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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: June 7, 2015                                    R. Ravindranath
                                                                T. Reddy
                                                           Cisco Systems
                                                              M. Thomson
                                                        December 4, 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 June 7, 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 . . . . . . . . . . . . . . . . . .   3
     4.2.  Immediate Revocation of Consent . . . . . . . . . . . . .   5
   5.  Connection Liveness . . . . . . . . . . . . . . . . . . . . .   6
   6.  DiffServ Treatment for Consent  . . . . . . . . . . . . . . .   6
   7.  API Recommendations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   7
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     11.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   To prevent attacks on peers, RTP 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 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

   This document defines what it takes to obtain, maintain, and lose
   consent to send.  Consent to send applies to a single 5-tuple.  How
   applications react to changes in consent is not described in this

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   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",
   document are to be interpreted as described in [RFC2119].

   Consent:  The mechanism of obtaining permission to send to a remote
      transport address.  Initial consent is obtained using ICE or a TCP

   Consent Freshness:  Maintaining and renewing consent over time.

   Session Liveness:  Detecting loss of connectivity to a certain
      transport address.

   Transport Address:  The remote peer's IP address and UDP or TCP port

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.

4.1.  Expiration of Consent

   A WebRTC implementation [I-D.ietf-rtcweb-overview], which implements
   full ICE, MUST perform a combined consent freshness and session
   liveness test using STUN request/response as described below:

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   An endpoint MUST NOT send data other than paced STUN connectivity
   checks or responses 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 maintained following the procedure described in this

   Explicit consent to send is obtained and maintained 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.

   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.,

   Initial consent to send traffic is obtained using ICE.  Consent
   expires after 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.

   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 and
   cryptographically strong [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, or that responses will be ordered, since there could be
   unreliable or unordered transports on the path.  Each STUN
   transaction ID is maintained until consent expires or a response is
   received for either this transaction or a more recent transaction.

   To meet the security needs of consent, an untrusted application
   (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.

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   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.

   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 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 data does not need to
   maintain consent.  However, failure to send could cause any NAT or
   firewall mappings for the flow to expire.  Furthermore, having one
   peer unable to send is detrimental to many protocols.

   After consent is lost for any reason, the same ICE credentials MUST
   NOT be used on the affected 5-tuple again.  That means that a new
   session, or an ICE restart, is needed to obtain consent to send.

4.2.  Immediate Revocation of Consent

   In some cases it is useful to signal that consent is terminated
   rather than relying on a timeout.

   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

   Note that an authenticated SRTCP BYE does not terminate consent; it
   only indicates the associated SRTP source has quit.

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5.  Connection Liveness

   Regular consent checks have the side effect of indicating liveness
   for the selected 5-tuple.  This allows for the timely detection of
   network faults.  A connection is considered "live" if authenticated
   messages are received from a remote endpoint within a given period.

   To support this use case, an application MAY be provided a means to
   request a notification when there are no authenticated messages
   received for a certain period.

   An application MAY also be provided a means to alter the basic
   consent check period from the default value (the suggested value
   being 5s) to any value up to 24 seconds.  This ensures that
   connectivity checks are not generated at an excessive rate and that
   at least one consent check is sent every 30 seconds, allowing for the
   maximal 1.2 times variation.  Note that increasing the consent check
   period increases the risk of packet loss causing consent expiration.

   Sending consent checks (heartbeats) at a high rate could allow a
   malicious application to generate congestion, so applications MUST
   NOT send consent checks at an average rate of more than 1 per second.

6.  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 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.  API Recommendations

   The W3C specification MAY provide the following API points to provide
   feedback and control over consent:

   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

   2.  Ability to set the consent check interval from its default
       (recommended: 5 seconds) to any value between 1 second and 24

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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
   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

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11.2.  Informative References

              Mattsson, J., McGrew, D., and D. Wing, "Encrypted Key
              Transport for Secure RTP", draft-ietf-avtcore-srtp-ekt-03
              (work in progress), October 2014.

              Alvestrand, H., "Overview: Real Time Protocols for
              Browser-based Applications", draft-ietf-rtcweb-overview-13
              (work in progress), November 2014.

              Dhesikan, S., Jennings, C., Druta, D., Jones, P., and J.
              Polk, "DSCP and other packet markings for RTCWeb QoS",
              draft-ietf-tsvwg-rtcweb-qos-03 (work in progress),
              November 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.

   [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.

   [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.

Authors' Addresses

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   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

   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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