| Network Working Group | C. Holmberg |
| Internet-Draft | Ericsson |
| Updates: 4572 (if approved) | June 10, 2016 |
| Intended status: Standards Track | |
| Expires: December 12, 2016 |
Updates to RFC 4572
draft-ietf-mmusic-4572-update-05.txt
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 with a stronger cipher suite, and removes the requirement to use the same hash function for calculating a certificate fingerprint that is used to calculate the certificate signature.
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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 (fingerprint) associated with a certificate. However, RFC 4572 is currently unclear on whether multiple 'fingerprint' attributes can be associated with a single SDP media description ("m= line") [RFC4566], and the associated semantics. Multiple fingerprints are needed if an endpoints 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 However, the currently preferred cipher suite is considered outdated, and the preference needs to be updated.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 change also requires that multiple 'fingerprint' attributes can be associated with a single "m=" line, so that implementations are able to provide fingerprints calculated using updated hash functions alongside those that are needed to interoperate with existing implementations.
This document updates RFC 4572 [RFC4572] by clarifying the usage of multiple SDP 'fingerprint' attributes. It is clarified that multiple 'fingerprint' attributes can be used to carry fingerprints, calculated using different hash functions, associated with a given certificate, and to carry fingerprints associated with multiple certificates. The fingerprint matching procedure, when multiple fingerprints are provided, are also clarified. The document also updates the preferred cipher suite with a stronger cipher suite, and removes the requirement to use the same hash function for calculating a certificate fingerprint and certificate signature.
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].
This section updates section 5 of RFC 4572.
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].
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 functions. It can also
occur if one or more fingerprints associated with multiple
certificates have been calculated. This might be needed if multiple
certificates will be used for media associated with an m- line
(e.g. if separate certificates are used for RTP and RTCP), or where
it is not known which certificate will be used when the
fingerprints are exchanged. In such cases, one or more fingerprints
MUST be calculated for each possible certificate. An endpoint
MUST, as a minimum, calculate a fingerprint using the 'SHA-256'
hash function algorithm for each possible certificate, unless the
endpoint knows that the peer supports a stronger algorithm, or
unless the endpoint knows that the peer has not been upgraded to
support the 'SHA-256' algorithm, or unless the endpoint is used for
a service, or within an environment that mandates usage of a
stronger algorithm.
If fingerprints associated with multiple certificates are
calculated, the same set of hash functions MUST be used to
calculate fingerprints for each certificate associated with the
m- line.
For each used certificate, an endpoint MUST be able to match at
least one fingerprint, calculated using the hash function that the
endpoint supports and considers most secure, with the used
certificate. If the checked fingerprint does not match the used
certificate, the endpoint MUST NOT establish the TLS connection. In
addition, the endpoint MAY also check fingerprints calculated using
other hash functions that it has received for a match. For each
hash function checked, one of the received fingerprints calculated
using the hash function MUST match the used certificate.
NOTE: The SDP fingerprint attribute does not contain a reference to
a specific certificate. Endpoints need to compare the fingerprint
with a certificate hash in order to look for a match.
This document improves security. It updates the preferred hash function cipher suite from SHA-1 to SHA-256. By clarifying the usage and handling of multiple fingerprints, the document also enables hash agility, and incremental deployment of newer, and more secure, cipher suites.
This document makes no requests from IANA.
Martin Thomson, Paul Kyzivat, Jonathan Lennox and Roman Shpount provided valuable comments and input on this document.
[RFC EDITOR NOTE: Please remove this section when publishing]
Changes from draft-ietf-mmusic-4572-update-04
Changes from draft-ietf-mmusic-4572-update-03
Changes from draft-ietf-mmusic-4572-update-02
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| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC4566] | Handley, M., Jacobson, V. and C. Perkins, "SDP: Session Description Protocol", RFC 4566, DOI 10.17487/RFC4566, July 2006. |
| [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. |