necessary properties to prevent impersonation.
The From header field indicates the identity of the sender of the 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 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. 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 The To header field provides the identity of the SIP user that this
request targets. Providing the To header field in the Identity request targets. Providing the To header field in the Identity
signature serves two purposes: first, it prevents replay attacks in signature serves two purposes: first, it prevents cut-and-paste
which an Identity header from legitimate request for one user is cut- attacks in which an Identity header from legitimate request for one
and-pasted into a request for a different user; second, it preserves user is cut-and-pasted into a request for a different user; second,
the starting URI scheme of the request, which helps prevent downgrade it preserves the starting URI scheme of the request, which helps
attacks against the use of SIPS. prevent downgrade attacks against the use of SIPS.
The Date and Contact headers provide reference integrity and replay The Date and Contact headers provide reference integrity and replay
protection, as described in RFC3261 Section 23.4.2. Implementations protection, as described in RFC3261 Section 23.4.2. Implementations
of this specification MUST NOT deem valid a request with an outdated of this specification MUST NOT deem valid a request with an outdated
Date header field (the RECOMMENDED interval is that the Date header Date header field (the RECOMMENDED interval is that the Date header
must indicate a time within 3600 seconds of the receipt of a must indicate a time within 3600 seconds of the receipt of a
message). Implementations MUST also record Call-IDs received in message). Implementations MUST also record Call-IDs received in
valid requests containing an Identity header, and MUST remember those valid requests containing an Identity header, and MUST remember those
Call-IDs for at least the duration of a single Date interval (i.e. Call-IDs for at least the duration of a single Date interval (i.e.
commonly 3600 seconds). This result of this is that if an Identity commonly 3600 seconds). Because a SIP-compliant UA never generates
header is replayed within the Date interval, verifiers will recognize the same Call-ID twice, verifiers can use the Call-ID to recognize
that it is invalid because of a Call-ID duplication; if an Identity cut-and-paste attacks; the Call-ID serves as a nonce. The result of
header is replayed after the Date interval, verifiers will recognize this is that if an Identity header is replayed within the Date
that it is invalid because the Date is stale. The CSeq header field interval, verifiers will recognize that it is invalid because of a
contains a numbered identifier for the transaction, and the name of Call-ID duplication; if an Identity header is replayed after the Date
the method of the request; without this information, an INVITE interval, verifiers will recognize that it is invalid because the
request could be cut-and-pasted by an attacker and transformed into a Date is stale. The CSeq header field contains a numbered identifier
BYE request without changing any fields covered by the Identity for the transaction, and the name of the method of the request;
header, and moreover requests within a certain transaction could be without this information, an INVITE request could be cut-and-pasted
replayed in potentially confusing or malicious ways. 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.
The Contact header field is included to tie the Identity header to a The Contact header field is included to tie the Identity header to a
particular user agent instance that generated the request. Were an particular user agent instance that generated the request. Were an
active attacker to intercept a request containing an Identity header, active attacker to intercept a request containing an Identity header,
and cut-and-paste the Identity header field into their own request and cut-and-paste the Identity header field into their own request
(reusing the From, To, Contact, Date and Call-ID fields that appear (reusing the From, To, Contact, Date and Call-ID fields that appear
in the original message), they would not be eligible to receive SIP in the original message), they would not be eligible to receive SIP
requests from the called user agent, since those requests are routed requests from the called user agent, since those requests are routed
to the URI identified in the Contact header field. However, the to the URI identified in the Contact header field. However, the
Contact header is only included in dialog-forming requests, so it Contact header is only included in dialog-forming requests, so it
skipping to change at page 25, line 46 skipping to change at page 26, line 9
proper operation of SIP for subsequent intermediaries to be capable proper operation of SIP for subsequent intermediaries to be capable
of inserting such Via header fields, and thus it cannot be prevented. of inserting such Via header fields, and thus it cannot be prevented.
As such, though it is desirable, securing Via is not possible through As such, though it is desirable, securing Via is not possible through
the sort of identity mechanism described in this document; the best the sort of identity mechanism described in this document; the best
known practice for securing Via is the use of SIPS. known practice for securing Via is the use of SIPS.
This mechanism also provides a signature over the bodies of SIP This mechanism also provides a signature over the bodies of SIP
requests. The most important reason for doing so is to protect SDP requests. The most important reason for doing so is to protect SDP
bodies carried in SIP requests. There is little purpose in bodies carried in SIP requests. There is little purpose in
establishing the identity of the user that originated a SIP request establishing the identity of the user that originated a SIP request
if this assurance is not coupled a comparable assurance over the if this assurance is not coupled with a comparable assurance over the
media descriptors. Note however that this is not perfect end-to-end media descriptors. Note however that this is not perfect end-to-end
security. The authentication service itself, when instantiated at a security. The authentication service itself, when instantiated at a
intermediary, could conceivably change the SDP (and SIP headers, for intermediary, could conceivably change the SDP (and SIP headers, for
that matter) before providing a signature. Thus, while this that matter) before providing a signature. Thus, while this
mechanism reduces the chance that a replayer or man-in-the-middle mechanism reduces the chance that a replayer or man-in-the-middle
will modify SDP, it does not eliminate it entirely. Since it is a will modify SDP, it does not eliminate it entirely. Since it is a
foundational assumption of this mechanism that the user trusts their foundational assumption of this mechanism that the user trusts their
local domain to vouch for their security, they must also trust the local domain to vouch for their security, they must also trust the
service not to violate the integrity of their message without good service not to violate the integrity of their message without good
reason. Note that RFC3261 16.6 states that SIP proxy servers "MUST reason. Note that RFC3261 16.6 states that SIP proxy servers "MUST
skipping to change at page 26, line 33 skipping to change at page 26, line 44
header field. This mechanism provides a way that an authorized user header field. This mechanism provides a way that an authorized user
can provide a definitive assurance of their identity which an can provide a definitive assurance of their identity which an
unauthorized user, an impersonator, cannot. unauthorized user, an impersonator, cannot.
One additional respect in which the Identity-Info header cannot One additional respect in which the Identity-Info header cannot
protect itself is the 'alg' parameter. The 'alg' parameter is not protect itself is the 'alg' parameter. The 'alg' parameter is not
included in the digest-string, and accordingly, a man-in-the-middle included in the digest-string, and accordingly, a man-in-the-middle
might attempt to modify the 'alg' parameter. However, it is might attempt to modify the 'alg' parameter. However, it is
important to note that preventing men-in-the-middle is not the important to note that preventing men-in-the-middle is not the
primary impetus for this mechanism. Moreover, changing the 'alg' primary impetus for this mechanism. Moreover, changing the 'alg'
would merely result in a failure at the verifier. Numerous changes would at worst result in some sort of bid-down attack, and at best
that a man-in-the-middle might make would have the same effect. As cause a failure in the verifier. Note that only one valid 'alg'
such, 'alg' does not seem to introduce any new security parameter is defined in this document, and that thus there is
considerations for this mechanism. currently no weaker algorithm to which the mechanism can be bid-down.
'alg' has been incorporated into this mechanism for forward-
compatibility reasons in case the current algorithm exhibits
weaknesses, and requires swift replacement, in the future.
14.2 Display Names and Identity 13.2. Display Names and Identity
As a matter of interface design, SIP user agents might render the As a matter of interface design, SIP user agents might render the
display-name portion of the From header field of a caller as the display-name portion of the From header field of a caller as the
identity of the caller; there is a significant precedent in email identity of the caller; there is a significant precedent in email
user interfaces for this practice. As such, it might seem that the user interfaces for this practice. As such, it might seem that the
lack of a signature over the display-name is a significant omission. lack of a signature over the display-name is a significant omission.
However, there are several important senses in which a signature over However, there are several important senses in which a signature over
the display-name does not prevent impersonation. In the first place, the display-name does not prevent impersonation. In the first place,
a particular display-name, like "Jon Peterson", is not unique in the a particular display-name, like "Jon Peterson", is not unique in the
world; many users in different administrative domains might world; many users in different administrative domains might
legitimately claim that name. Furthermore, enrollment practices for legitimately claim that name. Furthermore, enrollment practices for
SIP-based services might have a difficult term discerning the SIP-based services might have a difficult time discerning the
legitimate display-name for a user; it is safe to assume that legitimate display-name for a user; it is safe to assume that
impersonators will be capable of creating SIP accounts with impersonators will be capable of creating SIP accounts with
arbitrarily display-names. The same situation prevails in email arbitrarily display-names. The same situation prevails in email
today. Note that an impersonator who attempted to replay a message today. Note that an impersonator who attempted to replay a message
with an Identity header, changing only the display-name in the From with an Identity header, changing only the display-name in the From
header field, would be detected by the other replay protection header field, would be detected by the other replay protection
mechanisms described in Section 14.1. mechanisms described in Section 13.1.
Of course, an authentication service can enforce policies about the Of course, an authentication service can enforce policies about the
display-name even if the display-name is not signed. The exact display-name even if the display-name is not signed. The exact
mechanics for creating and operationalizing such policies is outside mechanics for creating and operationalizing such policies is outside
the scope of this document. The effect of this policy would not be the scope of this document. The effect of this policy would not be
to prevent impersonation of a particular unique identifier like a SIP to prevent impersonation of a particular unique identifier like a SIP
URI (since display-names are not unique identifiers), but to allow a URI (since display-names are not unique identifiers), but to allow a
domain to manage the claims made by its users. If such policies are domain to manage the claims made by its users. If such policies are
enforced, users would not be free to claim any display-name of their enforced, users would not be free to claim any display-name of their
choosing. In the absence of a signature, man-in-the-middle attackers choosing. In the absence of a signature, man-in-the-middle attackers
skipping to change at page 27, line 37 skipping to change at page 28, line 5
name aren't feasible. Distributing bit-exact and internationalizable name aren't feasible. Distributing bit-exact and internationalizable
display-names to end users as part of the enrollment or registration display-names to end users as part of the enrollment or registration
process would require mechanisms that are not explored in this process would require mechanisms that are not explored in this
document. In the absence of policy enforcement regarding domain document. In the absence of policy enforcement regarding domain
names, there are conceivably attacks that an adversary could mount names, there are conceivably attacks that an adversary could mount
against SIP systems that rely too heavily on the display-name in against SIP systems that rely too heavily on the display-name in
their user interface, but this argues for intelligent interface their user interface, but this argues for intelligent interface
design, not changes to the mechanisms. Relying on a non-unique design, not changes to the mechanisms. Relying on a non-unique
identifier for identity would ultimately result in a weak mechanism. identifier for identity would ultimately result in a weak mechanism.
14.3 Securing the Connection to the Authentication Service 13.3. Securing the Connection to the Authentication Service
The assurance provided by this mechanism is strongest when a user The assurance provided by this mechanism is strongest when a user
agent forms a direct connection, preferably one secured by TLS, to an agent forms a direct connection, preferably one secured by TLS, to an
intermediary-based authentication service. The reasons for this are intermediary-based authentication service. The reasons for this are
twofold: twofold:
If a user does not receive a certificate from the authentication If a user does not receive a certificate from the authentication
service over this TLS connection that corresponds to the expected service over this TLS connection that corresponds to the expected
domain (especially when they receive a challenge via a mechanism domain (especially when they receive a challenge via a mechanism
such as Digest), then it is possible that a rogue server is such as Digest), then it is possible that a rogue server is
attempting to pose as a authentication service for a domain that attempting to pose as an authentication service for a domain that
it does not control, possibly in an attempt to collect shared it does not control, possibly in an attempt to collect shared
secrets for that domain. secrets for that domain.
Without TLS, the various header field values and the body of the Without TLS, the various header field values and the body of the
request will not have integrity protection into the request request will not have integrity protection with the request
arrives at an authentication service. Accordingly, a prior arrives at an authentication service. Accordingly, a prior
legitimate or illegitimate intermediary could modify the message legitimate or illegitimate intermediary could modify the message
arbitrarily. arbitrarily.
Of these two concerns, the first is most material to the intended Of these two concerns, the first is most material to the intended
scope of this mechanism. This mechanism is intended to prevent scope of this mechanism. This mechanism is intended to prevent
impersonation attacks, not man-in-the-middle attacks; integrity over impersonation attacks, not man-in-the-middle attacks; integrity over
the header and bodies is provided by this mechanism only to prevent the header and bodies is provided by this mechanism only to prevent
replay attacks. However, it is possible that applications relying on replay attacks. However, it is possible that applications relying on
the presence of the Identity header could leverage this integrity the presence of the Identity header could leverage this integrity
protection, especially body integrity, for services other than replay protection, especially body integrity, for services other than replay
protection. protection.
Accordingly, direct TLS connections SHOULD be used between the UAC Accordingly, direct TLS connections SHOULD be used between the UAC
and the authentication service whenever possible. The opportunistic and the authentication service whenever possible. The opportunistic
nature of this mechanism, however, makes it very difficult to nature of this mechanism, however, makes it very difficult to
constrain UAC behavior, and moreover there will be some deployment constrain UAC behavior, and moreover there will be some deployment
architectures where a direct connection is simply infeasible and the architectures where a direct connection is simply infeasible and the
UAC cannot act as an authentication service itself. Accordingly, UAC cannot act as an authentication service itself. Accordingly,
when a direct connection and TLS is not possible, a UAC should use when a direct connection and TLS are not possible, a UAC should use
the SIPS mechanism, Digest 'auth-int' for body integrity, or both the SIPS mechanism, Digest 'auth-int' for body integrity, or both
when it can. The ultimate decision to add an Identity header to a when it can. The ultimate decision to add an Identity header to a
request lies with the authentication service, of course; domain request lies with the authentication service, of course; domain
policy must identify those cases where the UAC's security association policy must identify those cases where the UAC's security association
with the authentication service is too weak. with the authentication service is too weak.
14.4 Domain Names and Subordination 13.4. Domain Names and Subordination
When a verifier processes a request containing an Identity-Info When a verifier processes a request containing an Identity-Info
header, it must compare the domain portion of the URI in the From header, it must compare the domain portion of the URI in the From
header field of the request with the domain name which is the subject header field of the request with the domain name which is the subject
of the certificate acquired from the Identity-Info header. While it of the certificate acquired from the Identity-Info header. While it
might seem that this should be a straightforward process, it is might seem that this should be a straightforward process, it is
complicated by two deployment realities. In the first place, complicated by two deployment realities. In the first place,
certificates have varying ways of describing their subjects, and may certificates have varying ways of describing their subjects, and may
indeed have multiple subjects, especially in 'virtual hosting' cases indeed have multiple subjects, especially in 'virtual hosting' cases
where multiple domains are managed by a single application. where multiple domains are managed by a single application.
skipping to change at page 29, line 13 skipping to change at page 29, line 26
authentication service on a subordinate host MUST be willing to authentication service on a subordinate host MUST be willing to
supply that host with the private keying material associated with a supply that host with the private keying material associated with a
certificate whose subject is a domain name that corresponds to the certificate whose subject is a domain name that corresponds to the
domain portion of the AoRs that the domain distributes to users. domain portion of the AoRs that the domain distributes to users.
Note that this corresponds to the comparable case of routing inbound Note that this corresponds to the comparable case of routing inbound
SIP requests to a domain. When the NAPTR and SRV procedures of SIP requests to a domain. When the NAPTR and SRV procedures of
RFC3263 are used to direct requests to a domain name other than the RFC3263 are used to direct requests to a domain name other than the
domain in the original Request-URI (e.g., for 'sip:jon@example.com', domain in the original Request-URI (e.g., for 'sip:jon@example.com',
the corresponding SRV records point to the service the corresponding SRV records point to the service
'sip1.example.org'), the client expects that the certificate passed 'sip1.example.org'), the client expects that the certificate passed
back by in any TLS exchange with that host will correspond exactly back in any TLS exchange with that host will correspond exactly with
with the domain of the original Request-URI, not the domain name of the domain of the original Request-URI, not the domain name of the
the host. Consequently, in order to make inbound routing to such SIP host. Consequently, in order to make inbound routing to such SIP
services work, a domain administrator must similarly be willing to services work, a domain administrator must similarly be willing to
share the domain's private key with service. This design decision share the domain's private key with the service. This design
was made to compensate for the insecurity of the DNS, and it makes decision was made to compensate for the insecurity of the DNS, and it
certain potential approaches to DNS-based 'virtual hosting' makes certain potential approaches to DNS-based 'virtual hosting'
unsecurable for SIP in environments where domain administrators are unsecurable for SIP in environments where domain administrators are
unwilling to share keys with hosting services. unwilling to share keys with hosting services.
A verifier must evaluate the correspondence between the user's A verifier MUST evaluate the correspondence between the user's
identity and the signing certificate as follows: identity and the signing certificate by following the procedures
defined in RFC 2818 [11] Section 3.1. While RFC2818 deals with the
First, a verifier must acquire a list of one or more domain names use of HTTP in TLS, the procedures described are applicable to
which constitute the subject(s) of the certificate. A verifier MUST verifying identity if one subtitutes the "hostname of the server" in
extract the subject CN field from the certificate. If the CN HTTP for the domain portion of the user's identity in the From header
contains a domain name, it is added to a list we will call the field of a SIP request with an Identity header.
'subject list'. A verifier MUST also extract all subjectAltName
fields from the certificate. If any subjectAltName fields contain
domain names, these domain names should also be added to the subject
list.
Once it accumulates the subject list, the verifier MUST compare each
name in the subject list to the domain portion of the URI in the From
header field of the request. If the domain portion of that URI
matches any domain in the subject list, the verifier should consider
the certificate to match the URI in the From header field for the
purpose of verification.
If no member of the subject list matches the domain portion of the
URI in the From header field, then the verifier should consider the
certificate ineligible to sign the request.
Because the domain certificates that can be used by authentication Because the domain certificates that can be used by authentication
services need to assert only the hostname of the authentication services need to assert only the hostname of the authentication
service, existing certificate authorities can provide adequate service, existing certificate authorities can provide adequate
certificates for this mechanism. However, not all proxy servers and certificates for this mechanism. However, not all proxy servers and
user agents will be able support the root certificates of all user agents will be able to support the root certificates of all
certificate authorities, and moreover there are some significant certificate authorities, and moreover there are some significant
differences in the policies by which certificate authorities issue differences in the policies by which certificate authorities issue
their certificates. This document makes no recommendations for the their certificates. This document makes no recommendations for the
usage of particular certificate authorities, nor does it describe any usage of particular certificate authorities, nor does it describe any
particular policies that certificate authorities should follow, but particular policies that certificate authorities should follow, but
it is anticipated that operational experience will create de facto it is anticipated that operational experience will create de facto
standards for authentication services. Some federations of service standards for authentication services. Some federations of service
providers, for example, might only trust certificates that have been providers, for example, might only trust certificates that have been
provided by a certificate authority operated by the federation. It provided by a certificate authority operated by the federation. It
is strongly RECOMMENDED that self-signed domain certificates should is strongly RECOMMENDED that self-signed domain certificates should
not be trusted by verifiers, unless some pre-existing key exchange not be trusted by verifiers, unless some previous key exchange has
has justified such trust. justified such trust.
14.5 Authorization and Transitional Strategies For further information on certificate security and practices see
RFC3280 [9]. The Security Considerations of RFC3280 are applicable
to this document.
13.5. Authorization and Transitional Strategies
Ultimately, the worth of an assurance provided by an Identity header Ultimately, the worth of an assurance provided by an Identity header
is limited by the security practices of the domain that issues the is limited by the security practices of the domain that issues the
assurance. Relying on an Identity header generated by a remote assurance. Relying on an Identity header generated by a remote
administrative domain assumes that the issuing domain used its administrative domain assumes that the issuing domain used its
administrative practices to authenticate its users. However, it is administrative practices to authenticate its users. However, it is
possible that some domains will implement policies that effectively possible that some domains will implement policies that effectively
make users unaccountable (e.g., ones that accept unauthenticated make users unaccountable (e.g., ones that accept unauthenticated
registrations from arbitrary users). The value of an Identity header registrations from arbitrary users). The value of an Identity header
from such domains is questionable. While there is no magic way for a from such domains is questionable. While there is no magic way for a
skipping to change at page 31, line 8 skipping to change at page 31, line 11
service. There are a number of potential ways in which this could service. There are a number of potential ways in which this could
be implemented; use of the SIP OPTIONS method is one possibility. be implemented; use of the SIP OPTIONS method is one possibility.
This is left as a subject for future work. This is left as a subject for future work.
In the long term, some sort of identity mechanism, either the one In the long term, some sort of identity mechanism, either the one
documented in this specification or a successor, must become documented in this specification or a successor, must become
mandatory-to-use for the SIP protocol; that is the only way to mandatory-to-use for the SIP protocol; that is the only way to
guarantee that this protection can always be expected by verifiers. guarantee that this protection can always be expected by verifiers.
Finally, it is worth noting that the presence or absence of the Finally, it is worth noting that the presence or absence of the
Identity headers cannot be sole factor in making an authorization Identity headers cannot be the sole factor in making an authorization
decision. Permissions might be granted to a message on the basis of decision. Permissions might be granted to a message on the basis of
the specific verified Identity or really on any other aspect of a SIP the specific verified Identity or really on any other aspect of a SIP
request. Authorization policies are outside the scope of this request. Authorization policies are outside the scope of this
specification, but this specification advises any future specification, but this specification advises any future
authorization work not to assume that messages with valid Identity authorization work not to assume that messages with valid Identity
headers are always good. headers are always good.
15. IANA Considerations 14. IANA Considerations
This document requests changes to the header and response-code sub- This document requests changes to the header and response-code sub-
registries of the SIP parameters IANA registry, and requests the registries of the SIP parameters IANA registry, and requests the
creation of two new registries for parameters for the Identity-Info creation of two new registries for parameters for the Identity-Info
header. header.
15.1 Header Field Names 14.1. Header Field Names
This document specifies two new SIP headers: Identity and Identity- This document specifies two new SIP headers: Identity and Identity-
Info. Their syntax is given in Section 10. These headers are Info. Their syntax is given in Section 9. These headers are defined
defined by the following information, which is to be added to the by the following information, which is to be added to the header sub-
header sub-registry under registry under http://www.iana.org/assignments/sip-parameters.
http://www.iana.org/assignments/sip-parameters.
Header Name: Identity Header Name: Identity
Compact Form: y Compact Form: y
Header Name: Identity-Info Header Name: Identity-Info
Compact Form: n Compact Form: n
15.2 428 'Use Identity Header' Response Code 14.2. 428 'Use Identity Header' Response Code
This document registers a new SIP response code which is described in This document registers a new SIP response code which is described in
Section 7. It is sent when a verifier receives a SIP request that Section 6. It is sent when a verifier receives a SIP request that
lacks an Identity header in order to indicate that the request should lacks an Identity header in order to indicate that the request should
be re-sent with an Identity header. This response code is defined by be re-sent with an Identity header. This response code is defined by
the following information, which is to be added to the method and the following information, which is to be added to the method and
response-code sub-registry under response-code sub-registry under
http://www.iana.org/assignments/sip-parameters. http://www.iana.org/assignments/sip-parameters.
Response Code Number: 428 Response Code Number: 428
Default Reason Phrase: Use Identity Header Default Reason Phrase: Use Identity Header
15.3 436 'Bad Identity-Info' Response Code 14.3. 436 'Bad Identity-Info' Response Code
This document registers a new SIP response code which is described in This document registers a new SIP response code which is described in
Section 7. It is used when the Identity-Info header contains a URI Section 6. It is used when the Identity-Info header contains a URI
that cannot be dereferenced by the verifier (either the URI scheme is that cannot be dereferenced by the verifier (either the URI scheme is
unsupported by the verifier, or the resource designated by the URI is unsupported by the verifier, or the resource designated by the URI is
otherwise unavailable). This response code is defined by the otherwise unavailable). This response code is defined by the
following information, which is to be added to the method and following information, which is to be added to the method and
response-code sub-registry under response-code sub-registry under
http://www.iana.org/assignments/sip-parameters. http://www.iana.org/assignments/sip-parameters.
Response Code Number: 436 Response Code Number: 436
Default Reason Phrase: Bad Identity-Info Default Reason Phrase: Bad Identity-Info
15.4 437 'Unsupported Certificate' Response Code 14.4. 437 'Unsupported Certificate' Response Code
This document registers a new SIP response code which is described in This document registers a new SIP response code which is described in
Section 7. It is used when the verifier cannot validate the Section 6. It is used when the verifier cannot validate the
certificate referenced by the URI of the Identity-Info header, certificate referenced by the URI of the Identity-Info header,
because, for example, the certificate is self-signed, or signed by a because, for example, the certificate is self-signed, or signed by a
root certificate authority for whom the verifier does not possess a root certificate authority for whom the verifier does not possess a
root certificate. This response code is defined by the following root certificate. This response code is defined by the following
information, which is to be added to the method and response-code information, which is to be added to the method and response-code
sub-registry under http://www.iana.org/assignments/sip-parameters. sub-registry under http://www.iana.org/assignments/sip-parameters.
Response Code Number: 437 Response Code Number: 437
Default Reason Phrase: Unsupported Certificate Default Reason Phrase: Unsupported Certificate
15.5 Identity-Info Parameters 14.5. 438 'Invalid Identity Header' Response Code
This document registers a new SIP response code which is described in
Section 6. It is used when the verifier receives a message with an
Identity signature that does not correspond to the digest-string
calculated by the verifier. This response code 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: 438
Default Reason Phrase: Invalid Identity Header
14.6. Identity-Info Parameters
This document requests that the IANA create a new registry for This document requests that the IANA create a new registry for
Identity-Info headers. This registry is to be prepopulated with a Identity-Info headers. This registry is to be prepopulated with a
single entry for a parameter called 'alg', which describes the single entry for a parameter called 'alg', which describes the
algorithm used to create the signature which appears in the Identity algorithm used to create the signature which appears in the Identity
header. Registry entries must contain the name of the parameter and header. Registry entries must contain the name of the parameter and
the specification in which the parameter is defined. New parameters the specification in which the parameter is defined. New parameters
for the Identity-Info header may be defined only in Standards Track for the Identity-Info header may be defined only in Standards Track
RFCs. RFCs.
15.6 Identity-Info Algorithm Parameter Values 14.7. Identity-Info Algorithm Parameter Values
This document requests that the IANA create a new registry for This document requests that the IANA create a new registry for
Identity-Info 'alg' parameter values. This registry is to be Identity-Info 'alg' parameter values. This registry is to be
prepopulated with a single entry for a value called 'rsa-sha1', which prepopulated with a single entry for a value called 'rsa-sha1', which
describes the algorithm used to create the signature which appears in describes the algorithm used to create the signature which appears in
the Identity header. Registry entries must contain the name of the the Identity header. Registry entries must contain the name of the
'alg' parameter value and the specification in which the value is 'alg' parameter value and the specification in which the value is
described. New values for the 'alg' parameter may be defined only in described. New values for the 'alg' parameter may be defined only in
Standards Track RFCs. Standards Track RFCs.
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.
[7] Housley, R., "Cryptographic Message Syntax (CMS) Algorithms",
RFC 3370, August 2002.
[8] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
RFC 3548, July 2003.
16.2 Informative References
[9] Kohl, J. and C. Neumann, "The Kerberos Network Authentication
Service (V5)", RFC 1510, September 1993.
[10] 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.
[11] Housley, R. and P. Hoffman, "Internet X.509 Public Key
Infrastructure Operational Protocols: FTP and HTTP", RFC 2585,
May 1999.
[12] Schulzrinne, H., "The TEL URI for Telephone Numbers", RFC 3966,
December 2004.
[13] Faltstrom, P. and M. Mealling, "The E.164 to URI DDDS
Application", RFC 3761, April 2004.
[14] Peterson, J., "Retargeting and Security in SIP: A Framework and
Requirements", draft-peterson-sipping-retarget-00 (work in
progress), February 2005.
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 Appendix A. Acknowledgments
The authors would like to thank Eric Rescorla, Rohan Mahy, Robert The authors would like to thank Eric Rescorla, Rohan Mahy, Robert
Sparks, Jonathan Rosenberg, Mark Watson, Henry Sinnreich, Alan Sparks, Jonathan Rosenberg, Mark Watson, Henry Sinnreich, Alan
Johnston, Patrik Faltstrom, Paul Kyzviat, Adam Roach, John Elwell, Johnston, Patrik Faltstrom, Paul Kyzviat, Adam Roach, John Elwell,
Aki Niemi, and Jim Schaad for their comments. Jonathan Rosenberg Aki Niemi, and Jim Schaad for their comments. Jonathan Rosenberg
provided detailed fixed to innumerable sections of the document. The provided detailed fixes to innumerable sections of the document. The
bit-archive presented in Appendix B follows the pioneering example of bit-archive presented in Appendix B follows the pioneering example of
Robert Sparks' torture-test draft. Robert Sparks' torture-test draft. Thanks to Hans Persson and Tao
Wan for thorough nit reviews.
Appendix B. Bit-exact archive of example messages Appendix B. Bit-exact archive of example messages
The following text block is an encoded, gzip compressed TAR archive The following text block is an encoded, gzip compressed TAR archive
of files that represent the transformations performed on the example of files that represent the transformations performed on the example
messages discussed in Section 11. It includes for each example: messages discussed in Section 10. It includes for each example:
o (foo).message: the original message o (foo).message: the original message
o (foo).canonical: the canonical string constructed from that o (foo).canonical: the canonical string constructed from that
message message
o (foo).sha1: the SHA1 hash of the canonical string (hexadecimal) o (foo).sha1: the SHA1 hash of the canonical string (hexadecimal)
o (foo).signed: the RSA-signed SHA1 hash of the canonical string o (foo).signed: the RSA-signed SHA1 hash of the canonical string
(binary) (binary)
o (foo).signed.enc: the base64 encoding of the RSA-signed SHA1 hash o (foo).signed.enc: the base64 encoding of the RSA-signed SHA1 hash
of the canonical string as it would appear in the request of the canonical string as it would appear in the request
o (foo).identity: the original message with the Identity and o (foo).identity: the original message with the Identity and
Identity-Info headers added Identity-Info headers added
Also included in the archive are two public key/certificate pairs, Also included in the archive are two public key/certificate pairs,
for atlanta.example.com and biloxi.example.org, respectively, for atlanta.example.com and biloxi.example.org, respectively,
including: including:
o (foo).cert: the certificate of the domain o (foo).cer: the certificate of the domain
o (foo).privkey: the private key of the domain o (foo).privkey: the private key of the domain
o (foo).pubkey: the public key of the domain, extracted from the o (foo).pubkey: the public key of the domain, extracted from the
cert file for convenience cert file for convenience
To recover the compressed archive file intact, the text of this To recover the compressed archive file intact, the text of this
document may be passed as input to the following Perl script (the document may be passed as input to the following Perl script (the
output should be redirected to a file or piped to "tar -xzvf -"). output should be redirected to a file or piped to "tar -xzvf -").
#!/usr/bin/perl #!/usr/bin/perl
use strict; use strict;
my $bdata = ""; my $bdata = "";
use MIME::Base64; use MIME::Base64;
while(<>) { while(<>) {
if (/-- BEGIN MESSAGE ARCHIVE --/ .. /-- END MESSAGE ARCHIVE --/) { if (/-- BEGIN MESSAGE ARCHIVE --/ .. /-- END MESSAGE ARCHIVE --/) {
skipping to change at page 35, line 40 skipping to change at page 34, line 25
$bdata = $bdata . $_; $bdata = $bdata . $_;
} }
} }
} }
print decode_base64($bdata); print decode_base64($bdata);
Alternatively, the base-64 encoded block can be edited by hand to Alternatively, the base-64 encoded block can be edited by hand to
remove document structure lines and fed as input to any base-64 remove document structure lines and fed as input to any base-64
decoding utility. decoding utility.
B.1 Encoded Reference Files B.1. Encoded Reference Files
-- BEGIN MESSAGE ARCHIVE -- -- BEGIN MESSAGE ARCHIVE --
H4sICOOGdEICA2lkZW50cmVmLnRhcgDsW02v41haLpBYYFEb/sBEIxagTFX87eT2 H4sICPuIXEMCA25ld2lkZW50LnRhcgDsW0us5NhZboUVlloCDRI7VJpVUKXbb7t8
1GiOv78TfyfZINvxR2zHjj8SO6HEHwCh2aFBiA0LVixZgGYJG8SazWxYsOQfICGc J53M8dvlR5XLj3KVQiS/ys+yq8qusqvUEUJiARILyCobRJAQWYxgyQaBgiArxAJl
e6u6urv6dtdI3aXu6XskXyev7ZNz/J73ed73se9+F5VdE8WzZ99eg2Ecpghi3GMo HwFii9iEDWKB7+339PT0RJm+mkzuL5XsOj62zzm//+87/3fsKu6yKK5a+N67MwQh
hZHjHsVxEhn3n7ZnCIxixPiHxLBnMIKRKPpsQjz7CO3Udn4zmTzLjlEXNW1VPnLe EJokhy2O0Tg1bDGCoNBh+9zuodfHUITAsaEeilMEem9E3rsFOzatfxiN7uW7uI0P
IU+a6nR8UbzYPfstavu3/ve7wi87/2UYNd037X8Ehkkcf8z/KIJgo/8RFEEpBCWo TV29od62SA71cfegfBDd+xJZ9cz/flv6Ves/DOPD5+5/FEEogniT/zFkKHvufxQb
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-- END MESSAGE ARCHIVE -- -- END MESSAGE ARCHIVE --
Appendix C. Changelog Appendix C. Original Requirements
The following requirements were crafted throughout the development of
the mechanism described in this document. They are preserved here
for historical reasons.
o The mechanism must allow a UAC or a proxy server 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 this mechanism in order for an
identity assurance to be added to a request in this fashion.
o The mechanism must prevent replay of the identity assurance by an
attacker.
o In order to provide full replay protection, 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) which it is authorized to use within 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.
Appendix D. Changelog
NOTE TO THE RFC-EDITOR: Please remove this section prior to NOTE TO THE RFC-EDITOR: Please remove this section prior to
publication as an RFC. publication as an RFC.
Changes from draft-ietf-sip-identity-06:
- Disambiguated 428 response code, added new 438 for invalid
Identity headers
- Used RFC2585 format for Identity-Info URIs
- Updated example certificates to comply with RFC3280
- Replaced certificate validation and mapping procedures with
reference to RFC2818
- Numerous editorial fixes
Changes from draft-ietf-sip-identity-05:
- Removed the requirements section
- Numerous editorial fixes
Changes from draft-ietf-sip-identity-04: Changes from draft-ietf-sip-identity-04:
- Changed the delimiter of the digest-string from ":" to "|" - Changed the delimiter of the digest-string from ":" to "|"
- Removed support for the SIPS URI scheme from the Identity-Info - Removed support for the SIPS URI scheme from the Identity-Info
header header
- Made the Identity-Info header extensible; added an Identity-Info - Made the Identity-Info header extensible; added an Identity-Info
header for algorithm with an initial defined value of 'rsa-sha1' header for algorithm with an initial defined value of 'rsa-sha1'
- Broke up the Security Considerations into smaller chunks for - Broke up the Security Considerations into smaller chunks for
organizational reasons; expanded discussion of most issues organizational reasons; expanded discussion of most issues
- Added some guidelines for authentication service certificate - Added some guidelines for authentication service certificate
rollover and lifecycle management (also now based HTTP certificate rollover and lifecycle management (also now based HTTP certificate
skipping to change at page 40, line 5 skipping to change at page 38, line 47
strength) strength)
Changes from draft-peterson-sip-identity-00: Changes from draft-peterson-sip-identity-00:
- Added a section on authenticated identities in responses - Added a section on authenticated identities in responses
- Removed hostname convention for authentication services - Removed hostname convention for authentication services
- Added text about using 'message/sip' or 'message/sipfrag' in - Added text about using 'message/sip' or 'message/sipfrag' in
authenticated identity bodies, also RECOMMENDED a few more headers authenticated identity bodies, also RECOMMENDED a few more headers
in sipfrags to increase reference integrity in sipfrags to increase reference integrity
- Various other editorial corrections - Various other editorial corrections
15. References
15.1. 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.
[7] Housley, R., "Cryptographic Message Syntax (CMS) Algorithms",
RFC 3370, August 2002.
[8] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
RFC 3548, July 2003.
[9] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509
Public Key Infrastructure Certificate and Certificate
Revocation List (CRL) Profile", RFC 3280, April 2002.
[10] Housley, R. and P. Hoffman, "Internet X.509 Public Key
Infrastructure Operational Protocols: FTP and HTTP", RFC 2585,
May 1999.
[11] Rescorla, E., "HTTP over TLS", RFC 2818, May 2000.
15.2. Informative References
[12] 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.
[13] Schulzrinne, H., "The TEL URI for Telephone Numbers", RFC 3966,
December 2004.
[14] Faltstrom, P. and M. Mealling, "The E.164 to URI DDDS
Application", RFC 3761, April 2004.
[15] Peterson, J., "Retargeting and Security in SIP: A Framework and
Requirements", draft-peterson-sipping-retarget-00 (work in
progress), February 2005.
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
Intellectual Property Statement Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights 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 might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
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