< draft-ietf-sip-saml-00.txt   draft-ietf-sip-saml-01.txt >
SIP H. Tschofenig SIP H. Tschofenig
Internet-Draft Siemens Internet-Draft Siemens Networks GmbH & Co KG
Expires: December 18, 2006 J. Hodges Intended status: Standards Track J. Hodges
J. Peterson Expires: April 26, 2007 J. Peterson
NeuStar, Inc. NeuStar, Inc.
J. Polk J. Polk
Cisco Cisco
D. Sicker D. Sicker
CU Boulder CU Boulder
June 16, 2006 October 23, 2006
SIP SAML Profile and Binding SIP SAML Profile and Binding
draft-ietf-sip-saml-00.txt draft-ietf-sip-saml-01.txt
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
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have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on December 18, 2006. This Internet-Draft will expire on April 26, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document specifies a Session Initiation Protocol (SIP) profile This document specifies a Session Initiation Protocol (SIP) profile
of Security Assertion Markup Language (SAML) as well as a SAML SIP of Security Assertion Markup Language (SAML) as well as a SAML SIP
binding. The defined SIP SAML Profile composes with the mechanisms binding. The defined SIP SAML Profile composes with the mechanisms
defined in the SIP Identity specification and satisfy requirements defined in the SIP Identity specification and satisfy requirements
presented in "Trait-based Authorization Requirements for the Session presented in "Trait-based Authorization Requirements for the Session
Initiation Protocol (SIP)". Initiation Protocol (SIP)".
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. SAML Introduction . . . . . . . . . . . . . . . . . . . . . . 6 3. SAML Introduction . . . . . . . . . . . . . . . . . . . . . . 7
3.1. SAML Assertions . . . . . . . . . . . . . . . . . . . . . 7 3.1. SAML Assertions . . . . . . . . . . . . . . . . . . . . . 8
3.2. Abstract Request/Response Protocol . . . . . . . . . . . . 8 3.2. Abstract Request/Response Protocol . . . . . . . . . . . . 9
4. Specification Scope . . . . . . . . . . . . . . . . . . . . . 9 4. Specification Scope . . . . . . . . . . . . . . . . . . . . . 10
5. Employing SAML in SIP . . . . . . . . . . . . . . . . . . . . 11 5. Employing SAML in SIP . . . . . . . . . . . . . . . . . . . . 12
6. SIP SAML Profiles . . . . . . . . . . . . . . . . . . . . . . 13 6. SIP SAML Profiles . . . . . . . . . . . . . . . . . . . . . . 14
6.1. AS-driven SIP SAML URI-based Attribute Assertion 6.1. AS-driven SIP SAML URI-based Attribute Assertion
Fetch Profile . . . . . . . . . . . . . . . . . . . . . . 13 Fetch Profile . . . . . . . . . . . . . . . . . . . . . . 14
6.1.1. Required Information . . . . . . . . . . . . . . . . . 13 6.1.1. Required Information . . . . . . . . . . . . . . . . . 14
6.1.2. Profile Overview . . . . . . . . . . . . . . . . . . . 13 6.1.2. Profile Overview . . . . . . . . . . . . . . . . . . . 14
6.1.3. Profile Description . . . . . . . . . . . . . . . . . 17 6.1.3. Profile Description . . . . . . . . . . . . . . . . . 18
6.1.4. Assertion Profile Description . . . . . . . . . . . . 20 6.1.4. Assertion Profile Description . . . . . . . . . . . . 21
6.1.5. Assertion Verification . . . . . . . . . . . . . . . . 23 6.1.5. Assertion Verification . . . . . . . . . . . . . . . . 24
7. SAML SIP Binding . . . . . . . . . . . . . . . . . . . . . . . 25 7. SAML SIP Binding . . . . . . . . . . . . . . . . . . . . . . . 26
7.1. SAML HTTP-URI-based SIP Binding . . . . . . . . . . . . . 25 7.1. SAML HTTP-URI-based SIP Binding . . . . . . . . . . . . . 26
8. Example SAML Assertions . . . . . . . . . . . . . . . . . . . 26 8. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 27
9. Security Considerations . . . . . . . . . . . . . . . . . . . 31 8.1. 425 (Bad SAML Assertion) Response Code . . . . . . . . . . 27
9.1. Man-in-the-middle Attacks and Stolen Assertions . . . . . 31 8.2. The SAML Reason Protocol . . . . . . . . . . . . . . . . . 27
9.2. Forged Assertion . . . . . . . . . . . . . . . . . . . . . 32 8.3. Failure Reasons to be Registered . . . . . . . . . . . . . 28
9.3. Replay Attack . . . . . . . . . . . . . . . . . . . . . . 32 8.3.1. SAML Assertion Content Not Supported . . . . . . . . . 28
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 33 8.3.2. Authentication Statements Desired Instead . . . . . . 28
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 34 8.3.3. Authorization Statements Desired Instead . . . . . . . 29
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35 8.3.4. Attribute Statements Desired Instead . . . . . . . . . 29
13. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 36 8.3.5. Unsupported Content . . . . . . . . . . . . . . . . . 29
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 37 8.3.6. Unable to Dereference . . . . . . . . . . . . . . . . 30
14.1. Normative References . . . . . . . . . . . . . . . . . . . 37 8.3.7. Cannot Parse SAML Assertion . . . . . . . . . . . . . 30
14.2. Informative References . . . . . . . . . . . . . . . . . . 38 8.3.8. Conflicting SAML Assertions Supplied . . . . . . . . . 30
Appendix A. Appendix: Use-case Scenarios . . . . . . . . . . . . 41 8.3.9. Insufficient SAML Statements . . . . . . . . . . . . . 31
A.1. PSTN-to-SIP Phone Call . . . . . . . . . . . . . . . . . . 41 8.3.10. Dereference Timeout . . . . . . . . . . . . . . . . . 31
A.2. SIP Conferencing . . . . . . . . . . . . . . . . . . . . . 42 9. Example SAML Assertions . . . . . . . . . . . . . . . . . . . 32
A.3. Compensation using SIP and SAML . . . . . . . . . . . . . 44 10. Security Considerations . . . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 46 10.1. Man-in-the-middle Attacks and Stolen Assertions . . . . . 37
Intellectual Property and Copyright Statements . . . . . . . . . . 47 10.2. Forged Assertion . . . . . . . . . . . . . . . . . . . . . 38
10.3. Replay Attack . . . . . . . . . . . . . . . . . . . . . . 38
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 39
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 40
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 41
13.1. IANA Registration for Response Code 4XX . . . . . . . . . 41
13.2. IANA Registration of the SAML Reason Protocol . . . . . . 41
14. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 42
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 43
15.1. Normative References . . . . . . . . . . . . . . . . . . . 43
15.2. Informative References . . . . . . . . . . . . . . . . . . 44
Appendix A. Appendix: Use-case Scenarios . . . . . . . . . . . . 47
A.1. PSTN-to-SIP Phone Call . . . . . . . . . . . . . . . . . . 47
A.2. SIP Conferencing . . . . . . . . . . . . . . . . . . . . . 48
A.3. Compensation using SIP and SAML . . . . . . . . . . . . . 50
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 52
Intellectual Property and Copyright Statements . . . . . . . . . . 53
1. Introduction 1. Introduction
This document specifies composition of the Security Assertion Markup This document specifies composition of the Security Assertion Markup
Language (SAML) V2.0 with SIP [RFC3261] in order to accommodate Language (SAML) V2.0 with SIP [RFC3261] in order to accommodate
richer authorization mechanisms and enable "trait-based richer authorization mechanisms and enable "trait-based
authorization." Trait-based authorization is where one is authorized authorization." Trait-based authorization is where one is authorized
to make use of some resource based on roles or traits rather than to make use of some resource based on roles or traits rather than
ones identifier(s). Motivations for trait-based authorization, along ones identifier(s). Motivations for trait-based authorization, along
with use-case scenarios, are presented in [I-D.ietf-sipping-trait- with use-case scenarios, are presented in
authz]. [I-D.ietf-sipping-trait-authz].
Security Assertion Markup Language (SAML) v2.0, "SAMLv2", is an XML- Security Assertion Markup Language (SAML) v2.0, "SAMLv2", is an XML-
based framework for creating and exchanging security information. based framework for creating and exchanging security information.
[OASIS.sstc-saml-exec-overview-2.0-cd-01] and [OASIS.sstc-saml-tech- [OASIS.sstc-saml-exec-overview-2.0-cd-01] and
overview-2.0-draft-08] provide non-normative overviews of SAMLv2. [OASIS.sstc-saml-tech-overview-2.0-draft-08] provide non-normative
The SAMLv2 specification set is normatively defined by [OASIS.saml- overviews of SAMLv2. The SAMLv2 specification set is normatively
conformance-2.0-os]. defined by [OASIS.saml-conformance-2.0-os].
Various means of providing trait-based authorization exist: Various means of providing trait-based authorization exist:
authorization certificates [RFC3281], SPKI [RFC2693], or extensions authorization certificates [RFC3281], SPKI [RFC2693], or extensions
to the authenticated identity body [RFC3893]. The authors selected to the authenticated identity body [RFC3893]. The authors selected
SAML due to its increasing use in environments such as the Liberty SAML due to its increasing use in environments such as the Liberty
Alliance, and the Internet2 project, areas where the applicability to Alliance, and the Internet2 project, areas where the applicability to
SIP is widely desired. SIP is widely desired.
2. Terminology 2. Terminology
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one or more attributes of a "user profile". one or more attributes of a "user profile".
user profile, subject profile: user profile, subject profile:
the set of various attributes accompanying (i.e., mapped to) a the set of various attributes accompanying (i.e., mapped to) a
user account in many environments. user account in many environments.
3. SAML Introduction 3. SAML Introduction
SAML [OASIS.sstc-saml-exec-overview-2.0-cd-01] [OASIS.sstc-saml-tech- SAML [OASIS.sstc-saml-exec-overview-2.0-cd-01]
overview-2.0-draft-08] defines an XML-based framework for exchanging [OASIS.sstc-saml-tech-overview-2.0-draft-08] defines an XML-based
"security assertions" between entities. In the course of making, or framework for exchanging "security assertions" between entities. In
relying upon such assertions, SAML system entities may use SAML the course of making, or relying upon such assertions, SAML system
protocols, or other protocols, to communicate an assertion itself, or entities may use SAML protocols, or other protocols, to communicate
the subject of an assertion. an assertion itself, or the subject of an assertion.
Thus one can employ SAML to make and encode statements such as "Alice Thus one can employ SAML to make and encode statements such as "Alice
has these profile attributes and her domain's certificate is has these profile attributes and her domain's certificate is
available over there, and I'm making this statement, and here's who I available over there, and I'm making this statement, and here's who I
am." Then one can cause such an assertion to be conveyed to some am." Then one can cause such an assertion to be conveyed to some
party who can then rely on it in some fashion for some purpose, for party who can then rely on it in some fashion for some purpose, for
example input it into some local policy evaluation for access to some example input it into some local policy evaluation for access to some
resource. This is done in a particular "context of use". Such a resource. This is done in a particular "context of use". Such a
context of use could be, for example, deciding whether to accept and context of use could be, for example, deciding whether to accept and
act upon a SIP-based invitation to initiate a communication session. act upon a SIP-based invitation to initiate a communication session.
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based SIP communication session establishment, the topic of this based SIP communication session establishment, the topic of this
specification, is another. specification, is another.
4. Specification Scope 4. Specification Scope
The scope of this specification is: The scope of this specification is:
o Specify a SIP profile of SAML -- aka a "SIP SAML profile" -- such o Specify a SIP profile of SAML -- aka a "SIP SAML profile" -- such
that a subject's profile attributes, and their domain's that a subject's profile attributes, and their domain's
certificate, can be conveyed to a relying party using SAML. In certificate, can be conveyed to a relying party using SAML. In
doing so, satisfy the requirements outlined in [I-D.ietf-sipping- doing so, satisfy the requirements outlined in
trait-authz], and compose with [I-D.ietf-sip-identity]. [I-D.ietf-sipping-trait-authz], and compose with
[I-D.ietf-sip-identity].
The following are outside the scope of this specification: The following are outside the scope of this specification:
o Defining a means for configuring the runtime behavior, or o Defining a means for configuring the runtime behavior, or
deployment characteristics, of the Authentication Service. deployment characteristics, of the Authentication Service.
Discussion: Discussion:
For example, a SIP Authentication Service could be implemented For example, a SIP Authentication Service could be implemented
such that its SAML-based features are employed, or not, on a such that its SAML-based features are employed, or not, on a
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This specification defines a facility enabling "trait-based This specification defines a facility enabling "trait-based
authorization" as discussed in [I-D.ietf-sipping-trait-authz]. authorization" as discussed in [I-D.ietf-sipping-trait-authz].
The attributes of interest in trait-based authorization will be The attributes of interest in trait-based authorization will be
ones akin to, for example: roles, organizational membership, ones akin to, for example: roles, organizational membership,
access rights, or authentication event context. Definition of access rights, or authentication event context. Definition of
such attributes is application- and/or deployment-context- such attributes is application- and/or deployment-context-
dependent and are not defined in this specification. However, The dependent and are not defined in this specification. However, The
SAMLv2 specification defines several "SAML Attribute Profiles" for SAMLv2 specification defines several "SAML Attribute Profiles" for
encoding attributes from various application domains, e.g., LDAP, encoding attributes from various application domains, e.g., LDAP,
UUID/GUID, DCE PAC, and XACML, in SAML assertions [OASIS.saml- UUID/GUID, DCE PAC, and XACML, in SAML assertions
profiles-2.0-os]. [OASIS.saml-profiles-2.0-os].
In order for any trait-based system to be practical, participating In order for any trait-based system to be practical, participating
entities must agree on attributes and traits that will be conveyed entities must agree on attributes and traits that will be conveyed
and subsequently relied upon. Without such agreements, a trait- and subsequently relied upon. Without such agreements, a trait-
based system cannot be usefully deployed. This specification does based system cannot be usefully deployed. This specification does
not discuss the manner in which participating entites might not discuss the manner in which participating entites might
discover one another or agree on the syntax and semantics of discover one another or agree on the syntax and semantics of
attributes and traits. attributes and traits.
Note that SAMLv2 specifies a "metadata" facility that may be Note that SAMLv2 specifies a "metadata" facility that may be
useful in addressing this need. useful in addressing this need.
5. Employing SAML in SIP 5. Employing SAML in SIP
Employing SAML in SIP necessitates devising a new SAML profile(s) and Employing SAML in SIP necessitates devising a new SAML profile(s) and
binding(s) because the those already specified in the SAMLv2 binding(s) because the those already specified in the SAMLv2
specification set are specific to other use contexts, e.g., HTTP- specification set are specific to other use contexts, e.g., HTTP-
based web browsing. Although SIP bears some similarity to HTTP, it based web browsing. Although SIP bears some similarity to HTTP, it
is a seperately distinct protocol, thus requiring specification of is a seperately distinct protocol, thus requiring specification of
SIP-specific SAML profile(s) and binding(s). This is technically SIP-specific SAML profile(s) and binding(s). This is technically
straigh-forward as both SAML and SIP are explicitly extensible. straightforward as both SAML and SIP are explicitly extensible.
The "Authenticated Identity Management in SIP" specification The "Authenticated Identity Management in SIP" specification
[I-D.ietf-sip-identity] (aka "SIP Identity") facilitates the [I-D.ietf-sip-identity] (aka "SIP Identity") facilitates the
composition of SAML and SIP in that it defines a "mediated composition of SAML and SIP in that it defines a "mediated
authentication architecture" where verifying endpoints verify SIP authentication architecture" where verifying endpoints verify SIP
identity assertions -- i.e., the "Identity" header value -- signed by identity assertions -- i.e., the "Identity" header value -- signed by
an Authentication Service (AS). The semantic being that the AS is an Authentication Service (AS). The semantic being that the AS is
vouching that it did indeed authenticate the calling party. vouching that it did indeed authenticate the calling party.
Such an Authentication Service, which likely has access to various Such an Authentication Service, which likely has access to various
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| |<==================== | | |<==================== |
| | and domain cert | | | and domain cert |
| | | | | |
| | HTTP 200 OK + assn | | | HTTP 200 OK + assn |
| |=====================>| | |=====================>|
| | and domain cert | | | and domain cert |
| 200 OK | | | 200 OK | |
|<----------------------+----------------------| |<----------------------+----------------------|
| | | | | |
Figure 1: SIP-SAML-based Network Asserted Identity Figure 1: SIP-SAML-based Network Asserted Identity
Since the AS already being trusted to create and add the Identity Since the AS already being trusted to create and add the Identity
header containing the SIP Identity Assertion, and to supply a pointer header containing the SIP Identity Assertion, and to supply a pointer
to its domain certificate, having it point instead to a SAML to its domain certificate, having it point instead to a SAML
assertion conveying the domain certificate and possibly some user assertion conveying the domain certificate and possibly some user
profile attributes, does not significantly alter the first-order profile attributes, does not significantly alter the first-order
security considerations examined in [I-D.ietf-sip-identity]. This security considerations examined in [I-D.ietf-sip-identity]. This
specification provides some additional security considerations specification provides some additional security considerations
analysis below in Section 9. analysis below in Section 10.
6. SIP SAML Profiles 6. SIP SAML Profiles
This section defines one SIP SAML profile: This section defines one SIP SAML profile:
The "AS-driven SIP SAML URI-based Attribute Assertion Fetch The "AS-driven SIP SAML URI-based Attribute Assertion Fetch
Profile" Profile"
6.1. AS-driven SIP SAML URI-based Attribute Assertion Fetch Profile 6.1. AS-driven SIP SAML URI-based Attribute Assertion Fetch Profile
6.1.1. Required Information 6.1.1. Required Information
The information given in this section is similar to the info provided The information given in this section is similar to the info provided
when registering something, a MIME Media Type, say, with IANA. In when registering something, a MIME Media Type, say, with IANA. In
this case, it is for registering this profile with the OASIS SSTC. this case, it is for registering this profile with the OASIS SSTC.
See Section 2 "Specification of Additional Profiles" in [OASIS.saml- See Section 2 "Specification of Additional Profiles" in
profiles-2.0-os]. [OASIS.saml-profiles-2.0-os].
Identification: Identification:
urn:ietf:params:sip:sip-saml-profile:as:uri:attr:1.0 urn:ietf:params:sip:sip-saml-profile:as:uri:attr:1.0
@@ NOTE: This URN must be agreed upon, and then registered with @@ NOTE: This URN must be agreed upon, and then registered with
IANA per [RFC3553]. IANA per [RFC3553].
Contact Information: Contact Information:
@@ someone's or something's contact info goes here @@ someone's or something's contact info goes here
SAML Confirmation Method Identifiers: SAML Confirmation Method Identifiers:
The SAML V2.0 "{bearer,hok,?}" confirmation method identifier is The SAML V2.0 "{bearer,hok,?}" confirmation method identifier is
used in this profile. used in this profile.
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| | | | <saml:SubjConfData> | | | | <saml:SubjConfData>
| | | | <ds:KeyInfo>... | | | | <ds:KeyInfo>...
| | | | <saml:AttrStatement> | | | | <saml:AttrStatement>
| | | | foo=bar | | | | | foo=bar |
| | | 200 OK | | | | | 200 OK | |
| V |<----------------------+----------------------| (6) | V |<----------------------+----------------------| (6)
. - | | | . - | | |
V V
Figure 2: AS-driven SIP SAML Attribute Fetch Profile: Example INVITE Figure 2: AS-driven SIP SAML Attribute Fetch Profile: Example INVITE
Transaction Transaction
Step 1. Initial SIP Transaction between Caller and AS Step 1. Initial SIP Transaction between Caller and AS
This optional initial step is comprised of substeps 1a, 1b, This optional initial step is comprised of substeps 1a, 1b,
and 1c in Figure 2. In this step, the caller, Alice, sends a and 1c in Figure 2. In this step, the caller, Alice, sends
SIP request message, illustrated as an INVITE, indicating Bob a SIP request message, illustrated as an INVITE, indicating
as the callee (1a), is subsequently challenged by the AS Bob as the callee (1a), is subsequently challenged by the AS
(1b), and sends an ACK in response to the challenge (1c). (1b), and sends an ACK in response to the challenge (1c).
The latter message signals the completion of this SIP The latter message signals the completion of this SIP
transaction (which is an optional substep of this profile). transaction (which is an optional substep of this profile).
Step 2. Caller sends SIP Request Message with Authorization Step 2. Caller sends SIP Request Message with Authorization
Credentials to the AS Credentials to the AS
Alice then sends an INVITE message in response to the Alice then sends an INVITE message in response to the
challenge, or uses cached credentials for the domain if step challenge, or uses cached credentials for the domain if step
1 was skipped, as specified in [I-D.ietf-sip-identity] and 1 was skipped, as specified in [I-D.ietf-sip-identity] and
[RFC3261]. Depending on the chosen SIP security mechanism [RFC3261]. Depending on the chosen SIP security mechanism
either digest authentication, S/MIME or Transport Layer for client authentication either digest authentication,
Security is used to provide the AS with a strong assurance client side authentication of Transport Layer Security, or a
about the identity of Alice. combination of both is used to provide the AS with a strong
assurance about the identity of Alice.
Step 3. AS Authorizes the SIP Request and Forwards it to Callee Step 3. AS Authorizes the SIP Request and Forwards it to Callee
First, the AS authorizes the received INVITE message as First, the AS authorizes the received INVITE message as
specified in [I-D.ietf-sip-identity] and [RFC3261]. If the specified in [I-D.ietf-sip-identity] and [RFC3261]. If the
authorization is successful, the AS will form the "identity authorization is successful, the AS will form the "identity
signature" for the message and add Identity and Identity-Info signature" for the message and add Identity and Identity-
headers to the message. The AS also at this time constructs Info header fields to the message. The AS also at this time
and caches a SAML assertion asserting Alice's profile constructs and caches a SAML assertion asserting Alice's
attributes required by Bob's domain (example2.com), and also profile attributes required by Bob's domain (example2.com),
containing a the domain's (example.com) public key and also containing a the domain's (example.com) public key
certificate, or a reference to it. This certificate MUST certificate, or a reference to it. This certificate MUST
contain the public key corresponding to the private key used contain the public key corresponding to the private key used
to construct the signature whose value was placed in the to construct the signature whose value was placed in the
Identity header. The AS constructs a HTTP-based SAML URI Identity header. The AS constructs a HTTP-based SAML URI
Reference incorporating the assertion's Assertion ID (see Reference incorporating the assertion's Assertion ID (see
section 2.3.3 of [OASIS.saml-core-2.0-os]). The AS uses this section 2.3.3 of [OASIS.saml-core-2.0-os]). The AS uses
URI as the value for the Identity-Info header it adds to the this URI as the value for the Identity-Info header it adds
INVITE message. to the INVITE message.
The AS determines which profile attributes (if any) to assert The AS determines which profile attributes (if any) to
in the <AttributeStatement> via local configuration and/or assert in the <AttributeStatement> via local configuration
obtaining example2.com's metadata and/or obtaining example2.com's metadata
[OASIS.saml-metadata-2.0-os]. The AS then sends the updated [OASIS.saml-metadata-2.0-os]. The AS then sends the updated
INVITE message to Bob. INVITE message to Bob.
Step 4. Callee Dereferences HTTP-based SAML URI Reference Step 4. Callee Dereferences HTTP-based SAML URI Reference
Bob's UAC or SIP Proxy receives the message and begins Bob's UAC or SIP Proxy receives the message and begins
verifying it per the "Verifier Behavior" specified in verifying it per the "Verifier Behavior" specified in
[I-D.ietf-sip-identity]. In order to accomplish this task, [I-D.ietf-sip-identity]. In order to accomplish this task,
it needs to obtain Alice's domain certificate. It obtains it needs to obtain Alice's domain certificate. It obtains
the HTTP-based SAML URI Reference from the message's the HTTP-based SAML URI Reference from the message's
Identity-Info header and dereferences it per Section 7.1. Identity-Info header and dereferences it per Section 7.1.
Note that this is not a SIP message, but an HTTP message Note that this is not a SIP message, but an HTTP message
[RFC2616]. [RFC2616].
Step 5. AS Returns SAML Assertion Step 5. AS Returns SAML Assertion
Upon receipt of the above HTTP request, which contains an Upon receipt of the above HTTP request, which contains an
embedded reference to Alice's SAML Assertion, Alice's AS embedded reference to Alice's SAML Assertion, Alice's AS
returns her assertion in an HTTP response message. returns her assertion in an HTTP response message.
Upon receipt of Alice's SAML Assertion, the AS continues its Upon receipt of Alice's SAML Assertion, the AS continues its
verification of the INVITE message. If successful, it verification of the INVITE message. If successful, it
returns a 200 OK message directly to Alice. Otherwise it returns a 200 OK message directly to Alice. Otherwise it
returns an appropriate SIP error response. returns an appropriate SIP error response.
Step 6. Callee Returns SIP 200 OK to Caller Step 6. Callee Returns SIP 200 OK to Caller
If Bob determines, based upon Alice's identity as asserted by If Bob determines, based upon Alice's identity as asserted
the AS, and as further substantiated by the information in by the AS, and as further substantiated by the information
the SAML assertion, to accept the INVITE, he returns a SIP in the SAML assertion, to accept the INVITE, he returns a
200 OK message directly to Alice. SIP 200 OK message directly to Alice.
6.1.3. Profile Description 6.1.3. Profile Description
The following sections provide detailed definitions of the individual The following sections provide detailed definitions of the individual
profile steps. The relevant illustration is Figure 3, below. Note profile steps. The relevant illustration is Figure 3, below. Note
that this profile is agnostic to the specific SIP request, and also that this profile is agnostic to the specific SIP request, and also
that the Sender and Authentication Service (AS) may be seperate or that the Sender and Authentication Service (AS) may be seperate or
co-located in actuality. co-located in actuality.
+------------------+ +------------------+ +------------------+ +------------------+ +------------------+ +------------------+
skipping to change at page 18, line 41 skipping to change at page 19, line 41
| |<=====================| (4) | |<=====================| (4)
| | (via HTTP) | | | (via HTTP) |
| | | | | |
| | HTTP/1.1 200 OK | | | HTTP/1.1 200 OK |
| |=====================>| (5) | |=====================>| (5)
| | | | | |
| | | | | |
| | ? | (6) | | ? | (6)
| | | | | |
Figure 3: AS-driven SIP SAML Attribute Fetch Profile: Message Flow Figure 3: AS-driven SIP SAML Attribute Fetch Profile: Message Flow
6.1.3.1. Initial SIP Transaction between Sender and AS 6.1.3.1. Initial SIP Transaction between Sender and AS
This OPTIONAL step maps to Steps 1 and 2 of Section 5 "Authentication This OPTIONAL step maps to Steps 1 and 2 of Section 5 "Authentication
Service Behavior" of [I-D.ietf-sip-identity]. If the SIP request Service Behavior" of [I-D.ietf-sip-identity]. If the SIP request
sent by the caller in substep 1a is deemed insufficiently sent by the caller in substep 1a is deemed insufficiently
authenticated by the AS per the rules stipulated by [I-D.ietf-sip- authenticated by the AS per the rules stipulated by
identity] Steps 1 and 2, then the AS MUST authenticate the sender of [I-D.ietf-sip-identity] Steps 1 and 2, then the AS MUST authenticate
the message. The particulars of how this is accomplished depend upon the sender of the message. The particulars of how this is
implementation and/or deployment instantiation as discussed in accomplished depend upon implementation and/or deployment
instantiation as discussed in [I-D.ietf-sip-identity]. Substeps 1b
[I-D.ietf-sip-identity]. Substeps 1b and 1c as shown in Figure 3 are and 1c as shown in Figure 3 are non-normative and illustrative only.
non-normative and illustrative only.
6.1.3.2. Sender sends SIP Request Message with Authorization 6.1.3.2. Sender sends SIP Request Message with Authorization
Credentials to the AS Credentials to the AS
This step maps to Steps 1 and 2 of Section 5 "Authentication Service This step maps to Steps 1 and 2 of Section 5 "Authentication Service
Behavior" of [I-D.ietf-sip-identity]. This request is presumed to be Behavior" of [I-D.ietf-sip-identity]. This request is presumed to be
made in a context such that the AS will not challenge it -- i.e., the made in a context such that the AS will not challenge it -- i.e., the
AS will consider the sender of the message to be authenticated. If AS will consider the sender of the message to be authenticated. If
this is not true, then this procedure reverts back to Step 1, above. this is not true, then this procedure reverts back to Step 1, above.
skipping to change at page 19, line 36 skipping to change at page 20, line 35
The AS MUST construct a SAML assertion according to the "Assertion The AS MUST construct a SAML assertion according to the "Assertion
Profile Description" specified in Section 6.1.4 of this Profile Description" specified in Section 6.1.4 of this
specification. specification.
The AS SHOULD construct an HTTPS, and MAY construct an HTTP, URI The AS SHOULD construct an HTTPS, and MAY construct an HTTP, URI
per Section "3.7.5.1 URI Syntax" of [OASIS.saml-bindings-2.0-os]. per Section "3.7.5.1 URI Syntax" of [OASIS.saml-bindings-2.0-os].
The AS MUST use the URI constructed in the immediately preceding The AS MUST use the URI constructed in the immediately preceding
substep as the value of the Identity-Info header that is added to substep as the value of the Identity-Info header that is added to
the SIP request message per Step 4 of Section 5 of [I-D.ietf-sip- the SIP request message per Step 4 of Section 5 of
identity]. [I-D.ietf-sip-identity].
Upon successful completion of all of the above, the AS forwards the Upon successful completion of all of the above, the AS forwards the
request message. request message.
At this point in this step, after perhaps traversing some number of At this point in this step, after perhaps traversing some number of
intermediaries, the SIP request message arrives at a SIP network intermediaries, the SIP request message arrives at a SIP network
entity performing the "verifier" role. This role and its behavior entity performing the "verifier" role. This role and its behavior
are specified in Section 6 "Verifier Behavior" of [I-D.ietf-sip- are specified in Section 6 "Verifier Behavior" of
identity]. The verifier MUST perform the steps enumerated in the [I-D.ietf-sip-identity]. The verifier MUST perform the steps
aforementioned section, with the following modifications: enumerated in the aforementioned section, with the following
modifications:
Step 1 of [I-D.ietf-sip-identity] Section 6 maps to and is updated Step 1 of [I-D.ietf-sip-identity] Section 6 maps to and is updated
by, the following two steps in this procedure. by, the following two steps in this procedure.
Steps 2, 3, and 4 of [I-D.ietf-sip-identity] Section 6 may be Steps 2, 3, and 4 of [I-D.ietf-sip-identity] Section 6 may be
mapped across this latter portion of this step, and/or the mapped across this latter portion of this step, and/or the
following two steps, as appropriate. following two steps, as appropriate.
6.1.3.4. Verifier Dereferences HTTP-based SAML URI Reference 6.1.3.4. Verifier Dereferences HTTP-based SAML URI Reference
skipping to change at page 20, line 48 skipping to change at page 21, line 48
SIP request it received. SIP request it received.
6.1.4. Assertion Profile Description 6.1.4. Assertion Profile Description
This section defines the particulars of how the sender, i.e., the This section defines the particulars of how the sender, i.e., the
SAML Authority, MUST construct certain portions of the SAML SAML Authority, MUST construct certain portions of the SAML
assertions it issues. The schema for SAML assertions themselves is assertions it issues. The schema for SAML assertions themselves is
defined in Section 2.3 of [OASIS.saml-core-2.0-os]. defined in Section 2.3 of [OASIS.saml-core-2.0-os].
An example SAML assertion, formulated according to this profile is An example SAML assertion, formulated according to this profile is
given in Section 8. given in Section 9.
Overall SAML assertion profile requirements: Overall SAML assertion profile requirements:
The SAML assertion MUST be signed by the same key as used to sign The SAML assertion MUST be signed by the same key as used to sign
the contents of the Identity header field. Signing of SAML the contents of the Identity header field. Signing of SAML
assertions is defined in Section 5.4 of [OASIS.saml-core-2.0-os]. assertions is defined in Section 5.4 of [OASIS.saml-core-2.0-os].
In the following subsections, the SAML assertion profile is specified In the following subsections, the SAML assertion profile is specified
element-by-element, in a top-down, depth-first manner, beginning with element-by-element, in a top-down, depth-first manner, beginning with
the outermost element, "<Assertion>". Where applicable, the the outermost element, "<Assertion>". Where applicable, the
skipping to change at page 22, line 45 skipping to change at page 23, line 50
Attribute: NotOnOrAfter Attribute: NotOnOrAfter
The value of the NotOnOrAfter XML attribute MUST be set to a time The value of the NotOnOrAfter XML attribute MUST be set to a time
instant later than the value for NotBefore. instant later than the value for NotBefore.
6.1.4.1.4. Element: <AttributeStatement> 6.1.4.1.4. Element: <AttributeStatement>
The SAML assertion MAY contain an <AttributeStatement> element. If The SAML assertion MAY contain an <AttributeStatement> element. If
so, the <AttributeStatement> element will contain attribute-value so, the <AttributeStatement> element will contain attribute-value
pairs, e.g., of a user profile nature, encoded according to either pairs, e.g., of a user profile nature, encoded according to either
one of the "SAML Attribute Profiles" as specified in [OASIS.saml- one of the "SAML Attribute Profiles" as specified in
profiles-2.0-os], or encoded in some implementation- and/or [OASIS.saml-profiles-2.0-os], or encoded in some implementation-
deployment-specific attribute profile. and/or deployment-specific attribute profile.
The attribute-value pairs SHOULD in fact pertain to the entity The attribute-value pairs SHOULD in fact pertain to the entity
identified in the SIP From header field, since a SAML assertion identified in the SIP From header field, since a SAML assertion
formulated per this overall section is stating that they do. formulated per this overall section is stating that they do.
6.1.5. Assertion Verification 6.1.5. Assertion Verification
This section specifies the steps that a verifier participating in This section specifies the steps that a verifier participating in
this profile MUST perform in addition to the "Verifier Behavior" this profile MUST perform in addition to the "Verifier Behavior"
specified in Section 6 of [I-D.ietf-sip-identity]. specified in Section 6 of [I-D.ietf-sip-identity].
skipping to change at page 26, line 5 skipping to change at page 27, line 5
to [OASIS.saml-bindings-2.0-os]): to [OASIS.saml-bindings-2.0-os]):
Section 3.7.5.3 Security Considerations: Section 3.7.5.3 Security Considerations:
Support for TLS 1.0 or SSL 3.0 is mandatory to implement. Support for TLS 1.0 or SSL 3.0 is mandatory to implement.
Section 3.7.5.4 Error Reporting: Section 3.7.5.4 Error Reporting:
All SHOULDs in this section are to be interpreted as MUSTs. All SHOULDs in this section are to be interpreted as MUSTs.
8. Example SAML Assertions 8. Error Codes
8.1. 425 (Bad SAML Assertion) Response Code
If a UAS or SIP intermediary detects an error in a request message
specific to the location information, a new 4XX level error is
created here to indicate a problem with the request message. This
document creates and IANA registers the new error code:
425 (Bad SAML Assertion)
The 425 (Bad SAML Assertion) response code is a rejection of the
content of a SAML assertion within the original SIP Request
indicating the SAML assertion was malformed or not satisfactory for
the recipient's purpose or could not be dereferenced. No further
action by the UAC is required.
The UAC can use means outside the scope of this document to ensure
that subsequent requests are going to contain SAML assertions that
are acceptable to the UAS. There is no cross-transaction awareness
expected by either the UAS or SIP intermediary as a result of this
error message.
More resolution of the error for which the 425 was generated MAY be
included in a Reason header [RFC3326]. For these more granular
location specific errors, the 'protocol' in the Reason header is
'SAML', defined in Section 3.4. of RFC 3326 [RFC3326] states that the
Reason Header normally is not found in a response. This document
extends the use of Reason to include its use within a 425 response.
This new error code is IANA registered in Section 9 of this document.
An initial set of error codes can be found in Section 8.
8.2. The SAML Reason Protocol
For use with the Reason header, discussed in Section 8.1, this
document defines and IANA registers a new Reason Protocol per RFC
3326 [RFC3326].
Protocol Value Protocol Cause Reference
SAML Status RFCyyyy (i.e., this document)
8.3. Failure Reasons to be Registered
Here is the list and description of each IANA registered location
error reason code. If the location generator were to receive one of
these indications in a SIP response, it would be in a Reason header.
The protocol field of this Reason header would be "SAML", as defined
in Section 8.2. Examples of the Reason header are given for each
indication below.
8.3.1. SAML Assertion Content Not Supported
"SAML Assertion Content Not Supported" means the SAML content
supplied in the request was not processed even though the recipient
understood SAML. If the SAML content is understood, but not desired,
a cause=2 or cause=3 response SHOULD be returned.
Cause value: 1
Default text string: SAML Assertion Content Not Supported
An example usage in a SIP Reason header:
Reason: SAML; cause=1; SAML Assertion Content Not Supported
8.3.2. Authentication Statements Desired Instead
"Authentication Statements Desired Instead" means the SAML assertion
supplied in the request was understood and supported, but that the
recipient, or an application on the recipient demands authentication
statements.
Cause value: 2
Default text string: Authentication Statements Desired Instead
An example usage in a SIP Reason header:
Reason: SAML; cause=2; Authentication Statements Desired Instead
8.3.3. Authorization Statements Desired Instead
"Authorization Statements Desired Instead" means the SAML assertion
supplied in the request was understood and supported, but that the
recipient, or an application on the recipient demands authorization
statements.
Cause value: 3
Default text string: Authorization Statements Desired Instead
An example usage in a SIP Reason header:
Reason: SAML; cause=3; Authorization Statements Desired Instead
8.3.4. Attribute Statements Desired Instead
"Attribute Statements Desired Instead" means the SAML assertion
supplied in the request was understood and supported, but that the
recipient, or an application on the recipient demands attribute
statements.
Cause value: 4
Default text string: Attribute Statements Desired Instead
An example usage in a SIP Reason header:
Reason: SAML; cause=4; Attribute Statements Desired Instead
8.3.5. Unsupported Content
"Unsupported Content" means the recipient encounters a problem with
the content of the SAML assertion.
Cause value: 5
Default text string: Unsupported Content
An example usage in a SIP Reason header:
Reason: SAML; cause=5; Unsupported Content
8.3.6. Unable to Dereference
"Unable to Dereference" means the recipient cannot resolve the
reference to a SAML assertion. This may mean the URI is bad, or the
indicated server had some other error or rejected the request.
Cause value: 6
Default text string: Unable to Dereference
An example usage in a SIP Reason header:
Reason: SAML; cause=6; Unable to Dereference
8.3.7. Cannot Parse SAML Assertion
"Cannot Parse SAML Assertion" means the SAML assertion is not well
formed.
Cause value: 7
Default text string: Cannot Parse SAML Assertion
An example usage in a SIP Reason header:
Reason: SAML; cause=7; Cannot Parse SAML Assertion
8.3.8. Conflicting SAML Assertions Supplied
"Conflicting SAML Assertions Supplied" means a recipient received
more than one SAML assertion and their content is conflicting
Cause value: 8
Default text string: Conflicting SAML Assertion Supplied
An example usage in a SIP Reason header:
Reason: SAML; cause=8; Conflicting SAML Assertion Supplied
8.3.9. Insufficient SAML Statements
"Insufficient SAML Statements" means there is not enough information
in the SAML assertion to sufficiently authenticate or authorize the
requesting party.
Cause value: 9
Default text string: Insufficient SAML Statements
An example usage in a SIP Reason header:
Reason: SAML; cause=9; Insufficient SAML Statements
8.3.10. Dereference Timeout
"Dereference Timeout" means that the dereferencing node has not
received a response within a reasonable timeframe.
Cause value: 10
Default text string: Dereference Timeout
An example usage in a SIP Reason header:
Reason: SAML; cause=10; Dereference Timeout
9. Example SAML Assertions
This section presents two examples of a SAML assertion, one unsigned This section presents two examples of a SAML assertion, one unsigned
(for clarity), the other signed (for accuracy). (for clarity), the other signed (for accuracy).
In the first example, Figure 5, the assertion is attesting with In the first example, Figure 16, the assertion is attesting with
respect to the subject (lines 7-15) "Alice@example.com" (line 11). respect to the subject (lines 7-15) "Alice@example.com" (line 11).
The validity conditions are expressed in lines 16-23, via both a The validity conditions are expressed in lines 16-23, via both a
validity period expressed as temporal endpoints, and an "audience validity period expressed as temporal endpoints, and an "audience
restriction" stating that this assertion's semantics are valid for restriction" stating that this assertion's semantics are valid for
only the relying party named "example2.com". Also, the assertion's only the relying party named "example2.com". Also, the assertion's
issuer is noted in lines 4-5. issuer is noted in lines 4-5.
The above items correspond to some aspects of this specification's The above items correspond to some aspects of this specification's
SAML assertion profile, as noted below in Security Considerations SAML assertion profile, as noted below in Security Considerations
dicussions, see: Section 9.1 and Section 9.2. dicussions, see: Section 10.1 and Section 10.2.
In lines 24-36, Alice's telephone number is conveyed, in a "typed" In lines 24-36, Alice's telephone number is conveyed, in a "typed"
fashion, using LDAP/X.500 schema as the typing means. fashion, using LDAP/X.500 schema as the typing means.
1 <Assertion ID="_a75adf55-01d7-40cc-929f-dbd8372ebdfc" 1 <Assertion ID="_a75adf55-01d7-40cc-929f-dbd8372ebdfc"
2 IssueInstant="2003-04-17T00:46:02Z" Version="2.0" 2 IssueInstant="2003-04-17T00:46:02Z" Version="2.0"
3 xmlns="urn:oasis:names:tc:SAML:2.0:assertion"> 3 xmlns="urn:oasis:names:tc:SAML:2.0:assertion">
4 <Issuer> 4 <Issuer>
5 example.com 5 example.com
6 </Issuer> 6 </Issuer>
skipping to change at page 27, line 43 skipping to change at page 33, line 43
29 "urn:oasis:names:tc:SAML:2.0:attrname-format:uri" 29 "urn:oasis:names:tc:SAML:2.0:attrname-format:uri"
30 Name="urn:oid:2.5.4.20" 30 Name="urn:oid:2.5.4.20"
31 FriendlyName="telephoneNumber"> 31 FriendlyName="telephoneNumber">
32 <saml:AttributeValue xsi:type="xs:string"> 32 <saml:AttributeValue xsi:type="xs:string">
33 +1-888-555-1212 33 +1-888-555-1212
34 </saml:AttributeValue> 34 </saml:AttributeValue>
35 </saml:Attribute> 35 </saml:Attribute>
36 </AttributeStatement> 36 </AttributeStatement>
37 </Assertion> 37 </Assertion>
Figure 5: Unsigned SAML Assertion Illustrating Conveyance of Figure 16: Unsigned SAML Assertion Illustrating Conveyance of
Subject Attribute Subject Attribute
In the second example, Figure 6, the information described above is In the second example, Figure 17, the information described above is
the same, the addition is that this version of the assertion is the same, the addition is that this version of the assertion is
signed. All the signature information is conveyed in the <ds: signed. All the signature information is conveyed in the <ds:
signature> element, lines 7-47. Thus this assertion's origin and its signature> element, lines 7-47. Thus this assertion's origin and its
integrity are assured. Since this assertion is the same as the one integrity are assured. Since this assertion is the same as the one
in the first example above, other than having a signature added, the in the first example above, other than having a signature added, the
second example below addresses the same Security Considerations second example below addresses the same Security Considerations
aspects, plus those requiring a Signature. aspects, plus those requiring a Signature.
1 <Assertion ID="_a75adf55-01d7-40cc-929f-dbd8372ebdfc" 1 <Assertion ID="_a75adf55-01d7-40cc-929f-dbd8372ebdfc"
2 IssueInstant="2003-04-17T00:46:02Z" Version="2.0" 2 IssueInstant="2003-04-17T00:46:02Z" Version="2.0"
skipping to change at page 30, line 35 skipping to change at page 36, line 35
70 "urn:oasis:names:tc:SAML:2.0:attrname-format:uri" 70 "urn:oasis:names:tc:SAML:2.0:attrname-format:uri"
71 Name="urn:oid:2.5.4.20" 71 Name="urn:oid:2.5.4.20"
72 FriendlyName="telephoneNumber"> 72 FriendlyName="telephoneNumber">
73 <saml:AttributeValue xsi:type="xs:string"> 73 <saml:AttributeValue xsi:type="xs:string">
74 +1-888-555-1212 74 +1-888-555-1212
75 </saml:AttributeValue> 75 </saml:AttributeValue>
76 </saml:Attribute> 76 </saml:Attribute>
77 </AttributeStatement> 77 </AttributeStatement>
78 </Assertion> 78 </Assertion>
Figure 6: Signed SAML Assertion Illustrating Conveyance of Subject Figure 17: Signed SAML Assertion Illustrating Conveyance of Subject
Attribute Attribute
9. Security Considerations 10. Security Considerations
This section discusses security considerations when using SAML with This section discusses security considerations when using SAML with
SIP. SIP.
9.1. Man-in-the-middle Attacks and Stolen Assertions 10.1. Man-in-the-middle Attacks and Stolen Assertions
Threat: Threat:
By making SAML assertions available via HTTP-based requests by a By making SAML assertions available via HTTP-based requests by a
potentially unbounded set of requesters, it is conceivably potentially unbounded set of requesters, it is conceivably
possible that anyone would be able to simply request one and possible that anyone would be able to simply request one and
obtain it. By SIP intermediaries on the signaling path for obtain it. By SIP intermediaries on the signaling path for
example. Or, an HTTP intermediary/proxy could intercept the example. Or, an HTTP intermediary/proxy could intercept the
assertion as it is being returned to a requester. assertion as it is being returned to a requester.
skipping to change at page 32, line 7 skipping to change at page 38, line 7
* relying party is represented in the SAML assertion's Audience * relying party is represented in the SAML assertion's Audience
Restriction. Restriction.
* Issuer is represented in the SAML assertion. * Issuer is represented in the SAML assertion.
* validity period for assertion is restricted. * validity period for assertion is restricted.
* etc. * etc.
9.2. Forged Assertion 10.2. Forged Assertion
Threat: Threat:
A malicious user could forge or alter a SAML assertion in order to A malicious user could forge or alter a SAML assertion in order to
communicate with the SIP entities. communicate with the SIP entities.
Countermeasures: Countermeasures:
To avoid this kind of attack, the entities must assure that proper To avoid this kind of attack, the entities must assure that proper
mechanisms for protecting the SAML assertion are employed, e.g., mechanisms for protecting the SAML assertion are employed, e.g.,
signing the SAML assertion itself. Section 5.1 of [OASIS.saml- signing the SAML assertion itself. Section 5.1 of
core-2.0-os] specifies the signing of SAML assertions. [OASIS.saml-core-2.0-os] specifies the signing of SAML assertions.
Additionally, the assertion content dictated by the SAML assertion Additionally, the assertion content dictated by the SAML assertion
profile herein ensures ample evidence for a relying party to profile herein ensures ample evidence for a relying party to
verify the assertion and its relationship with the received SIP verify the assertion and its relationship with the received SIP
request. request.
9.3. Replay Attack 10.3. Replay Attack
Threat: Threat:
Theft of SIP message protected by the mechanisms described herein Theft of SIP message protected by the mechanisms described herein
and replay of it at a later time. and replay of it at a later time.
Countermeasures: Countermeasures:
There are various provisions within [I-D.ietf-sip-identity] that There are various provisions within [I-D.ietf-sip-identity] that
prevent a replay attack. prevent a replay attack.
10. Contributors 11. Contributors
The authors would like to thank Marcus Tegnander and Henning The authors would like to thank Marcus Tegnander and Henning
Schulzrinne for his contributions to earlier versions of this Schulzrinne for his contributions to earlier versions of this
document. document.
11. Acknowledgments 12. Acknowledgments
We would like to thank RL 'Bob' Morgan, Stefan Goeman, Shida We would like to thank RL 'Bob' Morgan, Stefan Goeman, Shida
Schubert, Jason Fischl and Vijay Gurbani for their comments to this Schubert, Jason Fischl and Vijay Gurbani for their comments to this
draft. The "AS-driven SIP SAML URI-based Attribute Assertion Fetch draft. The "AS-driven SIP SAML URI-based Attribute Assertion Fetch
Profile" is based on an idea by Jon Peterson. Profile" is based on an idea by Jon Peterson.
12. IANA Considerations 13. IANA Considerations
[Editor's Note: A future version of this document will provide IANA 13.1. IANA Registration for Response Code 4XX
considerations.]
13. Open Issues Reference: RFC-XXXX (i.e. this document)
Response code: 425
Default reason phrase: Bad SAML Assertion
This SIP Response code is defined in Section 8.1 of this document.
13.2. IANA Registration of the SAML Reason Protocol
The Reason Protocol value "SAML" is created by this document, with
the definition and values in Section 8.1.
Cause-Code Optional-Default-Text Reference
---------- --------------------- ---------
Cause=1 Location Format Not Supported [This doc]
Cause=2 Geo-location Format Desired [This doc]
Cause=3 Civic-location Format Desired [This doc]
Cause=4 Unsupported Schema [This doc]
Cause=5 Cannot Parse Location Supplied [This doc]
Cause=6 Cannot Find Location [This doc]
Cause=7 Cannot Dereference [This doc]
Cause=8 Conflicting Locations Supplied [This doc]
Cause=9 Incomplete Location Supplied [This doc]
Cause=10 Dereference Timeout [This doc]
Cause=11 Cannot Process Dereference [This doc]
Cause=400 Bad Request [This doc]
Cause=403 Forbidden [This doc]
Cause=404 Not Found [This doc]
Cause=414 Location Error [This doc]
Cause=500 Server Internal Error [This doc]
Cause=501 Service Not Implemented [This doc]
Cause=504 Server Time-Out [This doc]
Legend:
------
Cause-Code - Cause value for this indication
Optional-Default-Text - optional text string of indication
Reference - document which is the reference for this
cause value
14. Open Issues
A list of open issues can be found at: A list of open issues can be found at:
http://www.tschofenig.com:8080/saml-sip/ http://www.tschofenig.com:8080/saml-sip/
14. References 15. References
14.1. Normative References 15.1. Normative References
[I-D.ietf-sip-identity] [I-D.ietf-sip-identity]
Peterson, J. and C. Jennings, "Enhancements for Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session Authenticated Identity Management in the Session
Initiation Protocol (SIP)", draft-ietf-sip-identity-06 Initiation Protocol (SIP)", draft-ietf-sip-identity-06
(work in progress), October 2005. (work in progress), October 2005.
[I-D.ietf-sipping-trait-authz] [I-D.ietf-sipping-trait-authz]
Peterson, J., "Trait-based Authorization Requirements for Peterson, J., "Trait-based Authorization Requirements for
the Session Initiation Protocol (SIP)", the Session Initiation Protocol (SIP)",
skipping to change at page 38, line 16 skipping to change at page 44, line 16
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002. June 2002.
[RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet [RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280, Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002. April 2002.
[RFC3326] Schulzrinne, H., Oran, D., and G. Camarillo, "The Reason
Header Field for the Session Initiation Protocol (SIP)",
RFC 3326, December 2002.
[RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer [RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003. Method", RFC 3515, April 2003.
[RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An [RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
IETF URN Sub-namespace for Registered Protocol IETF URN Sub-namespace for Registered Protocol
Parameters", BCP 73, RFC 3553, June 2003. Parameters", BCP 73, RFC 3553, June 2003.
[RFC3893] Peterson, J., "Session Initiation Protocol (SIP) [RFC3893] Peterson, J., "Session Initiation Protocol (SIP)
Authenticated Identity Body (AIB) Format", RFC 3893, Authenticated Identity Body (AIB) Format", RFC 3893,
September 2004. September 2004.
[W3C.xmldsig-core] [W3C.xmldsig-core]
Eastlake, D., Reagle , J., and D. Solo, "XML-Signature Eastlake, D., Reagle , J., and D. Solo, "XML-Signature
Syntax and Processing", W3C Recommendation xmldsig-core, Syntax and Processing", W3C Recommendation xmldsig-core,
October 2000, <http://www.w3.org/TR/xmldsig-core/>. October 2000, <http://www.w3.org/TR/xmldsig-core/>.
14.2. Informative References 15.2. Informative References
[I-D.ietf-sip-content-indirect-mech] [I-D.ietf-sip-content-indirect-mech]
Burger, E., "A Mechanism for Content Indirection in Burger, E., "A Mechanism for Content Indirection in
Session Initiation Protocol (SIP) Messages", Session Initiation Protocol (SIP) Messages",
draft-ietf-sip-content-indirect-mech-05 (work in draft-ietf-sip-content-indirect-mech-05 (work in
progress), October 2004. progress), October 2004.
[I-D.ietf-sipping-certs] [I-D.ietf-sipping-certs]
Jennings, C. and J. Peterson, "Certificate Management Jennings, C. and J. Peterson, "Certificate Management
Service for The Session Initiation Protocol (SIP)", Service for The Session Initiation Protocol (SIP)",
draft-ietf-sipping-certs-03 (work in progress), draft-ietf-sipping-certs-03 (work in progress),
March 2006. March 2006.
[I-D.jennings-sipping-pay] [I-D.jennings-sipping-pay]
Jennings, C., "Payment for Services in Session Initiation Jennings, C., "Payment for Services in Session Initiation
Protocol (SIP)", draft-jennings-sipping-pay-03 (work in Protocol (SIP)", draft-jennings-sipping-pay-04 (work in
progress), October 2005. progress), June 2006.
[I-D.peterson-message-identity] [I-D.peterson-message-identity]
Peterson, J., "Security Considerations for Impersonation Peterson, J., "Security Considerations for Impersonation
and Identity in Messaging Systems", and Identity in Messaging Systems",
draft-peterson-message-identity-00 (work in progress), draft-peterson-message-identity-00 (work in progress),
October 2004. October 2004.
[IANA.application.samlassertion-xml] [IANA.application.samlassertion-xml]
OASIS Security Services Technical Committee (SSTC), OASIS Security Services Technical Committee (SSTC),
"application/samlassertion+xml MIME Media Type "application/samlassertion+xml MIME Media Type
skipping to change at page 42, line 25 skipping to change at page 48, line 25
| | +--------+ | | | +--------+ |
O | | Bob's | | O | | Bob's | |
O /|\ <----+----| SIP | | O /|\ <----+----| SIP | |
/|\ / \ SIP | | Proxy | | /|\ / \ SIP | | Proxy | |
/ \ Bob | | | | / \ Bob | | | |
Alice | +--------+ | Alice | +--------+ |
| SIP based | | SIP based |
| Network | | Network |
+---------------------+ +---------------------+
Figure 7: PSTN to SIP call Figure 20: PSTN to SIP call
Note that the INVITE emitted by the PSTN/SIP gateway could Note that the INVITE emitted by the PSTN/SIP gateway could
alternatively be simply forwarded by Bob's SIP Proxy to Bob's phone, alternatively be simply forwarded by Bob's SIP Proxy to Bob's phone,
and Bob's phone could take on the SIP Identity "verifier" role, which and Bob's phone could take on the SIP Identity "verifier" role, which
is being played by Bob's SIP proxy in the figure. is being played by Bob's SIP proxy in the figure.
Whichever approach is employed is a decision local to Bob's Whichever approach is employed is a decision local to Bob's
administrative domain and can be made independently. administrative domain and can be made independently.
A.2. SIP Conferencing A.2. SIP Conferencing
skipping to change at page 42, line 50 skipping to change at page 48, line 50
conferencing server may want or need various of her profile conferencing server may want or need various of her profile
attributes included and may also need to be authenticated by the attributes included and may also need to be authenticated by the
conference server. The following properties could be provided by conference server. The following properties could be provided by
this procedure: this procedure:
o The user identity can be replaced to allow the user to be o The user identity can be replaced to allow the user to be
anonymous with regard to the Focus. This can be accomplished via anonymous with regard to the Focus. This can be accomplished via
[RFC3323] in combination with [I-D.ietf-sip-identity], per the [RFC3323] in combination with [I-D.ietf-sip-identity], per the
latter, or, latter, or,
o The user identity could be asserted to the Focus, via [I-D.ietf- o The user identity could be asserted to the Focus, via
sip-identity] mechanisms, and/or, [I-D.ietf-sip-identity] mechanisms, and/or,
o the SAML assertion could provide additional user profile o the SAML assertion could provide additional user profile
information such as group membership (belongs to the students, information such as group membership (belongs to the students,
staff, faculty group of university X). This could, for non- staff, faculty group of university X). This could, for non-
identity-based authorization systems, imply certain rights. identity-based authorization systems, imply certain rights.
The corresponding SIP message flow (in high level detail) could have The corresponding SIP message flow (in high level detail) could have
the following shape: the following shape:
+-----+ +-----------+ +-----------+ +-----+ +-----------+ +-----------+
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| OK |<------------------| | OK |<------------------|
|<------------------| | |<------------------| |
| | | | | |
| ACK | | | ACK | |
|------------------>| ACK | |------------------>| ACK |
| |------------------>| | |------------------>|
| | | | | |
| | | | | |
... many more msgs... ... many more msgs...
Figure 8: SIP Conferencing and SAML Figure 21: SIP Conferencing and SAML
However, there are obvious scaling issues with the conference server However, there are obvious scaling issues with the conference server
having to do the outbound requests in order to obtain SAML assertions having to do the outbound requests in order to obtain SAML assertions
and certificates for conference participants. and certificates for conference participants.
This could be addressed by creating another SIP SAML Profile where This could be addressed by creating another SIP SAML Profile where
the caller obtains the necessary information, e.g., SAML assertions, the caller obtains the necessary information, e.g., SAML assertions,
and places them into its SIP request message prior to sending it. and places them into its SIP request message prior to sending it.
This would obviate the need for the callee relying party to make This would obviate the need for the callee relying party to make
requests in order to obtain said information. This is a topic for requests in order to obtain said information. This is a topic for
future work, and possibly future revisions of this specification. future work, and possibly future revisions of this specification.
A.3. Compensation using SIP and SAML A.3. Compensation using SIP and SAML
This section describes a scenario where SAML is used in SIP to This section describes a scenario where SAML is used in SIP to
realize compensation functionality as described in [I-D.jennings- realize compensation functionality as described in
sipping-pay]. [I-D.jennings-sipping-pay].
Note that this scenario is not directly addressed by the SIP SAML Note that this scenario is not directly addressed by the SIP SAML
Profile and SAML SIP Binding presently defined in this specification. Profile and SAML SIP Binding presently defined in this specification.
Rather, this use case calls for additional such profiles and bindings Rather, this use case calls for additional such profiles and bindings
to be developed. to be developed.
+--------+ +--------+ +--------+ +--------+ +--------+ +--------+
|Payment | | User | |Merchant| |Payment | | User | |Merchant|
|Provider| | Alice | |Bob | |Provider| | Alice | |Bob |
| | | | | | | | | | | |
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| | | | | |
| 4) SAML Assertion | | | 4) SAML Assertion | |
| (=Receipt) | | | (=Receipt) | |
|---------------------->| | |---------------------->| |
| | 5) Call + Receipt | | | 5) Call + Receipt |
| |------------------------>| | |------------------------>|
| | | | | |
| | 6) 200 OK | | | 6) 200 OK |
| |<------------------------| | |<------------------------|
| | | | | |
Figure 22: Message flow for SIP payment
Figure 9: Message flow for SIP payment
User Alice and the Merchant Bob interact with each other using SIP User Alice and the Merchant Bob interact with each other using SIP
and the Alice uses HTTP to exchange messages with a Payment Provider. and the Alice uses HTTP to exchange messages with a Payment Provider.
Initially, Alice makes a call to Bob (1). Bob determines that a Initially, Alice makes a call to Bob (1). Bob determines that a
payment is required and includes information about the payment in an payment is required and includes information about the payment in an
Offer body of a 402 (Payment Required) response to Alice (2). Alice Offer body of a 402 (Payment Required) response to Alice (2). Alice
looks at this Offer and decides to make a payment. Alice therefore looks at this Offer and decides to make a payment. Alice therefore
instructs her Payment Provider to make a transfer from Alice"s instructs her Payment Provider to make a transfer from Alice"s
account to the Merchants"s account (3) using a request for a SAML account to the Merchants"s account (3) using a request for a SAML
assertion with the extensions defined in this document. The Payment assertion with the extensions defined in this document. The Payment
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Provider made the transaction and protects the Receipt with a digital Provider made the transaction and protects the Receipt with a digital
signature. Alice resubmits the call to the Merchant Bob with the signature. Alice resubmits the call to the Merchant Bob with the
Receipt from the Payment Provier. Merchant Bob can check for replay Receipt from the Payment Provier. Merchant Bob can check for replay
attacks using the timestamp and a replay protection indiciator attacks using the timestamp and a replay protection indiciator
initially provided with the Offer. Bob can then check the signature initially provided with the Offer. Bob can then check the signature
is valid using the Payment Provider"s public key. is valid using the Payment Provider"s public key.
Authors' Addresses Authors' Addresses
Hannes Tschofenig Hannes Tschofenig
Siemens Siemens Networks GmbH & Co KG
Otto-Hahn-Ring 6 Otto-Hahn-Ring 6
Munich, Bavaria 81739 Munich, Bavaria 81739
Germany Germany
Email: Hannes.Tschofenig@siemens.com Email: Hannes.Tschofenig@siemens.com
Jeff Hodges Jeff Hodges
NeuStar, Inc. NeuStar, Inc.
2000 Broadway Street 2000 Broadway Street
Redwood City, CA 94063 Redwood City, CA 94063
skipping to change at page 47, line 5 skipping to change at page 53, line 5
Email: jmpolk@cisco.com Email: jmpolk@cisco.com
Douglas C. Sicker Douglas C. Sicker
University of Colorado at Boulder University of Colorado at Boulder
ECOT 430 ECOT 430
Boulder, CO 80309 Boulder, CO 80309
US US
Email: douglas.sicker@colorado.edu Email: douglas.sicker@colorado.edu
Intellectual Property Statement Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
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.
skipping to change at page 47, line 29 skipping to change at page 53, line 45
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
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rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is provided by the IETF
Internet Society. Administrative Support Activity (IASA).
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