| 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
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.
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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 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 However, the currently preferred cipher suite is considered outdated, and the preference needs to be updated.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.
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. 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:
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
; 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
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
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.
This document improves security.
TBD
[RFC EDITOR NOTE: Please remove this section when publishing]
Changes from draft-holmberg-mmusic-4572-update-xx
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [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. |