Guidelines for the Use of Variable Bit Rate Audio with Secure RTP
RFC 6562
Document | Type | RFC - Proposed Standard (March 2012; No errata) | |
---|---|---|---|
Authors | Colin Perkins , Jean-Marc Valin | ||
Last updated | 2015-10-14 | ||
Replaces | draft-perkins-avt-srtp-vbr-audio | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Reviews | |||
Stream | WG state | Submitted to IESG for Publication | |
Document shepherd | Magnus Westerlund | ||
Shepherd write-up | Show (last changed 2011-09-30) | ||
IESG | IESG state | RFC 6562 (Proposed Standard) | |
Action Holders |
(None)
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||
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Robert Sparks | ||
IESG note | Magnus Westerlund (magnus.westerlund@ericsson.com) is the document shepherd. | ||
Send notices to | (None) |
Internet Engineering Task Force (IETF) C. Perkins Request for Comments: 6562 University of Glasgow Category: Standards Track JM. Valin ISSN: 2070-1721 Mozilla Corporation March 2012 Guidelines for the Use of Variable Bit Rate Audio with Secure RTP Abstract This memo discusses potential security issues that arise when using variable bit rate (VBR) audio with the secure RTP profile. Guidelines to mitigate these issues are suggested. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6562. Copyright Notice Copyright (c) 2012 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 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. Perkins & Valin Standards Track [Page 1] RFC 6562 VBR Audio with SRTP March 2012 Table of Contents 1. Introduction ...................................................2 2. Scenario-Dependent Risk ........................................2 3. Guidelines for Use of VBR Audio with SRTP ......................3 4. Guidelines for Use of Voice Activity Detection with SRTP .......3 5. Padding the Output of VBR Codecs ...............................4 6. Security Considerations ........................................5 7. Acknowledgements ...............................................5 8. References .....................................................5 8.1. Normative References ......................................5 8.2. Informative References ....................................6 1. Introduction The Secure RTP (SRTP) framework [RFC3711] is a widely used framework for securing RTP sessions [RFC3550]. SRTP provides the ability to encrypt the payload of an RTP packet, and optionally add an authentication tag, while leaving the RTP header and any header extension in the clear. A range of encryption transforms can be used with SRTP, but none of the predefined encryption transforms use any padding; the RTP and SRTP payload sizes match exactly. When using SRTP with voice streams compressed using variable bit rate (VBR) codecs, the length of the compressed packets will depend on the characteristics of the speech signal. This variation in packet size will leak a small amount of information about the contents of the speech signal. This is potentially a security risk for some applications. For example, [spot-me] shows that known phrases in an encrypted call using the Speex codec in VBR mode can be recognized with high accuracy in certain circumstances, and [fon-iks] shows that approximate transcripts of encrypted VBR calls can be derived for some codecs without breaking the encryption. How significant these results are, and how they generalize to other codecs, is still an open question. This memo discusses ways in which such traffic analysis risks may be mitigated. 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 RFC 2119 [RFC2119]. 2. Scenario-Dependent Risk Whether the information leaks and attacks discussed in [spot-me], [fon-iks], and similar works are significant is highly dependent on the application and use scenario. In the worst case, using the rate information to recognize a prerecorded message knowing the set of all possible messages would lead to near-perfect accuracy. Even when the Perkins & Valin Standards Track [Page 2] RFC 6562 VBR Audio with SRTP March 2012 audio is not prerecorded, there is a real possibility of being ableShow full document text