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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: November 5, 2015                                R. Ravindranath
                                                                T. Reddy
                                                           Cisco Systems
                                                              M. Thomson
                                                                 Mozilla
                                                             May 4, 2015


                    STUN Usage for Consent Freshness
              draft-ietf-rtcweb-stun-consent-freshness-12

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.

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 November 5, 2015.

Copyright Notice

   Copyright (c) 2015 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



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   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.  DiffServ Treatment for Consent  . . . . . . . . . . . . . . .   6
   6.  DTLS applicability  . . . . . . . . . . . . . . . . . . . . .   6
   7.  API Recommendations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   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, 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
   terminated.

   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
   document.





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   Consent is obtained only by full ICE implementations.  An ICE-lite
   implementation will not generate consent checks, but will just
   respond to consent checks it receives.  No changes are required to
   ICE-lite implementations in order to respond to consent checks, as
   they are processed as normal ICE connectivity 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:  The mechanism of obtaining permission to send to a remote
      transport address.  Initial consent is obtained using ICE.

   Consent Freshness:  Maintaining and renewing consent over time.

   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 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].  If consent is
   performed then there is no need to send keepalive messages.

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 full ICE implementation performs consent freshness test using STUN
   request/response as described below:

   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,



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   consent MUST be maintained following the procedure described in this
   document.

   Explicit consent to send is obtained and maintained 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]).

   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
   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, 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 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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   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 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.  Absent better
   information about the network, an endpoint SHOULD maintain consent if
   there is any possibility that a flow might be needed again.

   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
   consent.

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





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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.

   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.  API Recommendations

   The W3C specification [W3C-WEBRTC] may provide an API hook that
   generates 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,
   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.






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10.  Acknowledgement

   Thanks to Eric Rescorla, Harald Alvestrand, Bernard Aboba, Magnus
   Westerland, Cullen Jennings, Christer Holmberg, Simon Perreault, Paul
   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.

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              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]
              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-13
              (work in progress), November 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-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.



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   [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
              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.

   [W3C-WEBRTC]
              Bergkvist, A., Burnett, D., Narayanan, A., and C.
              Jennings, "WebRTC 1.0: Real-time Communication Between
              Browsers", february 2015.

Authors' Addresses

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

   Email: muthu.arul@gmail.com


   Dan Wing
   Cisco Systems
   821 Alder Drive
   Milpitas, California  95035
   USA

   Email: dwing@cisco.com








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

   Email: rmohanr@cisco.com


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

   Email: tireddy@cisco.com


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

   Email: martin.thomson@gmail.com























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