--- 1/draft-ietf-rtcweb-stun-consent-freshness-07.txt 2014-10-27 10:14:52.272874971 -0700 +++ 2/draft-ietf-rtcweb-stun-consent-freshness-08.txt 2014-10-27 10:14:52.292875453 -0700 @@ -1,49 +1,48 @@ RTCWEB M. Perumal Internet-Draft Ericsson Intended status: Standards Track D. Wing -Expires: March 19, 2015 R. Ravindranath +Expires: April 30, 2015 R. Ravindranath T. Reddy Cisco Systems M. Thomson Mozilla - September 15, 2014 + October 27, 2014 STUN Usage for Consent Freshness - draft-ietf-rtcweb-stun-consent-freshness-07 + draft-ietf-rtcweb-stun-consent-freshness-08 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 Session - Traversal Utilities for NAT (STUN) usage. This same mechanism can - also determine connection loss ("liveness") with a remote peer. + Traversal Utilities for NAT (STUN) usage. 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 March 19, 2015. + This Internet-Draft will expire on April 30, 2015. 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 @@ -52,233 +51,216 @@ 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 . . . . . . . . . . . . . . . . . . . . . . . . . . 3 - 4.1. Expiration of Consent . . . . . . . . . . . . . . . . . . 4 + 4.1. Expiration of Consent . . . . . . . . . . . . . . . . . . 3 4.2. Immediate Revocation of Consent . . . . . . . . . . . . . 5 - 5. Connection Liveness . . . . . . . . . . . . . . . . . . . . . 5 - 6. DiffServ Treatment for Consent packets . . . . . . . . . . . 6 - 7. W3C API Implications . . . . . . . . . . . . . . . . . . . . 6 + 5. DiffServ Treatment for Consent . . . . . . . . . . . . . . . 5 + 6. DTLS applicability . . . . . . . . . . . . . . . . . . . . . 6 + 7. API Recommendations . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6 - 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 - 10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 7 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 + 10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 6 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 11.1. Normative References . . . . . . . . . . . . . . . . . . 7 11.2. Informative References . . . . . . . . . . . . . . . . . 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 + To prevent attacks on peers, endpoints have to ensure the remote peer + is willing to receive traffic. This is performed both when the session is first established to the remote peer using Interactive Connectivity Establishment ICE [RFC5245] connectivity checks, and periodically for the duration of the session using the procedures defined in this document. - When a session is first established, ICE implementations obtain - initial consent by performing STUN connectivity checks as part of - ICE. That initial consent is not described further in this document - and it is assumed that ICE is being used for that initial consent. - - 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 exchange of request and - response messages to verify the remote peer's consent to receive - traffic, and the absence of which for a period of time indicates a - loss of liveness. + When a session is first established, ICE implementations obtain an + initial consent to send by performing STUN connectivity checks. This + document describes a new STUN usage with exchange of request and + response messages that verifies the remote peer's ongoing consent to + receive traffic. This consent expires after a period of time and + needs to be continually renewed, which ensures that consent can be + terminated. - When a (full) ICE implementation interworks with an ICE-lite - implementation the ICE-lite implementation will not generate consent - checks, but will just just respond to consent checks it receives. + This applies to full ICE implementations. An ICE-lite implementation + will not generate consent checks, but will just respond to consent + checks it receives. ICE-lite implementation do not require any + changes to respond to consent checks. 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 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. + Consent: The mechanism of obtaining permission to send to a remote + transport address. Initial consent is obtained using ICE or a TCP + handshake. - Session Liveness: Detecting loss of connectivity to a certain - transport address. This is performed by the procedure described - in this document. + Consent Freshness: Maintaining and renewing consent over time. - Transport Address: The remote peer's IP address and (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 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 implementations are already - required to continue listening for ICE messages, as described in - section 10 of [RFC5245]. + response. A response is necessary for consent to continue sending + traffic. Thus, we need a request/response mechanism for consent + freshness. ICE can be used for that mechanism because ICE + implementations are already required to continue listening for ICE + messages, as described in section 10 of [RFC5245]. 4. Solution 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 implementation [I-D.ietf-rtcweb-overview], which implements - ICE, MUST perform a combined consent freshness and session liveness - test using STUN request/response as described below: + full ICE, performs consent freshness test using STUN request/response + as described below: - An endpoint MUST NOT send application data (e.g., RTP, RTCP, SCTP, - DTLS), over any transport protocol (e.g., UDP, TCP) 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. During ICE restart consent - checks MUST continue to be sent on previously validated pair, and - MUST be responded to on the previously validated pair, until ICE - restart completes. + An endpoint MUST NOT send paced STUN connectivity checks toward any + transport address unless the receiving endpoint consents to receive + data. That is, no application data (e.g., RTP or DTLS) can be sent + until consent is obtained. After a successful ICE connectivity check + on a particular transport address, consent MUST be obtained following + the procedure described in this document. + + Explicit consent to send is obtained by sending an STUN binding + request to the remote peer's transport address and receiving a + matching, authenticated, non-error STUN binding response from the + remote peer's transport address. These STUN binding requests and + responses are authenticated using the same short-term credentials as + the initial ICE exchange. Note: Although TCP has its own consent mechanism (TCP acknowledgements), consent is necessary over a TCP connection because it could be translated to a UDP connection (e.g., [RFC6062]). - Explicit consent to send is obtained by sending an ICE binding - request to the remote peer's Transport Address and receiving a - matching, authenticated, non-error ICE binding response from the - remote peer's Transport Address. These ICE binding requests and - responses are authenticated using the same short-term credentials as - the initial ICE exchange. Implementations MUST cease sending data if - their consent expires. To prevent expiry of consent, a STUN binding - request MUST be sent every N milliseconds, where N is chosen randomly - with each consent check in the interval [.8N, 1.2N] (to prevent - network synchronization), where N SHOULD be 5000. Using the value - 5000 milliseconds and that 20% randomization range, N would be a - value between 4000 and 6000. These STUN binding requests for consent - are not re-transmitted. Each STUN binding request for consent re- - calculates a new random value N and a new cryptographically-random - [RFC4086] STUN transaction ID. + Initial consent is granted as a result of a successful ICE + connectivity check on a particular transport address, and expires 30 + seconds after an ICE candidate par has been selected. Once an ICE + candidate pair has been selected, consent for the ICE candidate pairs + lasts for 30 seconds. That is, if a valid STUN binding response + corresponding to any STUN request sent in the last 30 seconds has not + been received from the remote peer's transport address, the endpoint + MUST cease transmission on that 5-tuple. STUN consent responses + received after consent expiry do not re-establish consent, and may be + discarded or cause an ICMP error. - 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 remote peer's Transport Address, the - endpoint MUST cease transmission on that 5-tuple. + To prevent expiry of consent, a STUN binding request can be sent + periodically. To prevent synchronization of consent checks, each + interval MUST be randomized from between 0.8 and 1.2 times the basic + period. Implementations SHOULD set a default interval of 5 seconds, + resulting in a period between checks of 4 to 6 seconds. + + Each STUN binding request for consent MUST use a new + cryptographically-random [RFC4086] STUN transaction ID. Each STUN + binding requests for consent is transmitted once only. Hence, the + sender cannot assume that it will receive a response for each consent + request, and a response might be for a previous request (rather than + for the most recently sent request). Consent expiration causes + immediate termination of all outstanding STUN consent transactions. + Each STUN transaction is maintained until one of the following + criteria is fulfilled: + + o A STUN response associated with the transaction is received; or + + o A STUN response associated to a newer transaction is received. To meet the security needs of consent, an untrusted application - (e.g., JavaScript) MUST NOT be able to obtain or control the STUN - transaction ID, because that enables spoofing STUN responses, - falsifying consent. + (e.g., JavaScript or signaling servers) MUST NOT be able to obtain or + control the STUN transaction ID, because that enables spoofing of + STUN responses, falsifying consent. + + To prevent attacks on the peer during ICE restart, an endpoint that + continues to send traffic on the previously validated candidate pair + during ICE restart MUST continue to perform consent freshness on that + candidate pair as described earlier. While TCP affords some protection from off-path attackers ([RFC5961], [RFC4953]), there is still a risk an attacker could cause a TCP - sender to send packets forever by spoofing ACKs. To prevent such an - attack, consent checks MUST be performed over all transport - connections, including TCP. In this way, an off-path attacker - spoofing TCP segments can not cause a TCP sender to send packets - longer than the consent timer (30 seconds). + sender to send forever by spoofing ACKs. To prevent such an attack, + consent checks MUST be performed over all transport connections, + including TCP. In this way, an off-path attacker spoofing TCP + segments can not cause a TCP sender to send once the consent timer + expires (30 seconds). - An endpoint that is not sending any application traffic 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 to - send application traffic, it needs to first obtain consent if its - consent has expired. + An endpoint that is not sending any application data does not need to + maintain consent. 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 to send application data, it needs to first obtain + consent if its consent has expired. 4.2. Immediate Revocation of Consent - 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. + In some cases it is useful to signal that consent is terminated + rather than relying on a timeout. - Consent for sending traffic on the media or data channel is - immediately revoked by receipt of an authenticated message that - closes the connection (e.g., a TLS fatal alert) or receipt of a valid - and authenticated STUN response with error code Forbidden (403). - Those consent revocation messages can be lost on the network, so an - implementation wanting to immediately revoke consent needs to - remember those credentials until consent expiry (30 seconds). + Consent for sending application data is immediately revoked by + receipt of an authenticated message that closes the connection (e.g., + a TLS fatal alert) or receipt of a valid and authenticated STUN + response with error code Forbidden (403). Note however that consent + revocation messages can be lost on the network, so an endpoint could + resend these messages, or wait for consent to expire. 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. Note that an authenticated SRTCP BYE does not terminate consent; it only indicates the associated SRTP source has quit. -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. - 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 at an average rate of more than 1 per - second. - -6. DiffServ Treatment for Consent packets +5. DiffServ Treatment for Consent It is RECOMMENDED that STUN consent checks use the same Diffserv Codepoint markings as the ICE connectivity checks described in - section 7.1.2.4 of [RFC5245] for a given 5-tuple. + Section 7.1.2.4 of [RFC5245] for a given 5-tuple. Note: It is possible that different Diffserv Codepoints are used by different media over the same transport address [I-D.ietf-tsvwg-rtcweb-qos]. Such a case is outside the scope of this document. -7. W3C API Implications +6. DTLS applicability - For the consent freshness and liveness test the W3C specification - should provide APIs as described below: + The DTLS applicability is identical to what is described in + Section 4.2 of [RFC7350]. - 1. Ability for the browser to notify the JavaScript that consent - freshness has failed for a 5-tuple and the browser has stopped - transmitting on that 5-tuple. +7. API Recommendations - 2. Ability for the JavaScript to start and stop liveness test and - set the liveness test interval. + The W3C specification MAY provide the following API to provide + feedback and control over consent: - 3. Ability for the browser to notify the JavaScript that a liveness - test has failed for a media stream. + 1. Generate an event when consent has expired for a given 5-tuple, + meaning that transmission of data has ceased. This could + indicate what application data is affected, such as media or data + channels. 8. Security Considerations This document describes a security mechanism. The security considerations discussed in [RFC5245] should also be taken into account. SRTP is encrypted and authenticated with symmetric keys; that is, both sender and receiver know the keys. With two party sessions, @@ -293,22 +275,23 @@ sufficient to verify consent. 9. IANA Considerations This document does not require any action from IANA. 10. Acknowledgement Thanks to Eric Rescorla, Harald Alvestrand, Bernard Aboba, Magnus Westerland, Cullen Jennings, Christer Holmberg, Simon Perreault, Paul - Kyzivat, Emil Ivov, and Jonathan Lennox for their valuable inputs and - comments. + Kyzivat, Emil Ivov, Jonathan Lennox, Inaki Baz Castillo, Rajmohan + Banavi and Christian Groves for their valuable inputs and comments. + Thanks to Christer Holmberg for doing a through review. 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. @@ -318,28 +301,28 @@ 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. + Mattsson, J., McGrew, D., and D. Wing, "Encrypted Key + Transport for Secure RTP", draft-ietf-avtcore-srtp-ekt-03 + (work in progress), October 2014. [I-D.ietf-rtcweb-overview] Alvestrand, H., "Overview: Real Time Protocols for - Browser-based Applications", draft-ietf-rtcweb-overview-11 - (work in progress), August 2014. + Browser-based Applications", draft-ietf-rtcweb-overview-12 + (work in progress), October 2014. [I-D.ietf-tsvwg-rtcweb-qos] Dhesikan, S., Jennings, C., Druta, D., Jones, P., and J. Polk, "DSCP and other packet markings for RTCWeb QoS", draft-ietf-tsvwg-rtcweb-qos-02 (work in progress), June 2014. [RFC3830] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K. Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830, August 2004. @@ -352,20 +335,24 @@ 4953, July 2007. [RFC5961] Ramaiah, A., Stewart, R., and M. Dalal, "Improving TCP's Robustness to Blind In-Window Attacks", RFC 5961, August 2010. [RFC6062] Perreault, S. and J. Rosenberg, "Traversal Using Relays around NAT (TURN) Extensions for TCP Allocations", RFC 6062, November 2010. + [RFC7350] Petit-Huguenin, M. and G. Salgueiro, "Datagram Transport + Layer Security (DTLS) as Transport for Session Traversal + Utilities for NAT (STUN)", RFC 7350, August 2014. + Authors' Addresses Muthu Arul Mozhi Perumal Ericsson Ferns Icon Doddanekundi, Mahadevapura Bangalore, Karnataka 560037 India Email: muthu.arul@gmail.com