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Versions: 00 01

Network Working Group                                        C. Holmberg
Internet-Draft                                                  Ericsson
Updates: 4572 (if approved)                            February 29, 2016
Intended status: Standards Track
Expires: September 1, 2016


                          Updates to RFC 4572
                draft-holmberg-mmusic-4572-update-00.txt

Abstract

   This document updates RFC 4572 by clarifying the usage of multiple
   SDP 'fingerprint' attributes with a single TLS connection.  The
   document also updates the preferred cipher suite to be used.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 1, 2016.

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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   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Update to RFC 4572  . . . . . . . . . . . . . . . . . . . . .   2
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   RFC 4572 [RFC4572] specifies how to establish Transport Layer
   Security (TLS) connections using the Session Description Protocol
   (SDP) [RFC4566].

   RFC 4572 defines the SDP 'fingerprint' attribute, which is used to
   carry a secure hash value associated with a certificate.  However,
   RFC 4572 is currently unclear on whether multiple 'fingerprint' can
   be associated with a single SDP media description ("m= line")
   [RFC4566], and the associated semantics.

   RFC 4572 also specifies a preferred cipher suite.  However, the
   currently preferred cipher suite is considered outdated, and the
   preference needs to be updated.

   This document updates RFC 4572 [RFC4572] by clarifying the usage of
   multiple SDP 'fingerprint' attributes with a single TLS connection.
   The document also updates the preferred cipher suite to be used.

2.  Conventions

   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 [RFC2119].

3.  Update to RFC 4572

   This section updates section 5 of RFC 4572.  The change clarifies the
   usage and semantics of multiple SDP "fingerprint" attributes, and
   updates the preferred cipher suite.


Update to section 8.3.2
-----------------------

OLD TEXT:



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   Parties to a TLS session indicate their identities by presenting
   authentication certificates as part of the TLS handshake procedure.
   Authentication certificates are X.509 [6] certificates, as profiled
   by RFC 3279 [7], RFC 3280 [8], and RFC 4055 [9].

   In order to associate media streams with connections and to prevent
   unauthorized barge-in attacks on the media streams, endpoints MUST
   provide a certificate fingerprint.  If the X.509 certificate
   presented for the TLS connection matches the fingerprint presented in
   the SDP, the endpoint can be confident that the author of the SDP is
   indeed the initiator of the connection.

   A certificate fingerprint is a secure one-way hash of the DER
   (distinguished encoding rules) form of the certificate.  (Certificate
   fingerprints are widely supported by tools that manipulate X.509
   certificates; for instance, the command "openssl x509 -fingerprint"
   causes the command-line tool of the openssl package to print a
   certificate fingerprint, and the certificate managers for Mozilla and
   Internet Explorer display them when viewing the details of a
   certificate.)

   A fingerprint is represented in SDP as an attribute (an 'a' line).
   It consists of the name of the hash function used, followed by the
   hash value itself.  The hash value is represented as a sequence of
   uppercase hexadecimal bytes, separated by colons.  The number of
   bytes is defined by the hash function.  (This is the syntax used by
   openssl and by the browsers' certificate managers.  It is different
   from the syntax used to represent hash values in, e.g., HTTP digest
   authentication [18], which uses unseparated lowercase hexadecimal
   bytes.  It was felt that consistency with other applications of
   fingerprints was more important.)

   The formal syntax of the fingerprint attribute is given in Augmented
   Backus-Naur Form [10] in Figure 2.  This syntax extends the BNF
   syntax of SDP [1].

   attribute              =/ fingerprint-attribute

   fingerprint-attribute  =  "fingerprint" ":" hash-func SP fingerprint

   hash-func              =  "sha-1" / "sha-224" / "sha-256" /
                             "sha-384" / "sha-512" /
                             "md5" / "md2" / token
                             ; Additional hash functions can only come
                             ; from updates to RFC 3279

   fingerprint            =  2UHEX *(":" 2UHEX)
                             ; Each byte in upper-case hex, separated



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                             ; by colons.

   UHEX                   =  DIGIT / %x41-46 ; A-F uppercase

   Figure 2: Augmented Backus-Naur Syntax for the Fingerprint Attribute

   A certificate fingerprint MUST be computed using the same one-way
   hash function as is used in the certificate's signature algorithm.
   (This ensures that the security properties required for the
   certificate also apply for the fingerprint.  It also guarantees that
   the fingerprint will be usable by the other endpoint, so long as the
   certificate itself is.)  Following RFC 3279 [7] as updated by RFC
   4055 [9], therefore, the defined hash functions are 'SHA-1' [11]
   [19], 'SHA-224' [11], 'SHA-256' [11], 'SHA-384' [11], 'SHA-512' [11],
   'MD5' [12], and 'MD2' [13], with 'SHA-1' preferred.  A new IANA
   registry of Hash Function Textual Names, specified in Section 8,
   allows for addition of future tokens, but they may only be added if
   they are included in RFCs that update or obsolete RFC 3279 [7].
   Self-signed certificates (for which legacy certificates are not a
   consideration) MUST use one of the FIPS 180 algorithms (SHA-1,
   SHA-224, SHA-256, SHA-384, or SHA-512) as their signature algorithm,
   and thus also MUST use it to calculate certificate fingerprints.

   The fingerprint attribute may be either a session-level or a media-
   level SDP attribute.  If it is a session-level attribute, it applies
   to all TLS sessions for which no media-level fingerprint attribute is
   defined.


NEW TEXT:

   Parties to a TLS session indicate their identities by presenting
   authentication certificates as part of the TLS handshake procedure.
   Authentication certificates are X.509 [6] certificates, as profiled
   by RFC 3279 [7], RFC 3280 [8], and RFC 4055 [9].

   In order to associate media streams with connections and to prevent
   unauthorized barge-in attacks on the media streams, endpoints MUST
   provide a certificate fingerprint.  If the X.509 certificate
   presented for the TLS connection matches the fingerprint presented in
   the SDP, the endpoint can be confident that the author of the SDP is
   indeed the initiator of the connection.

   A certificate fingerprint is a secure one-way hash of the DER
   (distinguished encoding rules) form of the certificate.  (Certificate
   fingerprints are widely supported by tools that manipulate X.509
   certificates; for instance, the command "openssl x509 -fingerprint"
   causes the command-line tool of the openssl package to print a



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   certificate fingerprint, and the certificate managers for Mozilla and
   Internet Explorer display them when viewing the details of a
   certificate.)

   A fingerprint is represented in SDP as an attribute (an 'a' line).
   It consists of the name of the hash function used, followed by the
   hash value itself.  The hash value is represented as a sequence of
   uppercase hexadecimal bytes, separated by colons.  The number of
   bytes is defined by the hash function.  (This is the syntax used by
   openssl and by the browsers' certificate managers.  It is different
   from the syntax used to represent hash values in, e.g., HTTP digest
   authentication [18], which uses unseparated lowercase hexadecimal
   bytes.  It was felt that consistency with other applications of
   fingerprints was more important.)

   The formal syntax of the fingerprint attribute is given in Augmented
   Backus-Naur Form [10] in Figure 2.  This syntax extends the BNF
   syntax of SDP [1].

   attribute              =/ fingerprint-attribute

   fingerprint-attribute  =  "fingerprint" ":" hash-func SP fingerprint

   hash-func              =  "sha-1" / "sha-224" / "sha-256" /
                             "sha-384" / "sha-512" /
                             "md5" / "md2" / token
                             ; Additional hash functions can only come
                             ; from updates to RFC 3279

   fingerprint            =  2UHEX *(":" 2UHEX)
                             ; Each byte in upper-case hex, separated
                             ; by colons.

   UHEX                   =  DIGIT / %x41-46 ; A-F uppercase

   Figure 2: Augmented Backus-Naur Syntax for the Fingerprint Attribute

   A certificate fingerprint MUST be computed using the same one-way
   hash function as is used in the certificate's signature algorithm.
   (This ensures that the security properties required for the
   certificate also apply for the fingerprint.  It also guarantees that
   the fingerprint will be usable by the other endpoint, so long as the
   certificate itself is.)  Following RFC 3279 [7] as updated by RFC
   4055 [9], therefore, the defined hash functions are 'SHA-1' [11]
   [19], 'SHA-224' [11], 'SHA-256' [11], 'SHA-384' [11], 'SHA-512' [11],
   'MD5' [12], and 'MD2' [13], with 'SHA-256' preferred.  A new IANA
   registry of Hash Function Textual Names, specified in Section 8,
   allows for addition of future tokens, but they may only be added if



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   they are included in RFCs that update or obsolete RFC 3279 [7].
   Self-signed certificates (for which legacy certificates are not a
   consideration) MUST use one of the FIPS 180 algorithms (SHA-1,
   SHA-224, SHA-256, SHA-384, or SHA-512) as their signature algorithm,
   and thus also MUST use it to calculate certificate fingerprints.

   The fingerprint attribute may be either a session-level or a media-
   level SDP attribute.  If it is a session-level attribute, it applies
   to all TLS sessions for which no media-level fingerprint attribute is
   defined.



4.  Security Considerations

   This document improves security.

5.  Acknowledgements

   TBD

6.  Change Log

   [RFC EDITOR NOTE: Please remove this section when publishing]

   Changes from draft-holmberg-mmusic-4572-update-xx

   o  Add text

7.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              DOI 10.17487/RFC3264, June 2002,
              <http://www.rfc-editor.org/info/rfc3264>.

   [RFC4572]  Lennox, J., "Connection-Oriented Media Transport over the
              Transport Layer Security (TLS) Protocol in the Session
              Description Protocol (SDP)", RFC 4572,
              DOI 10.17487/RFC4572, July 2006,
              <http://www.rfc-editor.org/info/rfc4572>.





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   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
              July 2006, <http://www.rfc-editor.org/info/rfc4566>.

Author's Address

   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: christer.holmberg@ericsson.com






































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