SIPPING J. Rosenberg Internet-Draft Cisco Systems Expires: August 21, 2005 G. Camarillo Ericsson D. Willis Cisco Systems February 20, 2005 A Framework for Consent-Based Communications in the Session Initiation Protocol (SIP) draft-ietf-sipping-consent-framework-01.txt Status of this Memo This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. 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 become aware will be disclosed, in accordance with RFC 3668. 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 21, 2005. Copyright Notice Copyright (C) The Internet Society (2005). Abstract The Session Initiation Protocol (SIP) supports communications across many media types, including real-time audio, video, text, instant messaging, and presence. In its current form, it allows session Rosenberg, et al. Expires August 21, 2005 [Page 1] Internet-Draft Consent Framework February 2005 invitations, instant messages, and other requests to be delivered from one party to another without requiring explicit consent of the recipient. Without such consent, it is possible for SIP to be used for malicious purposes, including spam and denial-of-service attacks. This document identifies a framework for consent-based communications in SIP. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Reference Architecture . . . . . . . . . . . . . . . . . . . . 4 5. Structure of a Permission . . . . . . . . . . . . . . . . . . 5 6. Single-Relay Scenario . . . . . . . . . . . . . . . . . . . . 6 6.1 Attempting Communication . . . . . . . . . . . . . . . . . 6 6.2 Requesting a Permission . . . . . . . . . . . . . . . . . 8 6.3 Waiting for Permissions . . . . . . . . . . . . . . . . . 9 6.4 Granting a Permission . . . . . . . . . . . . . . . . . . 9 6.5 Retrying the Original Request . . . . . . . . . . . . . . 10 6.6 Permission Revocation . . . . . . . . . . . . . . . . . . 10 7. Permission Servers . . . . . . . . . . . . . . . . . . . . . . 11 8. Multiple-Relay Scenario . . . . . . . . . . . . . . . . . . . 12 8.1 Initial Steps . . . . . . . . . . . . . . . . . . . . . . 12 8.2 Waiting for Permissions . . . . . . . . . . . . . . . . . 15 8.3 Intermediate Relays . . . . . . . . . . . . . . . . . . . 15 9. Installing Permissions in Advance . . . . . . . . . . . . . . 16 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 16 11. Security Considerations . . . . . . . . . . . . . . . . . . 16 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 12.1 Normative References . . . . . . . . . . . . . . . . . . . . 16 12.2 Informative References . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 17 Intellectual Property and Copyright Statements . . . . . . . . 18 Rosenberg, et al. Expires August 21, 2005 [Page 2] Internet-Draft Consent Framework February 2005 1. Introduction The Session Initiation Protocol (SIP) [1] supports communications across many media types, including real-time audio, video, text, instant messaging and presence. This communication is established by the transmission of various SIP requests (such as INVITE and MESSAGE [2]) from an initiator to the recipient, with whom communication is desired. Although a recipient of such a SIP request can reject the request, and therefore decline the session, a SIP network will deliver a SIP request to the recipient without their explicit consent. Receipt of these requests without explicit consent can cause a number of problems in SIP networks. These include spam and DoS (Denial of Service) attacks. These problems are described in more detail in a companion requirements document [5]. This specification defines a basic framework for adding consent-based communication to SIP. 2. Definitions Recipient URI: The request-URI of an outgoing request sent by an entity (e.g., a proxy) that has performed a translation operation. Target URI: The request-URI of an incoming request that arrives to an entity (e.g., a proxy) that will perform a translation operation. Translation operation: Operation by which an entity (e.g., a proxy) translates the request URI of an incoming request (i.e., the target URI) into one or more URIs (i.e., recipient URIs) which are used as the request URIs of one or more outgoing requests. 3. Relays A central concept in this framework is that of a relay. 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 request URI of the incoming request is referred to as 'target URI' and the destination URI of the outgoing requests is referred to as 'recipient URIs', as shown in Figure 1. Rosenberg, et al. Expires August 21, 2005 [Page 3] Internet-Draft Consent Framework February 2005 +---------------+ | | recipient URI | |----------------> target URI | Translation | -------------->| Operation | recipient URI | |----------------> | | +---------------+ Figure 1: Translation operation Thus, an essential aspect of a relay is that of translation. When a relay receives a request, it translates the request URI into one or more additional URIs. Or, more generally, it can create outgoing requests to one or more additional URIs. The translation operation is what creates the consent problem. Additionally, since the translation operation can result in more than one URI, it is also the source of amplification. Servers that do not perform translations, such as outbound proxy servers, do not cause amplification. Since the translation operation is based on local policy or local data (such as registrations), it is the vehicle by which a request is delivered directly to an endpoint, when it would not otherwise be possible to. In other words, if a spammer has the address of a user, 'sip:user@example.com', it cannot deliver a MESSAGE request to the UA (User Agent) of that user without having access to the registration data that maps 'sip:user@example.com' to the UA on which that user is present. Thus, it is the usage of this registration data, and more generally, the translation logic, which must be authorized in order to prevent undesired communications. 4. Reference Architecture The reference architecture is shown in Figure 2. In this architecture, a UAC wishes to send a message to a request URI representing a resource in domain A (sip:resource@A). This request may pass through a local outbound proxy (not shown), but eventually arrives at a server authoritative for domain A. This server, which acts as a relay, performs a translation operation, translating the target URI into one or more recipient URIs, which may or may not belong to domain A. This relay may be, for instance, a proxy server or a URI-list service [7]. Rosenberg, et al. Expires August 21, 2005 [Page 4] Internet-Draft Consent Framework February 2005 +-------+ | | >| UAS | +-------+ / | | | Rules | / +-------+ | DB | / +-------+ / | / V / +-----+ +-------+ / +-------+ | | | |/ | | | UAC |------>| Relay |-------->| Proxy | | | | |\ | | +-----+ +-------+ \ +-------+ \ \ [...] \ \ \ +-------+ \ | | >| B2BUA | | | +-------+ Figure 2: Relay performing a translation 5. Structure of a Permission This framework centers on the idea that a relay will only perform a translation if a permission is in place authorizing that translation. As such, the notion of a permission is another key part of this framework. A permission is an object, represented in XML, that contains several pieces of data: Identity of the Sender: A URI representing the identity of the sender for whom permissions are granted. Identity of the Original Recipient: A URI representing the identity of the original recipient, which is used as the input for the translation operation. This is also called the target URI. Identity of the Final Recipient: A URI representing the result of the translation. The permission grants ability for the sender to send requests to the target URI, and for a relay receiving those requests to forward them to this URI. This is also called the recipient URI. Rosenberg, et al. Expires August 21, 2005 [Page 5] Internet-Draft Consent Framework February 2005 Operations Permitted: A set of specific methods or qualifiers for which the permission applies. For example, the permission may only grant relaying for INVITE or MESSAGE, or for MESSAGE with specific MIME types. Signature: A digital signature over the rest of the permission, signed by an entity that can identify itself as the recipient URI. The signature is not always present. Permissions are installed on a resource by resource basis. That is, for each target URI to which a request is sent, there is a set of permissions installed for that URI. Each permission has the content described above. A natural format for representing permissions appears to be the common policy format [3]. This format is also used for presence permissions. 6. Single-Relay Scenario This section describes the fundamental operations of this framework in a single-relay scenario. The descriptions are illustrated with an example (see Figure 3). 6.1 Attempting Communication When a UA sends a request to a target resource (message 1 in Figure 3), the request eventually arrives at a server that is authoritative for the domain in the request URI. The server may require, as part of its processing logic, the relaying of the request to one or more next hops. If such relaying is required, the server first authenticates the sender of the request. Such authentication can be done using the SIP identity mechanism [4]. Once the sender is authenticated, the server checks its permission database for that target resource. It looks for permissions containing senders whose URI matches the identity of the sender of the request. Of those that are found, the server checks to see if the permitted translated URI matches the URIs to which the server wishes to relay the request. If at least one of the next hops to which the server wishes to relay have not been permitted, the server includes a Permission-Needed header field in the response to the request (message 2 in Figure 3). This Permission-Needed header field contains a list of URIs, each of which identify a translation for which permissions are needed. Rosenberg, et al. Expires August 21, 2005 [Page 6] Internet-Draft Consent Framework February 2005 Note that each of the URIs identify a translation at the server (i.e., at the relay). That is, the domain part of the URI will identify the server and the user part will be meaningful only to the server. A Relay B |(1) REQUEST school-friends@relay | |-------------------------->| | |(2) 470 Consent Needed | | |Call-Info: 123@relay; | | |purpose=wait-permission | | |Permission-Needed: xyz@relay | |<--------------------------| | |(3) CONSENT school-friends@relay | |Permission-From: xyz@relay | | |-------------------------->| | | |(4) CONSENT B | | |Permission-Requested: uri-req | |-------------------------->| | |(5) 202 Accepted | | |<--------------------------| |(6) 202 Accepted | | |<--------------------------| | |(7) SUBSCRIBE 123@relay | | |-------------------------->| | |(8) 200 OK | | |<--------------------------| | |(9) NOTIFY (no permission) | | |<--------------------------| | |(10) 200 OK | | |-------------------------->| | | |(11) HTTP uri-req | | |Get Requested Permission | | |<--------------------------| | |(12) 200 OK | | |Permission Document | | |URI to Upload: uri-up | | |-------------------------->| | |(13) PUBLISH uri-up | | |Permission Document | | |<--------------------------| | |(14) 200 OK | | |-------------------------->| |(15) NOTIFY (permission) | | |<--------------------------| | |(16) 200 OK | | |-------------------------->| | Rosenberg, et al. Expires August 21, 2005 [Page 7] Internet-Draft Consent Framework February 2005 |(17) REQUEST school-friends@relay | |-------------------------->| | | |(18) REQUEST B | | |Permission-Used: uri-perm | | |-------------------------->| Figure 3: Basic call flow The status code the server uses in its response depends on the service the translation is part of. For example, a URI-list service which receives a request with a list of recipient URIs may already have permissions for some of them. The URI-list service may choose to perform the translations which it has permissions for and return a 200 (OK) response with a list of URIs in a Permission-Needed header field for the translations for which permissions have not yet been obtained. Alternatively, the URI-list service may choose not to perform any translation and to return a 470 (Consent Needed) response with a list of URIs in a Permission-Needed header field for the translations for which permissions have not yet been obtained. The response from the server may carry a URI in a Call-Info header field (wait-permission purpose) where the client can SUBSCRIBE to using the wait-permission event package. This event package models the state of the permission granted to the client for communicating with the target URIs. When a permission is granted, the state changes, and the client receives a NOTIFY. This NOTIFY contains the permission(s) that have been granted for the sender. OPEN ISSUE: in which response does the server include the call-info header? Proposal: it can include it in any response (i.e., responses to the original request and responses to the CONSENTs, but it should include always the same URI. Usage of an event package has the benefit that the client can come back at any time and do a query SUBSCRIBE to see if permissions were granted, or it can wait for them to be granted, and find out when. There is no requirement that the client use this event package to wait. For some requests, it may not be important for the sender to find out when permission is granted (e.g., a presence subscription). 6.2 Requesting a Permission If a server returns a response with a Permission-Needed header field, the client knows that it needs to obtain some number of permissions. The response will include a list of URIs in a Permission-Needed header field for which permission must be obtained. To obtain permission, the client generates as many CONSENT request as entries the Permission-Needed header field contained. Rosenberg, et al. Expires August 21, 2005 [Page 8] Internet-Draft Consent Framework February 2005 Each CONSENT request (message 3 in Figure 3) is sent to the same URI as the original request and carries, in a Permission-From header field, one of the URIs received in the Permission-Needed header field. The server will forward these CONSENT requests on to the destinations whose permissions have not been obtained yet. OPEN ISSUE: it was proposed having clients send CONSENTs to the URIs received in the Permission-Needed header field (i.e., using them in the Request-URI instead of in a Request-From header field). This would require the server to store more state information and come up with a number of URIs in multiple-relay scenarios. When the CONSENT request arrives at the server, the relay adds a Permission-Requested header field which contains a URI (e.g., an HTTP URI) that the receiver can use to download a description of the permission being requested (e.g., an XML-based permission document). Then, the server forwards the request towards its destination (message 4 in Figure 3). If there are several relays between the sender and the final destination, those CONSENT requests may also fail if permissions have not yet been obtained, in which case the process recurses, as described in Section Section 8. Eventually, the client will have sent a request to all of the relays at the leaves of the translation tree between the sender and the final destinations. 6.3 Waiting for Permissions A CONSENT request is responded with a 202 (Accepted) response (message 5 in Figure 3). As stated earlier, if the client is interested in the status of the permissions, it can SUBSCRIBE (message 7 in Figure 3) to the the wait-permission event package using the URI received in the Call-Info header field (wait-permission purpose) of the response to the original request (responses to CONSENT requests may also carry a Call-Info header field with such a URI). 6.4 Granting a Permission On reception of a CONSENT request, the user fetches the permission being requested from the URI in the Permission-Requested header field (message 11 in Figure 3). This permission document includes the URI that the user needs to use to upload the permissions that the user chooses to grant. So, if the user wishes to grant a permission, it may use a SIP PUBLISH request (message 13 in Figure 3) to upload a permission document into that URI. This PUBLISH request is authenticated using the SIP identity mechanism. Rosenberg, et al. Expires August 21, 2005 [Page 9] Internet-Draft Consent Framework February 2005 OPEN ISSUE: XCAP could be useful for endpoints that support it. Do we want to allow XCAP to be used? If XCAP was allowed, how do we permorm authentication? Do endpoings using XCAP need to sign their permissions? Relaying on the routing architecture and SIPS to deliver a randomly-looking http URI to the proper endpoint does not seem to be secure enough. OPEN ISSUE: Using XCAP to grant permissions would require the definition of a new application usage. We note that this usage appears to be a generalization of the presence rules usage currently defined [6]. The owner of the target resource may choose to grant the permissions requested or a superset of them. For example, a CONSENT request may request permission to perform a given translation on MESSAGE requests, and the target resource owner may grant permission to perform the translation on any request (not only on MESSAGE requests). 6.5 Retrying the Original Request The sender learns about permissions through the wait-permission event package. Once it has obtained permissions for all of the resources that were identified in the Permission-Needed header field, the client can retry the original request (message 17 in Figure 3). When the server performs the translation, it adds a Permission-Used header field with a URI (e.g., an HTTP URI) where the permission document that authorizes the translation can be downloaded from. 6.6 Permission Revocation At any time, if a client wants to revoke any permission, it uses the same URI as before to upload a new permission document. If a client loses this URI for some reason, it needs to wait until it receives a new request, which will contain a Permission-Used header field. The permission documents that can be downloaded from the URIs in the Permission-Used header field contain a URI where the client can upload a new permission document (e.g., a permission document that does not allow a particular translation any longer). OPEN ISSUE: is it OK to force clients to download the permission document in order to obtain the SIP URI to send their PUBLISH requests to or we want to already include such a URI in the Permission-Used header field. Rosenberg, et al. Expires August 21, 2005 [Page 10] Internet-Draft Consent Framework February 2005 7. Permission Servers We described in Section 6.4 how a user agent that receives a CONSENT request can use a PUBLISH request to grant certain permissions. Nevertheless, users are not on-line all the time and, so, sometimes are not able to receive CONSENT requests. This issue is also found in presence, where a user's status is reported by a presence server instead of by the user's user agents, which can go on and off-line. Similarly, we define permission servers. Permission servers are network elements that act as SIP UAs and handle CONSENT requests for a user. Permission servers inform users about new CONSENT requests using the "grant-permission" event package. The user associated with the target URI SUBSCRIBEs (message 1 in Figure 4) to the "grant-permission" event package at the permission server. This event package models the state of all pending CONSENT requests for a particular resource, for which permissions do not yet exist. When a new CONSENT request (message 3 in Figure 4) arrives for which permissions have not been granted, a NOTIFY (message 5 in Figure 4) is sent to the user. This informs them that permission is needed for a particular sender. The NOTIFY contains information on the operation which was requested. There is a strong similarity between the watcherinfo event package and the grant-permission event package. Indeed, the grant-permission package is effectively a superset of watcherinfo. Once in place, presentities could use the grant-permission event package for presence in addition to all other services for which opt-in is being provided. When a user is notified of a new pending CONSENT request, the user follows regular procedures to upload the permissions that were requested (messages 9 to 11 in Figure 4). Rosenberg, et al. Expires August 21, 2005 [Page 11] Internet-Draft Consent Framework February 2005 Relay B's Permission B Server | |(1) SUBSCRIBE | | |grant-permission | | |<------------------| | |(2) 200 OK | | |------------------>| |(3) CONSENT B | | |Permission-Requested: uri-req | |------------------>| | |(4) 202 Accepted | | |<------------------| | | |(5) NOTIFY | | |Permission Requested: uri-req | |------------------>| | |(6) 200 OK | | |<------------------| |(7) HTTP uri-req | | |Get Requested Permission | |<--------------------------------------| |(8) 200 OK | | |Permission Document| | |URI to Upload: uri-up | |------------------>| | |(9) PUBLISH uri-up | | |Permission Document| | |<--------------------------------------| |(10) 200 OK | | |-------------------------------------->| Figure 4: Permission server operation 8. Multiple-Relay Scenario One of the results of a translation (i.e., a recipient URI) at a relay can route to another relay. In this case, there will be multiple relays between the UA generating a request and the destination UA or UAs. 8.1 Initial Steps The way UAs are informed that they need to request permissions for a translation and the way they request those permissions (i.e., using CONSENT requests) are identical to the single-relay case. In the example of Figure 5, Relay 1 handles the URI 'friends@relay1', which translates to a set of URIs. Relay 1 already has permissions Rosenberg, et al. Expires August 21, 2005 [Page 12] Internet-Draft Consent Framework February 2005 to perform all the translations but one. Relay 1 needs to obtain permission to perform the translation to 'school-friends@relay2'. Relay 1 returns a 470 (Consent Needed) response (message 2 in Figure 5) with a Permission-Needed header field. The UA generates a CONSENT request (message 2 in Figure 5) placing the URI received in that header field in a Request-From header field. The CONSENT request is forwarded by Relay 1 to Relay 2 (message 4 in Figure 5). The URI 'school-friends@relay2' translates to a set of URIs. Relay 1 already has permissions to perform all the translations but one. Relay 1 needs to obtain permission to perform the translation to B. Relay 2 returns a 470 (Consent Needed) response (message 5 in Figure 5) with a Permission-Needed header field. On reception of this response, Relay 1 adds the URI identifying the first translation to this header field (message 6 in Figure 5). The UA inserts the two URIs received in the Permission-Needed header field into the Permission-From header field of a new CONSENT request (message 7 in Figure 5). Relay 1 consumes the URI it added when it relays the CONSENT request to Relay 2 (message 8 in Figure 5). Relay 2 consumes the URI it added when it relays the CONSENT request to B (message 9 in Figure 5). A Relay1 Relay2 B |(1) REQUEST friends@relay1 | | |---------------->| | | |(2) 470 Consent Needed | | |Call-Info: 123@relay1; | | |purpose=wait-permission | | |Permission-Needed: xyz@relay1 | | |<----------------| | | |(3) CONSENT friends@relay1 | | |Permission-From: xyz@relay1 | | |---------------->| | | | |(4) CONSENT school-friends@relay2 | | |Permission-Requested: uri-req1 | | |---------------->| | | |(5) 470 Consent Needed | | |Call-Info:456@relay2; | | |purpose=wait-permission | | |Permission-Needed: abc@relay2 | | |<----------------| | |(6) 470 Consent Needed | | |Permission-Needed: xyz@relay1;abc@relay2 | Rosenberg, et al. Expires August 21, 2005 [Page 13] Internet-Draft Consent Framework February 2005 |<----------------| | | |(7) CONSENT friends@relay1 | | |Permission-From: xyz@relay1;abc@relay2 | |---------------->| | | | |(8) CONSENT school-friends@relay2 | | |Permission-Requested:uri-req1 | | |Permission-From: abc@relay2 | | |---------------->| | | | |(9) CONSENT B | | | |Permission-Requested: uri-req2 | | |---------------->| | | |(10) 202 Accepted| | | |<----------------| | |(11) 202 Accepted| | | |<----------------| | |(12) 202 Accepted| | | |<----------------| | | |(13) SUBSCRIBE 123@relay1 | | |---------------->| | | |(14) 200 OK | | | |<----------------| | | |(15) NOTIFY (no permission) | | |<----------------| | | |(16) 200 OK | | | |---------------->| | | | | |(17) HTTP uri-req| | | |Get Requested Permission | | |<----------------| | | |(18) 200 OK | | | |Permission Document | | |URI to Upload: uri-up2 | | |---------------->| | | |(19) PUBLISH uri-up2 | | |Permission Document | | |<----------------| | | |(20) 200 OK | | | |---------------->| | |(21) HTTP uri-req1 | | |Get Requested Permission | | |<----------------| | | |(22) 200 OK | | | |Permission Document | | |URI to Upload: uri-up1 | | |---------------->| | | |(23) PUBLISH uri-up1 | | |Permission Document | | |<----------------| | | |(24) 200 OK | | Rosenberg, et al. Expires August 21, 2005 [Page 14] Internet-Draft Consent Framework February 2005 | |---------------->| | |(25) NOTIFY (permission) | | |<----------------| | | |(26) 200 OK | | | |---------------->| | | |(27) REQUEST friends@relay1 | | |---------------->| | | | |(28) REQUEST school-friends@relay2 | | |Permission-Used: uri-perm1 | | |---------------->| | | | |(29) REQUEST B | | | |Permission-Used: uri-perm1 | | |Permission-Used: uri-perm2 | | |---------------->| Figure 5: Multiple-relay scenario 8.2 Waiting for Permissions In order to be informed of the status of the permissions, A subscribes (message 13 in Figure 5) to the URI it received from Relay 1 in a Call-Info header field (message 2 in Figure 5). Although Figure 5 does not show it, Relay 1 could subscribe to the status of the permissions at Relay 2 using the URI it received in a Call-Info header field (message 5 in Figure 5). 8.3 Intermediate Relays At this point, A needs to upload permissions to Relay 2 and Relay 2 needs to upload permissions to Relay 1. Therefore, Relay 2 acts as an intermediate relay between B and Relay 1. The policy followed by Relay 2 in Figure 5 is not to give permissions to Relay 1 to perform the translation from friends@relay1 to school-friends@relay2 until B gives Relay 2 permissions to perform the translation school-friends@relay2 to B. However, this is not the only possible policy. Relay 2 may choose to give permissions to Relay 1 before B gave Relay 2 permissions. This would probably be the case if Relay 2 was a forking proxy trying to locate a user registered at several UAs, one of which had not given permissions to the forking proxy yet. Therefore, how a relay decides when to give certain permissions to other relays is based on the local policy of the relay, which will generally depend on the type of service provided by the relay. Rosenberg, et al. Expires August 21, 2005 [Page 15] Internet-Draft Consent Framework February 2005 9. Installing Permissions in Advance The previous sections described how a relay can request a target resource owner to authorize a communication attempt. However, target resource owners may want to authorize a particular translation in advance. That is, before any communication attempt is performed. To do so, the target resource owner sends a CONSENT request to the target URI of the translation. This CONSENT request will trigger the mechanisms described in the previous sections. The result is that the target resource owner(s) will obtain a URI to upload a permission document. 10. IANA Considerations TBD. 11. Security Considerations TBD. Editor's note: we have to avoid that attackers provide permissions for translations that apply to other users (e.g., allow everyone to send traffic to a victim) and that attackers provide permissions for a translation that apply to them but routes to a victim (e.g., 3rd party registration that binds attacker@relay to victim@somewhere). For the former we need authentication (e.g., SIP identity) and for the latter we relay on the routing infrastructure to route CONSENTs to the same place the traffic will be sent to once permissions are obtained (i.e., a return routability test). 12. References 12.1 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] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C. and D. Gurle, "Session Initiation Protocol (SIP) Extension for Instant Messaging", RFC 3428, December 2002. 12.2 Informative References [3] Schulzrinne, H., "A Document Format for Expressing Privacy Preferences", draft-ietf-geopriv-common-policy-03 (work in progress), October 2004. Rosenberg, et al. Expires August 21, 2005 [Page 16] Internet-Draft Consent Framework February 2005 [4] Peterson, J., "Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)", draft-ietf-sip-identity-03 (work in progress), September 2004. [5] Rosenberg, J., "Requirements for Consent-Based Communications in the Session Initiation Protocol (SIP)", draft-ietf-sipping-consent-reqs-00 (work in progress), October 2004. [6] Rosenberg, J., "Presence Authorization Rules", draft-ietf-simple-presence-rules-01 (work in progress), October 2004. [7] Camarillo, G., "Requirements and Framework for Session Initiation Protocol (SIP)Uniform Resource Identifier (URI)-List Services", draft-ietf-sipping-uri-services-01 (work in progress), October 2004. Authors' Addresses 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 Gonzalo Camarillo Ericsson Hirsalantie 11 Jorvas 02420 Finland EMail: Gonzalo.Camarillo@ericsson.com Dean Willis Cisco Systems 2200 E. Pres. George Bush Turnpike Richardson, TX 75082 USA EMail: dean.willis@softarmor.com Rosenberg, et al. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Rosenberg, et al. Expires August 21, 2005 [Page 18]