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Versions: 00 01 02 03 04 draft-ietf-rtcweb-stun-consent-freshness

Behave                                                Muthu A M. Perumal
Internet-Draft                                                   D. Wing
Intended status: Standards Track                            R. Ram Mohan
Expires: January 17, 2013                                  Cisco Systems
                                                               H. Kaplan
                                                             Acme Packet
                                                           July 16, 2012


         STUN Usage for Consent Freshness and Session Liveness
                draft-muthu-behave-consent-freshness-01

Abstract

   Verification of peer consent is necessary in WebRTC deployments to
   ensure that a malicious JavaScript cannot use the browser as a
   platform for launching attacks.  A related problem is session
   liveness.  WebRTC applications may want to detect connection failure
   and take appropriate actions.  This document describes a STUN usage
   that enables a WebRTC browser to perform the following on a candidate
   pair ICE is using for a media component after session establishment:

   1.  Verify the peer consent for continuing to receive traffic.
   2.  Dectect connection failure.

   This also serves the purpose of refreshing NAT bindings.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 17, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



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   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
   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  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Solution Overview . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Design Considerations . . . . . . . . . . . . . . . . . . . . . 4
   6.  STUN Consent Method . . . . . . . . . . . . . . . . . . . . . . 5
   7.  STUN Consent Method Processing  . . . . . . . . . . . . . . . . 6
     7.1.  Generating a Consent Request  . . . . . . . . . . . . . . . 6
     7.2.  Receiving a Consent Request . . . . . . . . . . . . . . . . 6
     7.3.  Generating a Consent Response . . . . . . . . . . . . . . . 7
     7.4.  Receiving a Consent Response  . . . . . . . . . . . . . . . 7
   8.  Performing Consent Freshness  . . . . . . . . . . . . . . . . . 7
   9.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
   10. Generating Consent Freshness Response . . . . . . . . . . . . . 7
   11. SDP Extension for Consent Freshness . . . . . . . . . . . . . . 7
   12. Interaction with Keepalives used for Refreshing NAT
       Bindings  . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
   13. Open Items  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
   14. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
   15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
   16. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 8
   17. Normative References  . . . . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9















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1.  Introduction

   Consent verification is the mechanism using which WebRTC
   implementations can verify the peer consent for receiving traffic on
   candidate media transport addresses.  This has two parts

   1.  Verifying peer consent for receiving traffic on candidate media
       transport addresses at session establishment.
   2.  Verifying peer consent for continuing to receive traffic on
       candidate media transport addresses after session establishment.

   WebRTC implements are required to perform STUN connectivity checks at
   session establishment as part of ICE procedures [RFC5245].  This
   takes care of the first part of the consent verification described
   above.

   After session establishment ICE requires STUN Binding indications to
   be used for refreshing NAT bindings for a candidate pair ICE is using
   for a media component.  Since a STUN Binding indication does not
   evoke a response, it cannot be used for the second part of the
   consent verification describes above.

   A related problem is session liveness.  WebRTC applications may want
   to detect connection failure on candidate media transport addresses
   after session establishment and take appropriate actions.  Again, the
   STUN Binding indications in ICE sent after session establishment
   cannot be used for determining session liveness.

   This document describes a STUN usage based on STUN request/response
   that enables a WebRTC browser to perform the following on a candidate
   pair ICE is using for a media component after session establishment:

   1.  Verify the peer consent for continuing to receive traffic.
   2.  Dectect connection failure.

   This also serves the purpose of refreshing NAT bindings.


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].


3.  Definitions





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   Consent Freshness:  It is the mechanism of verifying peer consent for
      continuing to receive traffic on a candidate pair ICE is using for
      a media component after ICE has concluded.  This document uses
      completion of session establishment synonymous with the conclusion
      of ICE.

   Session Liveness:  It is the mechanism of detecting connectivity on a
      candidate pair ICE is using for a media component after ICE has
      concluded.

   Transport Address:  The combination of an IP address and port number
      (such as a UDP or TCP port number).


4.  Solution Overview

   The solution uses two timers:
   1.  A consent timer Tc whose value is determined by the browser.
   2.  A packet receipt timer whose value is determined by the
       application.

   A WebRTC browser performs a combined consent freshness and session
   liveness test using STUN resuest/respose as described below:

   o  Starts a consent timer Tc (no less than 15 sec).
   o  Starts a packet receipt timer Tr (no less than 500 msec);
      application configurable.
   o  When either timer expires it starts a STUN transaction.
   o  When the STUN transaction succeeds, it re-starts both timers.
   o  When the STUN transaction fails
      *  If the transaction was started by timer Tc, it stops sending
         traffic on that candidate pair.
      *  Else, it notifies the application of the failure and continues.
   o  It resets timer Tr on receiving any packet from the other side.

   While consent freshness serves as a circuit breaker (if there is a
   failure the WebRTC browser stops sending all traffic on that
   candidate pair), determining session liveness serves the purpose of
   notifying the application of connectivity failure so that the
   application can take appropriate action.


5.  Design Considerations

   As described earlier in this document, STUN indications are not
   suitable for performing consent freshness.  Hence, performing consent
   freshness requires the use of STUN request/response.




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   ICE requires the usage of message integrity with STUN using its
   short-term credential mechanism.  The need for this mechanism goes
   beyond just security and is required for the correct operation of the
   ICE connectivity check procedures; without message integrity the
   connectivity checks can yield false positives, as described in
   Appendix B section B.4 of RFC5245.  However, this problem is not
   applicable for consent freshness, since consent freshness is
   performed only after ICE concludes.

   One of the reasons for ICE choosing STUN Binding indications for
   keepalives is because Binding indication allows integrity to be
   disabled, allowing for better performance.  This is useful for large-
   scale endpoints, such as PSTN gateways and SBCs as described in
   Appendix B section B.10 of  RFC5245

   STUN requires the 96 bits transaction ID to be uniformly and randomly
   chosen from the interval 0 .. 2**96-1, and be cryptographically
   random.  This is good enough security against an off-path attacker.

   Though ICE specifies STUN Binding indications to be used for
   keepalives, it requires that an agent be prepared to receive
   connectivity check as well.  If a connectivity check is received, a
   response is generated, but there is no impact on ICE processing, as
   described in section 10 of RFC5245.

   Reusing STUN Binding request/response allows browsers to interoperate
   with existing ICE implementations; even ICE-lite implementations.
   This is considered very important.

   Conclusion: Considering all the above, there seems to be a rough
   consensus in the RTCWEB WG for reusing the STUN Binding request/
   response for determining consent freshness and session liveness.  The
   current thought is that the cost of the SHA-1 computation is not a
   good enough justification for the pain a new method would cause with
   existing IEC implementations.


6.  STUN Consent Method

   The STUN message type field from the STUN specification [RFC5389] is
   shown below










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                           2 3 4 5 6 7 8 9 A B C D E F

                          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          |M|M|M|M|M|C|M|M|M|C|M|M|M|M|
                          |b|a|9|8|7|1|6|5|4|0|3|2|1|0|
                          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 1: Format of STUN Message Type Field

   Here the bits in the message type field are shown as most significant
   (Mb) through least significant (M0).  C1 and C0 represent a 2-bit
   encoding of the class.  Mb through M0 represent a 12-bit encoding of
   the method.  The Consent method is encoded as 0b000000000010.

   A Consent request has class=0b00 (request) and method=0b000000000010
   (Consent) and is encoded into the first 16 bits of the STUN header as
   0x0002.

   A Consent success response has class=0b10 (success response) and
   method=0b000000000010 (Consent) and is encoded into the first 16 bits
   of the STUN header as 0x0102.

   A Consent error response has class=0b11 (error response) and
   method=0b000000000010 (Consent) and is encoded into the first 16 bits
   of the STUN header as 0x0112.

   A Consent indication has class=0b01 (indication) and
   method=0b000000000010 (Consent) and is encoded into the first 16 bits
   of the STUN header as 0x0012.


7.  STUN Consent Method Processing

   Processing of the STUN Consent method is similar to the processing of
   the STUN Binding method except that the procedures pertaining to the
   message integrity and short/long-term credential mechanisms are not
   applicable.  In particular, the USERNAME and MESSAGE-INTEGRITY
   attributes are not included in a Consent request or response.

7.1.  Generating a Consent Request

   TBD

7.2.  Receiving a Consent Request

   TBD





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7.3.  Generating a Consent Response

   TBD

7.4.  Receiving a Consent Response

   TBD


8.  Performing Consent Freshness

   TBD


9.  Examples

   TBD


10.  Generating Consent Freshness Response

   A STUN agent receiving a consent freshness request for a candidate
   pair ICE is using for a media component MUST generate a STUN Consent
   response.


11.  SDP Extension for Consent Freshness

   TBD


12.  Interaction with Keepalives used for Refreshing NAT Bindings

   An implementation that performs the procedures described in this
   document has no need to also perform the keepalives described in ICE
   [RFC5245] or RTP keepalive [RFC6263], as they both force recurring
   messages to be sent over the UDP port used by RTP.  Thus, an
   implementation that performs the procedures described in this
   document SHOULD NOT also do the keepalives described in ICE [RFC5245]
   or RTP keepalives [RFC6263] for the UDP port used for RTP.


13.  Open Items

   1.  Should STUN Binding request/response be reused for determining
       consent freshness and session liveness, considering
       interoperability with existing ICE and ICE-lite implementation
       even at the cost of the incurred SHA-1 computation?



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   2.  If the RTCP port is different from the RTP port, does RTCP need
       consent freshness and session liveness tests?


14.  Security Considerations

   TBD


15.  IANA Considerations

   TBD


16.  Acknowledgement

   Thanks to Eric Rescorla, Harald Alvestrand, Martin Thomson, Bernard
   Aboba, Cullen Jennings and Simon Perreault for their valuable inputs
   and comments


17.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              October 2008.

   [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.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              June 2002.






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Authors' Addresses

   Muthu Arul Mozhi Perumal
   Cisco Systems
   Cessna Business Park
   Sarjapur-Marathahalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Email: mperumal@cisco.com


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

   Email: dwing@cisco.com


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

   Email: rmohanr@cisco.com


   Hadriel Kaplan
   Acme Packet

   Email: hkaplan@acmepacket.com
















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