SIPPING H. Tschofenig Internet-Draft Nokia Siemens Networks Intended status: Informational H. Schulzrinne Expires: August 28, 2008 Columbia University D. Wing Cisco J. Rosenberg Cisco Systems D. Schwartz XConnect February 25, 2008 A Framework to tackle Spam and Unwanted Communication for Internet Telephony draft-tschofenig-sipping-framework-spit-reduction-03.txt 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 28, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Tschofenig, et al. Expires August 28, 2008 [Page 1] Internet-Draft Framework for Reducing Spam February 2008 Abstract Spam, defined as sending unsolicited messages to someone in bulk, is likely to become a problem on SIP open-wide deployed networks. A number of solutions have been proposed for dealing with Spam for Internet Telephony (SPIT) and unwanted communication, for example, content filtering, black lists, white lists, consent-based communication, reputation systems, address obfuscation, limited use addresses, turing tests, computational puzzles, payments at risk, circles of trust, and many others. This document describes the big picture that illustrates how the different building blocks fit together and can be deployed incrementally. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Framework . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Communication Patterns and User Groups . . . . . . . . . . . . 7 4.1. Closed Groups . . . . . . . . . . . . . . . . . . . . . . 7 4.2. Semi-Open Groups . . . . . . . . . . . . . . . . . . . . . 7 4.3. Open Groups . . . . . . . . . . . . . . . . . . . . . . . 8 4.4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.5. Usability . . . . . . . . . . . . . . . . . . . . . . . . 9 5. Protocol Interactions . . . . . . . . . . . . . . . . . . . . 9 5.1. Rule Enforcement via a Trusted Intermediary . . . . . . . 10 5.2. Incremental Deployment . . . . . . . . . . . . . . . . . . 10 5.3. Botnets . . . . . . . . . . . . . . . . . . . . . . . . . 12 6. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 13 7. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 8. Security Considerations . . . . . . . . . . . . . . . . . . . 16 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 10.1. Normative References . . . . . . . . . . . . . . . . . . . 17 10.2. Informative References . . . . . . . . . . . . . . . . . . 17 Appendix A. Outside the Scope . . . . . . . . . . . . . . . . . . 19 Appendix B. Authorization Engine in SIP UA . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 Intellectual Property and Copyright Statements . . . . . . . . . . 22 Tschofenig, et al. Expires August 28, 2008 [Page 2] Internet-Draft Framework for Reducing Spam February 2008 1. Introduction The problem of Spam for Internet Telephony (SPIT) is an imminent challenge and only the combination of several techniques can provide a framework for dealing with unwanted communication attempts. [I-D.ietf-sipping-spam] provides four core recommendations that need to be considered for a SPIT solution, namely o Strong Identity o White Lists o Solve the Introduction Problem o Don't Wait Until its Too Late This document illustrates how existing building blocks can be put together to form a solution to deal with SPIT. New building blocks can be added to provide more efficient SPIT handling, since there is no single solution that provides 100 % protection. The purpose of this document defines a model of internal device processing, protocol interfaces, and terminology to illustrate a way in which SPIT prevention techniques can be added in a seamless fashion. We focus only on the most important solution components and consider many other aspects either outside the scope of this work (see Appendix A) and postpone them for future work. 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 RFC 2119 [RFC2119]. 3. Framework Figure 1 shows the interaction between the end host and a SIP proxy belonging to its VoIP provider. One important part of the overall solution is the ability to make authorization decisions based on incoming communication attempts. The entity that writes these authorization rules is referred as Rule Maker. The Rule Maker might be a user via some form of user interface. Some rules may be generated automatically by a piece of software by observing the users behavior. Furthermore, in certain deployment environments an initial rule set will be provided by some third party entity, such as the enterprise system administrator or the VoIP provider. Policies are processed by corresponding module within the SIP proxy, Tschofenig, et al. Expires August 28, 2008 [Page 3] Internet-Draft Framework for Reducing Spam February 2008 called Authorization Engine, that interacts with the message routing component. By following this architectural approach the Policy Decision Point (PDP) and the Policy Enforcement Point (PEP) are closely combined. As such, authorization policies are stored at at a SIP proxy rather than the SIP UA client itself. The implications of relocating these two functions, PDP and PEP, to the SIP UA client are described in Appendix B. +---------------------------------------------------------+ | Authorization | | re-route Policy +------------+ | | ^ (implicit) ######| Rule Maker | | | o +#######+ # +------------+ | | o # # # | | +---o----------#-------#--+ # Authorization | | | o # # |<####### Policy | +--------+ | | o Proxy # # | | | | | | o # # |<*******************+ | | Sender |<***>|+-------+ v # | * | | | | ||Msg. | +-----------+| Authorization * | +--------+ | ||Routing| | Authz. || Policy (explicit) * | ^ o | ||Engine |<->| Engine |<#################+ * | * o | |+-------+ +-----------+| # * | * o | +-^--*--^-----------------+ # v | * o | o * o +-------------+ | * o | o * o | | | * +oooo|oooo+ * +ooooooooooooooooooooooooooooo>| Recipient/ | | +**************************************************>| Rule Maker | | | +-------------+ | | | | | +-------------------Domain Boundary-----------------------+ Legend: oooo: SIP message interaction ****: Protocol Interaction for authorizing the message sender ####: Management of authorization policies Figure 1: Overview Assume that an arbitrary entity transmits a message to a specific URI that finally hits the SIP proxy on the recipients side. Information provided within that message are used as input to the rule evaluation. Any part of the message may serve as input to the evaluation process but for practical reasons only a few selected fields do most of the work. The authenticated identity of the sender Tschofenig, et al. Expires August 28, 2008 [Page 4] Internet-Draft Framework for Reducing Spam February 2008 is probably the most valuable information item. One could, however, imagine that other information, such as reputation information obtained from social networks, could offer additional input to the authorization engine. The protocol interaction for authorizing the message sender refers to the ability of the recipient or the proxy to interact with the sender to request authorization. The request for authorization might require the message sender to be challenged (e.g., via hash cash [I-D.jennings-sip-hashcash], via SIP payment [I-D.jennings-sipping-pay], or via CAPTCHAs [I-D.tschofenig-sipping-captcha]). Some other mechanisms, such as SIP Identity do not require the verifying entity to challenge the authentication service since the identity assertion is pushed towards the recipient. Figure 2 shows this integration step. The conditions part of the rule offer a mechanisms to incrementally extend the overall framework with new components. Depending on the outcome of the rule evaluation, the message may be re-routed to another entity, such as an answering machine, to the recipient, rejected or other actions are triggered. The latter aspect is particularly interesting since it allows further solution components to be executed. SIP msg with authenticated identity +---------------+ -------------->| |----------------> Additional | | Spam marked msg Msg fields | Authorization | -------------->| Engine |----------------> Other SPIT | | Re-routed msg Prevention | | Components | |----------------> -------------->+---------------+ Forwarded to | | original recipient | | <-----------+ +----------->|| Politely blocked Blocked Figure 2: Message Filtering and Routing Note that some traffic analysis and consequently some form of content filtering (e.g., of MESSAGEs) message be applied locally within the VoIP provider's domain also under the control of the end user. However, this is largely an implementation-specific technique without protocol impact. For example, consider a VoIP provider that wants to Tschofenig, et al. Expires August 28, 2008 [Page 5] Internet-Draft Framework for Reducing Spam February 2008 utilize a statistical analysis tool for Spam prevention. It is not necessary to standardized the algorithms nor protocols; the impact for the authorization policies is mainly the ability to allow the Rule Maker to enable or to disable the usage of these statistical techniques and potentially to map the output of the analysis process to value range from 0 (i.e., the message is not classified as Spam) and 100 (i.e., the message was classified as Spam). A Rule Maker may decide to act with an appropriate action on a certain level of Spam marking. Authenticated Identities: Initial VoIP provider are likely to secure their SIP signaling using Transport Layer Security (TLS) or IP security (IPsec) between neighboring providers and use P-Asserted-ID [RFC3325]. Note: SIP Identity is comparable to DomainKeys Identified Mail (DKIM) [I-D.ietf-dkim-overview] used for associating a "responsible" identity with an email message and provides a means of verifying that the association is legitimate. SIP Identity [RFC4474] is a proposal for stronger security mechanisms used to provide the verification service with the authenticated identity. SIP Identity is a reasonably simple specification and does not rely on a huge amount of infrastructure support. This framework does not assume a specific mechanism for asserting identities to be used but a strong identity mechanism is a pre- requisity for authorization policy handling to be successful. Authorization Policies: Even if policy decision making and policy enforcement is done outside the SIP UA client then still there might not be a need to standardize an authorization policy language if the policies can be modified via a webpage. This approach of policy handling is done in many cases today already for various applications. Unfortunately, this approach tends to become cumbersome for end users and therefore it is better to hide a lot of policy details from the end user itself and to make use of context information, for example, address books and authorization policies available already created for presence based systems. Additionally, a user may have multiple devices and a consistent view of the policies should be provided. Tschofenig, et al. Expires August 28, 2008 [Page 6] Internet-Draft Framework for Reducing Spam February 2008 An example solution for authorization policies for dealing with reducing unwanted communication is described in [I-D.tschofenig-sipping-spit-policy] with the requirements detailed in [I-D.froment-sipping-spit-requirements]. There is still one significant problem unsolved: since white lists need to be created somehow and hence there is an introduction problem. Section 4 discusses this aspect in more details. 4. Communication Patterns and User Groups When communication takes place then at least three types of groups can be identified. 4.1. Closed Groups People in this group communicate only with the peers in their group. They do not appreciate communication attempts from outside. Communication is possible only for people within this list. Here is an example of a closed group: Consider parents that do not want their children from getting contacted by strangers. Hence, they may want to create a white list containing the identifies of known friends, parents and other relatives on behalf of their kids. The usage of authorization policies for usage with closed groups is straight forward. The introduction problem is also not considered very large given that the identities are typically known. 4.2. Semi-Open Groups In a semi-open environment all members of the same group are allowed to get in contact with everyone else (e.g., for example in a company environment). For members outside the company the communication patters depend on the role of the person (e.g., standardization people, sales people, etc.) and on the work style of the person. For this category we distinguish a number of (non-spam) message sources based on their characteristics: o "friends" or "acquaintances", i.e., those we have communicated with before. o strangers, divided into 'interesting' and 'uninteresting'. The latter are messages from people that someone does not care to have a conversation with or respond to, at least at that particular moment. Strangers can be defined by individual names or whole domains. A Tschofenig, et al. Expires August 28, 2008 [Page 7] Internet-Draft Framework for Reducing Spam February 2008 special class of 'stranger' messages are transaction-related communications, such as Instant Messaging or automated calls from an airline or shipping company. One way to deal with the introduction problem is to make use of techniques like hash cash [I-D.jennings-sip-hashcash] or Completely Automated Public Turing Test to Tell Computers and Humans Apart (CAPTCHA) based robot challenges [I-D.tschofenig-sipping-captcha]. Alternatively, a communication attempt may also be forwarded to an answering maschine or alternative ways of establishing the initial interaction may be proposed. The usage of authorization policies for usage with Semi-Open Groups is challenging but is considered manageable. 4.3. Open Groups People in this type of group are not allowed to limit communication attempts. Help desks, certain people in governmental agencies, banks, insurance companies, etc. For open groups a solution for providing SPIT prevention is far more complicated. Consider a person working on a customer support helpdesk. Ideally, they would like to receive only calls from friendly customers (although the motivation for calling is most likely a problem) and the topic of the calls only relates to problems they are able to solve. Without listening to the caller they will have a hard time to know whether the call could be classified as SPIT. Another extreme case is a Public Safety Answering Point where emergency service personell is not allowed to reject calls either. Many SPIT prevention techniques might not be applicable since blocking callers is likely not possible and applying other techniques, such as turing tests, might not be ideal in an case of open groups. Statistical analysis may be helpful in some cases to deliver additional information about the calling party. Social networks might provide similar techniques based on reputation based systems. 4.4. Summary Based on the discussions regarding communication patters and groups the following observations can be made: o A single person very likely has many roles and they may have an impact on the communication patterns. Tschofenig, et al. Expires August 28, 2008 [Page 8] Internet-Draft Framework for Reducing Spam February 2008 For example, consider a person who is working in a company but also want to be available for family members. o The context in which a person is may change at any time. For example, a person might be available for family members while at work except during an important meeting where communication attempts may be rejected. Switching a context has an impact for reachability and the means for communicating with a specific recipient, based on enabled rule sets. From an authorization policy point of view it is important to be able to express a sphere (i.e., the state a user is in) and to switch between different spheres easily by thereby switching to a different rule set. 4.5. Usability An important aspect in the usage of authorization policies is to assist the user when creating policies. Ideally, the policies should be established automatically. Below, there are a couple of examples to illustrate the idea given that these aspects are largely implementation issues: o It must be possible for the proxy to automatically add addresses on outbound messages and calls to the rule set. This approach is similar to stateful packet filtering firewalls where outbound packets establish state at the firewall to allow inbound packets to traverse it again. o Already available information in the address book can be used for building the policy rules there is quite likely already a relationship available with these persons existent. o A large amount of email is non-personal, automated communication, such as newsletters, confirmations and legitimate advertisements. These are often tagged as spam by content filters. This type of correspondence is usually initiated by a transaction over the web, such as a purchase or signing up for a service. [I-D.shacham-http-corr-uris], for example, defines an HTTP header for conveying future correspondence addresses that can be integrated in the rule set. 5. Protocol Interactions This section describes the necessary building blocks that are necessary to tie the framework together. Tschofenig, et al. Expires August 28, 2008 [Page 9] Internet-Draft Framework for Reducing Spam February 2008 5.1. Rule Enforcement via a Trusted Intermediary o Some from of strong identity assurance is required to build the basis for identity-based authorization. SIP Identity [RFC4474] or P-Asserted-ID [RFC3325] are examples of available mechanisms. These mechanisms allow the authenticated identity of the sending party to be determined. o Authorization Policies based on the Common Policy framework [RFC4745], as extended in [I-D.tschofenig-sipping-spit-policy] for the purpose of SPIT prevention, are mandatory to implement at the end host side and at the trusted intermediary. The implementation of the rule evaluation engine might only be necessary on the trusted VoIP proxy. Harmonization with the work done for presence authorization [I-D.ietf-simple-presence-rules], which is based on Common Policy [RFC4745], can be accomplished and is highly desirable. o XML Configuration Access Protocol (XCAP) [RFC4825] is used to create, modify and delete authorization policies and is mandatory to implement at the end host side and at the trusted intermediary. 5.2. Incremental Deployment An important property is incremental deployment of additional solution components that can be added and used when they become available. This section aims to illustrate how the extensibility is accomplished, based on an example. Consider a VoIP provider that provides authorization policies that provide the following functionality equivalent to the Common Policy framework, i.e., identity-based, sphere and validity based conditions initially. For actions only 'redirection' and 'blocking' is provided. In our example we give this basic functionality the AUID 'new-spit-policy-example' with the namespace 'urn:ietf:params:xml:ns:new-spit-policy-example'. When a client queries the capabilities of a SIP proxy in the VoIP providers network using XCAP the following exchange may take place. GET /xcap-caps/global/index HTTP/1.1 Host: xcap.example.com Initial XCAP Query for Capabilities Tschofenig, et al. Expires August 28, 2008 [Page 10] Internet-Draft Framework for Reducing Spam February 2008 HTTP/1.1 200 OK Etag: "wwhha" Content-Type: application/xcap-caps+xml new-spit-policy-example xcap-caps urn:ietf:params:xml:ns:xcap-caps urn:ietf:params:xml:ns:spit-policy urn:ietf:params:xml:ns:common-policy Initial XCAP Response with the supported Capabilities As shown in the example above, Common Policy and the example SPIT extension is implemented and the client can upload rules according to the definition of the rule set functionality. Later, when the VoIP provider updates the functionality of authorization policies as more sophisticated mechanisms become available and get implemented the functionality of the authorization policy engine is enhanced with, for example, hashcash and the ability to perform statistical analysis of signaling message. The latter functionality comes with the ability to mark messages are Spam and the ability for end users to enable/disable this functionality. We use the namespaces 'urn:ietf:params:xml:ns:hashcash' and 'urn:ietf:params:xml:ns:statistical-analysis' for those. A end user could now make use of these new functions and a capability query of the SIP proxy would provide the following response. GET /xcap-caps/global/index HTTP/1.1 Host: xcap.example.com Second XCAP Query for Capabilities Tschofenig, et al. Expires August 28, 2008 [Page 11] Internet-Draft Framework for Reducing Spam February 2008 HTTP/1.1 200 OK Etag: "wwhha" Content-Type: application/xcap-caps+xml spit-policy xcap-caps hashcash statistical-analysis urn:ietf:params:xml:ns:spit-policy urn:ietf:params:xml:ns:common-policy urn:ietf:params:xml:ns:hashcash urn:ietf:params:xml:ns:statistical-analysis Second XCAP Response with the supported Capabilities New SPIT handling functionality may extend condition, actions and/or transformation elements of a rule. 5.3. Botnets A botnet is a large number of compromised maschines that are used to create and send spam or viruses or flood a network with messages as a denial of service attack. Such a botnet represents a significant challenge for a VoIP infrastructure and also for the mechanisms proposed in this document. Recently observed attacks indicated that some botnets tried to steal credentials to distribute messages with "real" identities. To deal with the threat it is useful to classify the behavior of these bots into three categories, namely o The botnet does not have access to the user's credentials. In this case identity-based white lists provides adequate protection. o The botnets does have access to user's credentials of compromised maschines but distributes messages in a random fashion. In this case identity-based white lists provides adequate protection since it is unlikely that the recipient will have that person in their whitelist. o In this category the botnet has access to the user's credentials and utilizes addresses from the user's addressbook. In this case whitelists do not provide a proper protection. Since the Tschofenig, et al. Expires August 28, 2008 [Page 12] Internet-Draft Framework for Reducing Spam February 2008 recipient knows the sender of the message it would, in many cases, be able to get in contact with him or her and report the observed problem. This approach does not work with a pure maschine-to- maschine communication environment without user involvement. 6. Privacy Considerations This document does not propose to distribute the user's authorization policies to other VoIP providers nor is the configuration of policies at SIP proxies other than the trusted user's VoIP provider necessary. Furthemore, if blocking or influencing of the message processing is executed by the VoIP provider then they have to be explicitly enabled by the end user. Blocking of messages, even if it is based on "super-clever" machine learning techniques often introduces unpredictability. Legal norms from fields of law can take regulative effects in the context of SPIT processing, such as constitutional law, data protection law, telecommunication law, teleservices law, criminal law, and possibly administrative law. See, for example, [Law1], [Law2] and [Law3]. For example, it is mandatory to pass full control of SPIT filtering to the end user, as this minimises legal problems. An overview about regulatory aspects can be found in [Spit-AL]. 7. Example This section shows an example whereby we consider a user Bob@company-example.com that writes (most likely via a nice user interface) the following policies. We use a high-level language to show the main idea of the policies. Tschofenig, et al. Expires August 28, 2008 [Page 13] Internet-Draft Framework for Reducing Spam February 2008 RULE 1: IF identity=alice@foo.example.com THEN ACCEPT IF identity=tony@bar.example.com THEN ACCEPT RULE 2: IF domain=company-example.com THEN ACCEPT RULE 3: IF unauthenticated THEN EXECUTE hashcash RULE 4: IF THEN REDIRECT sip:voicebox@company-example.com RULE 5: IF THEN block Example of Bob's Rule Set At some point in time Bob uploads his policies to the SIP proxy at his VoIP providers SIP proxy. PUT /spit-policy/users/sip:bob@company-example.com/index/~~/ruleset HTTP/1.1 Content-Type:application/spit+xml Host: proxy.home-example.com <<<< Added policies go in here. >>>> [Editor's Note: In a future version an XML example policy document will be listed here.] Uploading Policies using XCAP When BoB receives a call from his friends, alice@foo.example and tony@bar.example.com, then all the rules related to the spit policy are checked. Only the first rule (rule 1) matches and is applied. Thus, the call is forwarded without any further checks based on Rule 1. The rules assume that the authenticated identity of the caller has been verified. When Bob receives a call from a co-worker, Tschofenig, et al. Expires August 28, 2008 [Page 14] Internet-Draft Framework for Reducing Spam February 2008 Charlie@company-example.com, Rule 2 is applied since the domain part in the rule matches the domain part of Charlie's identity. Now, when Bob receives a contact from an unknown user, called Mallice in this example. Rule 3 indicates that an extended return- routability test using hashcash [I-D.jennings-sip-hashcash] is used with the call being redirected to Bob's voicebox afterwards. This exchange is shown in Figure 9. UA Proxy Bob's Malice Voicebox | INVITE | | |------------------------->|Puzzle: work=15; | | |pre="VgVGYixbRg0mdSwTY3YIfCBuAAA="; | | 419 with Puzzle |image="NhhMQ2l7SE0VBmZFKksUC19ia04="; | | |value=160 | |<-------------------------| | | | | | ACK | | |------------------------->| | | |Puzzle: work=0; | | |pre="VgVGYixbRg0mdSwTY3YIfCBuYmg="; | | |image="NhhMQ2l7SE0VBmZFKksUC19ia04=" | | INVITE with Solution |value=160 | |------------------------->| INVITE | | |------------------------------------->| | | | | | 180 Ringing | | 180 Ringing |<-------------------------------------| |<-------------------------| | | | 200 OK | | 200 OK |<-------------------------------------| |<-------------------------| | | | ACK | |---------------------------------------------------------------->| | | | Figure 9: Example Exchange: Malice contacts Bob Depending on the outcome of the exchange the call is forwarded to a mailbox sip:voicebox@company-example.com (in case Malory returned the correct solution, see Rule 4) or blocked in case an incorrect response was provided. It might be quite easy to see how this rule set can be extended to support other SPIT handling mechanisms as well (e.g., CAPTCHAs, SIP Pay, etc.). Tschofenig, et al. Expires August 28, 2008 [Page 15] Internet-Draft Framework for Reducing Spam February 2008 8. Security Considerations This document aims to describe a framework for addressing Spam for Internet Telephony (SPIT) in order to make it simple for users to influence the behavior of SIP message routing with an emphasis on SPIT prevention. The framework relies on three building blocks, namely SIP Identity, authorization policies based on Common Policy and Presence Authorization Policy, and XCAP. As a high-level overview, the framework allows the user to control end-to-end connectivity at the SIP message routing level whereby the glue that lets all parts fit together is based on authorization policies. Several other solution components can be developed independently and can be plugged into the framework as soon as available. It must be avoided to introduce Denial of Service attacks against the recipient by misguiding him or her to install authorization policies that allow senders to bypass the policies although that was never intended by the recipient. Additionally, it must not be possible by extensions to the authorization policy framework to create policies to block legitimate senders or to stall the processing of the authorization policy engine. 9. Acknowledgments We would like to thank Jeremy Barkan, Dan York, Alexey Melnikov, Thomas Schreck, Eva Leppanen, Cullen Jennings, Marit Hansen and Markus Hansen for their review comments to a pre-00 version. Jeremy Barkan, Eva Leppanen, Michaela Greiler, Joachim Charzinski, Saverio Niccolini, Albert Caruana, and Juergen Quittek for their comments to the 00 version. Otmar Lendl, Jan Seedorf, Saverio Niccolini, Kai Fischer, Joachim Charzinski, Dan York, Peter Saint-Andre, Brian Azzopardi, Martin Stiemerling, and Juergen Quittek for their comments to the -01/-02 version. 10. References Tschofenig, et al. Expires August 28, 2008 [Page 16] Internet-Draft Framework for Reducing Spam February 2008 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", March 1997. [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. [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. [RFC4825] Rosenberg, J., "The Extensible Markup Language (XML) Configuration Access Protocol (XCAP)", RFC 4825, May 2007. 10.2. Informative References [I-D.ietf-sipping-spam] Rosenberg, J. and C. Jennings, "The Session Initiation Protocol (SIP) and Spam", draft-ietf-sipping-spam-05 (work in progress), July 2007. [I-D.ietf-simple-presence-rules] Rosenberg, J., "Presence Authorization Rules", draft-ietf-simple-presence-rules-10 (work in progress), July 2007. [I-D.jennings-sip-hashcash] Jennings, C., "Computational Puzzles for SPAM Reduction in SIP", draft-jennings-sip-hashcash-06 (work in progress), July 2007. [I-D.wing-sipping-spam-score] Wing, D., Niccolini, S., Stiemerling, M., and H. Tschofenig, "Spam Score for SIP", draft-wing-sipping-spam-score-02 (work in progress), February 2008. [I-D.ietf-sip-consent-framework] Rosenberg, J., Camarillo, G., and D. Willis, "A Framework for Consent-based Communications in the Session Initiation Tschofenig, et al. Expires August 28, 2008 [Page 17] Internet-Draft Framework for Reducing Spam February 2008 Protocol (SIP)", draft-ietf-sip-consent-framework-04 (work in progress), January 2008. [I-D.ietf-dkim-overview] Hansen, T., Crocker, D., and P. Hallam-Baker, "DomainKeys Identified Mail (DKIM) Service Overview", draft-ietf-dkim-overview-09 (work in progress), February 2008. [I-D.tschofenig-sipping-spit-policy] Tschofenig, H., Wing, D., Schulzrinne, H., Froment, T., and G. Dawirs, "A Document Format for Expressing Authorization Policies to tackle Spam and Unwanted Communication for Internet Telephony", draft-tschofenig-sipping-spit-policy-02 (work in progress), November 2007. [I-D.schwartz-sipping-spit-saml] Schwartz, D., "SPAM for Internet Telephony (SPIT) Prevention using the Security Assertion Markup Language (SAML)", draft-schwartz-sipping-spit-saml-01 (work in progress), June 2006. [I-D.shacham-http-corr-uris] Shacham, R. and H. Schulzrinne, "HTTP Header for Future Correspondence Addresses", draft-shacham-http-corr-uris-00 (work in progress), May 2007. [I-D.jennings-sipping-pay] Jennings, C., "Payment for Services in Session Initiation Protocol (SIP)", draft-jennings-sipping-pay-06 (work in progress), July 2007. [I-D.froment-sipping-spit-requirements] Tschofenig, H., Dawirs, G., Froment, T., Wing, D., and H. Schulzrinne, "Requirements for Authorization Policies to tackle Spam and Unwanted Communication for Internet Telephony", draft-froment-sipping-spit-requirements-02 (work in progress), February 2008. [I-D.niccolini-sipping-feedback-spit] Niccolini, S., "SIP Extensions for SPIT identification", draft-niccolini-sipping-feedback-spit-03 (work in progress), February 2007. [I-D.tschofenig-sipping-captcha] Tschofenig, H., Leppanen, E., Niccolini, S., and M. Arumaithurai, "Completely Automated Public Turing Test to Tschofenig, et al. Expires August 28, 2008 [Page 18] Internet-Draft Framework for Reducing Spam February 2008 Tell Computers and Humans Apart (CAPTCHA) based Robot Challenges for SIP", draft-tschofenig-sipping-captcha-01 (work in progress), February 2008. [Spit-AL] Hansen, M., Hansen, M., Moeller, J., Rohwer, T., Tolkmitt, C., and H. Waack, "Developing a Legally Compliant Reachability Management System as a Countermeasure against SPIT, Third Annual VoIP Security Workshop, Berlin, available at https://tepin.aiki.de/blog/uploads/spit-al.pdf", June 2006. [Law1] "Bundesnetzagentur: Eckpunkte der regulatorischen Behandlung von Voice over IP (VoIP), available at http://www.bundesnetzagentur.de/media/archive/3186.pdf", September 2005. [Law2] "70. Konferenz der Datenschutzbeauftragten des Bundes und der Laender: Entschliessung Telefonieren mit Internettechnologie (Voice over IP - VoIP), available at http://www.datenschutzzentrum.de/material/themen/press e/20051028-dsbk-voip.htm", Oktober 2005. [Law3] "Working Party 29 Opinion 2/2006 on privacy issues related to the provision of email screening services, WP 118, available at http://ec.europa.eu/justice_home/fsj/privacy/ docs/wpdocs/2006/wp118_en.pdf", February 2006. Appendix A. Outside the Scope We consider the following aspects outside the scope of this document: o Mechanisms to publish SPIT causing parties on the Internet, i.e., information about domains that create SPIT. o Determining the source of unwanted traffic in real-time. o Pushing packet filters and authorization policies towards the SPIT sending domain. Appendix B. Authorization Engine in SIP UA When white lists are stored and managed only at the SIP UA client then the authorization policies language and the protocol to modify the policies do not need to be standardized; they are purely implementation specific details. While this appears to be an advantage there are various drawbacks Tschofenig, et al. Expires August 28, 2008 [Page 19] Internet-Draft Framework for Reducing Spam February 2008 including the inability to synchronize policies among different devices. Additionally, some information that is typically available to the Policy Decision Point may not be available to the end host. To avoid standardizing the exchange of such type of information an abstract form of Spam marking is proposed in [I-D.wing-sipping-spam-score]. Authors' Addresses Hannes Tschofenig Nokia Siemens Networks Otto-Hahn-Ring 6 Munich, Bavaria 81739 Germany Email: Hannes.Tschofenig@nsn.com URI: http://www.tschofenig.com Henning Schulzrinne Columbia University Department of Computer Science 450 Computer Science Building New York, NY 10027 US Phone: +1 212 939 7004 Email: hgs@cs.columbia.edu URI: http://www.cs.columbia.edu Dan Wing Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134 USA Email: dwing@cisco.com Tschofenig, et al. Expires August 28, 2008 [Page 20] Internet-Draft Framework for Reducing Spam February 2008 Jonathan Rosenberg Cisco Systems 600 Lanidex Plaza Parsippany, New York 07054 USA Email: jdrosen@cisco.com URI: http://www.jdrosen.net David Schwartz XConnect Malcha Technology Park Jerusalem, 96951 Israel Email: dschwartz@xconnect.net Tschofenig, et al. Expires August 28, 2008 [Page 21] Internet-Draft Framework for Reducing Spam 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. 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, THE IETF TRUST 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. Intellectual Property 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. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Tschofenig, et al. Expires August 28, 2008 [Page 22]