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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SIPPING H. Tschofenig 3 Internet-Draft Nokia Siemens Networks 4 Intended status: Standards Track D. Wing 5 Expires: January 9, 2008 Cisco 6 H. Schulzrinne 7 Columbia University 8 T. Froment 9 Alcatel-Lucent 10 G. Dawirs 11 University of Namur 12 July 8, 2007 14 A Document Format for Expressing Authorization Policies to tackle Spam 15 and Unwanted Communication for Internet Telephony 16 draft-tschofenig-sipping-spit-policy-01.txt 18 Status of this Memo 20 By submitting this Internet-Draft, each author represents that any 21 applicable patent or other IPR claims of which he or she is aware 22 have been or will be disclosed, and any of which he or she becomes 23 aware will be disclosed, in accordance with Section 6 of BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF), its areas, and its working groups. Note that 27 other groups may also distribute working documents as Internet- 28 Drafts. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 The list of current Internet-Drafts can be accessed at 36 http://www.ietf.org/ietf/1id-abstracts.txt. 38 The list of Internet-Draft Shadow Directories can be accessed at 39 http://www.ietf.org/shadow.html. 41 This Internet-Draft will expire on January 9, 2008. 43 Copyright Notice 45 Copyright (C) The IETF Trust (2007). 47 Abstract 49 SPAM, defined as sending unsolicited messages to someone in bulk, 50 might be a problem on SIP open-wide deployed networks. The 51 responsibility for filtering or blocking calls can belong to 52 different elements in the call flow and may depend on various 53 factors. This document defines an authorization based policy 54 language that allows end users to upload anti-SPIT policies to 55 intermediaries, such as SIP proxies. These policies mitigate 56 unwanted SIP communications. It extends the Common Policy 57 authorization framework with additional conditions and actions. The 58 new conditions match a particular Session Initiation Protocol (SIP) 59 communication pattern based on a number of attributes. The range of 60 attributes includes information provided, for example, by SIP itself, 61 by the SIP identity mechanism, by information carried within SAML 62 assertions. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 67 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 68 3. Generic Processing . . . . . . . . . . . . . . . . . . . . . . 5 69 3.1. Structure of SPIT Authorization Documents . . . . . . . . 5 70 3.2. Rule Transport . . . . . . . . . . . . . . . . . . . . . . 5 71 4. Condition Elements . . . . . . . . . . . . . . . . . . . . . . 6 72 4.1. Identity . . . . . . . . . . . . . . . . . . . . . . . . . 6 73 4.1.1. Acceptable Forms of Authentication . . . . . . . . . . 6 74 4.1.2. Computing a URI for the Sender . . . . . . . . . . . . 7 75 4.2. Sphere . . . . . . . . . . . . . . . . . . . . . . . . . . 8 76 4.3. SPIT Handling . . . . . . . . . . . . . . . . . . . . . . 9 77 4.4. Media List . . . . . . . . . . . . . . . . . . . . . . . . 9 78 4.5. Method List . . . . . . . . . . . . . . . . . . . . . . . 10 79 4.6. MIME List . . . . . . . . . . . . . . . . . . . . . . . . 10 80 4.7. Presence Status . . . . . . . . . . . . . . . . . . . . . 10 81 4.8. Rule Deactivated . . . . . . . . . . . . . . . . . . . . . 10 82 4.9. Time Period Condition . . . . . . . . . . . . . . . . . . 10 83 5. Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 84 5.1. Execute Action . . . . . . . . . . . . . . . . . . . . . . 18 85 5.2. Forward To . . . . . . . . . . . . . . . . . . . . . . . . 18 86 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 87 7. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 20 88 8. XCAP USAGE . . . . . . . . . . . . . . . . . . . . . . . . . . 27 89 8.1. Application Unique ID . . . . . . . . . . . . . . . . . . 27 90 8.2. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . 27 91 8.3. Default Namespace . . . . . . . . . . . . . . . . . . . . 27 92 8.4. MIME Type . . . . . . . . . . . . . . . . . . . . . . . . 27 93 8.5. Validation Constraints . . . . . . . . . . . . . . . . . . 27 94 8.6. Data Semantics . . . . . . . . . . . . . . . . . . . . . . 27 95 8.7. Naming Conventions . . . . . . . . . . . . . . . . . . . . 28 96 8.8. Resource Interdependencies . . . . . . . . . . . . . . . . 28 97 8.9. Authorization Policies . . . . . . . . . . . . . . . . . . 28 98 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 99 9.1. Anti-SPIT Policy XML Schema Registration . . . . . . . . . 28 100 9.2. Anti-SPIT Policy Namespace Registration . . . . . . . . . 28 101 9.3. XCAP Application Usage ID . . . . . . . . . . . . . . . . 29 102 10. Security Considerations . . . . . . . . . . . . . . . . . . . 29 103 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 29 104 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 29 105 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30 106 13.1. Normative References . . . . . . . . . . . . . . . . . . . 30 107 13.2. Informative References . . . . . . . . . . . . . . . . . . 31 108 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34 109 Intellectual Property and Copyright Statements . . . . . . . . . . 36 111 1. Introduction 113 The problem of SPAM for Internet Telephony (SPIT) is an imminent 114 challenge and only the combination of several techniques can provide 115 a framework for dealing with unwanted communication, as stated in 116 [I-D.jennings-sip-hashcash]. 118 One important building block is to have a mechanism that can instruct 119 SIP intermediaries to react differently on incoming requests based on 120 policies. Different entities, such as end users, parents on behalf 121 of their children, system administrators in enterprise networks, 122 etc., might create and modify authorization policies. The conditions 123 in these policies can be created from many sources but some 124 information elements are more important than others. For example, 125 there is reason to believe that applying authorization policies based 126 on the authenticated identity is an effective way to accept a 127 communication attempt to deal with unsolicited communication. 128 Authentication based on the SIP identity mechanism, see [RFC4474], is 129 one important concept. 131 The requirements for the authorization policies described in this 132 document are outlined in [I-D.froment-sipping-spit-requirements]. A 133 framework document is available at 134 [I-D.tschofenig-sipping-framework-spit-reduction]. 136 2. Terminology 138 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 139 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 140 document are to be interpreted as described in RFC 2119 [RFC2119]. 142 This document reuses the terminology from RFC 4745 [RFC4745]: 144 Rule maker: 146 The RM is an entity that creates the authorization policies that 147 react to unwanted connection attempts. The rule maker might be an 148 end user that owns the device, a VoIP service provider, a person 149 with a relationship to the end user (e.g., the parents of a child 150 using a mobile phone). A standardized policy language is needed 151 when the creation, modification and deletion of authorization 152 policies are not only a local matter. 154 Authorization policy: 156 An authorization policy is given by a rule set. A rule set 157 contains an unordered list of rules. Each rule has a condition, 158 an action and a transformation component. The terms 159 'authorization policy', 'policy', 'rule set', 'authorization 160 policy rule', 'policy rule' and 'rule' are used interchangeably. 161 Authorization policies can be applied at the end host and/or by 162 intermediaries. 164 Permission: 166 The term permission refers to the action and transformation 167 components of a rule. 169 We use the term 'Recipient' for the entity that is target of the 170 communication attempt of a sender. 172 3. Generic Processing 174 3.1. Structure of SPIT Authorization Documents 176 A SPIT authorization document is an XML document, formatted according 177 to the schema defined in RFC 4745 [RFC4745]. SPIT authorization 178 documents inherit the MIME type of common policy documents, 179 application/auth-policy+xml. As described in [RFC4745], this 180 document is composed of rules which contain three parts - conditions, 181 actions, and transformations. Each action or transformation, which 182 is also called a permission, has the property of being a positive 183 grant to the authorization server to perform the resulting actions, 184 be it allow, block etc . As a result, there is a well-defined 185 mechanism for combining actions and transformations obtained from 186 several sources. This mechanism therefore can be used to filter 187 connection attempts thus leading to effective SPIT prevention. 189 3.2. Rule Transport 191 Policies are XML documents that are stored at a Proxy Server or a 192 dedicated device. The Rule Maker therefore needs to use a protocol 193 to create, modify and delete the authorization policies defined in 194 this document. Such a protocol is available with the Extensible 195 Markup Language (XML) Configuration Access Protocol (XCAP) [RFC4825]. 197 4. Condition Elements 199 This section describes the additional enhancements of the conditions- 200 part of the rule. This document inherits the Common Policy 201 functionality, including , , and 202 conditions. 204 Note that, as discussed in [RFC4745], a permission document applies 205 to a translation if all the expressions in its conditions part 206 evaluate to TRUE. 208 4.1. Identity 210 Although the element is defined in [RFC4745], that 211 specification indicates that the specific usages of the framework 212 document need to define details that are protocol and usage specific. 213 In particular, it is necessary for a usage of the common policy 214 framework to: 216 o Define acceptable means of authentication. 217 o Define the procedure for representing the identity as a URI or IRI 218 [RFC3987]. 220 This sub-section defines those details for systems based on 221 [RFC3856]. 223 4.1.1. Acceptable Forms of Authentication 225 When used with SIP, a request is considered authenticated if one of 226 the following techniques is used: 228 SIP Digest: 230 The proxy has authenticated the sender using SIP [RFC3261] digest 231 authentication [RFC2617]. However, if the anonymous 232 authentication described on page 194 of RFC 3261 [RFC3261] was 233 used, the sender is not considered authenticated. 235 Asserted Identity: 237 If a request contains a P-Asserted-ID header field [RFC3325] and 238 the request is coming from a trusted element, the sender is 239 considered authenticated. 241 Cryptographically Verified Identity: 243 If a request contains an Identity header field as defined in 244 [RFC4474], and it validates the From header field of the request, 245 the request is considered to be authenticated. Note that this is 246 true even if the request contained a From header field of the form 247 sip:anonymous@example.com. As long as the signature verifies that 248 the request legitimately came from this identity, it is considered 249 authenticated. 251 An anonymous From header field with RFC 4474 [RFC4474] is considered 252 authenticated, while anonymous digest is not considered 253 authenticated, because the former still involves the usage of an 254 actual username and credential as part of an authentication operation 255 in the originating domain. 257 4.1.2. Computing a URI for the Sender 259 For messages that are authenticated using SIP Digest, the identity of 260 the sender is set equal to the address of record (AoR) for the user 261 that has authenticated themselves. The AoR is always a URI, and can 262 be either a SIP URI or tel URI [RFC3966]. For example, consider the 263 following "user record" in a database: 265 SIP AOR: sip:alice@example.com 266 digest username: ali 267 digest password: f779ajvvh8a6s6 268 digest realm: example.com 270 If the proxy server receives an INVITE, challenges it with the realm 271 set to "example.com", and the subsequent INVITE contains an 272 Authorization header field with a username of "ali" and a digest 273 response generated with the password "f779ajvvh8a6s6", the identity 274 used in matching operations is "sip:alice@example.com". 276 For messages that are authenticated using RFC 3325 [RFC3325], the 277 identity of the sender is equal to the URI in the P-Asserted-ID 278 header field. If there are multiple values for the P-Asserted-ID 279 header field (there can be one sip URI and one tel URI [RFC3966]), 280 then each of them is used for the comparisons outlined in [RFC4745], 281 and if either of them match a or element, it is 282 considered a match. 284 For messages that are authenticated using the SIP Identity mechanism 285 [RFC4474], identity of the sender is equal to the SIP URI in the From 286 header field of the request, assuming that the signature in the 287 Identity header field has been validated. 289 In SIP systems, it is possible for a user to have aliases - that is, 290 there are multiple SIP AoRs "assigned" to a single user. In terms of 291 this specification, there is no relationship between those aliases. 292 Each would look like a different user. This will be the consequence 293 for systems where the sender is in a different domain than the 294 recipient. However, even if the sender and recipient are in the same 295 domain, and the proxy server knows that there are aliases for the 296 sender, these aliases are not mapped to each other or used in any 297 way. 299 SIP also allows for anonymous identities. If a message is anonymous 300 because the digest challenge/response used the "anonymous" username, 301 the message is considered unauthenticated and will match only an 302 empty element. If a message is anonymous because it 303 contains a Privacy header field [RFC3323], but still contains a 304 P-Asserted-ID header field, the identity in the P-Asserted-ID header 305 field is still used in the authorization computations; the fact that 306 the message was anonymous has no impact on the identity processing. 307 However, if the message had traversed a trust boundary and the 308 P-Asserted-ID header field and the Privacy header field had been 309 removed, the message will be considered unauthenticated when it 310 arrives at the proxy server. Finally, if a message contained an 311 Identity header field that was validated, and the From header field 312 contained a URI of the form sip:anonymous@example.com, then the 313 sender is considered authenticated, and it will have an identity 314 equal to sip:anonymous@example.com. Had such an identity been placed 315 into a or element, there will be a match. 317 It is important to note that SIP frequently uses both SIP URI and tel 318 URI [RFC3966] as identifiers, and to make matters more confusing, a 319 SIP URI can contain a phone number in its user part, in the same 320 format used in a tel URI. The sender's identity that is a SIP URI 321 with a phone number will not match the and conditions 322 whose 'id' is a tel URI with the same number. The same is true in 323 the reverse. If the sender's identity is a tel URI, this will not 324 match a SIP URI in the or conditions whose user part 325 is a phone number. URIs of different schemes are never equivalent. 327 4.2. Sphere 329 The element is defined in [RFC4745]. However, each 330 application making use of the common policy specification needs to 331 determine how the policy server computes the value of the sphere to 332 be used in the evaluation of the condition. 334 To compute the value of , the proxy server interacts with a 335 presence server who knows whether at least one of the published 336 presence documents includes the element [RFC4480] as part of 337 the person data component [RFC4479], and all of those containing the 338 element have the same value for it, that is the value used for the 339 sphere in policy policy processing. If, however, the 340 element was not available to the presence server (and hence not for 341 the proxy server), or it was present but had inconsistent values, its 342 value is considered undefined in terms of policy processing. 344 4.3. SPIT Handling 346 The element is a way to react on the execution of 347 certain SPIT handling mechanisms. For example, a rule might indicate 348 that a CAPTCHA has to be sent to the sender and the sender 349 subsequently has to return the result. Depending on the outcome of 350 the robot test the rules might enforce different actions. This 351 element provides such a condition capability. 353 The condition evaluates to TRUE if any of its child 354 elements evaluate to TRUE, i.e., the results of the individual child 355 element are combined using a logical OR. 357 The element MAY contain zero or more 358 elements. The elements has an attribute 'result' that 359 either contains "SUCCESS" or "FAILURE". 361 4.4. Media List 363 The condition evaluates to TRUE if any of its child 364 elements evaluate to TRUE, i.e., the results of the individual child 365 element are combined using a logical OR. 367 The element SHOULD include either 368 o an element or; 369 o a list of one or more >media> elements selected from the list of 370 possible media elements below. 372 List of possible media elements: 373 o The media element indicating session based 374 messaging as defined in [I-D.ietf-simple-message-sessions]; 375 o The media element indicating pager mode 376 message requests as defined in [RFC3428]; 377 o The media element indicating file transfer as 378 defined in [I-D.ietf-mmusic-file-transfer-mech]; 379 o The