--- 1/draft-ietf-rtcweb-stun-consent-freshness-02.txt 2014-05-19 02:14:28.300502875 -0700 +++ 2/draft-ietf-rtcweb-stun-consent-freshness-03.txt 2014-05-19 02:14:28.320503350 -0700 @@ -1,22 +1,22 @@ RTCWEB M. Perumal Internet-Draft D. Wing Intended status: Standards Track R. Ravindranath -Expires: October 13, 2014 T. Reddy +Expires: November 20, 2014 T. Reddy Cisco Systems M. Thomson Mozilla - April 11, 2014 + May 19, 2014 STUN Usage for Consent Freshness - draft-ietf-rtcweb-stun-consent-freshness-02 + draft-ietf-rtcweb-stun-consent-freshness-03 Abstract To prevent sending excessive traffic to an endpoint, periodic consent needs to be obtained from that remote endpoint. This document describes a consent mechanism using a new STUN usage. This same mechanism can also determine connection loss ("liveness") with a remote peer. @@ -28,21 +28,21 @@ 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 October 13, 2014. + This Internet-Draft will expire on November 20, 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 @@ -51,30 +51,33 @@ 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. Connection Liveness . . . . . . . . . . . . . . . . . . . . . 4 + 4.1. Expiration of Consent . . . . . . . . . . . . . . . . . . 3 + 4.2. Immediate Revocation of Consent . . . . . . . . . . . . . 4 + 5. Connection Liveness . . . . . . . . . . . . . . . . . . . . . 5 6. DiffServ Treatment for Consent packets . . . . . . . . . . . 5 7. W3C API Implications . . . . . . . . . . . . . . . . . . . . 5 - 8. Security Considerations . . . . . . . . . . . . . . . . . . . 5 + 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 6 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 11.1. Normative References . . . . . . . . . . . . . . . . . . 6 - 11.2. Informative References . . . . . . . . . . . . . . . . . 6 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 + 11.2. Informative References . . . . . . . . . . . . . . . . . 7 + Appendix A. Example Implementation . . . . . . . . . . . . . . . 7 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction 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 @@ -92,21 +95,22 @@ 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 to send traffic - to a certain transport address. This is usually obtained via ICE. + to a certain transport address. This is the initial consent to + send traffic, which is obtained by ICE or a TCP handshake. Consent Freshness: Permission to continue sending traffic to a certain transport address. This is performed by the procedure described in this document. Session Liveness: Detecting loss of connectivity to a certain transport address. This is performed by the procedure described in this document. Transport Address: The remote peer's IP address and (UDP or TCP) @@ -119,73 +123,91 @@ 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]. 4. Solution Overview + There are two ways consent to send traffic is revoked: expiration of + consent and immediate revocation of consent, which are discussed in + the following sections. + +4.1. Expiration of Consent + A WebRTC browser performs a combined consent freshness and session liveness test using STUN request/response as described below: - 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: - - 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. + An endpoint MUST NOT send application data (e.g., RTP, RTCP, SCTP, + DTLS) 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. - 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 + Explicit consent to send is indicated by 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. These ICE binding requests and + responses 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 refreshed. Implementations MUST obtain + fresh consent before their existing consent expires. If an ICE + binding response is not received within 1.5 times the previous round + trip time, another ICE binding request is sent using the a new + (fresh) transaction-id (so that round-trip time can be calculated), + 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. + matching transaction-id of its request with a valid MESSAGE-INTEGRITY + is considered a consent response. - 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. + The initial Consent to send traffic is obtained by ICE. Consent + expires after 30 seconds. That is, if a valid STUN binding response + corresponding to one of the STUN requests sent in the last 30 seconds + has not been received from the inverted 5-tuple, the endpoint MUST + cease transmission on that 5-tuple. - Consent is ended immediately by receipt of a an authenticated message - that closes the connection (for instance, a TLS fatal alert). + To meet the security needs of consent, an untrusted application + (e.g., JavaScript) MUST NOT be able to obtain or control the ICE + transaction-id, because that enables spoofing STUN responses, + falsifying consent - 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. + An endpoint that is only receiving application traffic (recvonly) + does not need to obtain consent which can slightly conserve its + resources. However, the endpoint needs to ensure its NAT or firewall + mappings persist which can be done using keepalive or other + techniques (see Section 10 of [RFC5245] and see [RFC6263]). If the + endpoint wants send application traffic, it needs to first obtain + consent if its consent expired. - 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]). +4.2. Immediate Revocation of Consent - 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. + The previous section explained how consent expires due to a timeout. + In some cases it is useful to signal a connection is terminated, + rather than relying on a timeout. This is done by immediately + revoking consent. + + Consent for sending traffic on the media or data channel is revoked + by receipt of a an authenticated message that closes the connection + (for instance, a TLS fatal alert). + + Receipt of an unauthenticated message that closes a connection (e.g., + TCP FIN) does not indicate revocation 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. 5. Connection Liveness 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). Similarly, if packets haven't been received within a certain period, an application can request a consent check (heartbeat) be generated. @@ -282,20 +303,66 @@ 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. +Appendix A. Example Implementation + + This section describes one possible implementation algorithm of + consent. This section is non-normative and provided for reference + only. + + The solution uses three values: + + 1. A consent timer, Tc, whose value is set to 30 seconds. + + 2. A packet receipt timer, Tr, whose value is determined by the + application. Tr can be greater than 1 but less than 30 seconds + and has a default value of 5 seconds. + + 3. A consent timeout, Tf, which is how many seconds elapse without a + consent response before the browser ceases transmission of media. + Its value is be 30 seconds or less. + + 4. A retransmission Timer, Tret, whose value is determined by the + RTT of a given path. The duration of this timer is set to 1.5 + times of (500 ms or the smoothened round-trip time (from previous + consent freshness checks or RTP round-trip time)), whichever is + less. + + A WebRTC browser performs a combined consent freshness and session + liveness test using STUN request/response as described below: + + Every Tc seconds, the WebRTC browser sends a STUN Binding Request to + the peer. The difference from ICE connectivity check is that there + is no exponential back off for retransmissions. + + If a valid STUN Binding Response is received, the consent timer is + reset to the time of receiving the response and fires again Tc + seconds later. + + If a valid STUN Binding Response is not received after Tret + milliseconds, the STUN Binding Request is retransmitted (with a new + Transaction ID). As long as a valid STUN Binding Response is not + received, this retransmission is repeated every Tret milliseconds + until Tf seconds have elapsed or a valid response is received. If no + valid response is received after Tf seconds, the WebRTC browser quits + transmitting traffic to this remote peer. The streams that are being + sent on a flow(5-tuple) for which a consent has failed will be + stopped. If the default value of Tf is 30 seconds then media + transmission will stop Consent (Tf) expires. + Authors' Addresses Muthu Arul Mozhi Perumal Cisco Systems Cessna Business Park Sarjapur-Marathahalli Outer Ring Road Bangalore, Karnataka 560103 India Email: mperumal@cisco.com