--- 1/draft-ietf-rtcweb-security-arch-03.txt 2012-10-22 19:14:23.677341720 +0200 +++ 2/draft-ietf-rtcweb-security-arch-04.txt 2012-10-22 19:14:23.741344206 +0200 @@ -1,18 +1,18 @@ RTCWEB E. Rescorla Internet-Draft RTFM, Inc. -Intended status: Standards Track July 16, 2012 -Expires: January 17, 2013 +Intended status: Standards Track October 22, 2012 +Expires: April 25, 2013 RTCWEB Security Architecture - draft-ietf-rtcweb-security-arch-03 + draft-ietf-rtcweb-security-arch-04 Abstract The Real-Time Communications on the Web (RTCWEB) working group is tasked with standardizing protocols for enabling real-time communications within user-agents using web technologies (e.g JavaScript). The major use cases for RTCWEB technology are real-time audio and/or video calls, Web conferencing, and direct data transfer. Unlike most conventional real-time systems (e.g., SIP-based soft phones) RTCWEB communications are directly controlled by some Web @@ -43,21 +43,21 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on January 17, 2013. + This Internet-Draft will expire on April 25, 2013. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -74,66 +74,68 @@ modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents - 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 3. Trust Model . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 3.1. Authenticated Entities . . . . . . . . . . . . . . . . . . 5 - 3.2. Unauthenticated Entities . . . . . . . . . . . . . . . . . 5 - 4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 - 4.1. Initial Signaling . . . . . . . . . . . . . . . . . . . . 7 - 4.2. Media Consent Verification . . . . . . . . . . . . . . . . 9 - 4.3. DTLS Handshake . . . . . . . . . . . . . . . . . . . . . . 9 - 4.4. Communications and Consent Freshness . . . . . . . . . . . 10 - 5. Detailed Technical Description . . . . . . . . . . . . . . . . 10 - 5.1. Origin and Web Security Issues . . . . . . . . . . . . . . 10 - 5.2. Device Permissions Model . . . . . . . . . . . . . . . . . 11 - 5.3. Communications Consent . . . . . . . . . . . . . . . . . . 12 - 5.4. IP Location Privacy . . . . . . . . . . . . . . . . . . . 13 - 5.5. Communications Security . . . . . . . . . . . . . . . . . 14 - 5.6. Web-Based Peer Authentication . . . . . . . . . . . . . . 15 - 5.6.1. Trust Relationships: IdPs, APs, and RPs . . . . . . . 16 - 5.6.2. Overview of Operation . . . . . . . . . . . . . . . . 17 - 5.6.3. Items for Standardization . . . . . . . . . . . . . . 19 - 5.6.4. Binding Identity Assertions to JSEP Offer/Answer - Transactions . . . . . . . . . . . . . . . . . . . . . 19 - 5.6.4.1. Input to Assertion Generation Process . . . . . . 19 - 5.6.4.2. Carrying Identity Assertions . . . . . . . . . . . 20 - 5.6.5. IdP Interaction Details . . . . . . . . . . . . . . . 20 - 5.6.5.1. General Message Structure . . . . . . . . . . . . 20 - 5.6.5.2. IdP Proxy Setup . . . . . . . . . . . . . . . . . 21 - 5.7. Security Considerations . . . . . . . . . . . . . . . . . 26 - 5.7.1. Communications Security . . . . . . . . . . . . . . . 26 - 5.7.2. Privacy . . . . . . . . . . . . . . . . . . . . . . . 27 - 5.7.3. Denial of Service . . . . . . . . . . . . . . . . . . 27 - 5.7.4. IdP Authentication Mechanism . . . . . . . . . . . . . 28 - 5.7.4.1. IdP Well-known URI . . . . . . . . . . . . . . . . 29 - 5.7.4.2. Privacy of IdP-generated identities and the - hosting site . . . . . . . . . . . . . . . . . . . 29 - 5.7.4.3. Security of Third-Party IdPs . . . . . . . . . . . 29 - 5.7.4.4. Web Security Feature Interactions . . . . . . . . 29 - 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 30 - 7. Changes since -02 . . . . . . . . . . . . . . . . . . . . . . 30 - 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30 - 8.1. Normative References . . . . . . . . . . . . . . . . . . . 30 - 8.2. Informative References . . . . . . . . . . . . . . . . . . 31 - Appendix A. Example IdP Bindings to Specific Protocols . . . . . 32 - A.1. BrowserID . . . . . . . . . . . . . . . . . . . . . . . . 32 - A.2. OAuth . . . . . . . . . . . . . . . . . . . . . . . . . . 35 - Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 36 + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 + 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 + 3. Trust Model . . . . . . . . . . . . . . . . . . . . . . . . . 5 + 3.1. Authenticated Entities . . . . . . . . . . . . . . . . . . 6 + 3.2. Unauthenticated Entities . . . . . . . . . . . . . . . . . 6 + 4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 + 4.1. Initial Signaling . . . . . . . . . . . . . . . . . . . . 8 + 4.2. Media Consent Verification . . . . . . . . . . . . . . . . 10 + 4.3. DTLS Handshake . . . . . . . . . . . . . . . . . . . . . . 11 + 4.4. Communications and Consent Freshness . . . . . . . . . . . 11 + 5. Detailed Technical Description . . . . . . . . . . . . . . . . 11 + 5.1. Origin and Web Security Issues . . . . . . . . . . . . . . 11 + 5.2. Device Permissions Model . . . . . . . . . . . . . . . . . 12 + 5.3. Communications Consent . . . . . . . . . . . . . . . . . . 14 + 5.4. IP Location Privacy . . . . . . . . . . . . . . . . . . . 14 + 5.5. Communications Security . . . . . . . . . . . . . . . . . 15 + 5.6. Web-Based Peer Authentication . . . . . . . . . . . . . . 16 + 5.6.1. Trust Relationships: IdPs, APs, and RPs . . . . . . . 17 + 5.6.2. Overview of Operation . . . . . . . . . . . . . . . . 19 + 5.6.3. Binding Identity Assertions to JSEP Offer/Answer + Transactions . . . . . . . . . . . . . . . . . . . . . 20 + 5.6.3.1. Input to Assertion Generation Process . . . . . . 20 + 5.6.3.2. Carrying Identity Assertions . . . . . . . . . . . 21 + 5.6.4. IdP Interaction Details . . . . . . . . . . . . . . . 21 + 5.6.4.1. General Message Structure . . . . . . . . . . . . 21 + 5.6.4.2. IdP Proxy Setup . . . . . . . . . . . . . . . . . 22 + 5.7. Security Considerations . . . . . . . . . . . . . . . . . 27 + 5.7.1. Communications Security . . . . . . . . . . . . . . . 27 + 5.7.2. Privacy . . . . . . . . . . . . . . . . . . . . . . . 28 + 5.7.3. Denial of Service . . . . . . . . . . . . . . . . . . 28 + 5.7.4. IdP Authentication Mechanism . . . . . . . . . . . . . 29 + 5.7.4.1. PeerConnection Origin Check . . . . . . . . . . . 29 + 5.7.4.2. IdP Well-known URI . . . . . . . . . . . . . . . . 30 + 5.7.4.3. Privacy of IdP-generated identities and the + hosting site . . . . . . . . . . . . . . . . . . . 30 + 5.7.4.4. Security of Third-Party IdPs . . . . . . . . . . . 30 + 5.7.4.5. Web Security Feature Interactions . . . . . . . . 30 + 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 31 + 7. Changes since -03 . . . . . . . . . . . . . . . . . . . . . . 31 + 8. Changes since -02 . . . . . . . . . . . . . . . . . . . . . . 31 + 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 32 + 9.1. Normative References . . . . . . . . . . . . . . . . . . . 32 + 9.2. Informative References . . . . . . . . . . . . . . . . . . 32 + Appendix A. Example IdP Bindings to Specific Protocols . . . . . 33 + A.1. BrowserID . . . . . . . . . . . . . . . . . . . . . . . . 33 + A.2. OAuth . . . . . . . . . . . . . . . . . . . . . . . . . . 36 + + Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 37 1. Introduction The Real-Time Communications on the Web (RTCWEB) working group is tasked with standardizing protocols for real-time communications between Web browsers. The major use cases for RTCWEB technology are real-time audio and/or video calls, Web conferencing, and direct data transfer. Unlike most conventional real-time systems, (e.g., SIP- based[RFC3261] soft phones) RTCWEB communications are directly controlled by some Web server, as shown in Figure 1. @@ -187,23 +189,22 @@ have a functional system. Other network elements fall into two categories: those which can be authenticated by the browser and thus are partly trusted--though to the minimum extent necessary--and those which cannot be authenticated and thus are untrusted. This is a natural extension of the end-to-end principle. 3.1. Authenticated Entities There are two major classes of authenticated entities in the system: - o Calling services: Web sites whose origin we can verify (optimally - via HTTPS, but in some cases because we are on a topologically - restricted network, such as behind a firewall). + o Calling services: Web sites whose origin we can verify (in + practice this means HTTPS). o Other users: RTCWEB peers whose origin we can verify cryptographically (optimally via DTLS-SRTP). Note that merely being authenticated does not make these entities trusted. For instance, just because we can verify that https://www.evil.org/ is owned by Dr. Evil does not mean that we can trust Dr. Evil to access our camera and microphone. However, it gives the user an opportunity to determine whether he wishes to trust Dr. Evil or not; after all, if he desires to contact Dr. Evil (perhaps to arrange for ransom payment), it's safe to temporarily @@ -313,31 +314,36 @@ two MediaStreams, one connected to an audio input and one connected to a video input. At this point the first security check is required: untrusted origins are not allowed to access the camera and microphone. In this case, because Alice is a long-term user of the calling service, she has made a permissions grant (i.e., a setting in the browser) to allow the calling service to access her camera and microphone any time it wants. The browser checks this setting when the camera and microphone requests are made and thus allows them. In the current W3C API, once some streams have been added, Alice's - browser + JS generates a signaling message [I-D.ietf-rtcweb-jsep] - contianing: + browser + JS generates a signaling message The format of this data is + currently undefined. It may be a complete message as defined by ROAP + [I-D.jennings-rtcweb-signaling] or separate media description and + transport messages as defined in [I-D.ietf-rtcweb-jsep] or may be + assembled piecemeal by the JS. In either case, it will contain: o Media channel information o ICE candidates o A fingerprint attribute binding the communication to Alice's public key [RFC5763] - Prior to sending out the signaling message, the PeerConnection code - contacts the identity service and obtains an assertion binding - Alice's identity to her fingerprint. The exact details depend on the + [Note that it is currently unclear where JSEP will eventually put + this information, in the SDP or in the transport info.] Prior to + sending out the signaling message, the PeerConnection code contacts + the identity service and obtains an assertion binding Alice's + identity to her fingerprint. The exact details depend on the identity service (though as discussed in Section 5.6 PeerConnection can be agnostic to them), but for now it's easiest to think of as a BrowserID assertion. The assertion may bind other information to the identity besides the fingerprint, but at minimum it needs to bind the fingerprint. This message is sent to the signaling server, e.g., by XMLHttpRequest [XmlHttpRequest] or by WebSockets [RFC6455] The signaling server processes the message from Alice's browser, determines that this is a call to Bob and sends a signaling message to Bob's browser (again, @@ -421,22 +427,24 @@ anticlimactic: Alice and Bob exchange data protected by the keys negotiated by DTLS. Because of the security guarantees discussed in the previous sections, they know that the communications are encrypted and authenticated. The one remaining security property we need to establish is "consent freshness", i.e., allowing Alice to verify that Bob is still prepared to receive her communications. ICE specifies periodic STUN keepalizes but only if media is not flowing. Because the consent issue is more difficult here, we require RTCWeb implementations to - periodically send keepalives. If a keepalive fails and no new ICE - channels can be established, then the session is terminated. + periodically send keepalives. As described in Section 5.3, these + keepalives MUST be based on the consent freshness mechanism specified + in [I-D.muthu-behave-consent-freshness]. If a keepalive fails and no + new ICEchannels can be established, then the session is terminated. 5. Detailed Technical Description 5.1. Origin and Web Security Issues The basic unit of permissions for RTCWEB is the origin [RFC6454]. Because the security of the origin depends on being able to authenticate content from that origin, the origin can only be securely established if data is transferred over HTTPS [RFC2818]. Thus, clients MUST treat HTTP and HTTPS origins as different @@ -477,27 +485,27 @@ refuse all permissions grants for HTTP origins, but it is RECOMMENDED that currently they support one-time camera/microphone access. In addition, they SHOULD support requests for access to a single communicating peer. E.g., "Call customerservice@ford.com". Browsers servicing such requests SHOULD clearly indicate that identity to the user when asking for permission. API Requirement: The API MUST provide a mechanism for the requesting JS to indicate which of these forms of permissions it is - requesting. This allows the browser to know what sort of user - interface experience to provide to the user, including what - permissions to request from the user and hence that to enforce - later. For instance, browsers might display a non-invasive door - hanger ("some features of this site may not work..." when asking - for long-term permissions) but a more invasive UI ("here is your - own video") for single-call permissions. The API MAY grant weaker + requesting. This allows the client to know what sort of user + interface experience to provide, i.e., to allow the client to + clearly indicate to the user what he is agreeing to. In + particular, browsers might display a non-invasive door hanger + ("some features of this site may not work..." when asking for + long-term permissions) but a more invasive UI ("here is your own + video") for single-call permissions. The API MAY grant weaker permissions than the JS asked for if the user chooses to authorize only those permissions, but if it intends to grant stronger ones it SHOULD display the appropriate UI for those permissions and MUST clearly indicate what permissions are being requested. API Requirement: The API MUST provide a mechanism for the requesting JS to relinquish the ability to see or modify the media (e.g., via MediaStream.record()). Combined with secure authentication of the communicating peer, this allows a user to be sure that the calling site is not accessing or modifying their conversion. @@ -531,41 +539,41 @@ address book (this only works with address book integration, of course). Implementations SHOULD also provide a different user interface indication when calls are in progress to users whose identities are directly verifiable. Section 5.5 provides more on this. 5.3. Communications Consent Browser client implementations of RTCWEB MUST implement ICE. Server - gateway implementations which operate only at public IP addresses - MUST implement either full ICE or ICE-Lite. + gateway implementations which operate only at public IP addresses may + implement ICE-Lite instead of ICE but MUST implement one of the two. Browser implementations MUST verify reachability via ICE prior to sending any non-ICE packets to a given destination. Implementations MUST NOT provide the ICE transaction ID to JavaScript during the lifetime of the transaction (i.e., during the period when the ICE stack would accept a new response for that transaction). [Note: this document takes no position on the split between ICE in JS and ICE in the browser. The above text is written the way it is for editorial convenience and will be modified appropriately if the WG - decides on ICE in the JS.] The JS MUST NOT be permitted to control - the local ufrag and password, though it of course knows it. + decides on ICE in the JS.] - While continuing consent is required, that ICE [RFC5245]; Section 10 - keepalives STUN Binding Indications are one-way and therefore not - sufficient. The current WG consensus is to use ICE Binding Requests - for continuing consent freshness. ICE already requires that - implementations respond to such requests, so this approach is - maximally compatible. A separate document will profile the ICE - timers to be used [[TODO: insert REF here when available.]] + Implementations MUST send keepalives no less frequently than every 30 + seconds regardless of whether traffic is flowing or not. If a + keepalive fails then the implementation MUST either attempt to find a + new valid path via ICE or terminate media for that ICE component. + Note that ICE [RFC5245]; Section 10 keepalives use STUN Binding + Indications which are one-way and therefore not sufficient. Instead, + the consent freshness mechanism [I-D.muthu-behave-consent-freshness] + MUST be used. 5.4. IP Location Privacy A side effect of the default ICE behavior is that the peer learns one's IP address, which leaks large amounts of location information, especially for mobile devices. This has negative privacy consequences in some circumstances. The API requirements in this section are intended to mitigate this issue. Note that these requirements are NOT intended to protect the user's IP address from a malicious site. In general, the site will learn at least a user's @@ -581,46 +589,43 @@ suppress ICE negotiation (though perhaps to allow candidate gathering) until the user has decided to answer the call [note: determining when the call has been answered is a question for the JS.] This enables a user to prevent a peer from learning their IP address if they elect not to answer a call and also from learning whether the user is online. API Requirement: The API MUST provide a mechanism for the calling application JS to indicate that only TURN candidates are to be used. This prevents the peer from learning one's IP address at - all. - - API Requirement: The API MUST provide a mechanism for the calling - application to reconfigure an existing call to add non-TURN - candidates. Taken together, this and the previous requirement - allow ICE negotiation to start immediately on incoming call - notification, thus reducing post-dial delay, but also to avoid - disclosing the user's IP address until they have decided to - answer. They also allow users to completely hide their IP address - for the duration of the call. Finally, they allow a mechanism for - the user to optimize performance by reconfiguring to allow non- - turn candidates during an active call if the user decides they no - longer need to hide their IP address + all. The API MUST provide a mechanism for the calling application + to reconfigure an existing call to add non-TURN candidates. Taken + together, these requirements allow ICE negotiation to start + immediately on incoming call notification, thus reducing post-dial + delay, but also to avoid disclosing the user's IP address until + they have decided to answer. They also allow users to completely + hide their IP address for the duration of the call. Finally, they + allow a mechanism for the user to optimize performance by + reconfiguring to allow non-TURN candidates during an active call + if the user decides they no longer need to hide their IP address 5.5. Communications Security Implementations MUST implement DTLS [RFC4347] and DTLS-SRTP [RFC5763][RFC5764]. All data channels MUST be secured via DTLS. DTLS-SRTP MUST be offered for every media channel and MUST be the default; i.e., if an implementation receives an offer for DTLS-SRTP and SDES, DTLS-SRTP MUST be selected. Media traffic MUST NOT be sent over plain (unencrypted) RTP. [OPEN ISSUE: What should the settings be here? MUST?] - Implementations MAY support SDES for media traffic for backward - compatibility purposes. + Implementations MAY support SDES and RTP for media traffic for + backward compatibility purposes. API Requirement: The API MUST provide a mechanism to indicate that a fresh DTLS key pair is to be generated for a specific call. This is intended to allow for unlinkability. Note that there are also settings where it is attractive to use the same keying material repeatedly, especially those with key continuity-based authentication. API Requirement: When DTLS-SRTP is used, the API MUST NOT permit the JS to obtain the negotiated keying material. This requirement @@ -641,25 +645,24 @@ determine the security characteristics for transmissions of their microphone audio and camera video. * The "security characteristics" MUST include an indication as to whether the cryptographic keys were delivered out-of-band (from a server) or were generated as a result of a pairwise negotiation. * If the far endpoint was directly verified, either via a third- party verifiable X.509 certificate or via a Web IdP mechanism (see Section 5.6) the "security characteristics" MUST include the verified information. - The following properties are more likely to require some "drill- down" from the user: - * The "security characteristics" MUST indicate the cryptographic + * The security characteristics MUST indicate the cryptographic algorithms in use (For example: "AES-CBC" or "Null Cipher".) * The "security characteristics" MUST indicate whether PFS is provided. * The "security characteristics" MUST include some mechanism to allow an out-of-band verification of the peer, such as a certificate fingerprint or an SAS. 5.6. Web-Based Peer Authentication In a number of cases, it is desirable for the endpoint (i.e., the @@ -667,36 +670,51 @@ side without trusting only the signaling service to which they are connected. For instance, users may be making a call via a federated system where they wish to get direct authentication of the other side. Alternately, they may be making a call on a site which they minimally trust (such as a poker site) but to someone who has an identity on a site they do trust (such as a social network.) Recently, a number of Web-based identity technologies (OAuth, BrowserID, Facebook Connect), etc. have been developed. While the details vary, what these technologies share is that they have a Web- - based (i.e., HTTP/HTTPS) identity provider which attests to your + based (i.e., HTTP/HTTPS identity provider) which attests to your identity. For instance, if I have an account at example.org, I could use the example.org identity provider to prove to others that I was alice@example.org. The development of these technologies allows us to separate calling from identity provision: I could call you on Poker Galaxy but identify myself as alice@example.org. Whatever the underlying technology, the general principle is that the party which is being authenticated is NOT the signaling site but rather the user (and their browser). Similarly, the relying party is the browser and not the signaling site. Thus, the browser MUST securely generate the input to the IdP assertion process and MUST securely display the results of the verification process to the user in a way which cannot be imitated by the calling site. - The mechanisms defined in this document do not require the browser to + In order to make this work, we must standardize the following items: + + o The precise information from the signaling message that must be + cryptographically bound to the user's identity and a mechanism for + carrying assertions in JSEP messages. Section 5.6.3 + o The interface to the IdP. Section 5.6.4 specifies a specific + protocol mechanism which allows the use of any identity protocol + without requiring specific further protocol support in the browser + o The JavaScript interfaces which the calling application can use to + specify the IdP to use to generate assertions and to discover what + assertions were received. + + The first two items are defined in this document. The final one is + defined in the companion W3C WebRTC API specification [TODO:REF] + + The mechanisms in this document do not require the browser to implement any particular identity protocol or to support any particular IdP. Instead, this document provides a generic interface which any IdP can implement. Thus, new IdPs and protocols can be introduced without change to either the browser or the calling service. This avoids the need to make a commitment to any particular identity protocol, although browsers may opt to directly implement some identity protocols in order to provide superior performance or UI properties. 5.6.1. Trust Relationships: IdPs, APs, and RPs @@ -810,65 +829,48 @@ This approach allows us to decouple the browser from any particular identity provider; the browser need only know how to load the IdP's JavaScript--which is deterministic from the IdP's identity--and the generic protocol for requesting and verifying assertions. The IdP provides whatever logic is necessary to bridge the generic protocol to the IdP's specific requirements. Thus, a single browser can support any number of identity protocols, including being forward compatible with IdPs which did not exist at the time the browser was written. -5.6.3. Items for Standardization - - In order to make this work, we must standardize the following items: - - o The precise information from the signaling message that must be - cryptographically bound to the user's identity and a mechanism for - carrying assertions in JSEP messages. Section 5.6.4 - o The interface to the IdP. Section 5.6.5 specifies a specific - protocol mechanism which allows the use of any identity protocol - without requiring specific further protocol support in the browser - o The JavaScript interfaces which the calling application can use to - specify the IdP to use to generate assertions and to discover what - assertions were received. - - The first two items are defined in this document. The final one is - defined in the companion W3C WebRTC API specification [TODO:REF] - -5.6.4. Binding Identity Assertions to JSEP Offer/Answer Transactions +5.6.3. Binding Identity Assertions to JSEP Offer/Answer Transactions -5.6.4.1. Input to Assertion Generation Process +5.6.3.1. Input to Assertion Generation Process As discussed above, an identity assertion binds the user's identity (as asserted by the IdP) to the JSEP offer/exchange transaction and specifically to the media. In order to achieve this, the PeerConnection must provide the DTLS-SRTP fingerprint to be bound to the identity. This is provided in a JSON structure for extensibility, as shown below: { - "fingerprint" : + "fingerprint" : { { "algorithm":"SHA-1", "digest":"4A:AD:B9:B1:3F:...:E5:7C:AB" } } The "algorithm" and digest values correspond directly to the algorithm and digest in the a=fingerprint line of the SDP. Note: this structure does not need to be interpreted by the IdP or the IdP proxy. It is consumed solely by the RP's browser. The IdP merely treats it as an opaque value to be attested to. Thus, new parameters can be added to the assertion without modifying the IdP. -5.6.4.2. Carrying Identity Assertions +5.6.3.2. Carrying Identity Assertions Once an IdP has generated an assertion, the JSEP message. This is done by adding a new a-line to the SDP, of the form a=identity. The sole contents of this value are a base-64-encoded version of the identity assertion. For example: v=0 o=- 1181923068 1181923196 IN IP4 ua1.example.com s=example1 c=IN IP4 ua1.example.com @@ -886,23 +888,23 @@ a=tcap:1 UDP/TLS/RTP/SAVP RTP/AVP a=pcfg:1 t=1 Each identity attribute should be paired (and attests to) with an a=fingerprint attribute and therefore can exist either at the session or media level. Multiple identity attributes may appear at either level, though implementations are discouraged from doing this unless they have a clear idea of what security claim they intend to be making. -5.6.5. IdP Interaction Details +5.6.4. IdP Interaction Details -5.6.5.1. General Message Structure +5.6.4.1. General Message Structure Messages between the PeerConnection object and the IdP proxy are formatted using JSON [RFC4627]. For instance, the PeerConnection would request a signature with the following "SIGN" message: { "type":"SIGN", "id": "1", "origin":"https://calling-site.example.com", "message":"012345678abcdefghijkl" @@ -921,130 +923,125 @@ the URL of the calling site). This origin value can be used by the IdP to make access control decisions. For instance, an IdP might only issue identity assertions for certain calling services in the same way that some IdPs require that relying Web sites have an API key before learning user identity. Any message-specific data is carried in a "message" field. Depending on the message type, this may either be a string or a richer JSON object. -5.6.5.1.1. Errors +5.6.4.1.1. Errors If an error occurs, the IdP sends a message of type "ERROR". The message MAY have an "error" field containing freeform text data which containing additional information about what happened. For instance: { "type":"ERROR", "error":"Signature verification failed" } Figure 3: Example error -5.6.5.2. IdP Proxy Setup +5.6.4.2. IdP Proxy Setup In order to perform an identity transaction, the PeerConnection must - first create an IdP proxy. While the details of this are specified - in the W3C API document, from the perspective of this specification, - however, the relevant facts are: + first create an IdP proxy. As stated above, the details of this are + specified in the W3C API document. From the perspective of this + specification, however, the relevant facts are: o The JS runs in the IdP's security context with the base page - retrieved from the URL specified in Section 5.6.5.2.1 + retrieved from the URL specified in Section 5.6.4.2.1 o The usual browser sandbox isolation mechanisms MUST be enforced with respect to the IdP proxy. o JS running in the IdP proxy MUST be able to send and receive messages to the PeerConnection and the PC and IdP proxy are able to verify the source and destination of these messages. Initially the IdP proxy is in an unready state; the IdP JS must be loaded and there may be several round trips to the IdP server, for instance to log the user in. When the IdP proxy is ready to receive commands, it delivers a "ready" message. As this message is unsolicited, it simply contains: { "type":"READY" } - [[ OPEN ISSUE: if the W3C half of this converges on WebIntents, then - the READY message will not be necessary.]] - Once the PeerConnection object receives the ready message, it can send commands to the IdP proxy. -5.6.5.2.1. Determining the IdP URI +5.6.4.2.1. Determining the IdP URI Each IdP proxy instance is associated with two values: domain name: The IdP's domain name protocol: The specific IdP protocol which the IdP is using. This is a completely IdP-specific string, but allows an IdP to implement two protocols in parallel. This value may be the empty string. Each IdP MUST serve its initial entry page (i.e., the one loaded by the IdP proxy) from the well-known URI specified in "/.well-known/ idp-proxy/" on the IdP's web site. This URI MUST be loaded via HTTPS [RFC2818]. For example, for the IdP "identity.example.com" and the protocol "example", the URL would be: https://example.com/.well-known/idp-proxy/example -5.6.5.2.1.1. Authenticating Party +5.6.4.2.1.1. Authenticating Party How an AP determines the appropriate IdP domain is out of scope of this specification. In general, however, the AP has some actual account relationship with the IdP, as this identity is what the IdP is attesting to. Thus, the AP somehow supplies the IdP information to the browser. Some potential mechanisms include: o Provided by the user directly. o Selected from some set of IdPs known to the calling site. E.g., a button that shows "Authenticate via Facebook Connect" -5.6.5.2.1.2. Relying Party +5.6.4.2.1.2. Relying Party Unlike the AP, the RP need not have any particular relationship with the IdP. Rather, it needs to be able to process whatever assertion is provided by the AP. As the assertion contains the IdP's identity, the URI can be constructed directly from the assertion, and thus the RP can directly verify the technical validity of the assertion with no user interaction. Authoritative assertions need only be verifiable. Third-party assertions also MUST be verified against - local policy, as described in Section 5.6.5.2.3.1. + local policy, as described in Section 5.6.4.2.3.1. -5.6.5.2.2. Requesting Assertions +5.6.4.2.2. Requesting Assertions In order to request an assertion, the PeerConnection sends a "SIGN" message. Aside from the mandatory fields, this message has a "message" field containing a string. The contents of this string are defined above, but are opaque from the perspective of the IdP. A successful response to a "SIGN" message contains a message field which is a JS dictionary dictionary consisting of two fields: idp: A dictionary containing the domain name of the provider and the protocol string assertion: An opaque field containing the assertion itself. This is only interpretable by the idp or its proxy. Figure 4 shows an example transaction, with the message "abcde..." - (remember, the messages are opaque at this layer) being signed and - bound to identity "ekr@example.org". In this case, the message has - presumably been digitally signed/MACed in some way that the IdP can - later verify it, but this is an implementation detail and out of - scope of this document. Line breaks are inserted solely for - readability. + being signed and bound to identity "ekr@example.org". In this case, + the message has presumably been digitally signed/MACed in some way + that the IdP can later verify it, but this is an implementation + detail and out of scope of this document. Line breaks are inserted + solely for readability. PeerConnection -> IdP proxy: { "type":"SIGN", "id":1, - "origin":"https://calling-service.example.com/", "message":"abcdefghijklmnopqrstuvwyz" } IdPProxy -> PeerConnection: { "type":"SUCCESS", "id":1, "message": { "idp":{ "domain": "example.org" @@ -1048,75 +1045,72 @@ "message": { "idp":{ "domain": "example.org" "protocol": "bogus" }, "assertion":\"{\"identity\":\"bob@example.org\", \"contents\":\"abcdefghijklmnopqrstuvwyz\", \"signature\":\"010203040506\"}" } } - Figure 4: Example assertion request -5.6.5.2.3. Verifying Assertions +5.6.4.2.3. Verifying Assertions In order to verify an assertion, an RP sends a "VERIFY" message to the IdP proxy containing the assertion supplied by the AP in the "message" field. The IdP proxy verifies the assertion. Depending on the identity protocol, this may require one or more round trips to the IdP. For instance, an OAuth-based protocol will likely require using the IdP as an oracle, whereas with BrowserID the IdP proxy can likely verify the signature on the assertion without contacting the IdP, provided that it has cached the IdP's public key. Regardless of the mechanism, if verification succeeds, a successful response from the IdP proxy MUST contain a message field consisting of a dictionary/hash with the following fields: identity The identity of the AP from the IdP's perspective. Details - of this are provided in Section 5.6.5.2.3.1 - + of this are provided in Section 5.6.4.2.3.1 contents The original unmodified string provided by the AP in the original SIGN request. Figure 5 shows an example transaction. Line breaks are inserted solely for readability. PeerConnection -> IdP Proxy: { "type":"VERIFY", "id":2, - "origin":"https://calling-service.example.com/", "message":\"{\"identity\":\"bob@example.org\", \"contents\":\"abcdefghijklmnopqrstuvwyz\", \"signature\":\"010203040506\"}" } IdP Proxy -> PeerConnection: { "type":"SUCCESS", "id":2, "message": { "identity" : { "name" : "bob@example.org", "displayname" : "Bob" }, "contents":"abcdefghijklmnopqrstuvwyz" } } Figure 5: Example verification request -5.6.5.2.3.1. Identity Formats +5.6.4.2.3.1. Identity Formats Identities passed from the IdP proxy to the PeerConnection are structured as JSON dictionaries with one mandatory field: "name". This field MUST consist of an RFC822-formatted string representing the user's identity. [[ OPEN ISSUE: Would it be better to have a typed field? ]] The PeerConnection API MUST check this string as follows: 1. If the RHS of the string is equal to the domain name of the IdP proxy, then the assertion is valid, as the IdP is authoritative @@ -1131,22 +1125,21 @@ (for instance, Facebook ids are simple numeric values) SHOULD convert them to this form by appending their IdP domain (e.g., 12345@identity.facebook.com), thus ensuring that they are authoritative for the identity. The IdP proxy MAY also include a "displayname" field which contains a more user-friendly identity assertion. Browsers SHOULD take care in the UI to distinguish the "name" assertion which is verifiable directly from the "displayname" which cannot be verified and thus relies on trust in the IdP. In future, we may define other fields to - allow the IdP to provide more information to the browser. [[OPEN - ISSUE: Should this field exist? Is it confusing? ]] + allow the IdP to provide more information to the browser. 5.7. Security Considerations Much of the security analysis of this problem is contained in [I-D.ietf-rtcweb-security] or in the discussion of the particular issues above. In order to avoid repetition, this section focuses on (a) residual threats that are not addressed by this document and (b) threats produced by failure/misbehavior of one of the components in the system. @@ -1171,21 +1164,21 @@ requirements in Section 5.5 are designed to provide such a mechanism for motivated/security conscious users, but are not suitable for general use. The identity service mechanisms in Section 5.6 are more suitable for general use. Note, however, that a malicious signaling service can strip off any such identity assertions, though it cannot forge new ones. Note that all of the third-party security mechanisms available (whether X.509 certificates or a third-party IdP) rely on the security of the third party--this is of course also true of your connection to the Web site itself. Users who wish to assure themselves of security against a malicious identity provider can only - do so by verifying peer credentials directly, e.g., by checking the + do so by verifing peer credentials directly, e.g., by checking the peer's fingerprint against a value delivered out of band. 5.7.2. Privacy The requirements in this document are intended to allow: o Users to participate in calls without revealing their location. o Potential callees to avoid revealing their location and even presence status prior to agreeing to answer a call. @@ -1225,142 +1218,155 @@ which are behaving badly, and especially to be prepared to remotely throttle the data channel in the absence of plausible audio and video (which the attacker cannot control). Another related attack is for the signaling service to swap the ICE candidates for the audio and video streams, thus forcing a browser to send video to the sink that the other victim expects will contain audio (perhaps it is only expecting audio!) potentially causing overload. Muxing multiple media flows over a single transport makes it harder to individually suppress a single flow by denying ICE - keepalives. Either media-level (RTCP) mechanisms must be used or the - implementation must deny responses entirely, thus termnating the - call. + keepalives. Media-level (RTCP) mechanisms must be used in this case. Yet another attack, suggested by Magnus Westerlund, is for the attacker to cross-connect offers and answers as follows. It induces the victim to make a call and then uses its control of other users browsers to get them to attempt a call to someone. It then translates their offers into apparent answers to the victim, which looks like large-scale parallel forking. The victim still responds to ICE responses and now the browsers all try to send media to the - victim. Implementations can defend themselves from this attack by - only responding to ICE Binding Requests for a limited number of - remote ufrags (this is the reason for the requirement that the JS not - be able to control the ufrag and password). + victim. [[ OPEN ISSUE: How do we address this? ]] + + [TODO: Should we have a mechanism for verifying total expected + bandwidth] Note that attacks based on confusing one end or the other about - consent are possible even in the face of the third-party identity - mechanism as long as major parts of the signaling messages are not - signed. On the other hand, signing the entire message severely - restricts the capabilities of the calling application, so there are - difficult tradeoffs here. + consent are possible primarily even in the face of the third-party + identity mechanism as long as major parts of the signaling messages + are not signed. On the other hand, signing the entire message + severely restricts the capabilities of the calling application, so + there are difficult tradeoffs here. 5.7.4. IdP Authentication Mechanism This mechanism relies for its security on the IdP and on the PeerConnection correctly enforcing the security invariants described above. At a high level, the IdP is attesting that the user identified in the assertion wishes to be associated with the assertion. Thus, it must not be possible for arbitrary third parties to get assertions tied to a user or to produce assertions that RPs will accept. -5.7.4.1. IdP Well-known URI +5.7.4.1. PeerConnection Origin Check - As described in Section 5.6.5.2.1 the IdP proxy HTML/JS landing page + Fundamentally, the IdP proxy is just a piece of HTML and JS loaded by + the browser, so nothing stops a Web attacker o from creating their + own IFRAME, loading the IdP proxy HTML/JS, and requesting a + signature. In order to prevent this attack, we require that all + signatures be tied to a specific origin ("rtcweb://...") which cannot + be produced by a page tied to a Web attacker. Thus, while an + attacker can instantiate the IdP proxy, they cannot send messages + from an appropriate origin and so cannot create acceptable + assertions. [[OPEN ISSUE: Where is this enforced? ]] + +5.7.4.2. IdP Well-known URI + + As described in Section 5.6.4.2.1 the IdP proxy HTML/JS landing page is located at a well-known URI based on the IdP's domain name. This requirement prevents an attacker who can write some resources at the IdP (e.g., on one's Facebook wall) from being able to impersonate the IdP. -5.7.4.2. Privacy of IdP-generated identities and the hosting site +5.7.4.3. Privacy of IdP-generated identities and the hosting site Depending on the structure of the IdP's assertions, the calling site may learn the user's identity from the perspective of the IdP. In many cases this is not an issue because the user is authenticating to the site via the IdP in any case, for instance when the user has logged in with Facebook Connect and is then authenticating their call with a Facebook identity. However, in other case, the user may not have already revealed their identity to the site. In general, IdPs SHOULD either verify that the user is willing to have their identity revealed to the site (e.g., through the usual IdP permissions dialog) or arrange that the identity information is only available to known RPs (e.g., social graph adjacencies) but not to the calling site. The "origin" field of the signature request can be used to check that the user has agreed to disclose their identity to the calling site; because it is supplied by the PeerConnection it can be trusted to be correct. -5.7.4.3. Security of Third-Party IdPs +5.7.4.4. Security of Third-Party IdPs As discussed above, each third-party IdP represents a new universal trust point and therefore the number of these IdPs needs to be quite limited. Most IdPs, even those which issue unqualified identities such as Facebook, can be recast as authoritative IdPs (e.g., 123456@facebook.com). However, in such cases, the user interface implications are not entirely desirable. One intermediate approach is to have special (potentially user configurable) UI for large authoritative IdPs, thus allowing the user to instantly grasp that the call is being authenticated by Facebook, Google, etc. -5.7.4.4. Web Security Feature Interactions +5.7.4.5. Web Security Feature Interactions A number of optional Web security features have the potential to cause issues for this mechanism, as discussed below. -5.7.4.4.1. Popup Blocking +5.7.4.5.1. Popup Blocking If the user is not already logged into the IdP, the IdP proxy may need to pop up a top level window in order to prompt the user for their authentication information (it is bad practice to do this in an IFRAME inside the window because then users have no way to determine the destination for their password). If the user's browser is configured to prevent popups, this may fail (depending on the exact algorithm that the popup blocker uses to suppress popups). It may be necessary to provide a standardized mechanism to allow the IdP proxy to request popping of a login window. Note that care must be taken here to avoid PeerConnection becoming a general escape hatch from popup blocking. One possibility would be to only allow popups when the user has explicitly registered a given IdP as one of theirs (this is only relevant at the AP side in any case). This is what WebIntents does, and the problem would go away if WebIntents is used. -5.7.4.4.2. Third Party Cookies +5.7.4.5.2. Third Party Cookies Some browsers allow users to block third party cookies (cookies associated with origins other than the top level page) for privacy reasons. Any IdP which uses cookies to persist logins will be broken by third-party cookie blocking. One option is to accept this as a limitation; another is to have the PeerConnection object disable third-party cookie blocking for the IdP proxy. 6. Acknowledgements Bernard Aboba, Harald Alvestrand, Dan Druta, Cullen Jennings, Hadriel - Kaplan, Matthew Kaufman, Jim McEachem, Martin Thomson, Magnus + Kaplan, Matthew Kaufman, Jim McEachern, Martin Thomson, Magnus Westerland. -7. Changes since -02 +7. Changes since -03 + + The following changes have been made since the -02 draft. + + o Editorial changes + +8. Changes since -02 The following changes have been made since the -02 draft. o Forbid persistent HTTP permissions. o Clarified the text in S 5.4 to clearly refer to requirements on the API to provide functionality to the site. o Fold in the IETF portion of draft-rescorla-rtcweb-generic-idp - o Retarget the continuing consent section to assume Binding Requests - o Editorial improvements - -8. References -8.1. Normative References +9. References +9.1. Normative References [I-D.ietf-rtcweb-security] Rescorla, E., "Security Considerations for RTC-Web", draft-ietf-rtcweb-security-03 (work in progress), June 2012. [I-D.muthu-behave-consent-freshness] Perumal, M., Wing, D., and H. Kaplan, "STUN Usage for Consent Freshness and Session Liveness", draft-muthu-behave-consent-freshness-01 (work in @@ -1387,21 +1393,21 @@ (SRTP) Security Context Using Datagram Transport Layer Security (DTLS)", RFC 5763, May 2010. [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer Security (DTLS) Extension to Establish Keys for the Secure Real-time Transport Protocol (SRTP)", RFC 5764, May 2010. [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, December 2011. -8.2. Informative References +9.2. Informative References [I-D.ietf-rtcweb-jsep] Uberti, J. and C. Jennings, "Javascript Session Establishment Protocol", draft-ietf-rtcweb-jsep-01 (work in progress), June 2012. [I-D.jennings-rtcweb-signaling] Jennings, C., Rosenberg, J., and R. Jesup, "RTCWeb Offer/ Answer Protocol (ROAP)", draft-jennings-rtcweb-signaling-01 (work in progress),