RTCWEB                                                        M. Perumal
Internet-Draft                                                  Ericsson
Intended status: Standards Track                                 D. Wing
Expires: March 19, April 30, 2015                                  R. Ravindranath
                                                                T. Reddy
                                                           Cisco Systems
                                                              M. Thomson
                                                      September 15,
                                                        October 27, 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

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   provisions of BCP 78 and BCP 79.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Design Considerations . . . . . . . . . . . . . . . . . . . .   3
   4.  Solution  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Expiration of Consent . . . . . . . . . . . . . . . . . .   4   3
     4.2.  Immediate Revocation of Consent . . . . . . . . . . . . .   5
   5.  Connection Liveness  DiffServ Treatment for Consent  . . . . . . . . . . . . . . .   5
   6.  DTLS applicability  . . . . . . . . . .   5
   6.  DiffServ Treatment for Consent packets . . . . . . . . . . .   6
   7.  W3C  API Implications Recommendations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7   6
   10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   7   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
   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 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). checks.  This
   document describes a new STUN usage with exchange of request and
   response messages to verify that verifies the remote peer's ongoing consent to
   traffic, and the absence of which for traffic.  This consent expires after a period of time indicates a
   loss of liveness.

   When a (full) and
   needs to be continually renewed, which ensures that consent can be

   This applies to full ICE implementation interworks with an ICE-lite
   implementation the implementations.  An ICE-lite implementation
   will not generate consent checks, but will just 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:  It is the  The mechanism of obtaining permission to send traffic to a certain remote
      transport address.  This is the initial  Initial consent to
      send traffic, which is obtained by using ICE or a TCP

   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.  Maintaining and renewing consent over time.

   Transport Address:  The remote peer's IP address and (UDP UDP or TCP) 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.
   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
   full ICE, MUST perform a combined performs 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 paced STUN connectivity checks toward any
   transport protocol (e.g., UDP, TCP) on an ICE-
   initiated connection address unless the receiving endpoint consents to receive the
   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, subsequent consent MUST be obtained following
   the procedure described in this document.  The consent
   expires after a fixed amount of time.  During ICE restart

   Explicit consent
   checks MUST continue to be sent on previously validated pair, and
   MUST be responded send is obtained by sending an STUN binding
   request to on the previously validated pair, until 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
   restart completes. 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 is obtained by sending granted as a result of a successful ICE
   connectivity check on a particular transport address, and expires 30
   seconds after an ICE binding
   request to candidate par has been selected.  Once an ICE
   candidate pair has been selected, consent for the remote peer's Transport Address and receiving a
   matching, authenticated, non-error 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.  These ICE binding requests and
   responses are authenticated using the same short-term credentials as transport address, the initial ICE exchange.  Implementations endpoint
   MUST cease sending data if
   their transmission on that 5-tuple.  STUN consent responses
   received after consent expires. expiry do not re-establish consent, and may be
   discarded or cause an ICMP error.

   To prevent expiry of consent, a STUN binding request MUST can be sent every N milliseconds, where N is chosen randomly
   with each
   periodically.  To prevent synchronization of consent check in the checks, each
   interval [.8N, 1.2N] (to prevent
   network synchronization), where N SHOULD MUST be 5000.  Using the value
   5000 milliseconds randomized from between 0.8 and that 20% randomization range, N would be 1.2 times the basic
   period.  Implementations SHOULD set a default interval of 5 seconds,
   resulting in a
   value period between 4000 and 6000.  These STUN binding requests for consent
   are not re-transmitted. checks of 4 to 6 seconds.

   Each STUN binding request for consent re-
   calculates a new random value N and MUST use 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  Each STUN
   binding requests for consent is transmitted once only.  Hence, the
   sender cannot assume that it will receive a response
   corresponding to 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 requests sent in the last 30 seconds
   has not been received from the remote peer's Transport Address, response associated with the
   endpoint MUST cease transmission on that 5-tuple. 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) 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 once the consent timer
   expires (30 seconds).

   An endpoint that is not sending any application traffic data does not need to obtain consent which can slightly conserve its resources.
   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 traffic, 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 that consent is terminated, terminated
   rather than relying on a timeout.  This is done by immediately
   revoking consent.

   Consent for sending traffic on the media or application 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  Note however that consent
   revocation messages can be lost on the network, so an
   implementation wanting to immediately revoke endpoint could
   resend these messages, or wait for consent needs to
   remember those credentials until consent expiry (30 seconds). 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.

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

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.

6.  DTLS applicability

   The DTLS applicability is identical to what is described in
   Section 4.2 of [RFC7350].

7.  W3C  API Implications

   For the consent freshness and liveness test the Recommendations

   The W3C specification
   should MAY provide APIs as described below:

   1.  Ability for the browser following API to notify the JavaScript that provide
   feedback and control over consent:

   1.  Generate an event when consent
       freshness has failed expired 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 given 5-tuple,
       meaning that a liveness
       test transmission of data has failed for a ceased.  This could
       indicate what application data is affected, such as media stream. or data

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 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.

   [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

              Mattsson, J., McGrew, D. D., and D. Wing, "Encrypted Key
              Transport for Secure RTP", draft-ietf-avtcore-srtp-ekt-02 draft-ietf-avtcore-srtp-ekt-03
              (work in progress), February October 2014.

              Alvestrand, H., "Overview: Real Time Protocols for
              Browser-based Applications", draft-ietf-rtcweb-overview-11 draft-ietf-rtcweb-overview-12
              (work in progress), August October 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-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.

   [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
   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