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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group C. Holmberg 3 Internet-Draft Ericsson 4 Updates: 5763,7345 (if approved) R. Shpount 5 Intended status: Standards Track TurboBridge 6 Expires: July 14, 2017 January 10, 2017 8 Using the SDP Offer/Answer Mechanism for DTLS 9 draft-ietf-mmusic-dtls-sdp-16.txt 11 Abstract 13 This document defines the SDP offer/answer procedures for negotiating 14 and establishing a DTLS association. The document also defines the 15 criteria for when a new DTLS association must be established. The 16 document updates RFC 5763 and RFC 7345, by replacing common SDP 17 offer/answer procedures with a reference to this specification. 19 This document defines a new SDP media-level attribute, 'dtls-id'. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on July 14, 2017. 38 Copyright Notice 40 Copyright (c) 2017 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 3. Establishing a new DTLS Association . . . . . . . . . . . . . 3 58 3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 3.2. Change of Local Transport Parameters . . . . . . . . . . 4 60 3.3. Change of ICE ufrag value . . . . . . . . . . . . . . . . 4 61 4. SDP dtls-id Attribute . . . . . . . . . . . . . . . . . . . . 4 62 5. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 5 63 5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 6 64 5.2. Generating the Initial SDP Offer . . . . . . . . . . . . 7 65 5.3. Generating the Answer . . . . . . . . . . . . . . . . . . 8 66 5.4. Offerer Processing of the SDP Answer . . . . . . . . . . 8 67 5.5. Modifying the Session . . . . . . . . . . . . . . . . . . 9 68 6. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 9 69 7. Transport Protocol Considerations . . . . . . . . . . . . . . 10 70 7.1. Transport Re-Usage . . . . . . . . . . . . . . . . . . . 10 71 8. SIP Considerations . . . . . . . . . . . . . . . . . . . . . 10 72 9. RFC Updates . . . . . . . . . . . . . . . . . . . . . . . . . 11 73 9.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 11 74 9.2. Update to RFC 5763 . . . . . . . . . . . . . . . . . . . 11 75 9.3. Update to RFC 7345 . . . . . . . . . . . . . . . . . . . 16 76 10. Security Considerations . . . . . . . . . . . . . . . . . . . 19 77 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 78 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20 79 13. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 20 80 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 23 81 14.1. Normative References . . . . . . . . . . . . . . . . . . 23 82 14.2. Informative References . . . . . . . . . . . . . . . . . 24 83 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 85 1. Introduction 87 [RFC5763] defines SDP Offer/Answer procedures for SRTP-DTLS. 88 [RFC7345] defines SDP offer/answer procedures for UDPTL-DTLS. This 89 specification defines general offer/answer procedures for DTLS, based 90 on the procedures in [RFC5763]. Other specifications, defining 91 specific DTLS usages, can then reference this specification, in order 92 to ensure that the DTLS aspects are common among all usages. Having 93 common procedures is essential when multiple usages share the same 94 DTLS association [I-D.ietf-mmusic-sdp-bundle-negotiation]. The 95 document updates [RFC5763] and [RFC7345], by replacing common SDP 96 offer/answer procedures with a reference to this specification. 98 As defined in [RFC5763], a new DTLS association MUST be established 99 when transport parameters are changed. Transport parameter change is 100 not well defined when Interactive Connectivity Establishment (ICE) 101 [I-D.ietf-ice-rfc5245bis] is used. One possible way to determine a 102 transport change is based on ufrag change, but the ufrag value is 103 changed both when ICE is negotiated and when ICE restart 104 [I-D.ietf-ice-rfc5245bis] occurs. These events do not always require 105 a new DTLS association to be established, but currently there is no 106 way to explicitly indicate in an SDP offer or answer whether a new 107 DTLS association is required. To solve that problem, this document 108 defines a new SDP attribute, 'dtls-id'. The 'dtls-id' attribute pair 109 in combination with 'fingerprint' attribute values from offer and 110 answer SDP uniquely identifies the DTLS association. Providing a new 111 value of 'dtls-id' attribute in SDP offer or answers can be used to 112 indicate whether a new DTLS association is to be established. 114 2. Conventions 116 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 117 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 118 document are to be interpreted as described in [RFC2119]. 120 3. Establishing a new DTLS Association 122 3.1. General 124 A new DTLS association MUST be established after a successfull SDP 125 offer/answer transaction in the following cases:: 127 o The negotiated DTLS setup roles change; or 129 o One or more fingerprint values are modified, added or removed in 130 either an SDP offer or answer; or 132 o The intent to establish a new DTLS association is explicitly 133 signaled by changing the value of the SDP 'dtls-id' attribute 134 defined in this document; 136 NOTE: The first two items list above are based on the procedures in 137 [RFC5763]. This specification adds the support for explicit 138 signaling using the SDP 'dtls-id' attribute. 140 A new DTLS association can only established as a result of the 141 successful SDP offer/answer transaction. Whenever an entity 142 determines that a new DTLS association is required, the entity MUST 143 initiate an SDP offer/answer transaction, following the procedures in 144 Section 5. 146 The sections below describe typical cases where a new DTLS 147 association needs to be established. 149 3.2. Change of Local Transport Parameters 151 If an endpoint modifies its local transport parameters (address and/ 152 or port), and if the modification requires a new DTLS association, 153 the endpoint MUST change its local SDP 'dtls-id' attribute value 154 Section 4. 156 If the underlying transport explicitly prohibits a DTLS association 157 to span multiple transports, and if the transport is changed, the 158 endpoint MUST change its local SDP 'dtls-id' attribute value 159 Section 4. An example of such case is when DTLS is carried over 160 SCTP, as described in [RFC6083]. 162 3.3. Change of ICE ufrag value 164 If an endpoint uses ICE, and modifies a local ufrag value, and if the 165 modification requires a new DTLS association, the endpoint MUST 166 change its local SDP 'dtls-id' attribute value Section 4. 168 4. SDP dtls-id Attribute 170 The pair of SDP 'dtls-id' attribute values (the attribute values of 171 the offerer and the answerer) uniquely identifies the DTLS 172 association. 174 Name: dtls-id 176 Value: dtls-id-value 178 Usage Level: media 180 Charset Dependent: no 182 Default Value: empty value 184 Syntax: 186 dtls-id-value = 0*256 188 Example: 190 a=dtls-id:abc3dl 192 Every time an endpoint requests to establish a new DTLS association, 193 the endpoint MUST generate a new unique local 'dtls-id' attribute 194 value. A non-changed local 'dtls-id' attribute value, in combination 195 with non-changed fingerprints, indicates that the endpoint intends to 196 reuse the existing DTLS association. 198 The mechanism to generate the unique local 'dtls-id' attribute value 199 MUST guarantee global uniqueness of the value for the lifetime of the 200 DTLS association associated with the attribute value. 202 No default value is defined for the SDP 'dtls-id' attribute. 203 Implementations that wish to use the attribute MUST explicitly 204 include it in SDP offers and answers. If an offer or answer does not 205 contain an attribute (this could happen if the offerer or answerer 206 represents an existing implementation that has not been updated to 207 support the 'dtls-id' attribute), the offer or answer MUST be treated 208 as if no 'dtls-id' attribute is included. Unless there is another 209 mechanism to explicitly indiciate that a new DTLS association is to 210 be established, a modification of one or more of the following 211 characteristics MUST be treated as an indication that an endpoint 212 wants to establish a new DTLS association: 214 o DTLS setup role; or 216 o fingerprint set; or 218 o local transport parameters; or 220 o ICE ufrag value 222 The mux category [I-D.ietf-mmusic-sdp-mux-attributes] for the 'dtls- 223 id' attribute is 'IDENTICAL', which means that the attribute value 224 must be identical across all media descriptions being multiplexed 225 [I-D.ietf-mmusic-sdp-bundle-negotiation]. 227 For RTP-based media, the 'dtls-id' attribute apply to whole 228 associated media description. The attribute MUST NOT be defined per 229 source (using the SDP 'ssrc' attribute [RFC5576]). 231 The SDP offer/answer [RFC3264] procedures associated with the 232 attribute are defined in Section 5 234 5. SDP Offer/Answer Procedures 235 5.1. General 237 This section defines the generic SDP offer/answer procedures for 238 negotiating a DTLS association. Additional procedures (e.g., 239 regarding usage of specific SDP attributes etc) for individual DTLS 240 usages (e.g., SRTP-DTLS) are outside the scope of this specification, 241 and need to be specified in a usage specific specification. 243 NOTE: The procedures in this section are generalizations of 244 procedures first specified in SRTP-DTLS [RFC5763], with the addition 245 of usage of the SDP 'dtls-id' attribute. That document is herein 246 updated to make use of these new procedures. 248 The procedures in this section apply to an SDP media description 249 ("m=" line) associated with DTLS-protected media/data. 251 When an offerer or answerer indicates that it wants to establish a 252 new DTLS association, it needs to make sure that media packets in the 253 existing DTLS association and new DTLS association can be de- 254 multiplexed. In case of ordered transport (e.g., SCTP) this can be 255 done simply by sending packets for new DTLS association after all 256 packets for existing DTLS association have been sent. In case of 257 unordered transport, such as UDP, packets for the old DTLS 258 association can arrive after the answer SDP was received and after 259 first packets for the new DTLS association were received. The only 260 way to de-multiplex packets belonging to old and new DTLS association 261 is on the basis of transport 5-tuple. Because of this, if unordered 262 transport is used for DTLS association, new transport (3-tuple) MUST 263 be allocated by at least one of the end points so that DTLS packets 264 can be de-multiplexed. 266 When an offerer needs to establish a new DTLS association, and if an 267 unordered transport (e.g., UDP) is used, the offerer MUST allocate a 268 new transport (3-tuple) for the offer in such a way that the offerer 269 can disambiguate any packets associated with the new DTLS association 270 from any packets associated with any other DTLS association. This 271 typically means using a local address and/or port, or a set of ICE 272 candidates (see Section 6), which were not recently used for any 273 other DTLS association. 275 When an answerer needs to establish a new DTLS association, if an 276 unordered transport is used, and if the offerer did not allocate a 277 new transport, the answerer MUST allocate a new transport for the 278 offer in answer a way that it can disambiguate any packets associated 279 with new DTLS association from any packets associated with any other 280 DTLS association. This typically means using a local address and/or 281 port, or a set of ICE candidates (see Section 6), which were not 282 recently used for any other DTLS association. 284 In order to negotiate a DTLS association, the following SDP 285 attributes are used: 287 o The SDP 'setup' attribute, defined in [RFC4145], is used to 288 negotiate the DTLS roles; 290 o The SDP 'fingerprint' attribute, defined in 291 [I-D.ietf-mmusic-4572-update], is used to provide one or more 292 fingerprint values; and 294 o The SDP 'dtls-id' attribute, defined in this specification. 296 This specification does not define the usage of the SDP 'connection' 297 attribute [RFC4145] for negotiating a DTLS connection. However, the 298 attribute MAY be used if the DTLS association is used together with 299 another protocol (e.g., SCTP or TCP) for which the usage of the 300 attribute has been defined. 302 Unlike for TCP and TLS connections, endpoints MUST NOT use the SDP 303 'setup' attribute 'holdconn' value when negotiating a DTLS 304 association. 306 Endpoints MUST support the cipher suites as defined in 307 [I-D.ietf-mmusic-4572-update]., 309 The certificate received during the DTLS handshake MUST match the 310 certificate fingerprints received in SDP 'fingerprint' attributes 311 according to procedures defined in [I-D.ietf-mmusic-4572-update]. If 312 fingerprints do not match the hashed certificate, then an endpoint 313 MUST tear down the media session immediately. Note that it is 314 permissible to wait until the other side's fingerprint has been 315 received before establishing the connection; however, this may have 316 undesirable latency effects. 318 SDP offerers and answerers might reuse certificates across multiple 319 DTLS associations, and provide identical fingerprint values for each 320 DTLS association. It MUST be ensured that the combination of SDP the 321 'dtls-id' attribute values of the SDP offerer and answerer is unique 322 across all DTLS associations that might be handled by the SDP offerer 323 and answerer. 325 5.2. Generating the Initial SDP Offer 327 When an offerer sends the initial offer, the offerer MUST insert an 328 SDP 'setup' attribute according to the procedures in [RFC4145], and 329 one or more SDP 'fingerprint' attributes according to the procedures 330 in [I-D.ietf-mmusic-4572-update]. In addition, the offerer MUST 331 insert in the offer an SDP 'dtls-id' attribute with a unique value. 333 If the offerer inserts the SDP 'setup' attribute with an 'actpass' or 334 'passive' attribute value, the offerer MUST be prepared to receive a 335 DTLS ClientHello message (if a new DTLS association is established by 336 the answerer) from the answerer before the offerer receives the SDP 337 answer. 339 5.3. Generating the Answer 341 When an answerer sends an answer, the answerer MUST insert in the 342 answer an SDP 'setup' attribute according to the procedures in 343 [RFC4145], and one or more SDP 'fingerprint' attributes according to 344 the procedures in [I-D.ietf-mmusic-4572-update]. If the answerer 345 determines, based on the criteria specified in Section 3.1, that a 346 new DTLS association is to be established, the answerer MUST insert 347 in the associated answer an SDP 'dtls-id' attribute with a unique 348 value. Note that the offerer and answerer generate their own local 349 'dtls-id' attribute values, and the combination of both values 350 identify the DTLS assocation. 352 If the answerer receives an offer that requires establishing a new 353 DTLS association, and if the answerer does not accept the 354 establishment of a new DTLS association, the answerer MUST reject the 355 "m=" lines associated with the suggested DTLS association [RFC3264]. 357 If an answerer receives an offer that does not require the 358 establishment of a new DTLS association, and if the answerer 359 determines that a new DTLS association is not to be established, the 360 answerer MUST insert an SDP 'dtls-id' attribute with the previously 361 assigned value in the associated answer. In addition, the answerer 362 MUST insert an SDP 'setup' attribute with a value that does not 363 change the previously negotiated DTLS roles, and one or more SDP 364 'fingerprint' attributes values that do not change the previously 365 sent fingerprint set, in the answer. 367 If the answerer receives an offer that does not contain an SDP 'dtls- 368 id' attribute, the answerer MUST NOT insert a 'dtls-id' attribute in 369 the answer. 371 If a new DTLS association is to be established, and if the answerer 372 inserts an SDP 'setup' attribute with an 'active' value in the 373 answer, the answerer MUST initiate a DTLS handshake by sending a DTLS 374 ClientHello message towards the offerer. 376 5.4. Offerer Processing of the SDP Answer 378 When an offerer receives an answer that establishes a new DTLS 379 association based on criteria defined in Section 3.1, and if the 380 offerer becomes DTLS client (based on the value of the SDP 'setup' 381 attribute value [RFC4145]), the offerer MUST establish a DTLS 382 association. If the offerer becomes DTLS server, it MUST wait for 383 the answerer to establish the DTLS association. 385 If the answer does not establish a new DTLS association, the offerer 386 will continue using the previously established DTLS association. 388 NOTE: A new DTLS association can be established based on changes in 389 either an SDP offer or answer. When communicating with legacy 390 endpoints, an offerer can receive an answer that include the same 391 fingerprint set and setup role. A new DTLS association MUST still be 392 established if such an answer was received as a response to an offer 393 which requested the establishment of a new DTLS association. 395 5.5. Modifying the Session 397 When the offerer sends a subsequent offer, and if the offerer wants 398 to establish a new DTLS association, the offerer MUST insert an SDP 399 'setup' attribute according to the procedures in [RFC4145], and one 400 or more SDP 'fingerprint' attributes according to the procedures in 401 [I-D.ietf-mmusic-4572-update]. In addition, the offerer MUST insert 402 in the offer an SDP 'dtls-id' attribute with a new unique value. 404 When the offerer sends a subsequent offer, and the offerer does not 405 want to establish a new DTLS association, and if a previously 406 established DTLS association exists, the offerer MUST insert an SDP 407 'dtls-id' attribute with the previously assigned value in the offer. 408 In addition, the offerer MUST insert an SDP 'setup' attribute with a 409 value that does not change the previously negotiated DTLS roles, and 410 one or more SDP 'fingerprint' attributes with values that do not 411 change the previously sent fingerprint set, in the offer. 413 NOTE: When a new DTLS association is being established, each endpoint 414 needs to be prepared to receive data on both the new and old DTLS 415 associations as long as both are alive. 417 6. ICE Considerations 419 When the Interactive Connectivity Establishment (ICE) mechansim 420 [I-D.ietf-ice-rfc5245bis] is used, the ICE connectivity checks are 421 performed before the DTLS handshake begins. Note that if aggressive 422 nomination mode is used, multiple candidate pairs may be marked valid 423 before ICE finally converges on a single candidate pair. 425 NOTE: Aggressive nomination has been deprecated from ICE, but must 426 still be supported for backwards compatibility reasons. 428 When new DTLS association is established over an unordered transport, 429 in order to disambiguate any packets associated with the newly 430 established DTLS association, at least one of the endpoints MUST 431 allocate a completely new set of ICE candidates which were not 432 recently used for any other DTLS association. This means the 433 answerer cannot initiate a new DTLS association unless the offerer 434 initiated ICE restart [I-D.ietf-ice-rfc5245bis]. If the answerer 435 wants to initiate a new DTLS association, it needs to initiate an ICE 436 restart and a new offer/answer exchange on its own. However, an ICE 437 restart does not by default require a new DTLS association to be 438 established. 440 NOTE: Simple Traversal of the UDP Protocol through NAT (STUN) packets 441 are sent directly over UDP, not over DTLS. [RFC5764] describes how 442 to demultiplex STUN packets from DTLS packets and SRTP packets. 444 Each ICE candidate associated with a component is treated as being 445 part of the same DTLS association. Therefore, from a DTLS 446 perspective it is not considered a change of local transport 447 parameters when an endpoint switches between those ICE candidates. 449 7. Transport Protocol Considerations 451 7.1. Transport Re-Usage 453 If DTLS is transported on top of a connection-oriented transport 454 protocol (e.g., TCP or SCTP), where all IP packets are acknowledged, 455 all DTLS packets associated with a previous DTLS association MUST be 456 acknowledged (or timed out) before a new DTLS association can be 457 established on the same transport. 459 8. SIP Considerations 461 When the Session Initiation Protocol (SIP) [RFC3261] is used as the 462 signal protocol for establishing a multimedia session, dialogs 463 [RFC3261] might be established between the caller and multiple 464 callees. This is referred to as forking. If forking occurs, 465 separate DTLS associations MUST be established between the caller and 466 each callee. 468 It is possible to send an INVITE request which does not contain an 469 SDP offer. Such an INVITE request is often referred to as an 'empty 470 INVITE', or an 'offer-less INVITE'. The receiving endpoint will 471 include the SDP offer in a response to the request. When the 472 endpoint generates such SDP offer, if a previously established DTLS 473 association exists, the offerer SHOULD insert an SDP 'dtls-id' 474 attribute, and one or more SDP 'fingerprint' attributes, with 475 previously assigned attribute values. If a previously established 476 DTLS association did not exists, the offer SHOULD be generated based 477 on the same rules as a new offer Section 5.2. Regardless of the 478 previous existence of a DTLS association, the SDP 'setup' attribute 479 MUST be included according to the rules defined in [RFC4145] and if 480 ICE is used, ICE restart MUST be initiated. 482 9. RFC Updates 484 9.1. General 486 This section updates specifications that use DTLS-protected media, in 487 order to reflect the procedures defined in this specification. 489 9.2. Update to RFC 5763 491 Update to section 5: 492 -------------------- 494 OLD TEXT: 496 5. Establishing a Secure Channel 498 The two endpoints in the exchange present their identities as part of 499 the DTLS handshake procedure using certificates. This document uses 500 certificates in the same style as described in "Connection-Oriented 501 Media Transport over the Transport Layer Security (TLS) Protocol in 502 the Session Description Protocol (SDP)" [RFC4572]. 504 If self-signed certificates are used, the content of the 505 subjectAltName attribute inside the certificate MAY use the uniform 506 resource identifier (URI) of the user. This is useful for debugging 507 purposes only and is not required to bind the certificate to one of 508 the communication endpoints. The integrity of the certificate is 509 ensured through the fingerprint attribute in the SDP. The 510 subjectAltName is not an important component of the certificate 511 verification. 513 The generation of public/private key pairs is relatively expensive. 514 Endpoints are not required to generate certificates for each session. 516 The offer/answer model, defined in [RFC3264], is used by protocols 517 like the Session Initiation Protocol (SIP) [RFC3261] to set up 518 multimedia sessions. In addition to the usual contents of an SDP 519 [RFC4566] message, each media description ("m=" line and associated 520 parameters) will also contain several attributes as specified in 521 [RFC5764], [RFC4145], and [RFC4572]. 523 When an endpoint wishes to set up a secure media session with another 524 endpoint, it sends an offer in a SIP message to the other endpoint. 525 This offer includes, as part of the SDP payload, the fingerprint of 526 the certificate that the endpoint wants to use. The endpoint SHOULD 527 send the SIP message containing the offer to the offerer's SIP proxy 528 over an integrity protected channel. The proxy SHOULD add an 529 Identity header field according to the procedures outlined in 530 [RFC4474]. The SIP message containing the offer SHOULD be sent to 531 the offerer's SIP proxy over an integrity protected channel. When 532 the far endpoint receives the SIP message, it can verify the identity 533 of the sender using the Identity header field. Since the Identity 534 header field is a digital signature across several SIP header fields, 535 in addition to the body of the SIP message, the receiver can also be 536 certain that the message has not been tampered with after the digital 537 signature was applied and added to the SIP message. 539 The far endpoint (answerer) may now establish a DTLS association with 540 the offerer. Alternately, it can indicate in its answer that the 541 offerer is to initiate the TLS association. In either case, mutual 542 DTLS certificate-based authentication will be used. After completing 543 the DTLS handshake, information about the authenticated identities, 544 including the certificates, are made available to the endpoint 545 application. The answerer is then able to verify that the offerer's 546 certificate used for authentication in the DTLS handshake can be 547 associated to the certificate fingerprint contained in the offer in 548 the SDP. At this point, the answerer may indicate to the end user 549 that the media is secured. The offerer may only tentatively accept 550 the answerer's certificate since it may not yet have the answerer's 551 certificate fingerprint. 553 When the answerer accepts the offer, it provides an answer back to 554 the offerer containing the answerer's certificate fingerprint. At 555 this point, the offerer can accept or reject the peer's certificate 556 and the offerer can indicate to the end user that the media is 557 secured. 559 Note that the entire authentication and key exchange for securing the 560 media traffic is handled in the media path through DTLS. The 561 signaling path is only used to verify the peers' certificate 562 fingerprints. 564 The offer and answer MUST conform to the following requirements. 566 o The endpoint MUST use the setup attribute defined in [RFC4145]. 567 The endpoint that is the offerer MUST use the setup attribute 568 value of setup:actpass and be prepared to receive a client_hello 569 before it receives the answer. The answerer MUST use either a 570 setup attribute value of setup:active or setup:passive. Note that 571 if the answerer uses setup:passive, then the DTLS handshake will 572 not begin until the answerer is received, which adds additional 573 latency. setup:active allows the answer and the DTLS handshake to 574 occur in parallel. Thus, setup:active is RECOMMENDED. Whichever 575 party is active MUST initiate a DTLS handshake by sending a 576 ClientHello over each flow (host/port quartet). 578 o The endpoint MUST NOT use the connection attribute defined in 579 [RFC4145]. 581 o The endpoint MUST use the certificate fingerprint attribute as 582 specified in [RFC4572]. 584 o The certificate presented during the DTLS handshake MUST match the 585 fingerprint exchanged via the signaling path in the SDP. The 586 security properties of this mechanism are described in Section 8. 588 o If the fingerprint does not match the hashed certificate, then the 589 endpoint MUST tear down the media session immediately. Note that 590 it is permissible to wait until the other side's fingerprint has 591 been received before establishing the connection; however, this 592 may have undesirable latency effects. 594 NEW TEXT: 596 5. Establishing a Secure Channel 598 The two endpoints in the exchange present their identities as part of 599 the DTLS handshake procedure using certificates. This document uses 600 certificates in the same style as described in "Connection-Oriented 601 Media Transport over the Transport Layer Security (TLS) Protocol in 602 the Session Description Protocol (SDP)" [RFC4572]. 604 If self-signed certificates are used, the content of the 605 subjectAltName attribute inside the certificate MAY use the uniform 606 resource identifier (URI) of the user. This is useful for debugging 607 purposes only and is not required to bind the certificate to one of 608 the communication endpoints. The integrity of the certificate is 609 ensured through the fingerprint attribute in the SDP. 611 The generation of public/private key pairs is relatively expensive. 612 Endpoints are not required to generate certificates for each session. 614 The offer/answer model, defined in [RFC3264], is used by protocols 615 like the Session Initiation Protocol (SIP) [RFC3261] to set up 616 multimedia sessions. 618 When an endpoint wishes to set up a secure media session with another 619 endpoint, it sends an offer in a SIP message to the other endpoint. 620 This offer includes, as part of the SDP payload, a fingerprint of 621 a certificate that the endpoint wants to use. The endpoint SHOULD 622 send the SIP message containing the offer to the offerer's SIP proxy 623 over an integrity protected channel. The proxy SHOULD add an 624 Identity header field according to the procedures outlined in 625 [RFC4474]. The SIP message containing the offer SHOULD be sent to 626 the offerer's SIP proxy over an integrity protected channel. When 627 the far endpoint receives the SIP message, it can verify the identity 628 of the sender using the Identity header field. Since the Identity 629 header field is a digital signature across several SIP header fields, 630 in addition to the body of the SIP message, the receiver can also be 631 certain that the message has not been tampered with after the digital 632 signature was applied and added to the SIP message. 634 The far endpoint (answerer) may now establish a DTLS association with 635 the offerer. Alternately, it can indicate in its answer that the 636 offerer is to initiate the DTLS association. In either case, mutual 637 DTLS certificate-based authentication will be used. After completing 638 the DTLS handshake, information about the authenticated identities, 639 including the certificates, are made available to the endpoint 640 application. The answerer is then able to verify that the offerer's 641 certificate used for authentication in the DTLS handshake can be 642 associated to the certificate fingerprint contained in the offer in 643 the SDP. At this point, the answerer may indicate to the end user 644 that the media is secured. The offerer may only tentatively accept 645 the answerer's certificate since it may not yet have the answerer's 646 certificate fingerprint. 648 When the answerer accepts the offer, it provides an answer back to 649 the offerer containing the answerer's certificate fingerprint. At 650 this point, the offerer can accept or reject the peer's certificate 651 and the offerer can indicate to the end user that the media is 652 secured. 654 Note that the entire authentication and key exchange for securing the 655 media traffic is handled in the media path through DTLS. The 656 signaling path is only used to verify the peers' certificate 657 fingerprints. 659 The offerer and answerer MUST follow the SDP offer/answer procedures 660 defined in [RFCXXXX]. 662 Update to section 6.6: 663 ---------------------- 664 OLD TEXT: 666 6.6. Session Modification 668 Once an answer is provided to the offerer, either endpoint MAY 669 request a session modification that MAY include an updated offer. 670 This session modification can be carried in either an INVITE or 671 UPDATE request. The peers can reuse the existing associations if 672 they are compatible (i.e., they have the same key fingerprints and 673 transport parameters), or establish a new one following the same 674 rules are for initial exchanges, tearing down the existing 675 association as soon as the offer/answer exchange is completed. Note 676 that if the active/passive status of the endpoints changes, a new 677 connection MUST be established. 679 NEW TEXT: 681 6.6. Session Modification 683 Once an answer is provided to the offerer, either endpoint MAY 684 request a session modification that MAY include an updated offer. 685 This session modification can be carried in either an INVITE or 686 UPDATE request. The peers can reuse an existing DTLS association, 687 or establish a new one, following the procedures in [RFCXXXX]. 689 Update to section 6.7.1: 690 ------------------------ 692 OLD TEXT: 694 6.7.1. ICE Interaction 696 Interactive Connectivity Establishment (ICE), as specified in 697 [RFC5245], provides a methodology of allowing participants in 698 multimedia sessions to verify mutual connectivity. When ICE is being 699 used, the ICE connectivity checks are performed before the DTLS 700 handshake begins. Note that if aggressive nomination mode is used, 701 multiple candidate pairs may be marked valid before ICE finally 702 converges on a single candidate pair. Implementations MUST treat all 703 ICE candidate pairs associated with a single component as part of the 704 same DTLS association. Thus, there will be only one DTLS handshake 705 even if there are multiple valid candidate pairs. Note that this may 706 mean adjusting the endpoint IP addresses if the selected candidate 707 pair shifts, just as if the DTLS packets were an ordinary media 708 stream. 710 Note that Simple Traversal of the UDP Protocol through NAT (STUN) 711 packets are sent directly over UDP, not over DTLS. [RFC5764] 712 describes how to demultiplex STUN packets from DTLS packets and SRTP 713 packets. 715 NEW TEXT: 717 6.7.1. ICE Interaction 719 The Interactive Connectivity Establishment (ICE) [RFC5245] 720 considerations for DTLS-protected media are described in 721 [RFCXXXX]. 723 9.3. Update to RFC 7345 725 Update to section 4: 726 -------------------- 728 OLD TEXT: 730 4. SDP Offerer/Answerer Procedures 732 4.1. General 734 An endpoint (i.e., both the offerer and the answerer) MUST create an 735 SDP media description ("m=" line) for each UDPTL-over-DTLS media 736 stream and MUST assign a UDP/TLS/UDPTL value (see Table 1) to the 737 "proto" field of the "m=" line. 739 The procedures in this section apply to an "m=" line associated with 740 a UDPTL-over-DTLS media stream. 742 In order to negotiate a UDPTL-over-DTLS media stream, the following 743 SDP attributes are used: 745 o The SDP attributes defined for UDPTL over UDP, as described in 746 [ITU.T38.2010]; and 748 o The SDP attributes, defined in [RFC4145] and [RFC4572], as 749 described in this section. 751 The endpoint MUST NOT use the SDP "connection" attribute [RFC4145]. 753 In order to negotiate the TLS roles for the UDPTL-over-DTLS transport 754 connection, the endpoint MUST use the SDP "setup" attribute 755 [RFC4145]. 757 If the endpoint supports, and is willing to use, a cipher suite with 758 an associated certificate, the endpoint MUST include an SDP 759 "fingerprint" attribute [RFC4572]. The endpoint MUST support SHA-256 760 for generating and verifying the SDP "fingerprint" attribute value. 761 The use of SHA-256 is preferred. UDPTL over DTLS, at a minimum, MUST 762 support TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 and MUST support 763 TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256. UDPTL over DTLS MUST prefer 764 TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 and any other Perfect Forward 765 Secrecy (PFS) cipher suites over non-PFS cipher suites. 766 Implementations SHOULD disable TLS-level compression. 768 If a cipher suite with an associated certificate is selected during 769 the DTLS handshake, the certificate received during the DTLS 770 handshake MUST match the fingerprint received in the SDP 771 "fingerprint" attribute. If the fingerprint does not match the 772 hashed certificate, then the endpoint MUST tear down the media 773 session immediately. Note that it is permissible to wait until the 774 other side's fingerprint has been received before establishing the 775 connection; however, this may have undesirable latency effects. 777 4.2. Generating the Initial Offer 779 The offerer SHOULD assign the SDP "setup" attribute with a value of 780 "actpass", unless the offerer insists on being either the sender or 781 receiver of the DTLS ClientHello message, in which case the offerer 782 can use either a value of "active" (the offerer will be the sender of 783 ClientHello) or "passive" (the offerer will be the receiver of 784 ClientHello). The offerer MUST NOT assign an SDP "setup" attribute 785 with a "holdconn" value. 787 If the offerer assigns the SDP "setup" attribute with a value of 788 "actpass" or "passive", the offerer MUST be prepared to receive a 789 DTLS ClientHello message before it receives the SDP answer. 791 4.3. Generating the Answer 793 If the answerer accepts the offered UDPTL-over-DTLS transport 794 connection, in the associated SDP answer, the answerer MUST assign an 795 SDP "setup" attribute with a value of either "active" or "passive", 796 according to the procedures in [RFC4145]. The answerer MUST NOT 797 assign an SDP "setup" attribute with a value of "holdconn". 799 If the answerer assigns an SDP "setup" attribute with a value of 800 "active" value, the answerer MUST initiate a DTLS handshake by 801 sending a DTLS ClientHello message on the negotiated media stream, 802 towards the IP address and port of the offerer. 804 4.4. Offerer Processing of the Answer 806 When the offerer receives an SDP answer, if the offerer ends up being 807 active it MUST initiate a DTLS handshake by sending a DTLS 808 ClientHello message on the negotiated media stream, towards the IP 809 address and port of the answerer. 811 4.5. Modifying the Session 813 Once an offer/answer exchange has been completed, either endpoint MAY 814 send a new offer in order to modify the session. The endpoints can 815 reuse the existing DTLS association if the key fingerprint values and 816 transport parameters indicated by each endpoint are unchanged. 817 Otherwise, following the rules for the initial offer/answer exchange, 818 the endpoints can negotiate and create a new DTLS association and, 819 once created, delete the previous DTLS association, following the 820 same rules for the initial offer/answer exchange. Each endpoint 821 needs to be prepared to receive data on both the new and old DTLS 822 associations as long as both are alive. 824 NEW TEXT: 826 4. SDP Offerer/Answerer Procedures 828 An endpoint (i.e., both the offerer and the answerer) MUST create an 829 SDP media description ("m=" line) for each UDPTL-over-DTLS media 830 stream and MUST assign a UDP/TLS/UDPTL value (see Table 1) to the 831 "proto" field of the "m=" line. 833 The offerer and answerer MUST follow the SDP offer/answer procedures 834 defined in [RFCXXXX] in order to negotiate the DTLS association 835 associated with the UDPTL-over-DTLS media stream. In addition, 836 the offerer and answerer MUST use the SDP attributes defined for 837 UDPTL over UDP, as defined in [ITU.T38.2010]. 839 Update to section 5.2.1: 840 ------------------------ 842 OLD TEXT: 844 5.2.1. ICE Usage 846 When Interactive Connectivity Establishment (ICE) [RFC5245] is being 847 used, the ICE connectivity checks are performed before the DTLS 848 handshake begins. Note that if aggressive nomination mode is used, 849 multiple candidate pairs may be marked valid before ICE finally 850 converges on a single candidate pair. User Agents (UAs) MUST treat 851 all ICE candidate pairs associated with a single component as part of 852 the same DTLS association. Thus, there will be only one DTLS 853 handshake even if there are multiple valid candidate pairs. Note 854 that this may mean adjusting the endpoint IP addresses if the 855 selected candidate pair shifts, just as if the DTLS packets were an 856 ordinary media stream. In the case of an ICE restart, the DTLS 857 handshake procedure is repeated, and a new DTLS association is 858 created. Once the DTLS handshake is completed and the new DTLS 859 association has been created, the previous DTLS association is 860 deleted. 862 NEW TEXT: 864 5.2.1. ICE Usage 866 The Interactive Connectivity Establishment (ICE) [RFC5245] 867 considerations for DTLS-protected media are described in 868 [RFCXXXX]. 870 10. Security Considerations 872 This specification does not modify the security considerations 873 associated with DTLS, or the SDP offer/answer mechanism. In addition 874 to the introduction of the SDP 'dtls-id' attribute, the specification 875 simply clarifies the procedures for negotiating and establishing a 876 DTLS association. 878 11. IANA Considerations 880 This document updates the "Session Description Protocol Parameters" 881 registry as specified in Section 8.2.2 of [RFC4566]. Specifically, 882 it adds the SDP dtls-id attribute to the table for SDP media level 883 attributes. 885 Attribute name: dtls-id 886 Type of attribute: media-level 887 Subject to charset: no 888 Purpose: Indicate whether a new DTLS association is to be 889 established/re-established. 890 Appropriate Values: see Section 4 891 Contact name: Christer Holmberg 892 Mux Category: IDENTICAL 894 12. Acknowledgements 896 Thanks to Justin Uberti, Martin Thomson, Paul Kyzivat, Jens Guballa, 897 Charles Eckel and Gonzalo Salgueiro for providing comments and 898 suggestions on the document. 900 13. Change Log 902 [RFC EDITOR NOTE: Please remove this section when publishing] 904 Changes from draft-ietf-mmusic-sdp-dtls-15 906 o dtls-id attribute value made globally unique 908 Changes from draft-ietf-mmusic-sdp-dtls-14 910 o Changes based on comments from Flemming: 912 o - Additional dtls-is clarifiations 914 o - Editorial fixes 916 Changes from draft-ietf-mmusic-sdp-dtls-13 918 o Text about the updated RFCs added to Abstract and Introduction 920 o Reference to RFC 5763 removed from section 6 (ICE Considerations) 922 o Reference to RFC 5763 removed from section 8 (SIP Considerations) 924 Changes from draft-ietf-mmusic-sdp-dtls-12 926 o "unreliable" changed to "unordered" 928 Changes from draft-ietf-mmusic-sdp-dtls-11 930 o Attribute name changed to dtls-id 932 o Additional text based on comments from Roman Shpount. 934 Changes from draft-ietf-mmusic-sdp-dtls-10 936 o Modified document to use dtls-id instead of dtls-connection 938 o Changes are based on comments from Eric Rescorla, Justin Uberti, 939 and Paul Kyzivat. 941 Changes from draft-ietf-mmusic-sdp-dtls-08 942 o Offer/Answer section modified in order to allow sending of 943 multiple SDP 'fingerprint' attributes. 945 o Terminology made consistent: 'DTLS connection' replaced with 'DTLS 946 association'. 948 o Editorial changes based on comments from Paul Kyzivat. 950 Changes from draft-ietf-mmusic-sdp-dtls-07 952 o Reference to RFC 7315 replaced with reference to RFC 7345. 954 Changes from draft-ietf-mmusic-sdp-dtls-06 956 o Text on restrictions regarding spanning a DTLS association over 957 multiple transports added. 959 o Mux category added to IANA Considerations. 961 o Normative text regarding mux category and source-specific 962 applicability added. 964 o Reference to RFC 7315 added. 966 o Clarified that offerer/answerer that has not been updated to 967 support this specification will not include the dtls-id attribute 968 in offers and answers. 970 o Editorial corrections based on WGLC comments from Charles Eckel. 972 Changes from draft-ietf-mmusic-sdp-dtls-05 974 o Text on handling offer/answer error conditions added. 976 Changes from draft-ietf-mmusic-sdp-dtls-04 978 o Editorial nits fixed based on comments from Paul Kyzivat: 980 Changes from draft-ietf-mmusic-sdp-dtls-03 982 o Changes based on comments from Paul Kyzivat: 984 o - Modification of dtls-id attribute section. 986 o - Removal of IANA considerations subsection. 988 o - Making note into normative text in o/a section. 990 o Changes based on comments from Martin Thompson: 992 o - Abbreviations section removed. 994 o - Clarify that a new DTLS association requires a new o/a 995 transaction. 997 Changes from draft-ietf-mmusic-sdp-dtls-02 999 o - Updated RFCs added to boilerplate. 1001 Changes from draft-ietf-mmusic-sdp-dtls-01 1003 o - Annex regarding 'dtls-id-id' attribute removed. 1005 o - Additional SDP offer/answer procedures, related to certificates, 1006 added. 1008 o - Updates to RFC 5763 and RFC 7345 added. 1010 o - Transport protocol considerations added. 1012 Changes from draft-ietf-mmusic-sdp-dtls-00 1014 o - SDP 'connection' attribute replaced with new 'dtls-id' 1015 attribute. 1017 o - IANA Considerations added. 1019 o - E-mail regarding 'dtls-id-id' attribute added as Annex. 1021 Changes from draft-holmberg-mmusic-sdp-dtls-01 1023 o - draft-ietf-mmusic version of draft submitted. 1025 o - Draft file name change (sdp-dtls -> dtls-sdp) due to collision 1026 with another expired draft. 1028 o - Clarify that if ufrag in offer is unchanged, it must be 1029 unchanged in associated answer. 1031 o - SIP Considerations section added. 1033 o - Section about multiple SDP fingerprint attributes added. 1035 Changes from draft-holmberg-mmusic-sdp-dtls-00 1037 o - Editorial changes and clarifications. 1039 14. References 1041 14.1. Normative References 1043 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1044 Requirement Levels", BCP 14, RFC 2119, 1045 DOI 10.17487/RFC2119, March 1997, 1046 . 1048 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 1049 A., Peterson, J., Sparks, R., Handley, M., and E. 1050 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 1051 DOI 10.17487/RFC3261, June 2002, 1052 . 1054 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1055 with Session Description Protocol (SDP)", RFC 3264, 1056 DOI 10.17487/RFC3264, June 2002, 1057 . 1059 [RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in 1060 the Session Description Protocol (SDP)", RFC 4145, 1061 DOI 10.17487/RFC4145, September 2005, 1062 . 1064 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1065 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 1066 July 2006, . 1068 [RFC5763] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework 1069 for Establishing a Secure Real-time Transport Protocol 1070 (SRTP) Security Context Using Datagram Transport Layer 1071 Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May 1072 2010, . 1074 [RFC7345] Holmberg, C., Sedlacek, I., and G. Salgueiro, "UDP 1075 Transport Layer (UDPTL) over Datagram Transport Layer 1076 Security (DTLS)", RFC 7345, DOI 10.17487/RFC7345, August 1077 2014, . 1079 [I-D.ietf-mmusic-4572-update] 1080 Lennox, J. and C. Holmberg, "Connection-Oriented Media 1081 Transport over TLS in SDP", draft-ietf-mmusic- 1082 4572-update-10 (work in progress), January 2017. 1084 14.2. Informative References 1086 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 1087 Media Attributes in the Session Description Protocol 1088 (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009, 1089 . 1091 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 1092 Security (DTLS) Extension to Establish Keys for the Secure 1093 Real-time Transport Protocol (SRTP)", RFC 5764, 1094 DOI 10.17487/RFC5764, May 2010, 1095 . 1097 [RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram 1098 Transport Layer Security (DTLS) for Stream Control 1099 Transmission Protocol (SCTP)", RFC 6083, 1100 DOI 10.17487/RFC6083, January 2011, 1101 . 1103 [I-D.ietf-ice-rfc5245bis] 1104 Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive 1105 Connectivity Establishment (ICE): A Protocol for Network 1106 Address Translator (NAT) Traversal", draft-ietf-ice- 1107 rfc5245bis-08 (work in progress), December 2016. 1109 [I-D.ietf-mmusic-sdp-mux-attributes] 1110 Nandakumar, S., "A Framework for SDP Attributes when 1111 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16 1112 (work in progress), December 2016. 1114 [I-D.ietf-mmusic-sdp-bundle-negotiation] 1115 Holmberg, C., Alvestrand, H., and C. Jennings, 1116 "Negotiating Media Multiplexing Using the Session 1117 Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle- 1118 negotiation-36 (work in progress), October 2016. 1120 Authors' Addresses 1122 Christer Holmberg 1123 Ericsson 1124 Hirsalantie 11 1125 Jorvas 02420 1126 Finland 1128 Email: christer.holmberg@ericsson.com 1129 Roman Shpount 1130 TurboBridge 1131 4905 Del Ray Avenue, Suite 300 1132 Bethesda, MD 20814 1133 USA 1135 Phone: +1 (240) 292-6632 1136 Email: rshpount@turbobridge.com