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Network Working Group C. Holmberg
Internet-Draft Ericsson
Updates: 4572 (if approved) March 21, 2016
Intended status: Standards Track
Expires: September 22, 2016


Updates to RFC 4572
draft-holmberg-mmusic-4572-update-01.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, and
removes the requirement to use the same hash function for calculating
the certificate fingerprint that is used to calculate the certificate
signature.

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
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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 22, 2016.

Copyright Notice

Copyright (c) 2016 IETF Trust and the persons identified as the
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Update to RFC 4572 . . . . . . . . . . . . . . . . . . . . . 3
3.1. Update to the sixth paragraph of section 5 . . . . . . . 3
3.2. New paragraphs to the end of section 5 . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
6. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 4
7. Normative References . . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5

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. Multiple 'fingerprint'
attributes are needed when an endpoint wants to provide multiple
fingerprint, using different hash functions, for a certificate.
Multiple 'fingerprint' attributes are also needed if an endpoint
wants to provide fingerprints associated with multiple certificates.
For example, with RTP-based media, an endpoint might use different
certificates for RTP and RTCP.

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currently preferred cipher suite is considered outdated, and the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

RFC 4572 mandates that the hash function used to calculate the
fingerprint is the same hash function used to calculate the
certificate signature. That requirement might prevent usage of
newer, stronger and more collision-safe hash functions for
calculating certificate fingerprints.

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, and




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removes the requirement to use the same hash function for calculating
the certificiate fingerprint and certificate signature.

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.

3.1. Update to the sixth paragraph of section 5


OLD TEXT:

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.


NEW TEXT:

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 they are included
in RFCs that update or obsolete RFC 3279 [7].






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3.2. New paragraphs to the end of section 5



NEW TEXT:

Multiple SDP fingerprint attributes can be associated with an m- line.
This can occur if multiple fingerprints have been calculated for a
certificate, using different hash algorithms. It can also occur if
multiple certificates might be used (e.g. separate certificates for
RTP and RTCP). In such cases, the same number of fingerprints MUST be
calculated for each certificate, and for each certificate the same set
of hash algorithms MUST be used.

An endpoint MUST be able to match at least one of the received
fingerprints with the cerficiate(s) to be used. If there is no match,
the endpoint MUST NOT establish the TLS connection.

NOTE: The SDP fingerprint attribute does not contain a reference to
a specific certificate. Endpoints need to compare all fingerprints with
the cerficiate hash when looking for a match.


4. Security Considerations

This document improves security.

5. Acknowledgements

Martin Thompson, Paul Kyzivat and Jonathan Lennox provided valuable
comments and input on this document.

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,
.





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[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002,
.

[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,
.

[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, .

Author's Address

Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland

Email: christer.holmberg@ericsson.com



























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