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Versions: (draft-thomson-rtcweb-consent) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 7675

RTCWEB                                                        M. Perumal
Internet-Draft                                                  Ericsson
Intended status: Standards Track                                 D. Wing
Expires: March 19, 2015                                  R. Ravindranath
                                                                T. Reddy
                                                           Cisco Systems
                                                              M. Thomson
                                                      September 15, 2014

                    STUN Usage for Consent Freshness


   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.

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.

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

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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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
     4.2.  Immediate Revocation of Consent . . . . . . . . . . . . .   5
   5.  Connection Liveness . . . . . . . . . . . . . . . . . . . . .   5
   6.  DiffServ Treatment for Consent packets  . . . . . . . . . . .   6
   7.  W3C API Implications  . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   7
   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
   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

   This document describes a new STUN usage with exchange of request and
   response messages to verify the remote peer's consent to receive

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   traffic, and the absence of which for a period of time indicates a
   loss of liveness.

   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.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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.

   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)
      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].

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.

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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:

   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.

      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.,

   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.

   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 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.

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   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).

   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.

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.

   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).

   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

   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).

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   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

6.  DiffServ Treatment for Consent packets

   It is RECOMMENDED that STUN consent checks use the same Diffserv
   Codepoint markings as the ICE connectivity checks described in
   section 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

   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 consent
       freshness has failed for a 5-tuple and the browser has stopped
       transmitting on that 5-tuple.

   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.

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,
   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

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   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 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

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

   [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

              McGrew, D. and D. Wing, "Encrypted Key Transport for
              Secure RTP", draft-ietf-avtcore-srtp-ekt-02 (work in
              progress), February 2014.

              Alvestrand, H., "Overview: Real Time Protocols for
              Browser-based Applications", draft-ietf-rtcweb-overview-11
              (work in progress), August 2014.

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              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

   [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.

   [RFC4953]  Touch, J., "Defending TCP Against Spoofing Attacks", RFC
              4953, July 2007.

   [RFC5961]  Ramaiah, A., Stewart, R., and M. Dalal, "Improving TCP's
              Robustness to Blind In-Window Attacks", RFC 5961, August

   [RFC6062]  Perreault, S. and J. Rosenberg, "Traversal Using Relays
              around NAT (TURN) Extensions for TCP Allocations", RFC
              6062, November 2010.

Authors' Addresses

   Muthu Arul Mozhi Perumal
   Ferns Icon
   Doddanekundi, Mahadevapura
   Bangalore, Karnataka  560037

   Email: muthu.arul@gmail.com

   Dan Wing
   Cisco Systems
   821 Alder Drive
   Milpitas, California  95035

   Email: dwing@cisco.com

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   Ram Mohan Ravindranath
   Cisco Systems
   Cessna Business Park
   Sarjapur-Marathahalli Outer Ring Road
   Bangalore, Karnataka  560103

   Email: rmohanr@cisco.com

   Tirumaleswar Reddy
   Cisco Systems
   Cessna Business Park, Varthur Hobli
   Sarjapur Marathalli Outer Ring Road
   Bangalore, Karnataka  560103

   Email: tireddy@cisco.com

   Martin Thomson
   Suite 300
   650 Castro Street
   Mountain View, California  94041

   Email: martin.thomson@gmail.com

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