RFC5361
Network Working Group G. Camarillo Request for Comments: 5361 Ericsson Category: Standards Track October 2008
A Document Format for Requesting Consent
Status of This Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
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.
Contents
Introduction
The framework for consent-based communications in the Session Initiation Protocol (SIP) RFC5360 identifies the need for a format to create permission documents. Such permission documents are used by SIP RFC3261 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 Common Policy RFC4745, an XML document format for expressing privacy preferences.
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 RFC2119.
This document uses the terms defined in RFC5360. For completeness, these terms are repeated here. Figure 1 of RFC5360 shows the relationship between target and recipient URIs in a translation operation.
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 can have been the result of a translation operation.
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.
Target URI:
The Request-URI of an incoming request that arrives to a relay that will perform a translation operation.
Translation logic:
The logic that defines a translation operation at a relay. This logic includes the translation's target and recipient URIs.
Translation operation:
Operation by which a relay translates the Request-URI of an incoming request (i.e., the target URI) into one or more URIs (i.e., recipient URIs) that are used as the Request-URIs of one or more outgoing requests.
Permission Document Structure
A permission document is an XML document, formatted according to the schema defined in RFC4745. Permission documents inherit the MIME type of common policy documents, 'application/auth-policy+xml'. As described in RFC4745, this type of document is composed of three parts: conditions, actions, and transformations.
This section defines the new conditions and actions defined by this specification. This specification does not define any new transformation.
Conditions
The conditions in a permission document are a set of expressions, each of which evaluates to either TRUE or FALSE. Note that, as discussed in RFC4745, a permission document applies to a translation if all the expressions in its conditions part evaluate to TRUE.
Recipient Condition
The recipient condition is matched against the recipient URI of a translation. Recipient conditions can contain the same elements and attributes as identity conditions.
When performing a translation, a relay matches the recipient 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 RFC5360), the relay matches the recipient 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). If there is a match, the recipient condition evaluates to TRUE. Otherwise, the recipient condition evaluates to FALSE.
Since only authenticated identities can be matched, this section defines acceptable means of authentication, which are in line with those described in Section 5.6.1 of RFC5360.
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 RFC4474, as described in Section 5.6.1.1 of
RFC5360. 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.
P-Asserted-Identity RFC3325 (which can only be used in closed
network environments) as described in Section 5.6.1.2 of RFC5360. 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 Section 5.6.1.3 of
RFC5360. It can be used for SIP PUBLISH and HTTP GET requests. No authentication is expected to be used with return routability tests and, therefore, no identity matching procedures are defined.
SIP digest, as described in Section 5.6.1.4 of RFC5360. The
identity of the sender is set equal to the SIP Address of Record (AOR) for the user that has authenticated themselves.
Identity Condition
The identity condition, which is defined in RFC4745, is matched against the URI of the sender of the request that is used as input for a translation.
When performing a translation, a relay matches the identity condition against the identity of the sender of the incoming request. If they match, the identity condition evaluates to TRUE. Otherwise, the identity condition evaluates to FALSE.
Since only authenticated identities can be matched, 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.
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 RFC2617. However, if the anonymous authentication described on page 194 of RFC3261 is used, the sender is not considered authenticated.
Asserted Identity: if a request contains a P-Asserted-ID header
field RFC3325 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 RFC4474, 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:[email protected]. As long as the signature verifies that the request legitimately came from this identity, it is considered authenticated.
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:[email protected] digest username: ali digest password: f779ajvvh8a6s6 digest realm: example.com
If the relay receives a request and 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:[email protected]".
For requests that are authenticated using RFC3325, 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 RFC3966), then each of them is used for the comparisons outlined in RFC4745; 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 RFC4474, 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 <identity> condition. If a request is anonymous because it contains a Privacy header field RFC3323, 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 relay, 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:[email protected], then the sender is considered authenticated, and it will have an identity equal to sip:[email protected]. Had such an identity been placed into a <one> or <except> element, there will be a match.
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 and, thus, the identity condition evaluates to FALSE. This happens, for example, when the user portion of the 'id' attribute contains UTF-8 characters.
Target Condition
The target condition is matched against the target URI of a translation. The target condition 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. If they match, the target condition evaluates to TRUE. Otherwise, the target condition evaluates to FALSE.
Validity Condition
The <validity> element is not applicable to this document. Each <permission> element has an infinite lifetime and can be revoked using an independent mechanism, as described in Section 5.8 of RFC5360. In any case, as discussed in Section 4.1 of RFC5360, permissions are only valid as long as the context where they were granted is valid. If present, <validity> elements MUST be ignored.
Sphere Condition
The <sphere> element is not applicable to this document and therefore is not used. If present, <sphere> elements MUST be ignored.
Actions
The actions in a permission document provide URIs to grant or deny permission to perform the translation described in the document.
Note that the <trans-handling> element is not an action, as defined in Common Policy RFC4745, but rather an informational element. Therefore, the conflict resolution mechanism does not apply to it.
Each policy rule contains at least two <trans-handling> elements; one element with a URI to grant and another with a URI to deny permission.
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.
Example Document
In the following example, a client adds 'sip:[email protected]' to the translation whose target URI is 'sip:[email protected]'. The relay handling the translation generates the following permission document in order to ask for permission to relay requests sent to 'sip:[email protected]' to 'sip:[email protected]'. The
target URI is 'sip:[email protected]', and the recipient URI is 'sip:[email protected]'. The sender's identity does not play a role in this example. Therefore, the permission document does not put any restriction on potential senders.
+--------+ +--------------------------------+ Permission | | | | Request | Client | | Relay | with | | | sip:[email protected] | Permission +--------+ | | Document | |+-------+ |-------------+ | ||Transl.| | | |Manipulation ||Logic | | | +------------>|+-------+ | | Add +--------------------------------+ | sip:[email protected] V +---------------------+ | | | Recipient | | sip:[email protected] | | | +---------------------+
<?xml version="1.0" encoding="UTF-8"?>
<cp:ruleset
xmlns="urn:ietf:params:xml:ns:consent-rules"
xmlns:cp="urn:ietf:params:xml:ns:common-policy">
<cp:rule id="f1">
<cp:conditions>
<cp:identity>
<cp:many/>
</cp:identity>
<recipient>
<cp:one id="sip:[email protected]"/>
</recipient>
<target>
<cp:one id="sip:[email protected]"/>
</target>
</cp:conditions>
<cp:actions>
<trans-handling
perm-uri="sips:[email protected]"
>grant</trans-handling>
<trans-handling
perm-uri="https://example.com/grant-1awdch5Fasddfce34"
>grant</trans-handling>
<trans-handling
perm-uri="sips:[email protected]"
>deny</trans-handling>
<trans-handling
perm-uri="https://example.com/deny-23rCsdfgvdT5sdfgye"
>deny</trans-handling>
</cp:actions>
<cp:transformations/>
</cp:rule>
</cp:ruleset>
XML Schema
<?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">
<xs:element name="recipient" type="cp:identityType"/>
<xs:element name="target" type="cp:identityType"/>
<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>
Extensibility
This specification defines elements that do not have extension points in the "urn:ietf:params:xml:ns:consent-rules" namespace. Instance documents that utilize these element definitions SHOULD be schema valid. Applications processing instance documents with content that is not understood by the application MUST ignore that content. IETF extension documents of this specification MAY reuse the "urn:ietf:params:xml:ns:consent-rules" namespace to define new elements.
IANA Considerations
This section registers a new XML namespace and a new XML schema per the procedures in RFC3688.
XML Namespace Registration
URI: urn:ietf:params:xml:ns:consent-rules
Registrant Contact: IETF SIPPING working group <[email protected]>,
Gonzalo Camarillo <[email protected]>
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>
Namespace for Permission Documents
urn:ietf:params:xml:ns:consent-rules
See <a href="http://www.rfc-editor.org/rfc/rfc5361.txt">RFC 5361 </a>.
</body> </html> END
XML Schema Registration
URI: urn:ietf:params:xml:schema:consent-rules
Registrant Contact: IETF SIPPING working group <[email protected]>,
Gonzalo Camarillo <[email protected]>
XML: The XML schema to be registered is contained in Section 5.
Security Considerations
RFC 5360 RFC5360 discusses security-related issues, such as how to authenticate SIP and HTTP requests granting permissions and how to transport permission documents between relays and recipients, that are directly related to this specification.
Acknowledgements
Jonathan Rosenberg provided useful ideas on this document. Hannes Tschofenig helped align this document with common policy. Ben Campbell and Mary Barnes performed a thorough review of this document. Lakshminath Dondeti provided useful comments.
10. References
10.1. Normative References
RFC2119 Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
RFC2617 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.
RFC3261 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.
RFC3323 Peterson, J., "A Privacy Mechanism for the Session
Initiation Protocol (SIP)", RFC 3323, November 2002.
RFC3688 Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
RFC4474 Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 4474, August 2006.
RFC4745 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.
RFC5360 Rosenberg, J., Camarillo, G., and D. Willis, "A Framework
for Consent-Based Communications in the Session Initiation
Protocol (SIP)", RFC 5360, October 2008.
10.2. Informative References
RFC3966 Schulzrinne, H., "The tel URI for Telephone Numbers",
RFC 3966, December 2004.
RFC3325 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.
Author's Address
Gonzalo Camarillo Ericsson Hirsalantie 11 Jorvas 02420 Finland
EMail: [email protected]
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