SIPPING G. Camarillo
Internet-Draft Ericsson
Intended status: Standards Track April 24, 2007
Expires: October 26, 2007
A Document Format for Requesting Consent
draft-ietf-sipping-consent-format-03.txt
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document defines an Extensible Markup Language (XML) format for
a permission document used to request consent. A permission document
written in this format is used by a relay to request a specific
recipient permission to perform a particular routing translation.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions and Terminology . . . . . . . . . . . . . . . . . 3
3. Permission Document Structure . . . . . . . . . . . . . . . . 3
3.1. Conditions . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1.1. Identity Condition . . . . . . . . . . . . . . . . . . 4
3.1.2. Sender Condition . . . . . . . . . . . . . . . . . . . 5
3.1.3. Target Condition . . . . . . . . . . . . . . . . . . . 7
3.2. Actions . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2.1. Translation Handling . . . . . . . . . . . . . . . . . 7
4. Example Document . . . . . . . . . . . . . . . . . . . . . . . 7
5. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6.1. XML Namespace Registration . . . . . . . . . . . . . . . . 9
6.2. XML Schema Registration . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 13
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1. Introduction
The framework for consent-based communications in the Session
Initiation Protocol (SIP) [9] identifies the need for a format to
create permission documents. Such permission documents are used by
SIP [3] relays to request permission to perform translations. A
relay is defined as any SIP server, be it a proxy, B2BUA (Back-to-
Back User Agent), or some hybrid, which receives a request and
translates the request URI into one or more next hop URIs to which it
then delivers a request.
The format for permission documents specified in this document is
based on the XML document format for expressing Privacy Preferences
[8].
2. Definitions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
Relay: Any SIP server, be it a proxy, B2BUA (Back-to-Back User
Agent), or some hybrid, that receives a request, translates its
Request-URI into one or more next-hop URIs (i.e., recipient URIs),
and delivers the request to those URIs.
Recipient URI: The Request-URI of an outgoing request sent by an
entity (e.g., a user agent or a proxy). The sending of such
request may have been the result of a translation operation.
Target URI: The Request-URI of an incoming request that arrives to
an entity (e.g., a proxy) that will perform a translation
operation.
Translation operation: Operation by which an entity (e.g., a proxy)
translates the request URI of an incoming request (i.e., the
target URI) into one or more URIs (i.e., recipient URIs) which are
used as the request URIs of one or more outgoing requests.
3. Permission Document Structure
A permission document is an XML document, formatted according to the
schema defined in [8]. Permission documents inherit the MIME type of
common policy documents, 'application/auth-policy+xml'. As described
in [8], this type of document is composed of three parts: conditions,
actions, and transformations. However, even though permission
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documents need to have a transformation part to comply to the common
policy syntax, effectively, permission documents do not make any use
of transformations.
This section defines the new conditions and actions defined by this
specification. This specification does not define any new
transformation.
3.1. Conditions
Note that, as discussed in [8], a permission document applies to a
translation if all the expressions in its conditions part evaluate to
TRUE.
3.1.1. Identity Condition
The identity condition, defined in [8], is matched against the
recipient URI of a translation.
When performing a translation, a relay matches the identity condition
of the permission document that was used to request permission for
that translation against the destination URI of the outgoing request.
When receiving a request granting or denying permissions (e.g., a SIP
PUBLISH request as described in [9]), the relay matches the identity
condition of the permission document that was used to request
permission against the identity of the entity granting or denying
permissions (i.e., the sender of the PUBLISH request).
The <identity> element is defined in [8], which indicates that the
specific usages of the framework document need to define details that
are protocol and usage specific. In particular, this section defines
acceptable means of authentication.
The 'id' attribute in the elements <one> and <except> MUST contain a
scheme when these elements appear in a permission document.
When used with SIP, a recipient granting or denying a relay
permissions is considered authenticated if one of the following
techniques is used:
SIP Identity [7], as described in [9]. For PUBLISH requests that
are authenticated using the SIP Identity mechanism, the identity
of the sender of the PUBLISH request is equal to the SIP URI in
the From header field of the request, assuming that the signature
in the Identity header field has been validated.
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P-Asserted-Identity [5], as described in [9]. For PUBLISH requests
that are authenticated using the P-Asserted-Identity mechanism,
the identity of the sender of the PUBLISH request is equal to the
P-Asserted-Identity header field of the request.
Return Routability Test, as described in [9].
SIP digest, as described in [9].
3.1.2. Sender Condition
The sender condition is matched against the URI of the sender of the
request that is used as input for a translation. Sender conditions
can contain the same elements and attributes as identity conditions.
When performing a translation, a relay matches the sender condition
against the identity of the sender of the incoming request.
The following subsections define acceptable means of authentication,
the procedure for representing the identity of the sender as a URI,
and the procedure for converting an identifier of the form
user@domain, present in the 'id' attribute of the <one> and <except>
elements, into a URI.
3.1.2.1. Acceptable Means of Authentication
When used with SIP, a request sent by a sender is considered
authenticated if one of the following techniques is used:
SIP Digest: the relay authenticates the sender using SIP digest
authentication [2]. However, if the anonymous authentication
described on page 194 of RFC 3261 [3] is used, the sender is not
considered authenticated.
Asserted Identity: if a request contains a P-Asserted-ID header
field [5] and the request is coming from a trusted element, the
sender is considered authenticated.
Cryptographically Verified Identity: if a request contains an
Identity header field as defined in [7], and it validates the From
header field of the request, the request is considered to be
authenticated. Note that this is true even if the request
contained a From header field of the form
sip:anonymous@example.com. As long as the signature verifies that
the request legitimately came from this identity, it is considered
authenticated.
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3.1.2.2. Computing a URI for the Sender
For requests that are authenticated using SIP Digest, the identity of
the sender is set equal to the SIP Address of Record (AOR) for the
user that has authenticated themselves. For example, consider the
following "user record" in a database:
SIP AOR: sip:alice@example.com
digest username: ali
digest password: f779ajvvh8a6s6
digest realm: example.com
If the relay receives a request, challenges it with the realm set to
"example.com", and the subsequent request contains an Authorization
header field with a username of "ali" and a digest response generated
with the password "f779ajvvh8a6s6", the identity used in matching
operations is "sip:alice@example.com".
For requests that are authenticated using RFC 3325 [5], the identity
of the sender is equal to the SIP URI in the P-Asserted-ID header
field. If there are multiple values for the P-Asserted-ID header
field (there can be one sip URI and one tel URI [10]), then each of
them is used for the comparisons outlined in [8], and if either of
them match a <one> or <except> element, it is considered a match.
For requests that are authenticated using the SIP Identity mechanism
[7], identity of the sender is equal to the SIP URI in the From
header field of the request, assuming that the signature in the
Identity header field has been validated.
SIP also allows for anonymous requests. If a request is anonymous
because the digest challenge/response used the "anonymous" username,
the request is considered unauthenticated and will not match the
<sender> condition. If a request is anonymous because it contains a
Privacy header field [4], but still contains a P-Asserted-ID header
field, the identity in the P-Asserted-ID header field is still used
in the authorization computations; the fact that the request was
anonymous has no impact on the identity processing. However, if the
request had traversed a trust boundary and the P-Asserted-ID header
field and the Privacy header field had been removed, the request will
be considered unauthenticated when it arrives at the presence server,
and thus not match the <sender> condition. Finally, if a request
contained an Identity header field that was validated, and the From
header field contained a URI of the form sip:anonymous@example.com,
then the watcher is considered authenticated, and it will have an
identity equal to sip:anonymous@example.com. Had such an identity
been placed into a <one> or <except> element, there will be a match.
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3.1.2.3. Computing a SIP URI from the id Attribute
If the <one> or <except> condition does not contain a scheme,
conversion of the value in the 'id' attribute to a SIP URI is done
trivially. If the characters in the 'id' attribute are valid
characters for the user and hostpart components of the SIP URI, a
'sip:' is appended to the contents of the 'id' attribute, and the
result is the SIP URI. If the characters in the 'id' attribute are
not valid for the user and hostpart components of the SIP URI,
conversion is not possible. This happens, for example, when the user
portion of the 'id' attribute contain UTF-8 characters.
3.1.3. Target Condition
The target condition is matched against the target URI of a
translation. Target conditions can contain the same elements and
attributes as identity conditions.
When performing a translation, a relay matches the target condition
against the destination of the incoming request, which is typically
contained in the Request-URI.
3.2. Actions
The actions in a permission document provide URIs to grant or deny
permission to perform the translation described in the document.
3.2.1. Translation Handling
The <trans-handling> provides URIs for a recipient to grant or deny
the relay permission to perform a translation. The defined values
are:
deny: this action tells the relay not to perform the translation.
grant: this action tells the server to perform the translation.
The 'perm-uri' attribute in the <trans-handling> element provides a
URI to grant or deny permission to perform a translation.
4. Example Document
The following permission document is generated by the relay handling
'sip:alices-friends@example.com' in order to ask for permission to
relay requests sent to that URI to 'sip:bob@example.org'.
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<?xml version="1.0" encoding="UTF-8"?>
<cr:ruleset
xmlns="urn:ietf:params:xml:ns:consent-rules"
xmlns:cp="urn:ietf:params:xml:ns:common-policy"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:ns:consent-rules
consent-rules.xsd">
<cp:rule id="1">
<cp:conditions>
<cp:identity>
<cp:one id="sip:bob@example.org"/>
</cp:identity>
<target>
<cp:one id="sip:alices-friends@example.com""/>
</target>
<sender>
<cp:any/>
</sender>
</cp:conditions>
<cp:actions>
<trans-handling
perm-uri="sip:foo@example.com">grant</trans-handling>
<trans-handling
perm-uri="sip:bar@example.com">deny</trans-handling>
</cp:actions>
<cp:transformations/>
</cp:rule>
</cp:ruleset>
5. XML Schema
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<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
targetNamespace="urn:ietf:params:xml:ns:consent-rules"
xmlns:cr="urn:ietf:params:xml:ns:consent-rules"
xmlns:cp="urn:ietf:params:xml:ns:common-policy"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<!-- Conditions -->
<xs:element name="sender" type="cp:identityType"/>
<xs:element name="target" type="cp:identityType"/>
<!-- Actions -->
<xs:simpleType name="trans-values">
<xs:restriction base="xs:string">
<xs:enumeration value="deny"/>
<xs:enumeration value="grant"/>
</xs:restriction>
</xs:simpleType>
<xs:element name="trans-handling">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="trans-values">
<xs:attribute name="perm-uri" type="xs:anyURI"
use="required"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
</xs:schema>
6. IANA Considerations
This section registers a new XML namespace and a new XML schema per
the procedures in [6].
6.1. XML Namespace Registration
URI: urn:ietf:params:xml:ns:consent-rules
Registrant Contact: IETF SIPPING working group,
<sipping@ietf.org>, Gonzalo Camarillo
<Gonzalo.Camarillo@ericsson.com>
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XML:
BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>Consent Rules Namespace</title>
</head>
<body>
<h1>Namespace for Permission Documents</h1>
<h2>urn:ietf:params:xml:ns:consent-rules</h2>
<p>See <a href="[URL of published RFC]">RFCXXXX
[NOTE TO IANA/RFC-EDITOR:
Please replace XXXX with the RFC number of this
specification.]</a>.</p>
</body>
</html>
END
6.2. XML Schema Registration
URI: urn:ietf:params:xml:schema:consent-rules
Registrant Contact: IETF SIPPING working group,
<sipping@ietf.org>, Gonzalo Camarillo
<Gonzalo.Camarillo@ericsson.com>
XML: The XML schema to be registered is contained in Section 5.
7. Security Considerations
Permission documents can reveal sensitive information. Additionally,
attackers may attempt to modify them in order to have clients grant
or deny permissions different to the ones they think are granting or
denying. For this reason, it is RECOMMENDED that relays use strong
means for information integrity protection and confidentiality when
sending permission documents to clients.
The mechanism used for conveying information to clients SHOULD ensure
the integrity and confidentially of the information. In order to
achieve these, an end-to-end SIP encryption mechanism, such as
S/MIME, as described in RFC 3261 [3], SHOULD be used.
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If strong end-to-end security means (such as above) is not available,
it is RECOMMENDED that hop-by-hop security based on TLS and SIPS
URIs, as described in [3], is used.
8. Acknowledgements
Jonathan Rosenberg provided useful ideas on this document. Ben
Campbell and Mary Barnes performed a thorough review of this
document.
9. References
9.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication:
Basic and Digest Access Authentication", RFC 2617, June 1999.
[3] 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.
[4] Peterson, J., "A Privacy Mechanism for the Session Initiation
Protocol (SIP)", RFC 3323, November 2002.
[5] 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.
[6] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[7] Peterson, J. and C. Jennings, "Enhancements for Authenticated
Identity Management in the Session Initiation Protocol (SIP)",
RFC 4474, August 2006.
[8] Schulzrinne, H., Tschofenig, H., Morris, J., Cuellar, J., Polk,
J., and J. Rosenberg, "Common Policy: A Document Format for
Expressing Privacy Preferences", RFC 4745, February 2007.
[9] Rosenberg, J., "A Framework for Consent-Based Communications in
the Session Initiation Protocol (SIP)",
draft-ietf-sip-consent-framework-01 (work in progress),
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November 2006.
9.2. Informative References
[10] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966,
December 2004.
Author's Address
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Gonzalo.Camarillo@ericsson.com
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