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'FIPS186' == Outdated reference: A later version (-07) exists of draft-ietf-mmusic-sdp-uks-03 == Outdated reference: A later version (-12) exists of draft-ietf-rtcweb-security-10 ** Obsolete normative reference: RFC 2818 (Obsoleted by RFC 9110) ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) ** Obsolete normative reference: RFC 5246 (Obsoleted by RFC 8446) ** Obsolete normative reference: RFC 5785 (Obsoleted by RFC 8615) ** Obsolete normative reference: RFC 6347 (Obsoleted by RFC 9147) ** Downref: Normative reference to an Informational RFC: RFC 7918 == Outdated reference: A later version (-26) exists of draft-ietf-rtcweb-jsep-25 Summary: 6 errors (**), 0 flaws (~~), 6 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 RTCWEB E. Rescorla 3 Internet-Draft RTFM, Inc. 4 Intended status: Standards Track February 1, 2019 5 Expires: August 5, 2019 7 WebRTC Security Architecture 8 draft-ietf-rtcweb-security-arch-18 10 Abstract 12 This document defines the security architecture for WebRTC, a 13 protocol suite intended for use with real-time applications that can 14 be deployed in browsers - "real time communication on the Web". 16 Status of This Memo 18 This Internet-Draft is submitted in full conformance with the 19 provisions of BCP 78 and BCP 79. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF). Note that other groups may also distribute 23 working documents as Internet-Drafts. The list of current Internet- 24 Drafts is at https://datatracker.ietf.org/drafts/current/. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 This Internet-Draft will expire on August 5, 2019. 33 Copyright Notice 35 Copyright (c) 2019 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents 40 (https://trustee.ietf.org/license-info) in effect on the date of 41 publication of this document. Please review these documents 42 carefully, as they describe your rights and restrictions with respect 43 to this document. Code Components extracted from this document must 44 include Simplified BSD License text as described in Section 4.e of 45 the Trust Legal Provisions and are provided without warranty as 46 described in the Simplified BSD License. 48 This document may contain material from IETF Documents or IETF 49 Contributions published or made publicly available before November 50 10, 2008. The person(s) controlling the copyright in some of this 51 material may not have granted the IETF Trust the right to allow 52 modifications of such material outside the IETF Standards Process. 53 Without obtaining an adequate license from the person(s) controlling 54 the copyright in such materials, this document may not be modified 55 outside the IETF Standards Process, and derivative works of it may 56 not be created outside the IETF Standards Process, except to format 57 it for publication as an RFC or to translate it into languages other 58 than English. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 64 3. Trust Model . . . . . . . . . . . . . . . . . . . . . . . . . 5 65 3.1. Authenticated Entities . . . . . . . . . . . . . . . . . 5 66 3.2. Unauthenticated Entities . . . . . . . . . . . . . . . . 6 67 4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 6 68 4.1. Initial Signaling . . . . . . . . . . . . . . . . . . . . 8 69 4.2. Media Consent Verification . . . . . . . . . . . . . . . 10 70 4.3. DTLS Handshake . . . . . . . . . . . . . . . . . . . . . 11 71 4.4. Communications and Consent Freshness . . . . . . . . . . 11 72 5. SDP Identity Attribute . . . . . . . . . . . . . . . . . . . 12 73 5.1. Offer/Answer Considerations . . . . . . . . . . . . . . . 13 74 5.1.1. Generating the Initial SDP Offer . . . . . . . . . . 13 75 5.1.2. Generating of SDP Answer . . . . . . . . . . . . . . 14 76 5.1.3. Processing an SDP Offer or Answer . . . . . . . . . . 14 77 5.1.4. Modifying the Session . . . . . . . . . . . . . . . . 14 78 6. Detailed Technical Description . . . . . . . . . . . . . . . 14 79 6.1. Origin and Web Security Issues . . . . . . . . . . . . . 14 80 6.2. Device Permissions Model . . . . . . . . . . . . . . . . 15 81 6.3. Communications Consent . . . . . . . . . . . . . . . . . 17 82 6.4. IP Location Privacy . . . . . . . . . . . . . . . . . . . 17 83 6.5. Communications Security . . . . . . . . . . . . . . . . . 18 84 7. Web-Based Peer Authentication . . . . . . . . . . . . . . . . 20 85 7.1. Trust Relationships: IdPs, APs, and RPs . . . . . . . . . 21 86 7.2. Overview of Operation . . . . . . . . . . . . . . . . . . 23 87 7.3. Items for Standardization . . . . . . . . . . . . . . . . 24 88 7.4. Binding Identity Assertions to JSEP Offer/Answer 89 Transactions . . . . . . . . . . . . . . . . . . . . . . 24 90 7.4.1. Carrying Identity Assertions . . . . . . . . . . . . 25 91 7.5. Determining the IdP URI . . . . . . . . . . . . . . . . . 26 92 7.5.1. Authenticating Party . . . . . . . . . . . . . . . . 27 93 7.5.2. Relying Party . . . . . . . . . . . . . . . . . . . . 28 94 7.6. Requesting Assertions . . . . . . . . . . . . . . . . . . 28 95 7.7. Managing User Login . . . . . . . . . . . . . . . . . . . 29 97 8. Verifying Assertions . . . . . . . . . . . . . . . . . . . . 29 98 8.1. Identity Formats . . . . . . . . . . . . . . . . . . . . 30 99 9. Security Considerations . . . . . . . . . . . . . . . . . . . 31 100 9.1. Communications Security . . . . . . . . . . . . . . . . . 31 101 9.2. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 32 102 9.3. Denial of Service . . . . . . . . . . . . . . . . . . . . 33 103 9.4. IdP Authentication Mechanism . . . . . . . . . . . . . . 34 104 9.4.1. PeerConnection Origin Check . . . . . . . . . . . . . 34 105 9.4.2. IdP Well-known URI . . . . . . . . . . . . . . . . . 34 106 9.4.3. Privacy of IdP-generated identities and the hosting 107 site . . . . . . . . . . . . . . . . . . . . . . . . 35 108 9.4.4. Security of Third-Party IdPs . . . . . . . . . . . . 35 109 9.4.4.1. Confusable Characters . . . . . . . . . . . . . . 35 110 9.4.5. Web Security Feature Interactions . . . . . . . . . . 35 111 9.4.5.1. Popup Blocking . . . . . . . . . . . . . . . . . 36 112 9.4.5.2. Third Party Cookies . . . . . . . . . . . . . . . 36 113 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36 114 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 37 115 12. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 116 12.1. Changes since -15 . . . . . . . . . . . . . . . . . . . 37 117 12.2. Changes since -11 . . . . . . . . . . . . . . . . . . . 37 118 12.3. Changes since -10 . . . . . . . . . . . . . . . . . . . 37 119 12.4. Changes since -06 . . . . . . . . . . . . . . . . . . . 37 120 12.5. Changes since -05 . . . . . . . . . . . . . . . . . . . 38 121 12.6. Changes since -03 . . . . . . . . . . . . . . . . . . . 38 122 12.7. Changes since -03 . . . . . . . . . . . . . . . . . . . 38 123 12.8. Changes since -02 . . . . . . . . . . . . . . . . . . . 38 124 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 39 125 13.1. Normative References . . . . . . . . . . . . . . . . . . 39 126 13.2. Informative References . . . . . . . . . . . . . . . . . 42 127 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 42 129 1. Introduction 131 The Real-Time Communications on the Web (WebRTC) working group is 132 tasked with standardizing protocols for real-time communications 133 between Web browsers. The major use cases for WebRTC technology are 134 real-time audio and/or video calls, Web conferencing, and direct data 135 transfer. Unlike most conventional real-time systems, (e.g., SIP- 136 based [RFC3261] soft phones) WebRTC communications are directly 137 controlled by some Web server, via a JavaScript (JS) API as shown in 138 Figure 1. 140 +----------------+ 141 | | 142 | Web Server | 143 | | 144 +----------------+ 145 ^ ^ 146 / \ 147 HTTP / \ HTTP 148 / \ 149 / \ 150 v v 151 JS API JS API 152 +-----------+ +-----------+ 153 | | Media | | 154 | Browser |<---------->| Browser | 155 | | | | 156 +-----------+ +-----------+ 158 Figure 1: A simple WebRTC system 160 A more complicated system might allow for interdomain calling, as 161 shown in Figure 2. The protocol to be used between the domains is 162 not standardized by WebRTC, but given the installed base and the form 163 of the WebRTC API is likely to be something SDP-based like SIP. 165 +--------------+ +--------------+ 166 | | SIP,XMPP,...| | 167 | Web Server |<----------->| Web Server | 168 | | | | 169 +--------------+ +--------------+ 170 ^ ^ 171 | | 172 HTTP | | HTTP 173 | | 174 v v 175 JS API JS API 176 +-----------+ +-----------+ 177 | | Media | | 178 | Browser |<---------------->| Browser | 179 | | | | 180 +-----------+ +-----------+ 182 Figure 2: A multidomain WebRTC system 184 This system presents a number of new security challenges, which are 185 analyzed in [I-D.ietf-rtcweb-security]. This document describes a 186 security architecture for WebRTC which addresses the threats and 187 requirements described in that document. 189 2. Terminology 191 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 192 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 193 "OPTIONAL" in this document are to be interpreted as described in BCP 194 14 [RFC2119] [RFC8174] when, and only when, they appear in all 195 capitals, as shown here. 197 3. Trust Model 199 The basic assumption of this architecture is that network resources 200 exist in a hierarchy of trust, rooted in the browser, which serves as 201 the user's Trusted Computing Base (TCB). Any security property which 202 the user wishes to have enforced must be ultimately guaranteed by the 203 browser (or transitively by some property the browser verifies). 204 Conversely, if the browser is compromised, then no security 205 guarantees are possible. Note that there are cases (e.g., Internet 206 kiosks) where the user can't really trust the browser that much. In 207 these cases, the level of security provided is limited by how much 208 they trust the browser. 210 Optimally, we would not rely on trust in any entities other than the 211 browser. However, this is unfortunately not possible if we wish to 212 have a functional system. Other network elements fall into two 213 categories: those which can be authenticated by the browser and thus 214 can be granted permissions to access sensitive resources, and those 215 which cannot be authenticated and thus are untrusted. 217 3.1. Authenticated Entities 219 There are two major classes of authenticated entities in the system: 221 o Calling services: Web sites whose origin we can verify (optimally 222 via HTTPS, but in some cases because we are on a topologically 223 restricted network, such as behind a firewall, and can infer 224 authentication from firewall behavior). 226 o Other users: WebRTC peers whose origin we can verify 227 cryptographically (optimally via DTLS-SRTP). 229 Note that merely being authenticated does not make these entities 230 trusted. For instance, just because we can verify that 231 https://www.evil.org/ is owned by Dr. Evil does not mean that we can 232 trust Dr. Evil to access our camera and microphone. However, it 233 gives the user an opportunity to determine whether he wishes to trust 234 Dr. Evil or not; after all, if he desires to contact Dr. Evil 235 (perhaps to arrange for ransom payment), it's safe to temporarily 236 give him access to the camera and microphone for the purpose of the 237 call, but he doesn't want Dr. Evil to be able to access his camera 238 and microphone other than during the call. The point here is that we 239 must first identify other elements before we can determine whether 240 and how much to trust them. Additionally, sometimes we need to 241 identify the communicating peer before we know what policies to 242 apply. 244 3.2. Unauthenticated Entities 246 Other than the above entities, we are not generally able to identify 247 other network elements, thus we cannot trust them. This does not 248 mean that it is not possible to have any interaction with them, but 249 it means that we must assume that they will behave maliciously and 250 design a system which is secure even if they do so. 252 4. Overview 254 This section describes a typical WebRTC session and shows how the 255 various security elements interact and what guarantees are provided 256 to the user. The example in this section is a "best case" scenario 257 in which we provide the maximal amount of user authentication and 258 media privacy with the minimal level of trust in the calling service. 259 Simpler versions with lower levels of security are also possible and 260 are noted in the text where applicable. It's also important to 261 recognize the tension between security (or performance) and privacy. 262 The example shown here is aimed towards settings where we are more 263 concerned about secure calling than about privacy, but as we shall 264 see, there are settings where one might wish to make different 265 tradeoffs--this architecture is still compatible with those settings. 267 For the purposes of this example, we assume the topology shown in the 268 figures below. This topology is derived from the topology shown in 269 Figure 1, but separates Alice and Bob's identities from the process 270 of signaling. Specifically, Alice and Bob have relationships with 271 some Identity Provider (IdP) that supports a protocol (such as OpenID 272 Connect) that can be used to demonstrate their identity to other 273 parties. For instance, Alice might have an account with a social 274 network which she can then use to authenticate to other web sites 275 without explicitly having an account with those sites; this is a 276 fairly conventional pattern on the Web. Section 7.1 provides an 277 overview of Identity Providers and the relevant terminology. Alice 278 and Bob might have relationships with different IdPs as well. 280 This separation of identity provision and signaling isn't 281 particularly important in "closed world" cases where Alice and Bob 282 are users on the same social network and have identities based on 283 that domain (Figure 3). However, there are important settings where 284 that is not the case, such as federation (calls from one domain to 285 another; Figure 4) and calling on untrusted sites, such as where two 286 users who have a relationship via a given social network want to call 287 each other on another, untrusted, site, such as a poker site. 289 Note that the servers themselves are also authenticated by an 290 external identity service, the SSL/TLS certificate infrastructure 291 (not shown). As is conventional in the Web, all identities are 292 ultimately rooted in that system. For instance, when an IdP makes an 293 identity assertion, the Relying Party consuming that assertion is 294 able to verify because it is able to connect to the IdP via HTTPS. 296 +----------------+ 297 | | 298 | Signaling | 299 | Server | 300 | | 301 +----------------+ 302 ^ ^ 303 / \ 304 HTTPS / \ HTTPS 305 / \ 306 / \ 307 v v 308 JS API JS API 309 +-----------+ +-----------+ 310 | | Media | | 311 Alice | Browser |<---------->| Browser | Bob 312 | | (DTLS+SRTP)| | 313 +-----------+ +-----------+ 314 ^ ^--+ +--^ ^ 315 | | | | 316 v | | v 317 +-----------+ | | +-----------+ 318 | |<--------+ | | 319 | IdP1 | | | IdP2 | 320 | | +------->| | 321 +-----------+ +-----------+ 323 Figure 3: A call with IdP-based identity 325 Figure 4 shows essentially the same calling scenario but with a call 326 between two separate domains (i.e., a federated case), as in 327 Figure 2. As mentioned above, the domains communicate by some 328 unspecified protocol and providing separate signaling and identity 329 allows for calls to be authenticated regardless of the details of the 330 inter-domain protocol. 332 +----------------+ Unspecified +----------------+ 333 | | protocol | | 334 | Signaling |<----------------->| Signaling | 335 | Server | (SIP, XMPP, ...) | Server | 336 | | | | 337 +----------------+ +----------------+ 338 ^ ^ 339 | | 340 HTTPS | | HTTPS 341 | | 342 | | 343 v v 344 JS API JS API 345 +-----------+ +-----------+ 346 | | Media | | 347 Alice | Browser |<--------------------------->| Browser | Bob 348 | | DTLS+SRTP | | 349 +-----------+ +-----------+ 350 ^ ^--+ +--^ ^ 351 | | | | 352 v | | v 353 +-----------+ | | +-----------+ 354 | |<-------------------------+ | | 355 | IdP1 | | | IdP2 | 356 | | +------------------------>| | 357 +-----------+ +-----------+ 359 Figure 4: A federated call with IdP-based identity 361 4.1. Initial Signaling 363 For simplicity, assume the topology in Figure 3. Alice and Bob are 364 both users of a common calling service; they both have approved the 365 calling service to make calls (we defer the discussion of device 366 access permissions till later). They are both connected to the 367 calling service via HTTPS and so know the origin with some level of 368 confidence. They also have accounts with some identity provider. 369 This sort of identity service is becoming increasingly common in the 370 Web environment (with technologies such as Federated Google Login, 371 Facebook Connect, OAuth, OpenID, WebFinger), and is often provided as 372 a side effect service of a user's ordinary accounts with some 373 service. In this example, we show Alice and Bob using a separate 374 identity service, though the identity service may be the same entity 375 as the calling service or there may be no identity service at all. 377 Alice is logged onto the calling service and decides to call Bob. 378 She can see from the calling service that he is online and the 379 calling service presents a JS UI in the form of a button next to 380 Bob's name which says "Call". Alice clicks the button, which 381 initiates a JS callback that instantiates a PeerConnection object. 382 This does not require a security check: JS from any origin is allowed 383 to get this far. 385 Once the PeerConnection is created, the calling service JS needs to 386 set up some media. Because this is an audio/video call, it creates a 387 MediaStream with two MediaStreamTracks, one connected to an audio 388 input and one connected to a video input. At this point the first 389 security check is required: untrusted origins are not allowed to 390 access the camera and microphone, so the browser prompts Alice for 391 permission. 393 In the current W3C API, once some streams have been added, Alice's 394 browser + JS generates a signaling message [I-D.ietf-rtcweb-jsep] 395 containing: 397 o Media channel information 399 o Interactive Connectivity Establishment (ICE) [RFC8445] candidates 401 o A fingerprint attribute binding the communication to a key pair 402 [RFC5763]. Note that this key may simply be ephemerally generated 403 for this call or specific to this domain, and Alice may have a 404 large number of such keys. 406 Prior to sending out the signaling message, the PeerConnection code 407 contacts the identity service and obtains an assertion binding 408 Alice's identity to her fingerprint. The exact details depend on the 409 identity service (though as discussed in Section 7 PeerConnection can 410 be agnostic to them), but for now it's easiest to think of as an 411 OAuth token. The assertion may bind other information to the 412 identity besides the fingerprint, but at minimum it needs to bind the 413 fingerprint. 415 This message is sent to the signaling server, e.g., by XMLHttpRequest 416 [XmlHttpRequest] or by WebSockets [RFC6455], preferably over TLS 417 [RFC5246]. The signaling server processes the message from Alice's 418 browser, determines that this is a call to Bob and sends a signaling 419 message to Bob's browser (again, the format is currently undefined). 420 The JS on Bob's browser processes it, and alerts Bob to the incoming 421 call and to Alice's identity. In this case, Alice has provided an 422 identity assertion and so Bob's browser contacts Alice's identity 423 provider (again, this is done in a generic way so the browser has no 424 specific knowledge of the IdP) to verify the assertion. This allows 425 the browser to display a trusted element in the browser chrome 426 indicating that a call is coming in from Alice. If Alice is in Bob's 427 address book, then this interface might also include her real name, a 428 picture, etc. The calling site will also provide some user interface 429 element (e.g., a button) to allow Bob to answer the call, though this 430 is most likely not part of the trusted UI. 432 If Bob agrees a PeerConnection is instantiated with the message from 433 Alice's side. Then, a similar process occurs as on Alice's browser: 434 Bob's browser prompts him for device permission, the media streams 435 are created, and a return signaling message containing media 436 information, ICE candidates, and a fingerprint is sent back to Alice 437 via the signaling service. If Bob has a relationship with an IdP, 438 the message will also come with an identity assertion. 440 At this point, Alice and Bob each know that the other party wants to 441 have a secure call with them. Based purely on the interface provided 442 by the signaling server, they know that the signaling server claims 443 that the call is from Alice to Bob. This level of security is 444 provided merely by having the fingerprint in the message and having 445 that message received securely from the signaling server. Because 446 the far end sent an identity assertion along with their message, they 447 know that this is verifiable from the IdP as well. Note that if the 448 call is federated, as shown in Figure 4 then Alice is able to verify 449 Bob's identity in a way that is not mediated by either her signaling 450 server or Bob's. Rather, she verifies it directly with Bob's IdP. 452 Of course, the call works perfectly well if either Alice or Bob 453 doesn't have a relationship with an IdP; they just get a lower level 454 of assurance. I.e., they simply have whatever information their 455 calling site claims about the caller/callee's identity. Moreover, 456 Alice might wish to make an anonymous call through an anonymous 457 calling site, in which case she would of course just not provide any 458 identity assertion and the calling site would mask her identity from 459 Bob. 461 4.2. Media Consent Verification 463 As described in ([I-D.ietf-rtcweb-security]; Section 4.2) media 464 consent verification is provided via ICE. Thus, Alice and Bob 465 perform ICE checks with each other. At the completion of these 466 checks, they are ready to send non-ICE data. 468 At this point, Alice knows that (a) Bob (assuming he is verified via 469 his IdP) or someone else who the signaling service is claiming is Bob 470 is willing to exchange traffic with her and (b) that either Bob is at 471 the IP address which she has verified via ICE or there is an attacker 472 who is on-path to that IP address detouring the traffic. Note that 473 it is not possible for an attacker who is on-path between Alice and 474 Bob but not attached to the signaling service to spoof these checks 475 because they do not have the ICE credentials. Bob has the same 476 security guarantees with respect to Alice. 478 4.3. DTLS Handshake 480 Once the ICE checks have completed [more specifically, once some ICE 481 checks have completed], Alice and Bob can set up a secure channel or 482 channels. This is performed via DTLS [RFC6347] and DTLS-SRTP 483 [RFC5763] keying for SRTP [RFC3711] for the media channel and SCTP 484 over DTLS [RFC8261] for data channels. Specifically, Alice and Bob 485 perform a DTLS handshake on every component which has been 486 established by ICE. The total number of channels depends on the 487 amount of muxing; in the most likely case we are using both RTP/RTCP 488 mux and muxing multiple media streams on the same channel, in which 489 case there is only one DTLS handshake. Once the DTLS handshake has 490 completed, the keys are exported [RFC5705] and used to key SRTP for 491 the media channels. 493 At this point, Alice and Bob know that they share a set of secure 494 data and/or media channels with keys which are not known to any 495 third-party attacker. If Alice and Bob authenticated via their IdPs, 496 then they also know that the signaling service is not mounting a man- 497 in-the-middle attack on their traffic. Even if they do not use an 498 IdP, as long as they have minimal trust in the signaling service not 499 to perform a man-in-the-middle attack, they know that their 500 communications are secure against the signaling service as well 501 (i.e., that the signaling service cannot mount a passive attack on 502 the communications). 504 4.4. Communications and Consent Freshness 506 From a security perspective, everything from here on in is a little 507 anticlimactic: Alice and Bob exchange data protected by the keys 508 negotiated by DTLS. Because of the security guarantees discussed in 509 the previous sections, they know that the communications are 510 encrypted and authenticated. 512 The one remaining security property we need to establish is "consent 513 freshness", i.e., allowing Alice to verify that Bob is still prepared 514 to receive her communications so that Alice does not continue to send 515 large traffic volumes to entities which went abruptly offline. ICE 516 specifies periodic STUN keepalives but only if media is not flowing. 517 Because the consent issue is more difficult here, we require WebRTC 518 implementations to periodically send keepalives. As described in 519 Section 5.3, these keepalives MUST be based on the consent freshness 520 mechanism specified in [RFC7675]. If a keepalive fails and no new 521 ICE channels can be established, then the session is terminated. 523 5. SDP Identity Attribute 525 The SDP 'identity' attribute is a session-level attribute that is 526 used by an endpoint to convey its identity assertion to its peer. 527 The identity assertion value is encoded as Base-64, as described in 528 Section 4 of [RFC4648]. 530 The procedures in this section are based on the assumption that the 531 identity assertion of an endpoint is bound to the fingerprints of the 532 endpoint. This does not preclude the definition of alternative means 533 of binding an assertion to the endpoint, but such means are outside 534 the scope of this specification. 536 The semantics of multiple 'identity' attributes within an offer or 537 answer are undefined. Implementations SHOULD only include a single 538 'identity' attribute in an offer or answer and relying parties MAY 539 elect to ignore all but the first 'identity' attribute. 541 Name: identity 543 Value: identity-assertion 545 Usage Level: session 547 Charset Dependent: no 549 Default Value: N/A 551 Name: identity 553 Syntax: 555 identity-assertion = identity-assertion-value 556 *(SP identity-extension) 557 identity-assertion-value = base64 558 identity-extension = extension-name [ "=" extension-value ] 559 extension-name = token 560 extension-value = 1*(%x01-09 / %x0b-0c / %x0e-3a / %x3c-ff) 561 ; byte-string from [RFC4566] 563 564 566 Example: 568 a=identity:\ 569 eyJpZHAiOnsiZG9tYWluIjoiZXhhbXBsZS5vcmciLCJwcm90b2NvbCI6ImJvZ3Vz\ 570 In0sImFzc2VydGlvbiI6IntcImlkZW50aXR5XCI6XCJib2JAZXhhbXBsZS5vcmdc\ 571 IixcImNvbnRlbnRzXCI6XCJhYmNkZWZnaGlqa2xtbm9wcXJzdHV2d3l6XCIsXCJz\ 572 aWduYXR1cmVcIjpcIjAxMDIwMzA0MDUwNlwifSJ9 574 Note that long lines in the example are folded to meet the column 575 width constraints of this document; the backslash ("\") at the end of 576 a line and the carriage return that follows shall be ignored. 578 This specification does not define any extensions for the attribute. 580 The identity-assertion value is a JSON [RFC8259] encoded string. The 581 JSON object contains two keys: "assertion" and "idp". The 582 "assertion" key value contains an opaque string that is consumed by 583 the IdP. The "idp" key value contains a dictionary with one or two 584 further values that identify the IdP. See Section 7.6 for more 585 details. 587 5.1. Offer/Answer Considerations 589 This section defines the SDP Offer/Answer [RFC6454] considerations 590 for the SDP 'identity' attribute. 592 Within this section, 'initial offer' refers to the first offer in the 593 SDP session that contains an SDP "identity" attribute. 595 5.1.1. Generating the Initial SDP Offer 597 When an offerer sends an offer, in order to provide its identity 598 assertion to the peer, it includes an 'identity' attribute in the 599 offer. In addition, the offerer includes one or more SDP 600 'fingerprint' attributes. The 'identity' attribute MUST be bound to 601 all the 'fingerprint' attributes in the session description. 603 5.1.2. Generating of SDP Answer 605 If the answerer elects to include an 'identity' attribute, it follows 606 the same steps as those in Section 5.1.1. The answerer can choose to 607 include or omit an 'identity' attribute independently, regardless of 608 whether the offerer did so. 610 5.1.3. Processing an SDP Offer or Answer 612 When an endpoint receives an offer or answer that contains an 613 'identity' attribute, the answerer can use the the attribute 614 information to contact the IdP, and verify the identity of the peer. 615 If the identity verification fails, the answerer MUST discard the 616 offer or answer as malformed. 618 5.1.4. Modifying the Session 620 When modifying a session, if the set of fingerprints is unchanged, 621 then the sender MAY send the same 'identity' attribute. In this 622 case, the established identity SHOULD be applied to existing DTLS 623 connections as well as new connections established using one of those 624 fingerprints. Note that [I-D.ietf-rtcweb-jsep], Section 5.2.1 625 requires that each media section use the same set of fingerprints for 626 every media section. 628 If the set of fingerprints changes, then the sender MUST either send 629 a new 'identity' attribute or none at all. Because a change in 630 fingerprints also causes a new DTLS connection to be established, the 631 receiver MUST discard all previously established identities. 633 6. Detailed Technical Description 635 6.1. Origin and Web Security Issues 637 The basic unit of permissions for WebRTC is the origin [RFC6454]. 638 Because the security of the origin depends on being able to 639 authenticate content from that origin, the origin can only be 640 securely established if data is transferred over HTTPS [RFC2818]. 641 Thus, clients MUST treat HTTP and HTTPS origins as different 642 permissions domains. [Note: this follows directly from the origin 643 security model and is stated here merely for clarity.] 645 Many web browsers currently forbid by default any active mixed 646 content on HTTPS pages. That is, when JavaScript is loaded from an 647 HTTP origin onto an HTTPS page, an error is displayed and the HTTP 648 content is not executed unless the user overrides the error. Any 649 browser which enforces such a policy will also not permit access to 650 WebRTC functionality from mixed content pages (because they never 651 display mixed content). Browsers which allow active mixed content 652 MUST nevertheless disable WebRTC functionality in mixed content 653 settings. 655 Note that it is possible for a page which was not mixed content to 656 become mixed content during the duration of the call. The major risk 657 here is that the newly arrived insecure JS might redirect media to a 658 location controlled by the attacker. Implementations MUST either 659 choose to terminate the call or display a warning at that point. 661 Also note that the security architecture depends on the keying 662 material not being available to move between origins. But, it is 663 assumed that the identity assertion can be passed to anyone that the 664 page cares to. 666 6.2. Device Permissions Model 668 Implementations MUST obtain explicit user consent prior to providing 669 access to the camera and/or microphone. Implementations MUST at 670 minimum support the following two permissions models for HTTPS 671 origins. 673 o Requests for one-time camera/microphone access. 675 o Requests for permanent access. 677 Because HTTP origins cannot be securely established against network 678 attackers, implementations MUST NOT allow the setting of permanent 679 access permissions for HTTP origins. Implementations MUST refuse all 680 permissions grants for HTTP origins. 682 In addition, they SHOULD support requests for access that promise 683 that media from this grant will be sent to a single communicating 684 peer (obviously there could be other requests for other peers). 685 E.g., "Call customerservice@ford.com". The semantics of this request 686 are that the media stream from the camera and microphone will only be 687 routed through a connection which has been cryptographically verified 688 (through the IdP mechanism or an X.509 certificate in the DTLS-SRTP 689 handshake) as being associated with the stated identity. Note that 690 it is unlikely that browsers would have an X.509 certificate, but 691 servers might. Browsers servicing such requests SHOULD clearly 692 indicate that identity to the user when asking for permission. The 693 idea behind this type of permissions is that a user might have a 694 fairly narrow list of peers he is willing to communicate with, e.g., 695 "my mother" rather than "anyone on Facebook". Narrow permissions 696 grants allow the browser to do that enforcement. 698 API Requirement: The API MUST provide a mechanism for the requesting 699 JS to relinquish the ability to see or modify the media (e.g., via 700 MediaStream.record()). Combined with secure authentication of the 701 communicating peer, this allows a user to be sure that the calling 702 site is not accessing or modifying their conversion. 704 UI Requirement: The UI MUST clearly indicate when the user's camera 705 and microphone are in use. This indication MUST NOT be 706 suppressable by the JS and MUST clearly indicate how to terminate 707 device access, and provide a UI means to immediately stop camera/ 708 microphone input without the JS being able to prevent it. 710 UI Requirement: If the UI indication of camera/microphone use are 711 displayed in the browser such that minimizing the browser window 712 would hide the indication, or the JS creating an overlapping 713 window would hide the indication, then the browser SHOULD stop 714 camera and microphone input when the indication is hidden. [Note: 715 this may not be necessary in systems that are non-windows-based 716 but that have good notifications support, such as phones.] 718 o Browsers MUST NOT permit permanent screen or application sharing 719 permissions to be installed as a response to a JS request for 720 permissions. Instead, they must require some other user action 721 such as a permissions setting or an application install experience 722 to grant permission to a site. 724 o Browsers MUST provide a separate dialog request for screen/ 725 application sharing permissions even if the media request is made 726 at the same time as camera and microphone. 728 o The browser MUST indicate any windows which are currently being 729 shared in some unambiguous way. Windows which are not visible 730 MUST NOT be shared even if the application is being shared. If 731 the screen is being shared, then that MUST be indicated. 733 Clients MAY permit the formation of data channels without any direct 734 user approval. Because sites can always tunnel data through the 735 server, further restrictions on the data channel do not provide any 736 additional security. (though see Section 6.3 for a related issue). 738 Implementations which support some form of direct user authentication 739 SHOULD also provide a policy by which a user can authorize calls only 740 to specific communicating peers. Specifically, the implementation 741 SHOULD provide the following interfaces/controls: 743 o Allow future calls to this verified user. 745 o Allow future calls to any verified user who is in my system 746 address book (this only works with address book integration, of 747 course). 749 Implementations SHOULD also provide a different user interface 750 indication when calls are in progress to users whose identities are 751 directly verifiable. Section 6.5 provides more on this. 753 6.3. Communications Consent 755 Browser client implementations of WebRTC MUST implement ICE. Server 756 gateway implementations which operate only at public IP addresses 757 MUST implement either full ICE or ICE-Lite [RFC8445]. 759 Browser implementations MUST verify reachability via ICE prior to 760 sending any non-ICE packets to a given destination. Implementations 761 MUST NOT provide the ICE transaction ID to JavaScript during the 762 lifetime of the transaction (i.e., during the period when the ICE 763 stack would accept a new response for that transaction). The JS MUST 764 NOT be permitted to control the local ufrag and password, though it 765 of course knows it. 767 While continuing consent is required, the ICE [RFC8445]; Section 10 768 keepalives use STUN Binding Indications which are one-way and 769 therefore not sufficient. The current WG consensus is to use ICE 770 Binding Requests for continuing consent freshness. ICE already 771 requires that implementations respond to such requests, so this 772 approach is maximally compatible. A separate document will profile 773 the ICE timers to be used; see [RFC7675]. 775 6.4. IP Location Privacy 777 A side effect of the default ICE behavior is that the peer learns 778 one's IP address, which leaks large amounts of location information. 779 This has negative privacy consequences in some circumstances. The 780 API requirements in this section are intended to mitigate this issue. 781 Note that these requirements are NOT intended to protect the user's 782 IP address from a malicious site. In general, the site will learn at 783 least a user's server reflexive address from any HTTP transaction. 784 Rather, these requirements are intended to allow a site to cooperate 785 with the user to hide the user's IP address from the other side of 786 the call. Hiding the user's IP address from the server requires some 787 sort of explicit privacy preserving mechanism on the client (e.g., 788 Tor Browser [https://www.torproject.org/projects/torbrowser.html.en]) 789 and is out of scope for this specification. 791 API Requirement: The API MUST provide a mechanism to allow the JS to 792 suppress ICE negotiation (though perhaps to allow candidate 793 gathering) until the user has decided to answer the call [note: 794 determining when the call has been answered is a question for the 795 JS.] This enables a user to prevent a peer from learning their IP 796 address if they elect not to answer a call and also from learning 797 whether the user is online. 799 API Requirement: The API MUST provide a mechanism for the calling 800 application JS to indicate that only TURN candidates are to be 801 used. This prevents the peer from learning one's IP address at 802 all. This mechanism MUST also permit suppression of the related 803 address field, since that leaks local addresses. 805 API Requirement: The API MUST provide a mechanism for the calling 806 application to reconfigure an existing call to add non-TURN 807 candidates. Taken together, this and the previous requirement 808 allow ICE negotiation to start immediately on incoming call 809 notification, thus reducing post-dial delay, but also to avoid 810 disclosing the user's IP address until they have decided to 811 answer. They also allow users to completely hide their IP address 812 for the duration of the call. Finally, they allow a mechanism for 813 the user to optimize performance by reconfiguring to allow non- 814 turn candidates during an active call if the user decides they no 815 longer need to hide their IP address 817 Note that some enterprises may operate proxies and/or NATs designed 818 to hide internal IP addresses from the outside world. WebRTC 819 provides no explicit mechanism to allow this function. Either such 820 enterprises need to proxy the HTTP/HTTPS and modify the SDP and/or 821 the JS, or there needs to be browser support to set the "TURN-only" 822 policy regardless of the site's preferences. 824 6.5. Communications Security 826 Implementations MUST implement SRTP [RFC3711]. Implementations MUST 827 implement DTLS [RFC6347] and DTLS-SRTP [RFC5763][RFC5764] for SRTP 828 keying. Implementations MUST implement [RFC8261]. 830 All media channels MUST be secured via SRTP and SRTCP. Media traffic 831 MUST NOT be sent over plain (unencrypted) RTP or RTCP; that is, 832 implementations MUST NOT negotiate cipher suites with NULL encryption 833 modes. DTLS-SRTP MUST be offered for every media channel. WebRTC 834 implementations MUST NOT offer SDP Security Descriptions [RFC4568] or 835 select it if offered. A SRTP MKI MUST NOT be used. 837 All data channels MUST be secured via DTLS. 839 All Implementations MUST implement DTLS 1.2 with the 840 TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 cipher suite and the P-256 841 curve [FIPS186]. Earlier drafts of this specification required DTLS 842 1.0 with the cipher suite TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA, and 843 at the time of this writing some implementations do not support DTLS 844 1.2; endpoints which support only DTLS 1.2 might encounter 845 interoperability issues. The DTLS-SRTP protection profile 846 SRTP_AES128_CM_HMAC_SHA1_80 MUST be supported for SRTP. 847 Implementations MUST favor cipher suites which support (Perfect 848 Forward Secrecy) PFS over non-PFS cipher suites and SHOULD favor AEAD 849 over non-AEAD cipher suites. 851 Implementations MUST NOT implement DTLS renegotiation and MUST reject 852 it with a "no_renegotiation" alert if offered. 854 Endpoints MUST NOT implement TLS False Start [RFC7918]. 856 API Requirement: The API MUST generate a new authentication key pair 857 for every new call by default. This is intended to allow for 858 unlinkability. 860 API Requirement: The API MUST provide a means to reuse a key pair 861 for calls. This can be used to enable key continuity-based 862 authentication, and could be used to amortize key generation 863 costs. 865 API Requirement: Unless the user specifically configures an external 866 key pair, different key pairs MUST be used for each origin. (This 867 avoids creating a super-cookie.) 869 API Requirement: When DTLS-SRTP is used, the API MUST NOT permit the 870 JS to obtain the negotiated keying material. This requirement 871 preserves the end-to-end security of the media. 873 UI Requirements: A user-oriented client MUST provide an "inspector" 874 interface which allows the user to determine the security 875 characteristics of the media. 877 The following properties SHOULD be displayed "up-front" in the 878 browser chrome, i.e., without requiring the user to ask for them: 880 * A client MUST provide a user interface through which a user may 881 determine the security characteristics for currently-displayed 882 audio and video stream(s) 884 * A client MUST provide a user interface through which a user may 885 determine the security characteristics for transmissions of 886 their microphone audio and camera video. 888 * If the far endpoint was directly verified, either via a third- 889 party verifiable X.509 certificate or via a Web IdP mechanism 890 (see Section 7) the "security characteristics" MUST include the 891 verified information. X.509 identities and Web IdP identities 892 have similar semantics and should be displayed in a similar 893 way. 895 The following properties are more likely to require some "drill- 896 down" from the user: 898 * The "security characteristics" MUST indicate the cryptographic 899 algorithms in use (For example: "AES-CBC".) However, if Null 900 ciphers are used, that MUST be presented to the user at the 901 top-level UI. 903 * The "security characteristics" MUST indicate whether PFS is 904 provided. 906 * The "security characteristics" MUST include some mechanism to 907 allow an out-of-band verification of the peer, such as a 908 certificate fingerprint or a Short Authentication String (SAS). 910 7. Web-Based Peer Authentication 912 In a number of cases, it is desirable for the endpoint (i.e., the 913 browser) to be able to directly identify the endpoint on the other 914 side without trusting the signaling service to which they are 915 connected. For instance, users may be making a call via a federated 916 system where they wish to get direct authentication of the other 917 side. Alternately, they may be making a call on a site which they 918 minimally trust (such as a poker site) but to someone who has an 919 identity on a site they do trust (such as a social network.) 921 Recently, a number of Web-based identity technologies (OAuth, 922 Facebook Connect etc.) have been developed. While the details vary, 923 what these technologies share is that they have a Web-based (i.e., 924 HTTP/HTTPS) identity provider which attests to your identity. For 925 instance, if I have an account at example.org, I could use the 926 example.org identity provider to prove to others that I was 927 alice@example.org. The development of these technologies allows us 928 to separate calling from identity provision: I could call you on 929 Poker Galaxy but identify myself as alice@example.org. 931 Whatever the underlying technology, the general principle is that the 932 party which is being authenticated is NOT the signaling site but 933 rather the user (and their browser). Similarly, the relying party is 934 the browser and not the signaling site. Thus, the browser MUST 935 generate the input to the IdP assertion process and display the 936 results of the verification process to the user in a way which cannot 937 be imitated by the calling site. 939 The mechanisms defined in this document do not require the browser to 940 implement any particular identity protocol or to support any 941 particular IdP. Instead, this document provides a generic interface 942 which any IdP can implement. Thus, new IdPs and protocols can be 943 introduced without change to either the browser or the calling 944 service. This avoids the need to make a commitment to any particular 945 identity protocol, although browsers may opt to directly implement 946 some identity protocols in order to provide superior performance or 947 UI properties. 949 7.1. Trust Relationships: IdPs, APs, and RPs 951 Any federated identity protocol has three major participants: 953 Authenticating Party (AP): The entity which is trying to establish 954 its identity. 956 Identity Provider (IdP): The entity which is vouching for the AP's 957 identity. 959 Relying Party (RP): The entity which is trying to verify the AP's 960 identity. 962 The AP and the IdP have an account relationship of some kind: the AP 963 registers with the IdP and is able to subsequently authenticate 964 directly to the IdP (e.g., with a password). This means that the 965 browser must somehow know which IdP(s) the user has an account 966 relationship with. This can either be something that the user 967 configures into the browser or that is configured at the calling site 968 and then provided to the PeerConnection by the Web application at the 969 calling site. The use case for having this information configured 970 into the browser is that the user may "log into" the browser to bind 971 it to some identity. This is becoming common in new browsers. 973 However, it should also be possible for the IdP information to simply 974 be provided by the calling application. 976 At a high level there are two kinds of IdPs: 978 Authoritative: IdPs which have verifiable control of some section 979 of the identity space. For instance, in the realm of e-mail, the 980 operator of "example.com" has complete control of the namespace 981 ending in "@example.com". Thus, "alice@example.com" is whoever 982 the operator says it is. Examples of systems with authoritative 983 identity providers include DNSSEC, RFC 4474, and Facebook Connect 984 (Facebook identities only make sense within the context of the 985 Facebook system). 987 Third-Party: IdPs which don't have control of their section of the 988 identity space but instead verify user's identities via some 989 unspecified mechanism and then attest to it. Because the IdP 990 doesn't actually control the namespace, RPs need to trust that the 991 IdP is correctly verifying AP identities, and there can 992 potentially be multiple IdPs attesting to the same section of the 993 identity space. Probably the best-known example of a third-party 994 identity provider is SSL/TLS certificates, where there are a large 995 number of CAs all of whom can attest to any domain name. 997 If an AP is authenticating via an authoritative IdP, then the RP does 998 not need to explicitly configure trust in the IdP at all. The 999 identity mechanism can directly verify that the IdP indeed made the 1000 relevant identity assertion (a function provided by the mechanisms in 1001 this document), and any assertion it makes about an identity for 1002 which it is authoritative is directly verifiable. Note that this 1003 does not mean that the IdP might not lie, but that is a 1004 trustworthiness judgement that the user can make at the time he looks 1005 at the identity. 1007 By contrast, if an AP is authenticating via a third-party IdP, the RP 1008 needs to explicitly trust that IdP (hence the need for an explicit 1009 trust anchor list in PKI-based SSL/TLS clients). The list of 1010 trustable IdPs needs to be configured directly into the browser, 1011 either by the user or potentially by the browser manufacturer. This 1012 is a significant advantage of authoritative IdPs and implies that if 1013 third-party IdPs are to be supported, the potential number needs to 1014 be fairly small. 1016 7.2. Overview of Operation 1018 In order to provide security without trusting the calling site, the 1019 PeerConnection component of the browser must interact directly with 1020 the IdP. The details of the mechanism are described in the W3C API 1021 specification, but the general idea is that the PeerConnection 1022 component downloads JS from a specific location on the IdP dictated 1023 by the IdP domain name. That JS (the "IdP proxy") runs in an 1024 isolated security context within the browser and the PeerConnection 1025 talks to it via a secure message passing channel. 1027 Note that there are two logically separate functions here: 1029 o Identity assertion generation. 1031 o Identity assertion verification. 1033 The same IdP JS "endpoint" is used for both functions but of course a 1034 given IdP might behave differently and load new JS to perform one 1035 function or the other. 1037 +--------------------------------------+ 1038 | Browser | 1039 | | 1040 | +----------------------------------+ | 1041 | | https://calling-site.example.com | | 1042 | | | | 1043 | | Calling JS Code | | 1044 | | ^ | | 1045 | +---------------|------------------+ | 1046 | | API Calls | 1047 | v | 1048 | PeerConnection | 1049 | ^ | 1050 | | API Calls | 1051 | +-----------|-------------+ | +---------------+ 1052 | | v | | | | 1053 | | IdP Proxy |<-------->| Identity | 1054 | | | | | Provider | 1055 | | https://idp.example.org | | | | 1056 | +-------------------------+ | +---------------+ 1057 | | 1058 +--------------------------------------+ 1060 When the PeerConnection object wants to interact with the IdP, the 1061 sequence of events is as follows: 1063 1. The browser (the PeerConnection component) instantiates an IdP 1064 proxy. This allows the IdP to load whatever JS is necessary into 1065 the proxy. The resulting code runs in the IdP's security 1066 context. 1068 2. The IdP registers an object with the browser that conforms to the 1069 API defined in [webrtc-api]. 1071 3. The browser invokes methods on the object registered by the IdP 1072 proxy to create or verify identity assertions. 1074 This approach allows us to decouple the browser from any particular 1075 identity provider; the browser need only know how to load the IdP's 1076 JavaScript--the location of which is determined based on the IdP's 1077 identity--and to call the generic API for requesting and verifying 1078 identity assertions. The IdP provides whatever logic is necessary to 1079 bridge the generic protocol to the IdP's specific requirements. 1080 Thus, a single browser can support any number of identity protocols, 1081 including being forward compatible with IdPs which did not exist at 1082 the time the browser was written. 1084 7.3. Items for Standardization 1086 There are two parts to this work: 1088 o The precise information from the signaling message that must be 1089 cryptographically bound to the user's identity and a mechanism for 1090 carrying assertions in JSEP messages. This is specified in 1091 Section 7.4. 1093 o The interface to the IdP, which is defined in the companion W3C 1094 WebRTC API specification [webrtc-api]. 1096 The WebRTC API specification also defines JavaScript interfaces that 1097 the calling application can use to specify which IdP to use. That 1098 API also provides access to the assertion-generation capability and 1099 the status of the validation process. 1101 7.4. Binding Identity Assertions to JSEP Offer/Answer Transactions 1103 An identity assertion binds the user's identity (as asserted by the 1104 IdP) to the SDP offer/answer exchange and specifically to the media. 1105 In order to achieve this, the PeerConnection must provide the DTLS- 1106 SRTP fingerprint to be bound to the identity. This is provided as a 1107 JavaScript object (also known as a dictionary or hash) with a single 1108 "fingerprint" key, as shown below: 1110 { 1111 "fingerprint": [ { 1112 "algorithm": "sha-256", 1113 "digest": "4A:AD:B9:B1:3F:...:E5:7C:AB" 1114 }, { 1115 "algorithm": "sha-1", 1116 "digest": "74:E9:76:C8:19:...:F4:45:6B" 1117 } ] 1118 } 1120 The "fingerprint" value is an array of objects. Each object in the 1121 array contains "algorithm" and "digest" values, which correspond 1122 directly to the algorithm and digest values in the "fingerprint" 1123 attribute of the SDP [RFC8122]. 1125 This object is encoded in a JSON [RFC8259] string for passing to the 1126 IdP. The identity assertion returned by the IdP, which is encoded in 1127 the "identity" attribute, is a JSON object that is encoded as 1128 described in Section 7.4.1. 1130 This structure does not need to be interpreted by the IdP or the IdP 1131 proxy. It is consumed solely by the RP's browser. The IdP merely 1132 treats it as an opaque value to be attested to. Thus, new parameters 1133 can be added to the assertion without modifying the IdP. 1135 7.4.1. Carrying Identity Assertions 1137 Once an IdP has generated an assertion (see Section 7.6), it is 1138 attached to the SDP offer/answer message. This is done by adding a 1139 new 'identity' attribute to the SDP. The sole contents of this value 1140 is the identity assertion. The identity assertion produced by the 1141 IdP is encoded into a UTF-8 JSON text, then Base64-encoded [RFC4648] 1142 to produce this string. For example: 1144 v=0 1145 o=- 1181923068 1181923196 IN IP4 ua1.example.com 1146 s=example1 1147 c=IN IP4 ua1.example.com 1148 a=fingerprint:sha-1 \ 1149 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 1150 a=identity:\ 1151 eyJpZHAiOnsiZG9tYWluIjoiZXhhbXBsZS5vcmciLCJwcm90b2NvbCI6ImJvZ3Vz\ 1152 In0sImFzc2VydGlvbiI6IntcImlkZW50aXR5XCI6XCJib2JAZXhhbXBsZS5vcmdc\ 1153 IixcImNvbnRlbnRzXCI6XCJhYmNkZWZnaGlqa2xtbm9wcXJzdHV2d3l6XCIsXCJz\ 1154 aWduYXR1cmVcIjpcIjAxMDIwMzA0MDUwNlwifSJ9 1155 a=... 1156 t=0 0 1157 m=audio 6056 RTP/SAVP 0 1158 a=sendrecv 1159 ... 1161 Note that long lines in the example are folded to meet the column 1162 width constraints of this document; the backslash ("\") at the end of 1163 a line and the carriage return that follows shall be ignored. 1165 The 'identity' attribute attests to all "fingerprint" attributes in 1166 the session description. It is therefore a session-level attribute. 1168 Multiple "fingerprint" values can be used to offer alternative 1169 certificates for a peer. The "identity" attribute MUST include all 1170 fingerprint values that are included in "fingerprint" attributes of 1171 the session description. 1173 The RP browser MUST verify that the in-use certificate for a DTLS 1174 connection is in the set of fingerprints returned from the IdP when 1175 verifying an assertion. 1177 7.5. Determining the IdP URI 1179 In order to ensure that the IdP is under control of the domain owner 1180 rather than someone who merely has an account on the domain owner's 1181 server (e.g., in shared hosting scenarios), the IdP JavaScript is 1182 hosted at a deterministic location based on the IdP's domain name. 1183 Each IdP proxy instance is associated with two values: 1185 Authority: The authority [RFC3986] at which the IdP's service is 1186 hosted. Note that this may include a non-default port or a 1187 userinfo component, but neither will be available in a certificate 1188 verifying the site. 1190 protocol: The specific IdP protocol which the IdP is using. This is 1191 a completely opaque IdP-specific string, but allows an IdP to 1192 implement two protocols in parallel. This value may be the empty 1193 string. If no value for protocol is provided, a value of 1194 "default" is used. 1196 Each IdP MUST serve its initial entry page (i.e., the one loaded by 1197 the IdP proxy) from a well-known URI [RFC5785]. The well-known URI 1198 for an IdP proxy is formed from the following URI components: 1200 1. The scheme, "https:". An IdP MUST be loaded using HTTPS 1201 [RFC2818]. 1203 2. The authority [RFC3986]. As noted above, the authority MAY 1204 contain a non-default port number or userinfo sub-component. 1205 Both are removed when determining if an asserted identity matches 1206 the name of the IdP. 1208 3. The path, starting with "/.well-known/idp-proxy/" and appended 1209 with the IdP protocol. Note that the separator characters '/' 1210 (%2F) and '\' (%5C) MUST NOT be permitted in the protocol field, 1211 lest an attacker be able to direct requests outside of the 1212 controlled "/.well-known/" prefix. Query and fragment values MAY 1213 be used by including '?' or '#' characters. 1215 For example, for the IdP "identity.example.com" and the protocol 1216 "example", the URL would be: 1218 https://identity.example.com/.well-known/idp-proxy/example 1220 The IdP MAY redirect requests to this URL, but they MUST retain the 1221 "https" scheme. This changes the effective origin of the IdP, but 1222 not the domain of the identities that the IdP is permitted to assert 1223 and validate. I.e., the IdP is still regarded as authoritative for 1224 the original domain. 1226 7.5.1. Authenticating Party 1228 How an AP determines the appropriate IdP domain is out of scope of 1229 this specification. In general, however, the AP has some actual 1230 account relationship with the IdP, as this identity is what the IdP 1231 is attesting to. Thus, the AP somehow supplies the IdP information 1232 to the browser. Some potential mechanisms include: 1234 o Provided by the user directly. 1236 o Selected from some set of IdPs known to the calling site. E.g., a 1237 button that shows "Authenticate via Facebook Connect" 1239 7.5.2. Relying Party 1241 Unlike the AP, the RP need not have any particular relationship with 1242 the IdP. Rather, it needs to be able to process whatever assertion 1243 is provided by the AP. As the assertion contains the IdP's identity 1244 in the "idp" field of the JSON-encoded object (see Section 7.6), the 1245 URI can be constructed directly from the assertion, and thus the RP 1246 can directly verify the technical validity of the assertion with no 1247 user interaction. Authoritative assertions need only be verifiable. 1248 Third-party assertions also MUST be verified against local policy, as 1249 described in Section 8.1. 1251 7.6. Requesting Assertions 1253 The input to identity assertion is the JSON-encoded object described 1254 in Section 7.4 that contains the set of certificate fingerprints the 1255 browser intends to use. This string is treated as opaque from the 1256 perspective of the IdP. 1258 The browser also identifies the origin that the PeerConnection is run 1259 in, which allows the IdP to make decisions based on who is requesting 1260 the assertion. 1262 An application can optionally provide a user identifier hint when 1263 specifying an IdP. This value is a hint that the IdP can use to 1264 select amongst multiple identities, or to avoid providing assertions 1265 for unwanted identities. The "username" is a string that has no 1266 meaning to any entity other than the IdP, it can contain any data the 1267 IdP needs in order to correctly generate an assertion. 1269 An identity assertion that is successfully provided by the IdP 1270 consists of the following information: 1272 idp: The domain name of an IdP and the protocol string. This MAY 1273 identify a different IdP or protocol from the one that generated 1274 the assertion. 1276 assertion: An opaque value containing the assertion itself. This is 1277 only interpretable by the identified IdP or the IdP code running 1278 in the client. 1280 Figure 5 shows an example assertion formatted as JSON. In this case, 1281 the message has presumably been digitally signed/MACed in some way 1282 that the IdP can later verify it, but this is an implementation 1283 detail and out of scope of this document. Line breaks are inserted 1284 solely for readability. 1286 { 1287 "idp":{ 1288 "domain": "example.org", 1289 "protocol": "bogus" 1290 }, 1291 "assertion": "{\"identity\":\"bob@example.org\", 1292 \"contents\":\"abcdefghijklmnopqrstuvwyz\", 1293 \"signature\":\"010203040506\"}" 1294 } 1296 Figure 5: Example assertion 1298 For use in signaling, the assertion is serialized into JSON, 1299 Base64-encoded [RFC4648], and used as the value of the "identity" 1300 attribute. 1302 7.7. Managing User Login 1304 In order to generate an identity assertion, the IdP needs proof of 1305 the user's identity. It is common practice to authenticate users 1306 (using passwords or multi-factor authentication), then use Cookies 1307 [RFC6265] or HTTP authentication [RFC7617] for subsequent exchanges. 1309 The IdP proxy is able to access cookies, HTTP authentication or other 1310 persistent session data because it operates in the security context 1311 of the IdP origin. Therefore, if a user is logged in, the IdP could 1312 have all the information needed to generate an assertion. 1314 An IdP proxy is unable to generate an assertion if the user is not 1315 logged in, or the IdP wants to interact with the user to acquire more 1316 information before generating the assertion. If the IdP wants to 1317 interact with the user before generating an assertion, the IdP proxy 1318 can fail to generate an assertion and instead indicate a URL where 1319 login should proceed. 1321 The application can then load the provided URL to enable the user to 1322 enter credentials. The communication between the application and the 1323 IdP is described in [webrtc-api]. 1325 8. Verifying Assertions 1327 The input to identity validation is the assertion string taken from a 1328 decoded 'identity' attribute. 1330 The IdP proxy verifies the assertion. Depending on the identity 1331 protocol, the proxy might contact the IdP server or other servers. 1332 For instance, an OAuth-based protocol will likely require using the 1333 IdP as an oracle, whereas with a signature-based scheme might be able 1334 to verify the assertion without contacting the IdP, provided that it 1335 has cached the relevant public key. 1337 Regardless of the mechanism, if verification succeeds, a successful 1338 response from the IdP proxy consists of the following information: 1340 identity: The identity of the AP from the IdP's perspective. 1341 Details of this are provided in Section 8.1. 1343 contents: The original unmodified string provided by the AP as input 1344 to the assertion generation process. 1346 Figure 6 shows an example response formatted as JSON for illustrative 1347 purposes. 1349 { 1350 "identity": "bob@example.org", 1351 "contents": "{\"fingerprint\":[ ... ]}" 1352 } 1354 Figure 6: Example verification result 1356 8.1. Identity Formats 1358 The identity provided from the IdP to the RP browser MUST consist of 1359 a string representing the user's identity. This string is in the 1360 form "@", where "user" consists of any character except 1361 '@', and domain is an internationalized domain name [RFC5890] encoded 1362 as a sequence of U-labels. 1364 The PeerConnection API MUST check this string as follows: 1366 1. If the domain portion of the string is equal to the domain name 1367 of the IdP proxy, then the assertion is valid, as the IdP is 1368 authoritative for this domain. Comparison of domain names is 1369 done using the label equivalence rule defined in Section 2.3.2.4 1370 of [RFC5890]. 1372 2. If the domain portion of the string is not equal to the domain 1373 name of the IdP proxy, then the PeerConnection object MUST reject 1374 the assertion unless: 1376 1. the IdP domain is trusted as an acceptable third-party IdP; 1377 and 1379 2. local policy is configured to trust this IdP domain for the 1380 domain portion of the identity string. 1382 Any "@" or "%" characters in the "user" portion of the identity MUST 1383 be escaped according to the "Percent-Encoding" rules defined in 1384 Section 2.1 of [RFC3986]. Characters other than "@" and "%" MUST NOT 1385 be percent-encoded. For example, with a user of "user@133" and a 1386 domain of "identity.example.com", the resulting string will be 1387 encoded as "user%40133@identity.example.com". 1389 Implementations are cautioned to take care when displaying user 1390 identities containing escaped "@" characters. If such characters are 1391 unescaped prior to display, implementations MUST distinguish between 1392 the domain of the IdP proxy and any domain that might be implied by 1393 the portion of the portion that appears after the escaped "@" 1394 sign. 1396 9. Security Considerations 1398 Much of the security analysis of this problem is contained in 1399 [I-D.ietf-rtcweb-security] or in the discussion of the particular 1400 issues above. In order to avoid repetition, this section focuses on 1401 (a) residual threats that are not addressed by this document and (b) 1402 threats produced by failure/misbehavior of one of the components in 1403 the system. 1405 9.1. Communications Security 1407 IF HTTPS is not used to secure communications to the signaling 1408 server, and the identity mechanism used in Section 7 is not used, 1409 then any on-path attacker can replace the DTLS-SRTP fingerprints in 1410 the handshake and thus substitute its own identity for that of either 1411 endpoint. 1413 Even if HTTPS is used, the signaling server can potentially mount a 1414 man-in-the-middle attack unless implementations have some mechanism 1415 for independently verifying keys. The UI requirements in Section 6.5 1416 are designed to provide such a mechanism for motivated/security 1417 conscious users, but are not suitable for general use. The identity 1418 service mechanisms in Section 7 are more suitable for general use. 1419 Note, however, that a malicious signaling service can strip off any 1420 such identity assertions, though it cannot forge new ones. Note that 1421 all of the third-party security mechanisms available (whether X.509 1422 certificates or a third-party IdP) rely on the security of the third 1423 party--this is of course also true of your connection to the Web site 1424 itself. Users who wish to assure themselves of security against a 1425 malicious identity provider can only do so by verifying peer 1426 credentials directly, e.g., by checking the peer's fingerprint 1427 against a value delivered out of band. 1429 In order to protect against malicious content JavaScript, that 1430 JavaScript MUST NOT be allowed to have direct access to---or perform 1431 computations with---DTLS keys. For instance, if content JS were able 1432 to compute digital signatures, then it would be possible for content 1433 JS to get an identity assertion for a browser's generated key and 1434 then use that assertion plus a signature by the key to authenticate a 1435 call protected under an ephemeral Diffie-Hellman (DH) key controlled 1436 by the content JS, thus violating the security guarantees otherwise 1437 provided by the IdP mechanism. Note that it is not sufficient merely 1438 to deny the content JS direct access to the keys, as some have 1439 suggested doing with the WebCrypto API [webcrypto]. The JS must also 1440 not be allowed to perform operations that would be valid for a DTLS 1441 endpoint. By far the safest approach is simply to deny the ability 1442 to perform any operations that depend on secret information 1443 associated with the key. Operations that depend on public 1444 information, such as exporting the public key are of course safe. 1446 9.2. Privacy 1448 The requirements in this document are intended to allow: 1450 o Users to participate in calls without revealing their location. 1452 o Potential callees to avoid revealing their location and even 1453 presence status prior to agreeing to answer a call. 1455 However, these privacy protections come at a performance cost in 1456 terms of using TURN relays and, in the latter case, delaying ICE. 1457 Sites SHOULD make users aware of these tradeoffs. 1459 Note that the protections provided here assume a non-malicious 1460 calling service. As the calling service always knows the users 1461 status and (absent the use of a technology like Tor) their IP 1462 address, they can violate the users privacy at will. Users who wish 1463 privacy against the calling sites they are using must use separate 1464 privacy enhancing technologies such as Tor. Combined WebRTC/Tor 1465 implementations SHOULD arrange to route the media as well as the 1466 signaling through Tor. Currently this will produce very suboptimal 1467 performance. 1469 Additionally, any identifier which persists across multiple calls is 1470 potentially a problem for privacy, especially for anonymous calling 1471 services. Such services SHOULD instruct the browser to use separate 1472 DTLS keys for each call and also to use TURN throughout the call. 1473 Otherwise, the other side will learn linkable information. 1474 Additionally, browsers SHOULD implement the privacy-preserving CNAME 1475 generation mode of [RFC7022]. 1477 9.3. Denial of Service 1479 The consent mechanisms described in this document are intended to 1480 mitigate denial of service attacks in which an attacker uses clients 1481 to send large amounts of traffic to a victim without the consent of 1482 the victim. While these mechanisms are sufficient to protect victims 1483 who have not implemented WebRTC at all, WebRTC implementations need 1484 to be more careful. 1486 Consider the case of a call center which accepts calls via WebRTC. 1487 An attacker proxies the call center's front-end and arranges for 1488 multiple clients to initiate calls to the call center. Note that 1489 this requires user consent in many cases but because the data channel 1490 does not need consent, he can use that directly. Since ICE will 1491 complete, browsers can then be induced to send large amounts of data 1492 to the victim call center if it supports the data channel at all. 1493 Preventing this attack requires that automated WebRTC implementations 1494 implement sensible flow control and have the ability to triage out 1495 (i.e., stop responding to ICE probes on) calls which are behaving 1496 badly, and especially to be prepared to remotely throttle the data 1497 channel in the absence of plausible audio and video (which the 1498 attacker cannot control). 1500 Another related attack is for the signaling service to swap the ICE 1501 candidates for the audio and video streams, thus forcing a browser to 1502 send video to the sink that the other victim expects will contain 1503 audio (perhaps it is only expecting audio!) potentially causing 1504 overload. Muxing multiple media flows over a single transport makes 1505 it harder to individually suppress a single flow by denying ICE 1506 keepalives. Either media-level (RTCP) mechanisms must be used or the 1507 implementation must deny responses entirely, thus terminating the 1508 call. 1510 Yet another attack, suggested by Magnus Westerlund, is for the 1511 attacker to cross-connect offers and answers as follows. It induces 1512 the victim to make a call and then uses its control of other users 1513 browsers to get them to attempt a call to someone. It then 1514 translates their offers into apparent answers to the victim, which 1515 looks like large-scale parallel forking. The victim still responds 1516 to ICE responses and now the browsers all try to send media to the 1517 victim. Implementations can defend themselves from this attack by 1518 only responding to ICE Binding Requests for a limited number of 1519 remote ufrags (this is the reason for the requirement that the JS not 1520 be able to control the ufrag and password). 1522 [I-D.ietf-rtcweb-rtp-usage] Section 13 documents a number of 1523 potential RTCP-based DoS attacks and countermeasures. 1525 Note that attacks based on confusing one end or the other about 1526 consent are possible even in the face of the third-party identity 1527 mechanism as long as major parts of the signaling messages are not 1528 signed. On the other hand, signing the entire message severely 1529 restricts the capabilities of the calling application, so there are 1530 difficult tradeoffs here. 1532 9.4. IdP Authentication Mechanism 1534 This mechanism relies for its security on the IdP and on the 1535 PeerConnection correctly enforcing the security invariants described 1536 above. At a high level, the IdP is attesting that the user 1537 identified in the assertion wishes to be associated with the 1538 assertion. Thus, it must not be possible for arbitrary third parties 1539 to get assertions tied to a user or to produce assertions that RPs 1540 will accept. 1542 9.4.1. PeerConnection Origin Check 1544 Fundamentally, the IdP proxy is just a piece of HTML and JS loaded by 1545 the browser, so nothing stops a Web attacker from creating their own 1546 IFRAME, loading the IdP proxy HTML/JS, and requesting a signature 1547 over his own keys rather than those generated in the browser. 1548 However, that proxy would be in the attacker's origin, not the IdP's 1549 origin. Only the browser itself can instantiate a context that (a) 1550 is in the IdP's origin and (b) exposes the correct API surface. 1551 Thus, the IdP proxy on the sender's side MUST ensure that it is 1552 running in the IdP's origin prior to issuing assertions. 1554 Note that this check only asserts that the browser (or some other 1555 entity with access to the user's authentication data) attests to the 1556 request and hence to the fingerprint. It does not demonstrate that 1557 the browser has access to the associated private key, and therefore 1558 an attacker can attach their own identity to another party's keying 1559 material, thus making a call which comes from Alice appear to come 1560 from the attacker. See [I-D.ietf-mmusic-sdp-uks] for defenses 1561 against this form of attack. 1563 9.4.2. IdP Well-known URI 1565 As described in Section 7.5 the IdP proxy HTML/JS landing page is 1566 located at a well-known URI based on the IdP's domain name. This 1567 requirement prevents an attacker who can write some resources at the 1568 IdP (e.g., on one's Facebook wall) from being able to impersonate the 1569 IdP. 1571 9.4.3. Privacy of IdP-generated identities and the hosting site 1573 Depending on the structure of the IdP's assertions, the calling site 1574 may learn the user's identity from the perspective of the IdP. In 1575 many cases this is not an issue because the user is authenticating to 1576 the site via the IdP in any case, for instance when the user has 1577 logged in with Facebook Connect and is then authenticating their call 1578 with a Facebook identity. However, in other case, the user may not 1579 have already revealed their identity to the site. In general, IdPs 1580 SHOULD either verify that the user is willing to have their identity 1581 revealed to the site (e.g., through the usual IdP permissions dialog) 1582 or arrange that the identity information is only available to known 1583 RPs (e.g., social graph adjacencies) but not to the calling site. 1584 The "origin" field of the signature request can be used to check that 1585 the user has agreed to disclose their identity to the calling site; 1586 because it is supplied by the PeerConnection it can be trusted to be 1587 correct. 1589 9.4.4. Security of Third-Party IdPs 1591 As discussed above, each third-party IdP represents a new universal 1592 trust point and therefore the number of these IdPs needs to be quite 1593 limited. Most IdPs, even those which issue unqualified identities 1594 such as Facebook, can be recast as authoritative IdPs (e.g., 1595 123456@facebook.com). However, in such cases, the user interface 1596 implications are not entirely desirable. One intermediate approach 1597 is to have special (potentially user configurable) UI for large 1598 authoritative IdPs, thus allowing the user to instantly grasp that 1599 the call is being authenticated by Facebook, Google, etc. 1601 9.4.4.1. Confusable Characters 1603 Because a broad range of characters are permitted in identity 1604 strings, it may be possible for attackers to craft identities which 1605 are confusable with other identities (see [RFC6943] for more on this 1606 topic). This is a problem with any identifier space of this type 1607 (e.g., e-mail addresses). Those minting identifers should avoid 1608 mixed scripts and similar confusable characters. Those presenting 1609 these identifiers to a user should consider highlighting cases of 1610 mixed script usage (see [RFC5890], section 4.4). Other best 1611 practices are still in development. 1613 9.4.5. Web Security Feature Interactions 1615 A number of optional Web security features have the potential to 1616 cause issues for this mechanism, as discussed below. 1618 9.4.5.1. Popup Blocking 1620 The IdP proxy is unable to generate popup windows, dialogs or any 1621 other form of user interactions. This prevents the IdP proxy from 1622 being used to circumvent user interaction. The "LOGINNEEDED" message 1623 allows the IdP proxy to inform the calling site of a need for user 1624 login, providing the information necessary to satisfy this 1625 requirement without resorting to direct user interaction from the IdP 1626 proxy itself. 1628 9.4.5.2. Third Party Cookies 1630 Some browsers allow users to block third party cookies (cookies 1631 associated with origins other than the top level page) for privacy 1632 reasons. Any IdP which uses cookies to persist logins will be broken 1633 by third-party cookie blocking. One option is to accept this as a 1634 limitation; another is to have the PeerConnection object disable 1635 third-party cookie blocking for the IdP proxy. 1637 10. IANA Considerations 1639 This specification defines the "identity" SDP attribute per the 1640 procedures of Section 8.2.4 of [RFC4566]. The required information 1641 for the registration is included here: 1643 Contact Name: Eric Rescorla (ekr@rftm.com) 1645 Attribute Name: identity 1647 Long Form: identity 1649 Type of Attribute: session-level 1651 Charset Considerations: This attribute is not subject to the charset 1652 attribute. 1654 Purpose: This attribute carries an identity assertion, binding an 1655 identity to the transport-level security session. 1657 Appropriate Values: See Section 5 of RFCXXXX [[Editor Note: This 1658 document.]] 1660 Mux Category: NORMAL. 1662 11. Acknowledgements 1664 Bernard Aboba, Harald Alvestrand, Richard Barnes, Dan Druta, Cullen 1665 Jennings, Hadriel Kaplan, Matthew Kaufman, Jim McEachern, Martin 1666 Thomson, Magnus Westerland. Matthew Kaufman provided the UI material 1667 in Section 6.5. Christer Holmberg provided the initial version of 1668 Section 5.1. 1670 12. Changes 1672 [RFC Editor: Please remove this section prior to publication.] 1674 12.1. Changes since -15 1676 Rewrite the Identity section in more conventional offer/answer 1677 format. 1679 Clarify rules on changing identities. 1681 12.2. Changes since -11 1683 Update discussion of IdP security model 1685 Replace "domain name" with RFC 3986 Authority 1687 Clean up discussion of how to generate IdP URI. 1689 Remove obsolete text about null cipher suites. 1691 Remove obsolete appendixes about older IdP systems 1693 Require support for ECDSA, PFS, and AEAD 1695 12.3. Changes since -10 1697 Update cipher suite profiles. 1699 Rework IdP interaction based on implementation experience in Firefox. 1701 12.4. Changes since -06 1703 Replaced RTCWEB and RTC-Web with WebRTC, except when referring to the 1704 IETF WG 1706 Forbade use in mixed content as discussed in Orlando. 1708 Added a requirement to surface NULL ciphers to the top-level. 1710 Tried to clarify SRTP versus DTLS-SRTP. 1712 Added a section on screen sharing permissions. 1714 Assorted editorial work. 1716 12.5. Changes since -05 1718 The following changes have been made since the -05 draft. 1720 o Response to comments from Richard Barnes 1722 o More explanation of the IdP security properties and the federation 1723 use case. 1725 o Editorial cleanup. 1727 12.6. Changes since -03 1729 Version -04 was a version control mistake. Please ignore. 1731 The following changes have been made since the -04 draft. 1733 o Move origin check from IdP to RP per discussion in YVR. 1735 o Clarified treatment of X.509-level identities. 1737 o Editorial cleanup. 1739 12.7. Changes since -03 1741 12.8. Changes since -02 1743 The following changes have been made since the -02 draft. 1745 o Forbid persistent HTTP permissions. 1747 o Clarified the text in S 5.4 to clearly refer to requirements on 1748 the API to provide functionality to the site. 1750 o Fold in the IETF portion of draft-rescorla-rtcweb-generic-idp 1752 o Retarget the continuing consent section to assume Binding Requests 1754 o Added some more privacy and linkage text in various places. 1756 o Editorial improvements 1758 13. References 1760 13.1. Normative References 1762 [FIPS186] National Institute of Standards and Technology (NIST), 1763 "Digital Signature Standard (DSS)", NIST PUB 186-4 , July 1764 2013. 1766 [I-D.ietf-mmusic-sdp-uks] 1767 Thomson, M. and E. Rescorla, "Unknown Key Share Attacks on 1768 uses of TLS with the Session Description Protocol (SDP)", 1769 draft-ietf-mmusic-sdp-uks-03 (work in progress), January 1770 2019. 1772 [I-D.ietf-rtcweb-rtp-usage] 1773 Perkins, C., Westerlund, M., and J. Ott, "Web Real-Time 1774 Communication (WebRTC): Media Transport and Use of RTP", 1775 draft-ietf-rtcweb-rtp-usage-26 (work in progress), March 1776 2016. 1778 [I-D.ietf-rtcweb-security] 1779 Rescorla, E., "Security Considerations for WebRTC", draft- 1780 ietf-rtcweb-security-10 (work in progress), January 2018. 1782 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1783 Requirement Levels", BCP 14, RFC 2119, 1784 DOI 10.17487/RFC2119, March 1997, 1785 . 1787 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, 1788 DOI 10.17487/RFC2818, May 2000, 1789 . 1791 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 1792 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 1793 RFC 3711, DOI 10.17487/RFC3711, March 2004, 1794 . 1796 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 1797 Resource Identifier (URI): Generic Syntax", STD 66, 1798 RFC 3986, DOI 10.17487/RFC3986, January 2005, 1799 . 1801 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1802 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 1803 July 2006, . 1805 [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session 1806 Description Protocol (SDP) Security Descriptions for Media 1807 Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006, 1808 . 1810 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 1811 Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, 1812 . 1814 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 1815 Specifications: ABNF", STD 68, RFC 5234, 1816 DOI 10.17487/RFC5234, January 2008, 1817 . 1819 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 1820 (TLS) Protocol Version 1.2", RFC 5246, 1821 DOI 10.17487/RFC5246, August 2008, 1822 . 1824 [RFC5763] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework 1825 for Establishing a Secure Real-time Transport Protocol 1826 (SRTP) Security Context Using Datagram Transport Layer 1827 Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May 1828 2010, . 1830 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 1831 Security (DTLS) Extension to Establish Keys for the Secure 1832 Real-time Transport Protocol (SRTP)", RFC 5764, 1833 DOI 10.17487/RFC5764, May 2010, 1834 . 1836 [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known 1837 Uniform Resource Identifiers (URIs)", RFC 5785, 1838 DOI 10.17487/RFC5785, April 2010, 1839 . 1841 [RFC5890] Klensin, J., "Internationalized Domain Names for 1842 Applications (IDNA): Definitions and Document Framework", 1843 RFC 5890, DOI 10.17487/RFC5890, August 2010, 1844 . 1846 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 1847 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 1848 January 2012, . 1850 [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, 1851 DOI 10.17487/RFC6454, December 2011, 1852 . 1854 [RFC7022] Begen, A., Perkins, C., Wing, D., and E. Rescorla, 1855 "Guidelines for Choosing RTP Control Protocol (RTCP) 1856 Canonical Names (CNAMEs)", RFC 7022, DOI 10.17487/RFC7022, 1857 September 2013, . 1859 [RFC7675] Perumal, M., Wing, D., Ravindranath, R., Reddy, T., and M. 1860 Thomson, "Session Traversal Utilities for NAT (STUN) Usage 1861 for Consent Freshness", RFC 7675, DOI 10.17487/RFC7675, 1862 October 2015, . 1864 [RFC7918] Langley, A., Modadugu, N., and B. Moeller, "Transport 1865 Layer Security (TLS) False Start", RFC 7918, 1866 DOI 10.17487/RFC7918, August 2016, 1867 . 1869 [RFC8122] Lennox, J. and C. Holmberg, "Connection-Oriented Media 1870 Transport over the Transport Layer Security (TLS) Protocol 1871 in the Session Description Protocol (SDP)", RFC 8122, 1872 DOI 10.17487/RFC8122, March 2017, 1873 . 1875 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1876 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1877 May 2017, . 1879 [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data 1880 Interchange Format", STD 90, RFC 8259, 1881 DOI 10.17487/RFC8259, December 2017, 1882 . 1884 [RFC8261] Tuexen, M., Stewart, R., Jesup, R., and S. Loreto, 1885 "Datagram Transport Layer Security (DTLS) Encapsulation of 1886 SCTP Packets", RFC 8261, DOI 10.17487/RFC8261, November 1887 2017, . 1889 [RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive 1890 Connectivity Establishment (ICE): A Protocol for Network 1891 Address Translator (NAT) Traversal", RFC 8445, 1892 DOI 10.17487/RFC8445, July 2018, 1893 . 1895 [webcrypto] 1896 Dahl, Sleevi, "Web Cryptography API", June 2013. 1898 Available at http://www.w3.org/TR/WebCryptoAPI/ 1900 [webrtc-api] 1901 Bergkvist, Burnett, Jennings, Narayanan, "WebRTC 1.0: 1902 Real-time Communication Between Browsers", October 2011. 1904 Available at http://dev.w3.org/2011/webrtc/editor/ 1905 webrtc.html 1907 13.2. Informative References 1909 [I-D.ietf-rtcweb-jsep] 1910 Uberti, J., Jennings, C., and E. Rescorla, "JavaScript 1911 Session Establishment Protocol", draft-ietf-rtcweb-jsep-25 1912 (work in progress), October 2018. 1914 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 1915 A., Peterson, J., Sparks, R., Handley, M., and E. 1916 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 1917 DOI 10.17487/RFC3261, June 2002, 1918 . 1920 [RFC5705] Rescorla, E., "Keying Material Exporters for Transport 1921 Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705, 1922 March 2010, . 1924 [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, 1925 DOI 10.17487/RFC6265, April 2011, 1926 . 1928 [RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol", 1929 RFC 6455, DOI 10.17487/RFC6455, December 2011, 1930 . 1932 [RFC6943] Thaler, D., Ed., "Issues in Identifier Comparison for 1933 Security Purposes", RFC 6943, DOI 10.17487/RFC6943, May 1934 2013, . 1936 [RFC7617] Reschke, J., "The 'Basic' HTTP Authentication Scheme", 1937 RFC 7617, DOI 10.17487/RFC7617, September 2015, 1938 . 1940 [XmlHttpRequest] 1941 van Kesteren, A., "XMLHttpRequest Level 2", January 2012. 1943 Author's Address 1944 Eric Rescorla 1945 RTFM, Inc. 1946 2064 Edgewood Drive 1947 Palo Alto, CA 94303 1948 USA 1950 Phone: +1 650 678 2350 1951 Email: ekr@rtfm.com