RUCUS Exploratory Working Group D. Wing Internet-Draft Cisco Intended status: Experimental S. Niccolini Expires: August 16, 2008 M. Stiemerling NEC H. Tschofenig Nokia Siemens Networks February 13, 2008 Spam Score for SIP draft-wing-sipping-spam-score-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 16, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract This document defines a mechanism for SIP proxies to communicate a spam score to downstream SIP proxies and to SIP user agents. This information can then be used as input to other decision making engines, for example, to provide alternate call routing or call Wing, et al. Expires August 16, 2008 [Page 1] Internet-Draft SIP Spam Score February 2008 handling. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Operation of Spam-Scoring Proxy . . . . . . . . . . . . . . . . 3 4. Operation of Proxy or User Agent . . . . . . . . . . . . . . . 4 5. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 10.1. Normative References . . . . . . . . . . . . . . . . . . . 6 10.2. Informational References . . . . . . . . . . . . . . . . . 7 Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . . 7 A.1. Changes from -00 to -01 . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Intellectual Property and Copyright Statements . . . . . . . . . . 9 Wing, et al. Expires August 16, 2008 [Page 2] Internet-Draft SIP Spam Score February 2008 1. Introduction It is desirable for SIP proxies to insert a spam score so that downstream SIP proxies and downstream SIP user agents can use a high score to decide that special handling is required. For example, a score above 20 might cause one of the spam avoidance techniques described in [RFC5039] to be triggered for this call. This specification allows each SIP proxy to contribute spam scoring information that can be useful to downstream SIP proxies and the SIP user agent (UA). The downstream SIP proxies or SIP UA might ignore that information (e.g., it doesn't trust the SIP proxy that generated the spam score) or might use it. Note that this document does not make the attempt to define how the spam score was derived nor to distribute information that could be used to verify the spam score generation. Furthermore, this document does not attempt to cryptographically bind the identity of the entity generating the score to the value itself. Hence, its usage is likely to be useful only between neighboring administrative domains communicating such a score. 2. 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]. 3. Operation of Spam-Scoring Proxy A SIP proxy evaluates an incoming SIP request and generates a spam score using a local mechanism. This score is between 0 (indicating the message is not spam) and 100 (indicating the message is spam). Values between 0 and 100 indicate the 'likelihood' that the SIP request is spam, with higher values indicating a higher likelihood the message is spam. This spam score is inserted into the new "Spam-Score" header. This header field contains a summary spam score and optionally contains detail information. The detail information is implementation dependent. The detail information is valuable for debugging and to provide the SIP user agent or SIP proxy with additional information regarding how the spam-scoring SIP proxy's local mechanism arrived at the summary spam score. Wing, et al. Expires August 16, 2008 [Page 3] Internet-Draft SIP Spam Score February 2008 4. Operation of Proxy or User Agent A downstream proxy or the SIP user agent MAY use the spam score or spam-detail information to change call routing or call handling. It is envisioned that some form of policies indicate the trusted proxies in order to decide which spam scores to consider for special call treatment. In some jurisdictions, the end user needs to authorize call handling, including rejection of a call based on a spam score. Mechanisms to allow users to influence such policies are, however, out of scope of this document. The behavior of the SIP proxy or user agent when the spam score is above a certain value is a local policy matter. Examples of behavior include: o a SIP request with a high spam score might cause a proxy or user agent to redirect the SIP request to company's main telephone extension or to the user's voicemail o a user agent might alert the user by flashing the phone (without audible ringing) o a user agent might allow calls with a spam score below a certain value during daylight hours, but deny such calls at night. o a proxy might challenge the caller to complete a Turing test. Wing, et al. Expires August 16, 2008 [Page 4] Internet-Draft SIP Spam Score February 2008 5. Grammar ABNF using the ABNF syntax of [RFC3261]: extension-header = spam-score [ SP ";" spam-detail ] spam-score = score SP "by" SP hostname score = 1*3DIGIT [ "." 0*3DIGIT ] spam-detail = "detail" EQUAL detail detail = QUOTE mech SEMI rule-score *(COMMA rule-score) QUOTE ; mathematical average of the rule-scores ; MUST be same as spam-score rule-score = rule [ "=" score ] mech = token rule = token Figure 1: ABNF 6. Examples The following example shows a SIP score generated and inserted by two SIP proxies, sip.example.com and sip.example.net. In this example, sip.example.com is owned by a spammer who is trying to fool downstream systems with their low spam score (0). However, the example.net proxies and user agents only pay attention to spam scores from Spam-Score headers generated by example.net proxies, so example.com's attempts to fool the downstream proxies (with its low spam score) are in vain. Wing, et al. Expires August 16, 2008 [Page 5] Internet-Draft SIP Spam Score February 2008 INVITE sip:bob@example.net SIP/2.0 Via: SIP/2.0/UDP sip.example.net;branch=z9hG4bKnashds8 ;received=192.0.2.1 Spam-Score: 75 by sip.example.net ;detail="SIPfilter-1.0;call_volume=75" Via: SIP/2.0/UDP sip.example.com;branch=z9hG4bKfjzc ;received=192.0.2.127 Max-Forwards: 70 To: Bob From: Alice ;tag=1928301774 Call-ID: a84b4c76e66710@pc33.example.com CSeq: 314159 INVITE Contact: Content-Type: application/sdp Content-Length: 142 [... SDP elided from this example...] Figure 2: Example with spam scores 7. Security Considerations SIP proxies and SIP user agents need to ignore spam scores generated by proxies that aren't trusted. [[This section will be completed in a later version of this document.]] 8. Acknowledgements Thanks to Joachim Charzinski, Daniel Quinlan, and S. Moonesamy for their suggestions to improve this document. 9. IANA Considerations [[This section will be completed in a later version of this document.]] 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. Wing, et al. Expires August 16, 2008 [Page 6] Internet-Draft SIP Spam Score February 2008 [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 [RFC5039] Rosenberg, J. and C. Jennings, "The Session Initiation Protocol (SIP) and Spam", RFC 5039, January 2008. Appendix A. Changes Note to RFC Editor: please remove this section prior to publication. A.1. Changes from -00 to -01 o Changed scoring from positive/negative to 0-100 range. o Moved score from a "Via:" extension to a new header "Spam-Score:". o Changed from Standards Track to Experimental. Authors' Addresses Dan Wing Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134 USA Email: dwing@cisco.com Saverio Niccolini Network Laboratories, NEC Europe Ltd. Kurfuersten-Anlage 36 Heidelberg 69115 Germany Phone: +49 (0) 6221 4342 118 Email: saverio.niccolini@netlab.nec.de URI: http://www.netlab.nec.de Wing, et al. Expires August 16, 2008 [Page 7] Internet-Draft SIP Spam Score February 2008 Martin Stiemerling Network Laboratories, NEC Europe Ltd. Kurfuersten-Anlage 36 Heidelberg 69115 Germany Phone: +49 (0) 6221 4342 113 Email: stiemerling@netlab.nec.de URI: http://www.netlab.nec.de Hannes Tschofenig Nokia Siemens Networks Linnoitustie 6 Espoo 02600 Finland Phone: +358 (50) 4871445 Email: Hannes.Tschofenig@nsn.com URI: http://www.tschofenig.com Wing, et al. Expires August 16, 2008 [Page 8] Internet-Draft SIP Spam Score February 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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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. Acknowledgments Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). This document was produced using xml2rfc v1.33pre66 (of http://xml.resource.org/) from a source in RFC-2629 XML format. Wing, et al. Expires August 16, 2008 [Page 9]