Network Working Group D. Wing Internet-Draft Cisco Intended status: Standards Track February 8, 2008 Expires: August 11, 2008 SIP E.164 Return Routability Check (RRC) draft-wing-sip-e164-rrc-01 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware 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. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 11, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract SIP lacks a mechanism to determine which domain can claim ownership of a certain telephone number. Due to this, it is impossible to establish meaningful identity or to authenticate endpoints that use telephone number URIs and domain names in their From address. This document proposes a solution to this problem using a return routability test. Wing Expires August 11, 2008 [Page 1] Internet-Draft SIP E.164 RRC February 2008 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3 3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Verifier Operation . . . . . . . . . . . . . . . . . . . . 4 3.2. Authentication Service or Calling Endpoint Operation . . . 5 4. Performance Considerations . . . . . . . . . . . . . . . . . . 5 5. Deployment Considerations . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 8.1. Reverse-Route Event Package . . . . . . . . . . . . . . . 9 8.2. The "application/return-routability-nonce" Media Type . . 9 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 10.1. Normative References . . . . . . . . . . . . . . . . . . . 10 10.2. Informational References . . . . . . . . . . . . . . . . . 10 Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . . 10 A.1. Changes from -00 to -01 . . . . . . . . . . . . . . . . . 11 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11 Intellectual Property and Copyright Statements . . . . . . . . . . 12 Wing Expires August 11, 2008 [Page 2] Internet-Draft SIP E.164 RRC February 2008 1. Introduction SIP [RFC3261] allows using both email-style addresses (user@domain) and telephone-style addresses (1234@domain). The latter is most often used with E.164 [ITU.E164.1991] numbers (designated with ";user=phone") especially between different administrative domains. SIP's use of E.164 numbers poses several problems. This draft provides a solution to one of the problems: determining if a domain name rightfully 'owns' an E.164 phone number. In order to do this, a new SIP request is routed towards that E.164 and, if it is received by the same domain, that domain is deemed to 'own' that E.164 number. This is termed a 'return routability check' (RRC). The return routability check relies on SIP routing to ascertain which domain 'owns' a certain E.164 number. 2. Notational Conventions 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]. 3. Operation In order to check if a domain actually 'owns' the E.164 number it claims to own, a new SIP request is sent towards that E.164. Upon receipt of a SIP request conaining an E.164 number in the From address, the verifying agent in the receiving domain sends a new, out-of-dialog request (a SUBSCRIBE) towards that E.164 using the verifiering domain's normal routing rules. This SUBSCRIBE contains a body (with a nonce) that the verifying domains wants the owner of the E.164 to sign. That SIP SUBSCRIBE request is routed to the 'owner' of that E.164. Upon receipt of the SUBSCRIBE, the owner of that E.164 number generates a NOTIFY request. This is signed, using RFC4474, and sent to the verifying domain. The verifing domain verifies the signature on the NOTIFY. If it verified, and if the same public key was used in the original SIP request and in this NOTIFY, the verifying domain has now verified the remote domain 'owns' that E.164 number. If a different public key was used in the original SIP request and in this NOTIFY, the verifying domain has no verified the remote domain does not own that E.164 number. Wing Expires August 11, 2008 [Page 3] Internet-Draft SIP E.164 RRC February 2008 3.1. Verifier Operation Upon receipt of an INVITE where the From: address contains a SIP URI with an E.164, a Verifier (as defined in [RFC4474]) needs to verify if the signer is authorized to sign for that domain. To do this, the Verifier has an additional task: it sends an out of dialog SIP SUBSCRIBE request containing a random nonce to that E.164, using the Verifier's default SIP routing rules for routing an E.164 address. The domain that owns the E.164 will sign the nonce and send a NOTIFY request back. The steps the Verifier uses to perform this operation are: 1. Strip the domain name of the From: of the incoming INVITE. This results in a TEL URI. For example, "sip:+14085551234@example.com;user=phone" is rewritten to "tel:+14085551212". 2. Rewrite the TEL URI to a SIP URI, following the Verifier's default routing rules. For example, if outgoing calls are sent to the service provider example.net, then "tel:+14085551212" is rewritten to "sip:+14085551212@example.net;user=phone". 3. Generate a random nonce. 4. Using the SIP URI constructed in step (2), construct a SIP SUBSCRIBE message with Request-URI and To headers that use that SIP URI, and an "Expires" header of 0. The SUBSCRIBE contains the random nonce in its body as Content-Type application/ return-routability-nonce. 5. Send the SUBSCRIBE message. This will cause the calling party to send a NOTIFY. Upon receipt of the NOTIFY message, the Verifier performs the following steps: 1. Validate the [RFC4474] signature of the NOTIFY. 2. Extract the application/return-routability-nonce from the NOTIFY, and compare it to the nonce that was sent in the SUBSCRIBE. 3. Compare the certificate used to sign the NOTIFY is the same certificate used to sign the original SIP request that it is attempting to validate with this procedure. A. If they match, the E.164 return routability test has succeeded. Wing Expires August 11, 2008 [Page 4] Internet-Draft SIP E.164 RRC February 2008 B. If they do not match, the E.164 return routability test has failed. 3.2. Authentication Service or Calling Endpoint Operation The steps described in this section can be performed by the authentication service or by the calling endpoint. The authentication service or the calling endpoint, upon receiving a SUBSCRIBE for the return-routability event package, performs the following steps: 1. The SUBSCRIBE should be immediately acknowledged with a 200 Ok message. 2. A NOTIFY should be immediately created, containing the same application/return-routability-nonce copied from the SUBSCRIBE. This NOTIFY contains a To and Request-URI which match the From of the SUBSCRIBE. 3. This NOTIFY is sent. 4. The RFC4474 authentication service, operating at the domain, will create a signature over the NOTIFY. This is used by the remote domain's verification service (see Section 3.1). 4. Performance Considerations To reduce SUBSCRIBE/NOTIFY traffic, a verifier SHOULD cache successful and failed return routability checks. Successful checks will only become unsuccessful if SIP E.164 routing is changed to a different terminating domain. This only occurs when a domain relinquishes an E.164, so it is RECOMMENDED that the result of ssuccessful tests be cached for 24 hours. However, unsuccessful tests could be a result of misconfiguration and it is useful to re- verify such failures in the event the misconfiguration is fixed. Thus, it is RECOMMENDED that the result of unsuccessful tests be cached for 1 hour. 5. Deployment Considerations Intermediate SIP elements (proxies, SBCs, B2BUAs) MUST all forward the application/return-routability-nonce Content-Type. Wing Expires August 11, 2008 [Page 5] Internet-Draft SIP E.164 RRC February 2008 6. Security Considerations An attacker could cause a domain to perform public key operations by sending a bunch of bogus SUBSCRIBE messages. This can be thwarted by only responding with NOTIFYs if there is an active INVITE dialog. However, that could disclose information about active calls, and also restricts the usefulness of this feature to INVITEs. More evaluation of countermeasures against such an attack is needed. [[This section will be completed in a later version of this document.]] 7. Examples Example message flow for a successful return routability check. Calling Auth. Called UA Service proxies Verifier UA ------- ------- -------- -------- ------ -------- | | | | | ^ | INVITE | | | | | |--------->| | | | | | | | | | | | (signs request) | | | | | | | | | | |100 | INVITE | | | | steps which |<---------|--------->| | | | are part of | | | | | | normal RFC4474 | |100 | INVITE | | | | |<---------|--------->| | | | | | | | | | | |100 | | | | | |<---------| | | | | | | | | | | | (validates | | | | | signature) | V | | | | | ---------- | | |SUBSCRIBE | | | | |(containing nonce) | | |SUBSCRIBE |<---------| | | |<---------| | | | | | | | | |200 Ok | | | | |--------->|200 Ok | | | | |--------->| | | NOTIFY | | | | | (containing nonce) | | | Wing Expires August 11, 2008 [Page 6] Internet-Draft SIP E.164 RRC February 2008 | +----| | | | | | | | | | | +--->| | | | | | | | | | (signs NOTIFY) | | | | | | | | | |NOTIFY | | | | |--------->|NOTIFY | | | | |--------->| | | | | | | | | |200 Ok | | | |200 Ok |<---------| | | |<---------| | | | | | | | | | | (validates NOTIFY | | | | signature, and | | | | checks that same | | | | cert. signed both | | | | the INVITE and | | | | the NOTIFY) | | | | | | | | | | INVITE | | | | |--------->| | | | | | | | | | |display e.164 | | | | |------------> | | | | | Figure 1: Message Flow -- Return Routability Check Success Example message flow for an unsuccessful return routability check, where the NOTIFY is signed by a different RFC4474 authentication service: Calling E.164 User's Owner's Calling Auth. Auth. Called UA Service Service proxies Verifier UA ------- ------- ------- ------- -------- ------ | | | | | | | INVITE | | | | | |--------->| | | | | | | | | | | | (signs request) | | | | | | | | | | |100 | INVITE | | | | |<---------|-------------------->| | | | | | | | | Wing Expires August 11, 2008 [Page 7] Internet-Draft SIP E.164 RRC February 2008 | |100 | | INVITE | | | |<--------------------|--------->| | | | | | | | | | | |100 | | | | | |<---------| | | | | | | | | | | | (validates | | | | | signature) | | | | | | | | | | |SUBSCRIBE | | | | |SUBSCRIBE |(containing nonce) | | | |<---------| | | | | |200 Ok | | | | | |--------->|200 Ok | | | | NOTIFY | |--------->| | | | (containing nonce) | | | | | +----| | | | | | | | | | | | | +--->| | | | | | | | | | | | (signs NOTIFY) | | | | | | | | | | | |NOTIFY | | | | | |--------->|NOTIFY | | | | | |--------->| | | | | | | | | | | |200 Ok | | | | |200 Ok |<---------| | | | |<---------| | | | | | | | | | | | | (NOTIFY validates; | | | | | however, different | | | | | cert. was used for | | | | | INVITE) | | | | | | | | | | | | | | | | | | INVITE | | | | | |--------->| | | | | | | | | | | | |display | | | | | |e.164 | | | | | |------> | | | | | | Figure 2: Message Flow -- Return Routability Check Failure Wing Expires August 11, 2008 [Page 8] Internet-Draft SIP E.164 RRC February 2008 8. IANA Considerations IANA is requested to register the following new event package and one new media type. 8.1. Reverse-Route Event Package This specification registers an event package, based on the registration procedures defined in [RFC3265]. The following is the information required for such a registration: Package Name: reverse-route Package or Package-Template: This is a package. Published Specification: . Person to Contact: Dan Wing, 8.2. The "application/return-routability-nonce" Media Type Type name: application Subtype name: return-routability-nonce Required parameters: None. Optional parameters: None. Encoding considerations: The nonce is primarily binary content. Security considerations: See Section 6 of . Interoperability considerations: See . Published specification: Applications which use this media type: SIP. Additional information: Magic number(s): None. File extension(s): None. Macintosh File Type Code(s): none. Person & email address to contact for further information: Dan Wing Wing Expires August 11, 2008 [Page 9] Internet-Draft SIP E.164 RRC February 2008 Intended Usage: COMMON Author/Change Controller: Dan Wing 9. Acknowledgements Thanks to Paul Kyzivat and Hannes Tschofenig for their review and comments on this document. Thanks to Joel Halpern for pointing out the missing ";user=phone" parameter. 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. [RFC4474] Peterson, J. and C. Jennings, "Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)", RFC 4474, August 2006. [RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific Event Notification", RFC 3265, June 2002. [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. 10.2. Informational References [ITU.E164.1991] International Telecommunications Union, "The International Public Telecommunication Numbering Plan", ITU- T Recommendation E.164, 1991. Appendix A. Changes [[RFC Editor: Please remove this section prior to publication.]] Wing Expires August 11, 2008 [Page 10] Internet-Draft SIP E.164 RRC February 2008 A.1. Changes from -00 to -01 o Added ";user=phone" to identify E.164 number. Author's Address Dan Wing Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134 USA Email: dwing@cisco.com Wing Expires August 11, 2008 [Page 11] Internet-Draft SIP E.164 RRC February 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Wing Expires August 11, 2008 [Page 12]