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Versions: 00 01 02 03 04                                                
BEHAVE                                                          T. Reddy
Internet-Draft                                  Ram. Mohan. Ravindranath
Intended status: Standards Track                    Muthu. A. M. Perumal
Expires: October 25, 2013                                          Cisco
                                                                A. Yegin
                                                          April 23, 2013

                   Problems with TURN Authentication


   This document discusses some of the issues with TURN authentication.

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
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   This Internet-Draft will expire on October 25, 2013.

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   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Notational Conventions  . . . . . . . . . . . . . . . . . . .   3
   3.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Problems with TURN Authentication . . . . . . . . . . . . . .   3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   4
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   TURN server plays a vital and is a building block to support direct,
   interactive, real-time communication using audio, video,
   collaboration, games, etc., between two peers' web-browsers in Web
   Real-Time communication (WebRTC) [I-D.ietf-rtcweb-overview]
   framework.  The use-case explained in Section of
   [I-D.ietf-rtcweb-use-cases-and-requirements] refers to deploying a
   TURN[RFC5766] server to audit all media sessions from inside an
   Enterprise premises to any external peer.  TURN server could also be
   deployed for recording, RTP Mobility [I-D.wing-mmusic-ice-mobility]

   TURN server is also used in the following scenarios :

   o  Users of RTCWEB based web application may choose to use TURN so as
      to not expose the host candidate addresses to the remote peer for

   o  Enterprise networks deploy firewalls typically configured to block
      UDP traffic.  When SIP user agents or WebRTC endpoints are
      deployed behind such firewalls, media cannot be sent over UDP
      across the firewall, but must be sent using TCP (which causes a
      different user experience).  In such cases a TURN server deployed
      in the DMZ MAY be used to traverse Firewalls.

   o  IPv6 support in TURN includes IPv4-to-IPv6, IPv6-to-IPv6, and IPv6
      -to-IPv4 relaying[RFC6156].

   o  ICE connectivity checks using server-reflexive candidates could
      fail because endpoint is behind NAT that performs Address-
      dependent mapping and relayed candidate allocated from the TURN
      server gets selected for media.

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   STUN [RFC5389] specifies an authentication mechanism called the long-
   term credential mechanism.  TURN servers and clients are required to
   implement this mechanism.  The server requires that all requests from
   the client be authenticated using this mechanism, or that a equally
   strong or stronger mechanism for client authentication be used.

   In the above scenarios RTCWEB based web applications would use
   Interactive Connectivity Establishment (ICE) protocol [RFC5245] for
   gathering candidates.  ICE agent can use TURN to learn server-
   reflexive and relayed candidates.  If the TURN server requires the
   TURN request to be authenticated then ICE agent will use the long-
   term credential mechanism explained in section 10 of [RFC5389] for
   authentication and message integrity.  TURN specification [RFC5766]
   in section 10 explains the importance of long-term credential
   mechanism to mitigate various attacks.  With proposals
   like[I-D.thomson-mmusic-rtcweb-bw-consent] that defines a STUN
   BANDWIDTH attribute for requesting bandwidth allocation at a TURN
   server, TURN authentication becomes further important to prevent un-
   authorized users from accessing the TURN server.

   This note focuses on listing the problems with current TURN
   authentication so that It can serve as the basis for stronger TURN
   authentication mechanisms.

2.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   This note uses terminology defined in [RFC5389], [RFC5766].

3.  Scope

   This document can be used as a tool to design solution(s) to address
   the problems with the current TURN authentication.

4.  Problems with TURN Authentication

   1.  The long-term credential mechanism in [RFC5389] could use
       traditional "log-in" username and password given to users which
       does not change for extended periods of time and uses the key
       derived from user credentials to generate message integrity for
       every TURN request/response.  An attacker that is capable of
       eavesdropping on a message exchange between a client and server
       can determine the password by trying a number of candidate
       passwords and checking if one of them is correct by calculating
       the message-integrity of the message using these candidate

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       passwords and comparing with the message integrity value in the
       MESSAGE-INTEGRITY attribute.

   2.  The long-term credential mechanism in [RFC5389] is susceptible to
       offline dictionary attacks.  This attack can be mitigated by
       using strong passwords with large entropy.

   3.  When TURN server is deployed in DMZ and requires requests to be
       authenticated using the long-term credential mechanism in
       [RFC5389], TURN server needs to be aware of the username and
       password to validate the message integrity of the requests and to
       provide message integrity for responses.  Thus requiring
       management overhead to maintain credential database on the TURN

   4.  The long-term credential mechanism in [RFC5389] requires that the
       TURN client must include username value in the USERNAME STUN
       attribute.  An adversary snooping the TURN messages between the
       TURN client and server can identify the users involved in the
       call resulting in privacy leakage.  In certain scenarios TURN
       usernames need not be linked to any real usernames given to users
       as they are just provisioned on a per company basis.

   5.  An Attacker posing as a TURN server challenges the client to
       authenticate, learns the USERNAME of the host and later snoops
       the traffic from the host identifying the user activity resulting
       in privacy leakage.

5.  Security Considerations

   This document does not define an architecture nor a protocol; as such
   it does not raise any security concern.

6.  IANA Considerations

   This document does not require any action from IANA.

7.  Acknowledgments

   Authors would like to thank Dan Wing, Sandeep Rao, Prashanth Patil
   and Pal Martinsen for their comments and review.

8.  References

8.1.  Normative References

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

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

   [RFC5766]  Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
              Relays around NAT (TURN): Relay Extensions to Session
              Traversal Utilities for NAT (STUN)", RFC 5766, April 2010.

   [RFC6156]  Camarillo, G., Novo, O., and S. Perreault, "Traversal
              Using Relays around NAT (TURN) Extension for IPv6", RFC
              6156, April 2011.

8.2.  Informative References

              Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)", draft-ietf-pcp-
              base-29 (work in progress), November 2012.

              Alvestrand, H., "Overview: Real Time Protocols for Brower-
              based Applications", draft-ietf-rtcweb-overview-06 (work
              in progress), February 2013.

              Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real-
              Time Communication Use-cases and Requirements", draft-
              ietf-rtcweb-use-cases-and-requirements-10 (work in
              progress), December 2012.

              Thomson, M. and B. Aboba, "Bandwidth Constraints for
              Session Traversal Utilities for NAT (STUN)", draft-
              thomson-mmusic-rtcweb-bw-consent-00 (work in progress),
              October 2012.

              Wing, D., Patil, P., Reddy, T., and P. Martinsen,
              "Mobility with ICE (MICE)", draft-wing-mmusic-ice-
              mobility-03 (work in progress), January 2013.

   [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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   [RFC6544]  Rosenberg, J., Keranen, A., Lowekamp, B.B., and A.B.
              Roach, "TCP Candidates with Interactive Connectivity
              Establishment (ICE)", RFC 6544, March 2012.

Authors' Addresses

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

   Email: tireddy@cisco.com

   Ram Mohan Ravindranath
   Cisco Systems, Inc.
   Cessna Business Park, Varthur Hobli
   Sarjapur Marathalli Outer Ring Road
   Bangalore, Karnataka  560103

   Email: rmohanr@cisco.com

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

   Email: mperumal@cisco.com

   Alper Yegin

   Email: alper.yegin@yegin.org

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