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Baushke 3 Internet-Draft Juniper Networks, Inc. 4 Updates: 4250, 4253 (if approved) May 8, 2017 5 Intended status: Standards Track 6 Expires: November 9, 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-sha2-05 12 Abstract 14 This document defines added Modular Exponential (MODP) Groups for the 15 Secure Shell (SSH) protocol using SHA-2 hashes. This document 16 updates RFC 4250. This document updates RFC 4253. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on November 9, 2017. 35 Copyright Notice 37 Copyright (c) 2017 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 This document may contain material from IETF Documents or IETF 51 Contributions published or made publicly available before November 52 10, 2008. The person(s) controlling the copyright in some of this 53 material may not have granted the IETF Trust the right to allow 54 modifications of such material outside the IETF Standards Process. 55 Without obtaining an adequate license from the person(s) controlling 56 the copyright in such materials, this document may not be modified 57 outside the IETF Standards Process, and derivative works of it may 58 not be created outside the IETF Standards Process, except to format 59 it for publication as an RFC or to translate it into languages other 60 than English. 62 1. Overview and Rationale 64 Secure Shell (SSH) is a common protocol for secure communication on 65 the Internet. Due to recent security concerns with SHA-1 [RFC6194] 66 and with MODP groups with less than 2048 bits [NIST-SP-800-131Ar1] 67 implementer and users request support for larger Diffie Hellman (DH) 68 MODP group sizes with data integrity verification using the SHA-2 69 family of secure hash algorithms as well as MODP groups providing 70 more security. 72 The United States Information Assurance Directorate at the National 73 Security Agency has published a FAQ [MFQ-U-OO-815099-15] suggesting 74 both: a) DH groups using less than 3072-bits, and b) the use of SHA-2 75 based hashes less than SHA2-384, are no longer sufficient for 76 transport of Top Secret information. For this reason, the new MODP 77 groups are being introduced starting with the MODP 3072-bit group 15 78 are all using SHA2-512 as the hash algorithm. 80 The DH 2048-bit MODP group 14 is already present in most SSH 81 implementations and most implementations already have a SHA2-256 82 implementation, so diffie-hellman-group14-sha256 is provided as an 83 easy to implement and faster to use key exchange for small embedded 84 applications. 86 It is intended that these new MODP groups with SHA-2 based hashes 87 update the [RFC4253] section 6.4 and [RFC4250] section 4.10 88 standards. 90 [TO BE REMOVED: Please send comments on this draft to 91 curdle@ietf.org.] 93 2. Requirements Language 95 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 96 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 97 document are to be interpreted as described in RFC 2119 [RFC2119]. 99 3. Key Exchange Algorithms 101 This memo adopts the style and conventions of [RFC4253] in specifying 102 how the use of new data key exchange is indicated in SSH. 104 The following new key exchange algorithms are defined: 106 Key Exchange Method Name 107 diffie-hellman-group14-sha256 108 diffie-hellman-group15-sha512 109 diffie-hellman-group16-sha512 110 diffie-hellman-group17-sha512 111 diffie-hellman-group18-sha512 113 Figure 1 115 The SHA-2 family of secure hash algorithms are defined in [RFC6234]. 117 The method of key exchange used for the name "diffie-hellman- 118 group14-sha256" is the same as that for "diffie-hellman-group14-sha1" 119 except that the SHA2-256 hash algorithm is used. It is recommended 120 that diffie-hellman-group14-sha256 SHOULD be supported to smooth the 121 transition to newer group sizes. 123 The group15 through group18 names are the same as those specified in 124 [RFC3526] 3072-bit MODP Group 15, 4096-bit MODP Group 16, 6144-bit 125 MODP Group 17, and 8192-bit MODP Group 18. 127 The SHA2-512 algorithm is to be used when "sha512" is specified as a 128 part of the key exchange method name. 130 4. IANA Considerations 132 This document augments the Key Exchange Method Names in [RFC4253] and 133 [RFC4250]. 135 IANA is requested to add to the Key Exchange Method Names algorithm 136 registry [IANA-KEX] with the following entries: 138 Key Exchange Method Name Reference 139 ----------------------------- ---------- 140 diffie-hellman-group14-sha256 This Draft 141 diffie-hellman-group15-sha512 This Draft 142 diffie-hellman-group16-sha512 This Draft 143 diffie-hellman-group17-sha512 This Draft 144 diffie-hellman-group18-sha512 This Draft 146 [TO BE REMOVED: This registration should take place at the following 147 location: ] 150 5. Security Considerations 152 The security considerations of [RFC4253] apply to this document. 154 The security considerations of [RFC3526] suggest that these MODP 155 groups have security strengths given in this table. They are based 156 on [RFC3766] Determining Strengths For Public Keys Used For 157 Exchanging Symmetric Keys. 159 Group modulus security strength estimates (RFC3526) 161 +--------+----------+---------------------+---------------------+ 162 | Group | Modulus | Strength Estimate 1 | Strength Estimate 2 | 163 | | +----------+----------+----------+----------+ 164 | | | | exponent | | exponent | 165 | | | in bits | size | in bits | size | 166 +--------+----------+----------+----------+----------+----------+ 167 | 14 | 2048-bit | 110 | 220- | 160 | 320- | 168 | 15 | 3072-bit | 130 | 260- | 210 | 420- | 169 | 16 | 4096-bit | 150 | 300- | 240 | 480- | 170 | 17 | 6144-bit | 170 | 340- | 270 | 540- | 171 | 18 | 8192-bit | 190 | 380- | 310 | 620- | 172 +--------+----------+---------------------+---------------------+ 174 Figure 2 176 Using a fixed set of Diffie-Hellman parameters makes them a high 177 value target for precomputation. Generating additional sets of 178 primes to be used, or moving to larger values is a mitigation against 179 this issue. Care should be taken to avoid backdoored primes ([SNFS]) 180 by using "nothing up my sleve" parameters. 182 6. References 184 6.1. Normative References 186 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 187 Requirement Levels", BCP 14, RFC 2119, 188 DOI 10.17487/RFC2119, March 1997, 189 . 191 [RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP) 192 Diffie-Hellman groups for Internet Key Exchange (IKE)", 193 RFC 3526, DOI 10.17487/RFC3526, May 2003, 194 . 196 [RFC4250] Lehtinen, S. and C. Lonvick, Ed., "The Secure Shell (SSH) 197 Protocol Assigned Numbers", RFC 4250, 198 DOI 10.17487/RFC4250, January 2006, 199 . 201 [RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 202 Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253, 203 January 2006, . 205 6.2. Informative References 207 [IANA-KEX] 208 Internet Assigned Numbers Authority (IANA), "Secure Shell 209 (SSH) Protocol Parameters: Key Exchange Method Names", 210 March 2017, . 213 [MFQ-U-OO-815099-15] 214 "National Security Agency/Central Security Service", "CNSA 215 Suite and Quantum Computing FAQ", January 2016, 216 . 220 [NIST-SP-800-131Ar1] 221 Barker, and Roginsky, "Transitions: Recommendation for the 222 Transitioning of the Use of Cryptographic Algorithms and 223 Key Lengths", NIST Special Publication 800-131A Revision 224 1, November 2015, 225 . 228 [RFC3766] Orman, H. and P. Hoffman, "Determining Strengths For 229 Public Keys Used For Exchanging Symmetric Keys", BCP 86, 230 RFC 3766, DOI 10.17487/RFC3766, April 2004, 231 . 233 [RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security 234 Considerations for the SHA-0 and SHA-1 Message-Digest 235 Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011, 236 . 238 [RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms 239 (SHA and SHA-based HMAC and HKDF)", RFC 6234, 240 DOI 10.17487/RFC6234, May 2011, 241 . 243 [SNFS] Fried, , Gaudry, , Heninger, , and Thome, "A kilobit 244 hidden SNFS discrete logarithm computation", 2016, 245 . 247 Author's Address 249 Mark D. Baushke 250 Juniper Networks, Inc. 251 1133 Innovation Way 252 Sunnyvale, CA 94089-1228 253 US 255 Phone: +1 408 745 2952 256 Email: mdb@juniper.net 257 URI: http://www.juniper.net/