--- 1/draft-ietf-rtcweb-stun-consent-freshness-01.txt 2014-04-10 21:14:16.344821429 -0700 +++ 2/draft-ietf-rtcweb-stun-consent-freshness-02.txt 2014-04-10 21:14:16.364821917 -0700 @@ -1,47 +1,48 @@ -RTCWEB Muthu. Perumal + +RTCWEB M. Perumal Internet-Draft D. Wing Intended status: Standards Track R. Ravindranath -Expires: September 25, 2014 T. Reddy +Expires: October 13, 2014 T. Reddy Cisco Systems - March 24, 2014 + M. Thomson + Mozilla + April 11, 2014 STUN Usage for Consent Freshness - draft-ietf-rtcweb-stun-consent-freshness-01 + draft-ietf-rtcweb-stun-consent-freshness-02 Abstract - Verification of peer consent before sending traffic is necessary in - WebRTC deployments to ensure that a malicious JavaScript cannot use - the browser as a platform for launching attacks. A related problem - is session liveness. WebRTC application may want to detect - connection failure and take appropriate action. + To prevent sending excessive traffic to an endpoint, periodic consent + needs to be obtained from that remote endpoint. - This document describes how a WebRTC browser can verify peer consent - to continue sending traffic and detect connection failure. + This document describes a consent mechanism using a new STUN usage. + This same mechanism can also determine connection loss ("liveness") + with a remote peer. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. 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 September 25, 2014. + This Internet-Draft will expire on October 13, 2014. Copyright Notice Copyright (c) 2014 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 @@ -50,206 +51,251 @@ include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Design Considerations . . . . . . . . . . . . . . . . . . . . 3 4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 3 - 5. W3C API Implications . . . . . . . . . . . . . . . . . . . . 5 - 6. Interaction with Keepalives used for Refreshing NAT Bindings 5 - 7. Security Considerations . . . . . . . . . . . . . . . . . . . 5 - 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 - 9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 5 - 10. Normative References . . . . . . . . . . . . . . . . . . . . 5 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 + 5. Connection Liveness . . . . . . . . . . . . . . . . . . . . . 4 + 6. DiffServ Treatment for Consent packets . . . . . . . . . . . 5 + 7. W3C API Implications . . . . . . . . . . . . . . . . . . . . 5 + 8. Security Considerations . . . . . . . . . . . . . . . . . . . 5 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 + 10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 6 + 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 + 11.1. Normative References . . . . . . . . . . . . . . . . . . 6 + 11.2. Informative References . . . . . . . . . . . . . . . . . 6 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction - To prevent attacks on WebRTC peers, WebRTC browsers have to ensure - the remote peer wants to receive traffic. This is performed both - when the session is first established to the remote peer (using ICE - connectivity checks), and periodically for the duration of the - session (using the procedure defined in this document). + To prevent attacks on peers, RTP endpoints have to ensure the remote + peer wants to receive traffic. This is performed both when the + session is first established to the remote peer using ICE + connectivity checks, and periodically for the duration of the session + using the procedures defined in this document. When a session is first established, WebRTC implementations are required to perform STUN connectivity checks as part of ICE [RFC5245]. That initial consent is not described further in this - document. + document and it is assumed that ICE is being used for that initial + consent. - Related to consent is loss of connectivity ("liveness"). WebRTC - applications want notification of connection failure to take - appropriate actions (e.g., alert the user, try switching to a - different interface). + Related to consent is loss of connectivity ("liveness"). Many + applications want notification of connection loss to take appropriate + actions (e.g., alert the user, try switching to a different + interface). This document describes a new STUN usage with a request and response - which verifies the remote peer consents to receive traffic, and - detects loss of liveness. To meet the security needs of consent, the - JavaScript application has no control over the consent requests or - the requirement to receive a consent response. However, the - JavaScript does get notification of consent failure and loss of - connectivity. + messages which verifies the remote peer's consent to receive traffic, + and can also detect loss of liveness. 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. - Consent: It is the mechanism of obtaining permission from the peer - to send traffic on a candidate pair. + Consent: It is the mechanism of obtaining permission to send traffic + to a certain transport address. This is usually obtained via ICE. - Consent Freshness: It is the mechanism of obtaining permission from - the peer to continue sending traffic on a nominated candidate pair - after ICE has concluded. + Consent Freshness: Permission to continue sending traffic to a + certain transport address. This is performed by the procedure + described in this document. - Session Liveness: It is the mechanism of detecting connectivity on a - nominated candidate pair after ICE has concluded. + Session Liveness: Detecting loss of connectivity to a certain + transport address. This is performed by the procedure described + in this document. - Transport Address: The combination of an IP address and port number - (such as a UDP or TCP port number). + Transport Address: The remote peer's IP address and (UDP or TCP) + port number. 3. Design Considerations - Although ICE requires periodic keepalive traffic to be sent in order - to keep NAT bindings alive (Section 10 of [RFC5245], [RFC6263]), - those keepalives are send-and-forget, and do not evoke a response. A - response is necessary both for consent to continue sending traffic, - as well as to ensure connectivity. Thus, we need a request/response - mechanism. + Although ICE requires periodic keepalive traffic to keep NAT bindings + alive (Section 10 of [RFC5245], [RFC6263]), those keepalives are sent + as STUN Indications which are send-and-forget, and do not evoke a + response. A response is necessary both for consent to continue + sending traffic, as well as to verify session liveness. Thus, we + need a request/response mechanism for consent freshness. ICE can be + used for that mechanism because ICE already requires ICE agents + continue listening for ICE messages, as described in section 10 of + [RFC5245]. - Though ICE specifies STUN Binding indications to be used for - keepalives, it requires that an agent be prepared to receive - connectivity check as well. If a connectivity check is received, a - response is generated and there is no impact on ICE processing, as - described in section 10 of [RFC5245]. +4. Solution Overview - The above considerations suggest that STUN Binding request/response - is most suitable for performing consent freshness. + A WebRTC browser performs a combined consent freshness and session + liveness test using STUN request/response as described below: -4. Solution Overview + An endpoint MUST NOT send application data (in WebRTC this means RTP + or SCTP data) on an ICE-initiated connection unless the receiving + endpoint consents to receive the data. After a successful ICE + connectivity check on a particular transport address, subsequent + consent MUST be obtained following the procedure described in this + document. The consent expires after a fixed amount of time. + Explicit consent to send is indicated by: - Consent freshness serves as a circuit breaker (so that if the path or - remote peer fails the WebRTC browser stops sending all traffic on - that remote peer), determining session liveness serves the purpose of - notifying the application of connectivity failure so that the - application can take appropriate action. + 1. Sending an ICE binding request to the remote peer's Transport + Address and receiving a matching and authenticated ICE binding + response from the inverted remote peer's Transport Address. - The solution uses three values: + These ICE binding request/response are authenticated using the + same short- term credentials as the initial ICE exchange, but + using a new (fresh) transaction-id each time consent needs to be + refresh. Implementations MUST obtain fresh consent before their + existing consent expires. When obtaining fresh consent a STUN + connectivity check (or response) could be lost, and re- + transmissions MUST use the same STUN transaction-id, and re- + transmissions MUST NOT be sent more frequently than every 500ms + or the smoothed round-trip time (from previous consent freshness + checks or RTP round-trip time), whichever is less. For the + purposes of this document, receipt of an ICE response with the + matching transaction-id of its request with a valid MESSAGE- + INTEGRITY is considered an authenticated packet. - 1. A consent timer, Tc, whose value is determined by the browser. - This value MUST be 15 seconds. + Consent expires after 15 seconds. That is, if an authenticated + packet (e.g., DTLS, SRTP, ICE) has not been received from the + inverted 5-tuple after 15 seconds, the application MUST cease + transmission on that 5-tuple. - 2. A packet receipt timer, Tr, whose value is determined by the - application, but MUST NOT be shorter than 1 second or longer than - 15 seconds, and SHOULD have a default value of 5 seconds. + Consent is ended immediately by receipt of a an authenticated message + that closes the connection (for instance, a TLS fatal alert). - 3. A consent timeout, Tf, which is how many seconds elapse without a - consent response before the browser ceases transmission of media. - Its value MUST be 15 seconds or less, and the value 15 seconds is - RECOMMENDED. + Receipt of an unauthenticated end-of-session message (e.g., TCP FIN) + does not indicate loss of consent. Thus, an endpoint receiving an + unauthenticated end-of-session message SHOULD continue sending media + (over connectionless transport) or attempt to re-establish the + connection (over connection-oriented transport) until consent expires + or it receives an authenticated message revoking consent. - A WebRTC browser performs a combined consent freshness and session - liveness test using STUN request/response as described below: + Although receiving authenticated packets is sufficient for consent, + it is still RECOMMENDED to send messages to keep NAT or firewall + bindings alive (see Section 10 of [RFC5245] and [RFC6263]). - Every Tc seconds, the WebRTC browser sends a STUN Binding Request to - the peer. This request MUST use a new, cryptographically random - Transaction ID [RFC4086], and is formatted as for an ICE connectivity - check [RFC5245]. A valid STUN Binding Response is also formatted as - for an ICE connectivity check [RFC5245]. The STUN Binding Request - and STUN Binding Response are validated as for an ICE connectivity - check [RFC5245]. The difference from ICE connectivity check is that - there is no exponential back off for retransmissions. + To meet the security needs of consent, an implementation MUST ensure + that an application (e.g., Javascript application) is not able to + obtain or control STUN information relevant to consent, specifically + the ICE transaction-id MUST NOT be accessible to upper-level + applications. - If a valid STUN Binding Response is received, the consent timer is - reset and fires again Tc seconds later. +5. Connection Liveness - If a valid STUN Binding Response is not received after 500ms, the - STUN Binding Request is retransmitted (with the same Transaction ID - and all other fields). As long as a valid STUN Binding Response is - not received, this retransmission is repeated every 500ms until Tf - seconds have elapsed or a valid response is received. If no valid - response is received after Tf seconds, the WebRTC browser MUST quit - transmitting traffic to this remote peer. Considering the default - value of Tf=15 seconds, this means transmission will stop after 30 - consent check packets have resulted in no response. + A connection is considered "live" if packets are received from a + remote endpoint within an application-dependent period. An + application can request a notification when there are no packets + received for a certain period (configurable). - Liveness timer: If no packets have been received on the local port in - Tr seconds, the WebRTC browser MUST inform the JavaScript that - connectivity has been lost. The JavaScript application will use this - notification however it desires (e.g., cease transmitting to the - remote peer, provide a notification to the user, etc.). Note the - definition of a received packet is liberal, and includes an SRTP - packet that fails authentication, a STUN Binding Request with an - invalid USERNAME or PASSWORD, or any other packet. + Similarly, if packets haven't been received within a certain period, + an application can request a consent check (heartbeat) be generated. -5. W3C API Implications + These two time intervals might be controlled by the same + configuration item. + + Sending consent checks (heartbeats) at a high rate could allow a + malicious application to generate congestion, so applications MUST + NOT be able to send heartbeats faster than 1 per second. + +6. DiffServ Treatment for Consent packets + + It is RECOMMENDED that STUN consent checks use the same Diffserv + Codepoint markings as the media packets sent on that transport + address. This follows the recommendation of ICE connectivity check + described in section 7.1.2.4 of [RFC5245]. + + Note: It is possible that different Diffserv Codepoints are used by + different media over the same transport address + [I-D.ietf-tsvwg-rtcweb-qos]. In that case, what should this document + recommend as the Codepoint for STUN consent packets ? + +7. W3C API Implications For the consent freshness and liveness test the W3C specification should provide APIs as described below: 1. Ability for the browser to notify the JavaScript that a consent freshness transaction has failed for a media stream and the browser has stopped transmitting for that stream. 2. Ability for the JavaScript to start and stop liveness test and set the liveness test interval. 3. Ability for the browser to notify the JavaScript that a liveness test has failed for a media stream. -6. Interaction with Keepalives used for Refreshing NAT Bindings - - When not actively sending traffic on a nominated candidate pair, - performing consent freshness does not serve any purpose from a - security perspective. If consent freshness is not performed during - this period, the browser continues to performs the ICE keepalives - [RFC5245] or RTP keepalive [RFC6263] to refresh NAT bindings. +8. Security Considerations -7. Security Considerations + This document describes a security mechanism. - Security considerations discussed in [RFC5245] are to be taken into - account. + The security considerations discussed in [RFC5245] should also be + taken into account. - The browser MUST use short-term credential to authenticate the STUN - messages used for Consent freshness, session liveness and perform - message integrity check on STUN binding request/response. + SRTP is encrypted and authenticated with symmetric keys; that is, + both sender and receiver know the keys. With two party sessions, + receipt of an authenticated packet from the single remote party is a + strong assurance the packet came from that party. However, when a + session involves more than two parties, all of whom know each others + keys, any of those parties could have sent (or spoofed) the packet. + Such shared key distributions are possible with some MIKEY [RFC3830] + modes, Security Descriptions [RFC4568], and EKT + [I-D.ietf-avtcore-srtp-ekt]. Thus, in such shared keying + distributions, receipt of an authenticated SRTP packet is not + sufficient. -8. IANA Considerations +9. IANA Considerations This document does not require any action from IANA. -9. Acknowledgement +10. Acknowledgement - Thanks to Eric Rescorla, Harald Alvestrand, Martin Thomson, Bernard - Aboba, Cullen Jennings and Simon Perreault for their valuable inputs - and comments. + Thanks to Eric Rescorla, Harald Alvestrand, Bernard Aboba, Magnus + Westerland, Cullen Jennings and Simon Perreault for their valuable + inputs and comments. -10. Normative References +11. References + +11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. - [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness - Requirements for Security", BCP 106, RFC 4086, June 2005. - [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols", RFC 5245, April 2010. [RFC6263] Marjou, X. and A. Sollaud, "Application Mechanism for Keeping Alive the NAT Mappings Associated with RTP / RTP Control Protocol (RTCP) Flows", RFC 6263, June 2011. +11.2. Informative References + + [I-D.ietf-avtcore-srtp-ekt] + McGrew, D. and D. Wing, "Encrypted Key Transport for + Secure RTP", draft-ietf-avtcore-srtp-ekt-02 (work in + progress), February 2014. + + [I-D.ietf-tsvwg-rtcweb-qos] + Dhesikan, S., Druta, D., Jones, P., and J. Polk, "DSCP and + other packet markings for RTCWeb QoS", draft-ietf-tsvwg- + rtcweb-qos-00 (work in progress), April 2014. + + [RFC3830] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K. + Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830, + August 2004. + + [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session + Description Protocol (SDP) Security Descriptions for Media + Streams", RFC 4568, July 2006. + Authors' Addresses Muthu Arul Mozhi Perumal Cisco Systems Cessna Business Park Sarjapur-Marathahalli Outer Ring Road Bangalore, Karnataka 560103 India Email: mperumal@cisco.com @@ -263,18 +309,27 @@ Email: dwing@cisco.com Ram Mohan Ravindranath Cisco Systems Cessna Business Park Sarjapur-Marathahalli Outer Ring Road Bangalore, Karnataka 560103 India Email: rmohanr@cisco.com + Tirumaleswar Reddy Cisco Systems Cessna Business Park, Varthur Hobli Sarjapur Marathalli Outer Ring Road Bangalore, Karnataka 560103 India Email: tireddy@cisco.com + Martin Thomson + Mozilla + Suite 300 + 650 Castro Street + Mountain View, California 94041 + US + + Email: martin.thomson@gmail.com