draft-ietf-avtcore-srtp-encrypted-header-ext-03.txt   draft-ietf-avtcore-srtp-encrypted-header-ext-04.txt 
AVTCORE J. Lennox AVTCORE J. Lennox
Internet-Draft Vidyo Internet-Draft Vidyo
Updates: 3711 (if approved) October 22, 2012 Updates: 3711 (if approved) January 3, 2013
Intended status: Standards Track Intended status: Standards Track
Expires: April 25, 2013 Expires: July 7, 2013
Encryption of Header Extensions in the Secure Real-Time Transport Encryption of Header Extensions in the Secure Real-Time Transport
Protocol (SRTP) Protocol (SRTP)
draft-ietf-avtcore-srtp-encrypted-header-ext-03 draft-ietf-avtcore-srtp-encrypted-header-ext-04
Abstract Abstract
The Secure Real-Time Transport Protocol (SRTP) provides The Secure Real-Time Transport Protocol (SRTP) provides
authentication, but not encryption, of the headers of Real-Time authentication, but not encryption, of the headers of Real-Time
Transport Protocol (RTP) packets. However, RTP header extensions may Transport Protocol (RTP) packets. However, RTP header extensions may
carry sensitive information for which participants in multimedia carry sensitive information for which participants in multimedia
sessions want confidentiality. This document provides a mechanism, sessions want confidentiality. This document provides a mechanism,
extending the mechanisms of SRTP, to selectively encrypt RTP header extending the mechanisms of SRTP, to selectively encrypt RTP header
extensions in SRTP. extensions in SRTP.
This document updates RFC 3711, the Secure Real-Time Transport This document updates RFC 3711, the Secure Real-Time Transport
Protocol specification, to require that all SRTP encryption Protocol specification, to require that all future SRTP encryption
transforms specify how RTP header extensions are to be encrypted. transforms specify how RTP header extensions are to be encrypted.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 25, 2013. This Internet-Draft will expire on July 7, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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3.1. Example Encryption Mask . . . . . . . . . . . . . . . . . 5 3.1. Example Encryption Mask . . . . . . . . . . . . . . . . . 5
3.2. Header Extension Keystream Generation for Existing 3.2. Header Extension Keystream Generation for Existing
Encryption Transforms . . . . . . . . . . . . . . . . . . 7 Encryption Transforms . . . . . . . . . . . . . . . . . . 7
3.3. Header Extension Keystream Generation for Future 3.3. Header Extension Keystream Generation for Future
Encryption Transforms . . . . . . . . . . . . . . . . . . 7 Encryption Transforms . . . . . . . . . . . . . . . . . . 7
4. Signaling (Setup) Information . . . . . . . . . . . . . . . . 7 4. Signaling (Setup) Information . . . . . . . . . . . . . . . . 7
4.1. Backward compatibility . . . . . . . . . . . . . . . . . . 8 4.1. Backward compatibility . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 10 8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 11 8.2. Informative References . . . . . . . . . . . . . . . . . . 11
Appendix A. Test Vectors . . . . . . . . . . . . . . . . . . . . 11 Appendix A. Test Vectors . . . . . . . . . . . . . . . . . . . . 12
A.1. Key derivation test vectors . . . . . . . . . . . . . . . 11 A.1. Key derivation test vectors . . . . . . . . . . . . . . . 12
A.2. Header Encryption Test Vectors using AES-CM . . . . . . . 12 A.2. Header Encryption Test Vectors using AES-CM . . . . . . . 13
Appendix B. Changes From Earlier Versions . . . . . . . . . . . . 14 Appendix B. Changes From Earlier Versions . . . . . . . . . . . . 14
B.1. Changes from draft-ietf-avtcore -02 . . . . . . . . . . . 14 B.1. Changes from draft-ietf-avtcore -03 . . . . . . . . . . . 14
B.2. Changes from draft-ietf-avtcore -01 . . . . . . . . . . . 14 B.2. Changes from draft-ietf-avtcore -02 . . . . . . . . . . . 14
B.3. Changes from draft-ietf-avtcore -00 . . . . . . . . . . . 14 B.3. Changes from draft-ietf-avtcore -01 . . . . . . . . . . . 14
B.4. Changes from draft-lennox-avtcore -00 . . . . . . . . . . 15 B.4. Changes from draft-ietf-avtcore -00 . . . . . . . . . . . 15
B.5. Changes from draft-lennox-avt -02 . . . . . . . . . . . . 15 B.5. Changes from draft-lennox-avtcore -00 . . . . . . . . . . 15
B.6. Changes From Individual Submission Draft -01 . . . . . . . 15 B.6. Changes from draft-lennox-avt -02 . . . . . . . . . . . . 15
B.7. Changes From Individual Submission Draft -00 . . . . . . . 15 B.7. Changes From Individual Submission Draft -01 . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15 B.8. Changes From Individual Submission Draft -00 . . . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
The Secure Real-Time Transport Protocol [RFC3711] specification The Secure Real-Time Transport Protocol [RFC3711] specification
provides confidentiality, message authentication, and replay provides confidentiality, message authentication, and replay
protection for multimedia payloads sent using of the Real-Time protection for multimedia payloads sent using the Real-Time Protocol
Protocol (RTP) [RFC3550]. However, in order to preserve RTP header (RTP) [RFC3550]. However, in order to preserve RTP header
compression efficiency, SRTP provides only authentication and replay compression efficiency, SRTP provides only authentication and replay
protection for the headers of RTP packets, not confidentiality. protection for the headers of RTP packets, not confidentiality.
For the standard portions of an RTP header, this does not normally For the standard portions of an RTP header, this does not normally
present a problem, as the information carried in an RTP header does present a problem, as the information carried in an RTP header does
not provide much information beyond that which an attacker could not provide much information beyond that which an attacker could
infer by observing the size and timing of RTP packets. Thus, there infer by observing the size and timing of RTP packets. Thus, there
is little need for confidentiality of the header information. is little need for confidentiality of the header information.
However, this is not necessarily true for information carried in RTP However, this is not necessarily true for information carried in RTP
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believed to be cryptographically adequate for the transform in believed to be cryptographically adequate for the transform in
question. question.
4. Signaling (Setup) Information 4. Signaling (Setup) Information
Encrypted header extension elements are signaled in the SDP extmap Encrypted header extension elements are signaled in the SDP extmap
attribute, using the URI "urn:ietf:params:rtp-hdrext:encrypt", attribute, using the URI "urn:ietf:params:rtp-hdrext:encrypt",
followed by the URI of the header extension element being encrypted followed by the URI of the header extension element being encrypted
as well as any extensionattributes that extension normally takes. as well as any extensionattributes that extension normally takes.
Figure 3 gives a formal Augmented Backus-Naur Form (ABNF) [RFC5234] Figure 3 gives a formal Augmented Backus-Naur Form (ABNF) [RFC5234]
showing this grammar extension. showing this grammar extension, extending the grammar defined in
[RFC5285].
enc-extensionattributes = extensionname [SP extensionattributes] enc-extensionname = %x75.72.6e.3a.69.65.74.66.3a.70.61.72.61.6d.73.3a
%x72.74.70.2d.68.64.72.65.78.74.3a.65.6e.63.72.79.70.74
; "urn:ietf:params:rtp-hdrext:encrypt" in lower case
extensionattributes /= enc-extensionattributes extmap /= mapentry SP enc-extensionname SP extensionname
[SP extensionattributes]
Figure 3: Syntax of the "encrypt" extensionattributes ; extmap, mapentry, extensionname and extensionattributes
; are defined in [RFC5285]
Figure 3: Syntax of the "encrypt" extmap
Thus, for example, to signal an SRTP session using encrypted SMPTE Thus, for example, to signal an SRTP session using encrypted SMPTE
timecodes [RFC5484], while simultaneously signaling plaintext timecodes [RFC5484], while simultaneously signaling plaintext
transmission time offsets [RFC5450], an SDP document could contain transmission time offsets [RFC5450], an SDP document could contain
(line breaks added for formatting): (line breaks added for formatting):
m=audio 49170 RTP/SAVP 0 m=audio 49170 RTP/SAVP 0
a=crypto:1 AES_CM_128_HMAC_SHA1_32 \ a=crypto:1 AES_CM_128_HMAC_SHA1_32 \
inline:NzB4d1BINUAvLEw6UzF3WSJ+PSdFcGdUJShpX1Zj|2^20|1:32 inline:NzB4d1BINUAvLEw6UzF3WSJ+PSdFcGdUJShpX1Zj|2^20|1:32
a=extmap:1 urn:ietf:params:rtp-hdrext:encrypt \ a=extmap:1 urn:ietf:params:rtp-hdrext:encrypt \
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Description: Encrypted extension header element Description: Encrypted extension header element
Contact: jonathan@vidyo.com Contact: jonathan@vidyo.com
Reference: RFC XXXX Reference: RFC XXXX
(Note to the RFC-Editor: please replace "XXXX" with the number of (Note to the RFC-Editor: please replace "XXXX" with the number of
this document prior to publication as an RFC.) this document prior to publication as an RFC.)
7. Acknowledgments 7. Acknowledgments
Thanks to Roni Even, Kevin Igoe, David McGrew, Magnus Westerlund, Thanks to Roni Even, Kevin Igoe, David McGrew, Magnus Westerlund,
David Singer, Qin Wu, and Felix Wyss for their comments and David Singer, Robert Sparks, Qin Wu, and Felix Wyss for their
suggestions in the development of this specification. comments and suggestions in the development of this specification.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003. Applications", STD 64, RFC 3550, July 2003.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
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Plaintext: 17414273A475262748220000C8308E46 Plaintext: 17414273A475262748220000C8308E46
55996386B395FB00 55996386B395FB00
Ciphertext: 17588A9270F4E15E1C220000C8309546 Ciphertext: 17588A9270F4E15E1C220000C8309546
A994F0BC54789700 A994F0BC54789700
Appendix B. Changes From Earlier Versions Appendix B. Changes From Earlier Versions
Note to the RFC-Editor: please remove this section prior to Note to the RFC-Editor: please remove this section prior to
publication as an RFC. publication as an RFC.
B.1. Changes from draft-ietf-avtcore -02 B.1. Changes from draft-ietf-avtcore -03
o Modified the ABNF syntax to avoid rule recursion.
o Added Robert Sparks to the Acknowledgments.
B.2. Changes from draft-ietf-avtcore -02
o Clarified that the header extension encryption mask must be o Clarified that the header extension encryption mask must be
calculated separately for each packet, and can always be derived calculated separately for each packet, and can always be derived
from the plaintext portions of the encrypted header extension. from the plaintext portions of the encrypted header extension.
o Presented an alternate formulation of the header extension o Presented an alternate formulation of the header extension
encryption process, so implementations can use their existing encryption process, so implementations can use their existing
encryption algorithms unmodified. encryption algorithms unmodified.
o Added a security consideration emphasizing that this mechanism o Added a security consideration emphasizing that this mechanism
must only be used with keystream-based encryption algorithms. must only be used with keystream-based encryption algorithms.
B.2. Changes from draft-ietf-avtcore -01 B.3. Changes from draft-ietf-avtcore -01
o Made the draft update RFC 3711, and added a section specifying o Made the draft update RFC 3711, and added a section specifying
that all future SRTP encryption transforms must specify how header that all future SRTP encryption transforms must specify how header
extension encryption is to be done. extension encryption is to be done.
o Explicitly distinguished the processing of existing encryption o Explicitly distinguished the processing of existing encryption
transforms from future ones. transforms from future ones.
o Clarified description of the process by which the encryption mask o Clarified description of the process by which the encryption mask
is applied, and that encryption does not apply to the header is applied, and that encryption does not apply to the header
extension "defined by profile" or "length" fields. extension "defined by profile" or "length" fields.
o Defined how header extension encryption is to be done with the o Defined how header extension encryption is to be done with the
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o Clarified that header extension encryption must not be applied to o Clarified that header extension encryption must not be applied to
itself. itself.
o Expanded discussion of bid-down attacks. o Expanded discussion of bid-down attacks.
o Pointed out that this mechanism can't protect non-RFC5285 header o Pointed out that this mechanism can't protect non-RFC5285 header
extensions, and that there's no way to give different protection extensions, and that there's no way to give different protection
to header extensions than to payloads. to header extensions than to payloads.
o Updated references to now-published RFCs. o Updated references to now-published RFCs.
o Editorial clarifications. o Editorial clarifications.
o Added Magnus Westerlund to the Acknowledgments. o Added Magnus Westerlund to the Acknowledgments.
B.3. Changes from draft-ietf-avtcore -00 B.4. Changes from draft-ietf-avtcore -00
o Clarified usage of Key Derivation Algorithm o Clarified usage of Key Derivation Algorithm
o Provided non-normative guidance for how to use this mechanism with o Provided non-normative guidance for how to use this mechanism with
Authenticated Encryption with Associated Data (AEAD) transforms. Authenticated Encryption with Associated Data (AEAD) transforms.
o Corrected SMPTE Timecode header extension element in example o Corrected SMPTE Timecode header extension element in example
header extension (it's eight bytes, not sixteen). Added an NTP header extension (it's eight bytes, not sixteen). Added an NTP
timestamp to the example to fill it back out to original size. timestamp to the example to fill it back out to original size.
o Specified applicability of the extmap attribute if it's specified o Specified applicability of the extmap attribute if it's specified
as a session-level attribute. as a session-level attribute.
o Added description of backward compatibility, including a o Added description of backward compatibility, including a
description of how you can negotiate best-effort encryption. description of how you can negotiate best-effort encryption.
o Added a note to the security considerations about the dangers for o Added a note to the security considerations about the dangers for
middleboxes observing unencrypted headers (both header extension middleboxes observing unencrypted headers (both header extension
elements and RTP headers) without being able to verify the elements and RTP headers) without being able to verify the
authentication keys. authentication keys.
o Added test vectors. o Added test vectors.
o Added acknowledgments section. o Added acknowledgments section.
skipping to change at page 15, line 16 skipping to change at page 15, line 34
as a session-level attribute. as a session-level attribute.
o Added description of backward compatibility, including a o Added description of backward compatibility, including a
description of how you can negotiate best-effort encryption. description of how you can negotiate best-effort encryption.
o Added a note to the security considerations about the dangers for o Added a note to the security considerations about the dangers for
middleboxes observing unencrypted headers (both header extension middleboxes observing unencrypted headers (both header extension
elements and RTP headers) without being able to verify the elements and RTP headers) without being able to verify the
authentication keys. authentication keys.
o Added test vectors. o Added test vectors.
o Added acknowledgments section. o Added acknowledgments section.
B.4. Changes from draft-lennox-avtcore -00 B.5. Changes from draft-lennox-avtcore -00
o Published as working group item. o Published as working group item.
o Added discussion of limitations when used with the two-byte-header o Added discussion of limitations when used with the two-byte-header
form of header extension elements. form of header extension elements.
o Added open issue about how to use this mechanism with o Added open issue about how to use this mechanism with
Authenticated Encryption with Associated Data (AEAD) transforms. Authenticated Encryption with Associated Data (AEAD) transforms.
o Updated references. o Updated references.
B.5. Changes from draft-lennox-avt -02 B.6. Changes from draft-lennox-avt -02
o Retargeted at AVTCORE working group. o Retargeted at AVTCORE working group.
o Updated references. o Updated references.
B.6. Changes From Individual Submission Draft -01 B.7. Changes From Individual Submission Draft -01
o Minor editorial changes. o Minor editorial changes.
B.7. Changes From Individual Submission Draft -00 B.8. Changes From Individual Submission Draft -00
o Clarified description of encryption mask creation. o Clarified description of encryption mask creation.
o Added example encryption mask. o Added example encryption mask.
o Editorial changes. o Editorial changes.
Author's Address Author's Address
Jonathan Lennox Jonathan Lennox
Vidyo, Inc. Vidyo, Inc.
433 Hackensack Avenue 433 Hackensack Avenue
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