Unknown Key Share Attacks on uses of Transport Layer Security with the Session Description Protocol (SDP)
draft-thomson-avtcore-sdp-uks-00

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Network Working Group                                         M. Thomson
Internet-Draft                                               E. Rescorla
Intended status: Informational                                   Mozilla
Expires: April 12, 2017                                  October 9, 2016

 Unknown Key Share Attacks on uses of Transport Layer Security with the
                   Session Description Protocol (SDP)
                    draft-thomson-avtcore-sdp-uks-00

Abstract

   Unknown key-share attacks on the use of Datagram Transport Layer
   Security for the Secure Real-Time Transport Protocol (DTLS-SRTP) and
   its use with Web Real-Time Communications (WebRTC) identity
   assertions are described.  Simple mitigation techniques are defined.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on April 12, 2017.

Copyright Notice

   Copyright (c) 2016 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
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Unknown Key-Share Attack  . . . . . . . . . . . . . . . . . .   3
     2.1.  Attack Overview . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Limits on Attack Feasibility  . . . . . . . . . . . . . .   4
     2.3.  Example . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.4.  Interactions with Key Continuity  . . . . . . . . . . . .   6
   3.  Adding a Session Identifier . . . . . . . . . . . . . . . . .   6
     3.1.  The sdp_session_id TLS Extension  . . . . . . . . . . . .   7
   4.  WebRTC Identity Binding . . . . . . . . . . . . . . . . . . .   8
     4.1.  The webrtc_id_hash TLS Extension  . . . . . . . . . . . .   9
   5.  Session Concatenation . . . . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   The use of Transport Layer Security (TLS) [RFC5246] with the Session
   Description Protocol (SDP) [RFC4566] is defined in [RFC4572].
   Further use with Datagram Transport Layer Security (DTLS) [RFC6347]
   and the Secure Real-time Transport Protocol (SRTP) [RFC3711] is
   defined as DTLS-SRTP [RFC5763].

   In these specifications, key agreement is performed using the TLS or
   DTLS handshaking protocol, with authentication being tied back to the
   session description (or SDP) through the use of certificate
   fingerprints.  Communication peers check that a hash, or fingerprint,
   provided in the SDP matches the certificate that is used in the TLS
   (or DTLS) handshake.  This is defined in [RFC4572].

   The design of DTLS-SRTP relies on the integrity of the signaling
   channel.  Certificate fingerprints are assumed to be provided by the
   communicating peers and carried by the signaling channel without
   being subject to modification.  However, this design is vulnerable to
   an unknown key-share (UKS) attack where a misbehaving endpoint is
   able to advertise a key that it does not control.  This leads to the
   creation of sessions where peers are confused about the identify of
   the participants.

   An extension to TLS is defined that can be used to mitigate this
   attack.

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