SIPPING J. Rosenberg Internet-Draft Cisco Systems Expires: May 12, 2006 November 8, 2005 Rejecting Anonymous Requests in the Session Initiation Protocol (SIP) draft-rosenberg-sipping-acr-code-00 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 May 12, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract The Session Initiation Protocol (SIP) allows for users to make anonymous calls. However, users receiving such calls have the right to reject them because they are anonymous. SIP has no way to indicate to the caller that the reason for call rejection was that the call was anonymous. Such an indication is useful to allow the call to be retried without anonymity. This specification defines a new SIP response code for this purpose. Rosenberg Expires May 12, 2006 [Page 1]
Internet-Draft ACR Response Code November 2005 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. UAS Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. UAC Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. 433 (Anonymity Disallowed) Definition . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 6. Security Considerations . . . . . . . . . . . . . . . . . . . 4 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 8.1 Normative References . . . . . . . . . . . . . . . . . . . 5 8.2 Informative References . . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 6 Intellectual Property and Copyright Statements . . . . . . . . 7 Rosenberg Expires May 12, 2006 [Page 2]
Internet-Draft ACR Response Code November 2005 1. Introduction The Session Initiation Protocol (SIP) [1] allows for users to make anonymous calls. In RFC 3261, this is done by including a From header field whose display name has the value of "Anonymous". Greater levels of anonymity were subsequently defined in RFC 3323 [2], which introduces the Privacy header field. The Privacy header field allows a requesting UA to ask for various levels of anonymity, including user level anonymity, header level anonymity, and session level anonymity. RFC 3325 [3] additionally defined the P-Asserted-ID header field, used to contain an asserted identity. RFC 3325 also defined the 'id' value for the Privacy header field, which is used to request the network to remove the P-Asserted-ID header field. Though users need to be able to make anonymous calls, users that receive such calls retain the right to reject the call because it is anonymous. SIP does not provide a response code that allows the UAS to explicitly to indicate that the request was rejected because it was anonymous. The closest response code is 403 (Forbidden), which doesn't convey a specific reason. While it is possible to include a reason phrase in a 403 response that indicates to the human user that the call was rejected because it was anonymous, that reason phrase is not useful for automata. An indication that can be understood by an automata would allow for programmatic handling, including user interface prompts, automatic retries, or conversion to equivalent error codes in the Public Switched Telephone Network (PSTN) when the client is a gateway. To remedy this, this specification defines the 433 (Anonymity Disallowed) response code. 2. UAS Behavior A UAS MAY generate a 433 (Anonymity Disallowed) response when it receives an anonymous request, and the UAS refuses to fulfill the request because the requestor is anonymous. A request is considered anonymous when the identity of the originator of the request has been explicitly witheld by the originator. This occurs in several cases: o The From header field contains a display name of anonymous or a URI within the anonymous.invalid domain. o The request contained a Privacy header field whose value was 'id' [3] or 'user'. This explicitly excludes the 'header' and 'session' privacy services, since those do not directly convey the identity of the requestor. Rosenberg Expires May 12, 2006 [Page 3]
Internet-Draft ACR Response Code November 2005 o The From or P-Asserted-ID header field contains a URI which has an explicit indication that it is anonymous. One such example of a mechanism that would meet this criteria is [4]. It is important to note that lack of a P-Asserted-ID header field, in and of itself, is not an indication of anonymity. Even though a Privacy header field value of 'id' will cause the removal of the P-Asserted-ID header field, there is no way to differentiate this case from one in which P-Asserted-ID was not supported by the originating domain. As a consequence, a request without a P-Asserted-ID is considered anonymous only when there is some other indication of this, such as a From header field with a display name of 'Anonymous'. 3. UAC Behavior A UAC receiving a 433 (Anonymity Disallowed) response MAY retry the request without requesting anonymity. It SHOULD only do so if it obtains confirmation that the user that this is desirable. Such confirmation could be obtained through the user interface, or by accessing user defined policy. The UAC SHOULD NOT retry the request if it continues to request anonymity. A UAC the does not understand or care about the specific semantics of the 433 response will treat it as a 400 response. 4. 433 (Anonymity Disallowed) Definition This response indicates that the UAS refused the fulfill the request because the requestor was anonymous. Its default reason phrase is "Anonymity Disallowed". 5. IANA Considerations This section registers a new SIP response code according to the procedures of RFC 3261. RFC Number: RFC XXXX [[NOTE TO IANA: Please replace XXXX with the RFC number of this specification]] Response Code Number: 433 Default Reason Phrase: Anonymity Disallowed 6. Security Considerations The fact that an request was rejected because it was anonymous does Rosenberg Expires May 12, 2006 [Page 4]
Internet-Draft ACR Response Code November 2005 reveal information about the called party - that they do not accept anonymous calls. This information may or may not be sensitive. If it is, a UAS SHOULD reject the request with a 403 instead. 7. Acknowledgements This draft was motivated based on the requirements in [6], and has benefitted from the concepts in [5]. 8. References 8.1 Normative References [1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [2] Peterson, J., "A Privacy Mechanism for the Session Initiation Protocol (SIP)", RFC 3323, November 2002. [3] 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. 8.2 Informative References [4] Rosenberg, J., "Identity Privacy in the Session Initiation Protocol (SIP)", draft-rosenberg-sip-identity-privacy-00 (work in progress), July 2005. [5] Hautakorpi, J. and G. Camarillo, "Extending the Session Initiation Protocol Reason Header with Warning Codes", draft-hautakorpi-reason-header-for-warnings-00 (work in progress), October 2005. [6] Jesske, R., "Input Requirements for the Session Initiation Protocol (SIP) in support for the European Telecommunications Standards Institute", draft-jesske-sipping-tispan-requirements-02 (work in progress), October 2005. Rosenberg Expires May 12, 2006 [Page 5]
Internet-Draft ACR Response Code November 2005 Author's Address Jonathan Rosenberg Cisco Systems 600 Lanidex Plaza Parsippany, NJ 07054 US Phone: +1 973 952-5000 Email: jdrosen@cisco.com URI: http://www.jdrosen.net Rosenberg Expires May 12, 2006 [Page 6]
Internet-Draft ACR Response Code November 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in 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 made any independent effort to identify any such rights. 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. 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 (2005). 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 Funding for the RFC Editor function is currently provided by the Internet Society. Rosenberg Expires May 12, 2006 [Page 7]