Unknown Key Share Attacks on uses of TLS with the Session Description Protocol (SDP)
draft-ietf-mmusic-sdp-uks-04

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Document Type Active Internet-Draft (mmusic WG)
Last updated 2019-05-22 (latest revision 2019-05-07)
Replaces draft-thomson-mmusic-sdp-uks
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Send notices to Bo Burman <bo.burman@ericsson.com>
Network Working Group                                         M. Thomson
Internet-Draft                                               E. Rescorla
Updates: 8122 (if approved)                                      Mozilla
Intended status: Standards Track                            May 07, 2019
Expires: November 8, 2019

 Unknown Key Share Attacks on uses of TLS with the Session Description
                             Protocol (SDP)
                      draft-ietf-mmusic-sdp-uks-04

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 the identity bindings used in Web Real-Time
   Communications (WebRTC) and SIP identity.  These attacks are
   difficult to mount, but they 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 November 8, 2019.

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Thomson & Rescorla      Expires November 8, 2019                [Page 1]
Internet-Draft                   SDP UKS                        May 2019

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Unknown Key-Share Attack  . . . . . . . . . . . . . . . . . .   3
     2.1.  Limits on Attack Feasibility  . . . . . . . . . . . . . .   4
     2.2.  Interactions with Key Continuity  . . . . . . . . . . . .   5
     2.3.  Third-Party Call Control  . . . . . . . . . . . . . . . .   5
   3.  Attack on Identity Bindings . . . . . . . . . . . . . . . . .   6
     3.1.  Example . . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.2.  The external_id_hash TLS Extension  . . . . . . . . . . .   8
   4.  Unknown Key-Share with Fingerprints . . . . . . . . . . . . .   9
     4.1.  Example . . . . . . . . . . . . . . . . . . . . . . . . .  10
     4.2.  Unique Session Identity Solution  . . . . . . . . . . . .  12
     4.3.  The external_session_id TLS Extension . . . . . . . . . .  12
   5.  Consequences of Session Concatenation . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   The use of Transport Layer Security (TLS) [TLS13] with the Session
   Description Protocol (SDP) [SDP] is defined in [FINGERPRINT].
   Further use with Datagram Transport Layer Security (DTLS) [DTLS] and
   the Secure Real-time Transport Protocol (SRTP) [SRTP] is defined as
   DTLS-SRTP [DTLS-SRTP].

   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.

   WebRTC identity (see Section 7 of [WEBRTC-SEC]) and SIP identity
   [SIP-ID] both provide a mechanism that binds an external identity to
   the certificate fingerprints from a session description.  However,
   this binding is not integrity-protected and therefore vulnerable to
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