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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force L. Velvindron, Ed. 3 Internet-Draft Hackers.mu 4 Intended status: Standards Track April 18, 2017 5 Expires: October 20, 2017 7 Increase minimum recommended modulus size to 2048 bits 8 draft-lvelvindron-curdle-dh-group-exchange-00 10 Abstract 12 The Diffie-Hellman (DH) Group Exchange for the Secure Shell (SSH) 13 Transport layer Protocol specifies that servers and clients should 14 support groups with a modulus length of k bits, where the recommended 15 minumum value is 1024 bits. Recent security research has shown that 16 a minimum value of 1024 bits is insufficient against state-sponsored 17 actors. As such, this document formally updates RFC 4419 [RFC4419] 18 such that the minimum recommended value for k is 2048 bits and the 19 group size is 2048 bits at minimum. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on October 20, 2017. 38 Copyright Notice 40 Copyright (c) 2017 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 57 2. 2048 bits DH Group . . . . . . . . . . . . . . . . . . . . . 2 58 3. Security Considerations . . . . . . . . . . . . . . . . . . . 2 59 4. References . . . . . . . . . . . . . . . . . . . . . . . . . 3 60 4.1. Normative References . . . . . . . . . . . . . . . . . . 3 61 4.2. Informative References . . . . . . . . . . . . . . . . . 3 62 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 3 64 1. Introduction 66 RFC4419 [RFC4419] specifies a recommended minimum size of 1024 bits 67 for k, which is the modulus length of the DH Group. It also suggests 68 that in all cases, the size of the group needs be at least 1024 bits. 69 This document updates RFC 4419 [RFC4419] so that the minimum 70 recommended size be 2048 bits. 72 1.1. Requirements Language 74 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 75 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 76 document are to be interpreted as described in RFC 2119 [RFC2119]. 78 2. 2048 bits DH Group 80 Recent research [LOGJAM] strongly suggests that DH groups that are 81 1024 bits can be broken by state actors, and possibly an organization 82 with enough computing resources. The authors show how they are able 83 to break 768 bits DH group and extrapolate the attack to 1024 bits DH 84 groups. In their analysis, they show that breaking 1024 bits can be 85 done with enough computing resources. This document updates section 86 3 Paragraph 9 : Servers and clients SHOULD support groups with a 87 modulus length of k bits where 2048 <= k <= 8192. The recommended 88 minimum values for min and max are 2048 and 8192, respectively. This 89 document also updates Section 3 Paragraph 11: In all cases, ths size 90 of the group SHOULD be at least 2048 bits. 92 3. Security Considerations 94 This document discusses security issues of DH groups that are 1024 95 bits in size, and formally updates the minimum size of DH groups to 96 be 2048 bits. 98 4. References 100 4.1. Normative References 102 [LOGJAM] Adrian, D., Bhargavan, K., Durumeric, Z., Gaudry, P., 103 Green, M., Halderman, J., Heninger, N., Springall, D., 104 ThomA(C), E., Valenta, L., VanderSloot, B., Wustrow, E., 105 Zanella-BA(C)guelin, S., and P. Zimmermann, "Imperfect 106 Forward Secrecy: How Diffie-Hellman Fails in Practice", 107 ACM Conference on Computer and Communications Security 108 (CCS) 2015, 2015, . 111 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 112 Requirement Levels", BCP 14, RFC 2119, 113 DOI 10.17487/RFC2119, March 1997, 114 . 116 4.2. Informative References 118 [RFC4419] Friedl, M., Provos, N., and W. Simpson, "Diffie-Hellman 119 Group Exchange for the Secure Shell (SSH) Transport Layer 120 Protocol", RFC 4419, DOI 10.17487/RFC4419, March 2006, 121 . 123 Author's Address 125 Loganaden Velvindron (editor) 126 Hackers.mu 127 88, Avenue De Plevitz 128 Roches Brunes 129 MU 131 Phone: +230 59762817 132 Email: logan@hackers.mu