Internet Engineering Task Force M. Baushke Internet-Draft Juniper Networks, Inc. Updates: 4253 (if approved) December 10, 2015 Intended status: Standards Track Expires: June 12, 2016 More Modular Exponential (MODP) Diffie-Hellman Groups for SSH draft-baushke-ssh-dh-group-sha2-01 Abstract This document defines two added Modular Exponential (MODP) Groups for the Secure Shell (SSH) protocol. It also updates [RFC4253] by specifying new RECOMMENDED and new OPTIONAL Diffie-Hellman key exchange algorithms using SHA-2 hashes. 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/. 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Baushke Expires June 12, 2016 [Page 1] Internet-Draft More MODP DH groups for SSH December 2015 1. Overview and Rationale Secure Shell (SSH) is a common protocol for secure communication on the Internet. In [RFC4253], SSH originally defined the Key Exchange Method Name diffie-hellman-group1-sha1 which used [RFC2409] Oakley Group 1 (a MODP group with 768 bits) and SHA-1 [RFC3174]. Due to recent security concerns with SHA-1 [RFC6194] and with MODP groups with less than 2048 bits [NIST-SP-800-131Ar1] implementors and users request support for larger MODP group sizes with data integrity verification using the SHA-2 family of secure hash algorithms as well as MODP groups providing more security. Please send comments on this draft to ietf-ssh@NetBSD.org. 2. Requirements Language 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. Key Exchange Algorithms This memo adopts the style and conventions of [RFC4253] in specifying how the use of new data key exchange is indicated in SSH. The following new key exchange algorithms are defined: Key Exchange Method Name Note diffie-hellman-group1-sha1 NOT RECOMMENDED diffie-hellman-group14-sha256 RECOMMENDED diffie-hellman-group15-sha256 RECOMMENDED diffie-hellman-group16-sha256 OPTIONAL Figure 1 The SHA-2 family of secure hash algorithms are defined in [FIPS-180-4]. The method of key exchange used for the name "diffie-hellman- group14-sha256" is the same as that for "diffie-hellman-group14-sha1" escept that the SHA2-256 hash algorith is used. The group15 and group16 names are the same as those specified in [RFC3526] as 3072-bit MODP Group 14 and 4096-bit MODP Group 15. Baushke Expires June 12, 2016 [Page 2] Internet-Draft More MODP DH groups for SSH December 2015 4. IANA Considerations This document augments the Key Exchange Method Names in [RFC4253]. IANA is requested to update the SSH algorithm registry with the following entries: Key Exchange Method Name Reference Note diffie-hellman-group1-sha1 RFC4253 NOT RECOMMENDED diffie-hellman-group14-sha256 This draft RECOMMENDED diffie-hellman-group15-sha256 This draft RECOMMENDED diffie-hellman-group16-sha256 This draft OPTIONAL Figure 2 It is RECOMMENDED that the new diffie-hellman-group14-sha256 method be proposed before the diffie-hellman-group14-sha1 method. 5. Security Considerations The security considerations of [RFC4253] apply to this document. The security considerations of [RFC3526] suggest that these MODP groups have security strengths given in this table. Group modulus security strength estimates +--------+----------+---------------------+---------------------+ | Group | Modulus | Strength Estimate 1 | Strength Estimate 2 | | | +----------+----------+----------+----------+ | | | | exponent | | exponent | | | | in bits | size | in bits | size | +--------+----------+----------+----------+----------+----------+ | 14 | 2048-bit | 110 | 220- | 160 | 320- | | 15 | 3072-bit | 130 | 260- | 210 | 420- | | 16 | 4096-bit | 150 | 300- | 240 | 480- | +--------+----------+---------------------+---------------------+ Figure 3 Many users seem to be interested in the perceived safety of using the SHA2-based algorithms for hashing. 6. References Baushke Expires June 12, 2016 [Page 3] Internet-Draft More MODP DH groups for SSH December 2015 6.1. Normative References [FIPS-180-4] National Institute of Standards and Technology, "Secure Hash Standard (SHS)", FIPS PUB 180-4, August 2015, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP) Diffie-Hellman groups for Internet Key Exchange (IKE)", RFC 3526, DOI 10.17487/RFC3526, May 2003, . [RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253, January 2006, . 6.2. Informative References [NIST-SP-800-131Ar1] Barker, and Roginsky, "Transitions: Recommendation for the Transitioning of the Use of Cryptographic Algorithms and Key Lengths", NIST Special Publication 800-131A Revision 1, November 2015, . [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998, . [RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1 (SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001, . [RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security Considerations for the SHA-0 and SHA-1 Message-Digest Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011, . Baushke Expires June 12, 2016 [Page 4] Internet-Draft More MODP DH groups for SSH December 2015 Author's Address Mark D. Baushke Juniper Networks, Inc. 1133 Innovation Way Sunnyvale, CA 94089-1228 US Phone: +1 408 745 2952 Email: mdb@juniper.net URI: http://www.juniper.net/ Baushke Expires June 12, 2016 [Page 5]