Network Working Group d. bider Internet-Draft Bitvise Limited Updates: 4253 (if approved) M. Baushke Intended status: Standards Track Juniper Networks, Inc. Expires: May 17, 2012 November 14, 2011 SHA-2 Data Integrity Verification for the Secure Shell (SSH) Transport Layer Protocol draft-dbider-sha2-mac-for-ssh-04 Abstract This memo defines algorithm names and parameters for use of some of the SHA-2 family of secure hash algorithms for data integrity verification in the Secure Shell (SSH) protocol. This document adds new Message Authentication Code (MAC) algorithms to the set defined in RFC 4253 [RFC4253]. 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 May 17, 2012. Copyright Notice Copyright (c) 2011 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 bider & Baushke Expires May 17, 2012 [Page 1]
Internet-Draft SHA-2 MAC for SSH November 2011 include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. 1. Overview and Rationale SSH [RFC4251] is a very common protocol for secure remote login on the Internet. Currently, SSH defines data integrity verification using SHA-1 and MD5 algorithms [RFC4253]. Due to recent security concerns with these two algorithms [RFC6151][RFC6194], implementors and users request support for data integrity verification using some of the SHA-2 family of of secure hash algorithms. Please send comments on this draft to ietf-ssh@NetBSD.org. 1.1. Requirements Terminology 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]. 2. Data Integrity Algorithms This memo adopts the style and conventions of [RFC4253] in defining new data integrity algorithms. The following new data integrity algorithms are defined: hmac-sha2-256 RECOMMENDED HMAC-SHA2-256 (digest length = 32 bytes, key length = 32 bytes) hmac-sha2-256-96 OPTIONAL first 96 bits of HMAC-SHA2-256 (digest length = 12 bytes, key length = 32 bytes) hmac-sha2-512 OPTIONAL HMAC-SHA2-512 (digest length = 64 bytes, key length = 64 bytes) hmac-sha2-512-96 OPTIONAL first 96 bits of HMAC-SHA2-512 (digest length = 12 bytes, key length = 64 bytes) Figure 1 bider & Baushke Expires May 17, 2012 [Page 2]
Internet-Draft SHA-2 MAC for SSH November 2011 The HMAC mechanism is defined in [RFC2104]. The SHA-2 family of secure hash algorithms are defined in [FIPS-180-3]. Sample code for the SHA-based HMAC algorithms are available in [RFC6234]. The variants HMAC-SHA2-224 and HMAC-SHA2-384 algorithms were considered, but not added to this list as they have the same computational requirements of HMAC-SHA2-256 and HMAC-SHA2-512 respectively and do not seem to be much used in practice. Test vectors for use of HMAC with SHA-2 are provided in [RFC4231]. Users, implementors, and administrators may choose to put these new Macs into the proposal ahead of the REQUIRED hmac-sha1 algorithm defined in [RFC4253] so that they would be negotiated first. 3. IANA Considerations This document augments the MAC Algorithm Names in [RFC4253] and [RFC4250]. IANA is requested to update the SSH algorithm registry with the following entries: MAC Algorithm Name Reference Note hmac-sha2-256 This draft Section 2 hmac-sha2-256-96 This draft Section 2 hmac-sha2-512 This draft Section 2 hmac-sha2-512-96 This draft Section 2 Figure 2 4. Security Considerations The security considerations of RFC 4253 [RFC4253] apply to this document. The current attacks on HMAC-SHA1 do not yet seem to indicate a practical vulnerability when used as a message authentication code. National Institute of Standards and Technology (NIST) publications: NIST Special Publication (SP) 800-107 [800-107] and NIST SP 800-131 [800-131] suggest that HMAC-SHA1 and HMAC-SHA2-256 have a security strength of 128 bits and 256 bits respectively. Even so, many users seem to be interested in the perceived safety of bider & Baushke Expires May 17, 2012 [Page 3]
Internet-Draft SHA-2 MAC for SSH November 2011 using a stronger algorithm than HMAC-SHA1. 5. References 5.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4231] Nystrom, M., "Identifiers and Test Vectors for HMAC-SHA- 224, HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512", RFC 4231, December 2005. [RFC4253] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Transport Layer Protocol", RFC 4253, January 2006. 5.2. Informative References [FIPS-180-3] National Institute of Standards and Technology (NIST), "Secure Hash Standard (SHS)", FIPS PUB 180-3, October 2008. [800-107] National Institute of Standards and Technology (NIST), "Recommendation for Applications Using Approved Hash Algorithms", NIST Special Publication 800-107, February 2009. [800-131] National Institute of Standards and Technology (NIST), "Recommendation for the Transitioning of Cryptographic Algorithms and Key Sizes", DRAFT NIST Special Publication 800-131, January 2010. [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- Hashing for Message Authentication", RFC 2104, February 1997. [RFC4250] Lehtinen, S. and C. Lonvick, "SSH Protocol Assigned Numbers", RFC 4250, January 2006. [RFC4251] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Protocol Architecture", RFC 4251, January 2006. [RFC6151] Turner, S. and L. Chen, "Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms", RFC 6151, March 2011. bider & Baushke Expires May 17, 2012 [Page 4]
Internet-Draft SHA-2 MAC for SSH November 2011 [RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security Considerations for the SHA-0 and SHA-1 Message-Digest Algorithms", RFC 6194, March 2011. [RFC6234] Eastlake, D. and T. Hansen, "US Secure Hash Algorithms (SHA and SHA-based HMAC and HKDF)", RFC 6234, May 2011. Authors' Addresses denis bider Bitvise Limited Suites 41/42, Victoria House 26 Main Street Gibraltar GI Phone: +1 869 762 1410 Email: ietf-ssh2@denisbider.com URI: http://www.bitvise.com/ Mark D. Baushke Juniper Networks, Inc. 1194 N Mathilda Av Sunnyvale, CA 94089-1206 US Phone: +1 408 745 2952 Email: mdb@juniper.net URI: http://www.juniper.net/ bider & Baushke Expires May 17, 2012 [Page 5]
