Updates to RFC 4572
Ericsson
Hirsalantie 11
Jorvas
02420
Finland
christer.holmberg@ericsson.com
RAI
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.
RFC 4572 specifies
how to establish Transport Layer Security (TLS) connections using
the Session Description Protocol (SDP) .
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")
, 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cipher suite is considered outdated, and the preference needs to be updated.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
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 .
This section updates section 5 of RFC 4572.
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
Removed prevously added requirement that endpoint must calcuate
at least one fingerprint using a hash function that was also used
by the peer.
Changes from draft-ietf-mmusic-4572-update-03
Mandatory (except in specific situations) to provide a fingerprint calculated using SHA-256.
When an endpoint receives fingerprints from its peer, the endpoint must (except in specific
situations) calculate at least one fingerpint using a hash function that was also used by the peer.
Changes from draft-ietf-mmusic-4572-update-02
Editorial fixes based on comments from Martin Thomson.
Non-used references removed.
Changes from draft-ietf-mmusic-4572-update-01
Changes based on comments from Martin Thomson.
- Editorial fixes
Changes in handling of multiple fingerprints.
- Sender must send same set of hash functions for each offered certificate.
- Receiver must check the hash function it considers most secure for a match. It may check other hash functions.
Changes from draft-ietf-mmusic-4572-update-00
Changes in handling of multiple fingerprints.
- Number of fingerprints calculated for each certificate does not have to match.
- Clarified that receiver shall check check fingerprints using hash algorithms it considers safe.
- Additional text added to security considerations section.
Changes from draft-holmberg-mmusic-4572-update-01
Adopted WG document (draft-ietf-mmusic-4572-update-00) submitted.
IANA considerations section added.