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 working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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 document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Holmberg Expires September 22, 2016 [Page 1] Internet-Draft Updates to RFC 4572 March 2016 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 Holmberg Expires September 22, 2016 [Page 2] Internet-Draft Updates to RFC 4572 March 2016 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]. Holmberg Expires September 22, 2016 [Page 3] Internet-Draft Updates to RFC 4572 March 2016 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, . Holmberg Expires September 22, 2016 [Page 4] Internet-Draft Updates to RFC 4572 March 2016 [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 Holmberg Expires September 22, 2016 [Page 5]