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Baushke 3 Internet-Draft Juniper Networks, Inc. 4 Updates: 4253, 4432 (if approved) March 6, 2017 5 Intended status: Standards Track 6 Expires: September 7, 2017 8 More Modular Exponential (MODP) Diffie-Hellman (DH) Key Exchange (KEX) 9 Groups for Secure Shell (SSH) 10 draft-ietf-curdle-ssh-modp-dh-sha2-02 12 Abstract 14 This document defines added Modular Exponential (MODP) Groups for the 15 Secure Shell (SSH) protocol using SHA-2 hashes. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at http://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on September 7, 2017. 34 Copyright Notice 36 Copyright (c) 2017 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (http://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 1. Overview and Rationale 51 Secure Shell (SSH) is a common protocol for secure communication on 52 the Internet. Due to recent security concerns with SHA-1 [RFC6194] 53 and with MODP groups with less than 2048 bits [NIST-SP-800-131Ar1] 54 implementer and users request support for larger Diffie Hellman (DH) 55 MODP group sizes with data integrity verification using the SHA-2 56 family of secure hash algorithms as well as MODP groups providing 57 more security. 59 The United States Information Assurance Directorate at the National 60 Security Agency has published a FAQ [MFQ-U-OO-815099-15] suggesting 61 both: a) DH groups using less than 3072-bits, and b) the use of SHA-2 62 based hashes less than SHA2-384, are no longer sufficient for 63 transport of Top Secret information. For this reason, the new MODP 64 groups are being introduced starting with the MODP 3072-bit group 15 65 are all using SHA2-512 as the hash algorithm. 67 The DH 2048-bit MODP group 14 is already present in most SSH 68 implementations and most implementations already have a SHA2-256 69 implementation, so diffie-hellman-group14-sha256 is provided as an 70 easy to implement and faster to use key exchange for small embedded 71 applications. 73 Please send comments on this draft to ietf-ssh@NetBSD.org and ietf- 74 curdle@ietf.org. 76 2. Requirements Language 78 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 79 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 80 document are to be interpreted as described in [RFC2119]. 82 3. Key Exchange Algorithms 84 This memo adopts the style and conventions of [RFC4253] in specifying 85 how the use of new data key exchange is indicated in SSH. 87 The following new key exchange algorithms are defined: 89 Key Exchange Method Name 90 diffie-hellman-group14-sha256 91 diffie-hellman-group15-sha512 92 diffie-hellman-group16-sha512 93 diffie-hellman-group17-sha512 94 diffie-hellman-group18-sha512 96 Figure 1 98 The SHA-2 family of secure hash algorithms are defined in 99 [FIPS-180-4]. 101 The method of key exchange used for the name "diffie-hellman- 102 group14-sha256" is the same as that for "diffie-hellman-group14-sha1" 103 except that the SHA2-256 hash algorithm is used. 105 The method of key exchange used for the name "gss-group14-sha256-*" 106 is the same as that for "gss-group14-sha1-*" except that the SHA2-256 107 hash algorithm is used. 109 The group15 through group18 names are the same as those specified in 110 [RFC3526] 3071-bit MODP Group 15, 4096-bit MODP Group 16, 6144-bit 111 MODP Group 17, and 8192-bit MODP Group 18. 113 The SHA2-512 algorithm is to be used when "sha512" is specified as a 114 part of the key exchange method name. 116 4. IANA Considerations 118 This document augments the Key Exchange Method Names in [RFC4253]. 120 IANA is requested to add to the Key Exchange Method Names algorithm 121 registry with the following entries: 123 Key Exchange Method Name Reference 124 ----------------------------- ---------- 125 diffie-hellman-group14-sha256 This Draft 126 diffie-hellman-group15-sha512 This Draft 127 diffie-hellman-group16-sha512 This Draft 128 diffie-hellman-group17-sha512 This Draft 129 diffie-hellman-group18-sha512 This Draft 131 [TO BE REMOVED: This registration should take place at the following 132 location: ] 135 5. Security Considerations 137 The security considerations of [RFC4253] apply to this document. 139 The security considerations of [RFC3526] suggest that these MODP 140 groups have security strengths given in this table. They are based 141 on [RFC3766] Determining Strengths For Public Keys Used For 142 Exchanging Symmetric Keys. 144 Group modulus security strength estimates (RFC3526) 146 +--------+----------+---------------------+---------------------+ 147 | Group | Modulus | Strength Estimate 1 | Strength Estimate 2 | 148 | | +----------+----------+----------+----------+ 149 | | | | exponent | | exponent | 150 | | | in bits | size | in bits | size | 151 +--------+----------+----------+----------+----------+----------+ 152 | 14 | 2048-bit | 110 | 220- | 160 | 320- | 153 | 15 | 3072-bit | 130 | 260- | 210 | 420- | 154 | 16 | 4096-bit | 150 | 300- | 240 | 480- | 155 | 17 | 6144-bit | 170 | 340- | 270 | 540- | 156 | 18 | 8192-bit | 190 | 380- | 310 | 620- | 157 +--------+----------+---------------------+---------------------+ 159 Figure 2 161 Many users seem to be interested in the perceived safety of using 162 larger MODP groups and hashing with SHA2-based algorithms. 164 6. References 166 6.1. Normative References 168 [FIPS-180-4] 169 National Institute of Standards and Technology, "Secure 170 Hash Standard (SHS)", FIPS PUB 180-4, August 2015, 171 . 174 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 175 Requirement Levels", BCP 14, RFC 2119, 176 DOI 10.17487/RFC2119, March 1997, 177 . 179 [RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP) 180 Diffie-Hellman groups for Internet Key Exchange (IKE)", 181 RFC 3526, DOI 10.17487/RFC3526, May 2003, 182 . 184 [RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 185 Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253, 186 January 2006, . 188 6.2. Informative References 190 [MFQ-U-OO-815099-15] 191 "National Security Agency/Central Security Service", "CNSA 192 Suite and Quantum Computing FAQ", January 2016, 193 . 197 [NIST-SP-800-131Ar1] 198 Barker, and Roginsky, "Transitions: Recommendation for the 199 Transitioning of the Use of Cryptographic Algorithms and 200 Key Lengths", NIST Special Publication 800-131A Revision 201 1, November 2015, 202 . 205 [RFC3766] Orman, H. and P. Hoffman, "Determining Strengths For 206 Public Keys Used For Exchanging Symmetric Keys", BCP 86, 207 RFC 3766, DOI 10.17487/RFC3766, April 2004, 208 . 210 [RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security 211 Considerations for the SHA-0 and SHA-1 Message-Digest 212 Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011, 213 . 215 Author's Address 217 Mark D. Baushke 218 Juniper Networks, Inc. 219 1133 Innovation Way 220 Sunnyvale, CA 94089-1228 221 US 223 Phone: +1 408 745 2952 224 Email: mdb@juniper.net 225 URI: http://www.juniper.net/