Unknown Key Share Attacks on uses of Transport Layer Security with the Session Description Protocol (SDP)
draft-ietf-mmusic-sdp-uks-02

Document Type Active Internet-Draft (mmusic WG)
Last updated 2018-08-07
Replaces draft-thomson-mmusic-sdp-uks
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Stream WG state WG Document (wg milestone: Apr 2019 - Submit Unknown Key S... )
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Network Working Group                                         M. Thomson
Internet-Draft                                               E. Rescorla
Intended status: Standards Track                                 Mozilla
Expires: February 9, 2019                                August 08, 2018

 Unknown Key Share Attacks on uses of Transport Layer Security with the
                   Session Description Protocol (SDP)
                      draft-ietf-mmusic-sdp-uks-02

Abstract

   This document describes unknown key-share attacks on the use of
   Datagram Transport Layer Security for the Secure Real-Time Transport
   Protocol (DTLS-SRTP).  Similar attacks are described on the use of
   DTLS-SRTP with Web Real-Time Communications (WebRTC) identity
   assertions.  Both attacks cause a victim to be mislead about the
   identity of a communicating peer.  Simple mitigation techniques are
   defined for each.

Status of This Memo

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   This Internet-Draft will expire on February 9, 2019.

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   Copyright (c) 2018 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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Thomson & Rescorla      Expires February 9, 2019                [Page 1]
Internet-Draft                   SDP UKS                     August 2018

   include Simplified BSD License text as described in Section 4.e of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Unknown Key-Share Attack  . . . . . . . . . . . . . . . . . .   3
     2.1.  Attack Overview . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Limits on Attack Feasibility  . . . . . . . . . . . . . .   4
     2.3.  Example . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.4.  Interactions with Key Continuity  . . . . . . . . . . . .   6
     2.5.  Third-Party Call Control  . . . . . . . . . . . . . . . .   6
   3.  Adding a Session Identifier . . . . . . . . . . . . . . . . .   7
     3.1.  The external_session_id TLS Extension . . . . . . . . . .   7
   4.  WebRTC Identity Binding . . . . . . . . . . . . . . . . . . .   8
     4.1.  The webrtc_id_hash TLS Extension  . . . . . . . . . . . .   9
   5.  Consequences of Session Concatenation . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   The use of Transport Layer Security (TLS) [RFC5246] with the Session
   Description Protocol (SDP) [RFC4566] is defined in [RFC8122].
   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 TLS or
   DTLS, 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 [RFC8122].

   The design in RFC 8122 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
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