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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFCTBD' is mentioned on line 186, but not defined ** Obsolete normative reference: RFC 5246 (Obsoleted by RFC 8446) ** Obsolete normative reference: RFC 7525 (Obsoleted by RFC 9325) Summary: 2 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force L. Velvindron 3 Internet-Draft cyberstorm.mu 4 Updates: 5246 7525 (if approved) K. Moriarty 5 Intended status: Standards Track Dell Technologies 6 Expires: September 30, 2021 A. Ghedini 7 Cloudflare Inc. 8 March 29, 2021 10 Deprecating MD5 and SHA-1 signature hashes in TLS 1.2 11 draft-ietf-tls-md5-sha1-deprecate-06 13 Abstract 15 The MD5 and SHA-1 hashing algorithms are increasingly vulnerable to 16 attack and this document deprecates their use in TLS 1.2 digital 17 signatures. However, this document does not deprecate SHA-1 in HMAC 18 for record protection. This document updates RFC 5246 and RFC 7525. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at https://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on September 30, 2021. 37 Copyright Notice 39 Copyright (c) 2021 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (https://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 55 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 56 2. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 3 57 3. Certificate Request . . . . . . . . . . . . . . . . . . . . . 3 58 4. Server Key Exchange . . . . . . . . . . . . . . . . . . . . . 3 59 5. Certificate Verify . . . . . . . . . . . . . . . . . . . . . 3 60 6. Updates to RFC5246 . . . . . . . . . . . . . . . . . . . . . 3 61 7. Updates to RFC7525 . . . . . . . . . . . . . . . . . . . . . 4 62 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 63 9. Security Considerations . . . . . . . . . . . . . . . . . . . 5 64 10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 5 65 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 11.1. Normative References . . . . . . . . . . . . . . . . . . 5 67 11.2. Informative References . . . . . . . . . . . . . . . . . 6 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 70 1. Introduction 72 The usage of MD5 and SHA-1 for signature hashing in TLS 1.2 is 73 specified in [RFC5246]. MD5 and SHA-1 have been proven to be 74 insecure, subject to collision attacks [Wang]. In 2011, [RFC6151] 75 detailed the security considerations, including collision attacks for 76 MD5. NIST formally deprecated use of SHA-1 in 2011 77 [NISTSP800-131A-R2] and disallowed its use for digital signatures at 78 the end of 2013, based on both the Wang, et. al, attack and the 79 potential for brute-force attack. In 2016, researchers from INRIA 80 identified a new class of transcript collision attacks on TLS (and 81 other protocols) that rely on efficient collision-finding algorithms 82 on the underlying hash constructions [Transcript-Collision]. 83 Further, in 2017, researchers from Google and CWI Amsterdam 84 [SHA-1-Collision] proved SHA-1 collision attacks were practical. 85 This document updates [RFC5246] and [RFC7525] in such a way that MD5 86 and SHA-1 MUST NOT be used for digital signatures. However, this 87 document does not deprecate SHA-1 in HMAC for record protection. 89 1.1. Requirements Language 91 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 92 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 93 "OPTIONAL" in this document are to be interpreted as described in BCP 94 14 [RFC2119] [RFC8174] when, and only when, they appear in all 95 capitals, as shown here. 97 2. Signature Algorithms 99 Clients MUST NOT include MD5 and SHA-1 in the signature_algorithms 100 extension. If a client does not send a signature_algorithms 101 extension, then the server MUST abort the handshake and send a 102 handshake_failure alert, except when digital signatures are not used 103 (for example, when using PSK ciphers). 105 3. Certificate Request 107 Servers SHOULD NOT include MD5 and SHA-1 in CertificateRequest 108 messages. 110 4. Server Key Exchange 112 Servers MUST NOT include MD5 and SHA-1 in ServerKeyExchange messages. 113 If a client receives a MD5 or SHA-1 signature in a ServerKeyExchange 114 message it MUST abort the connection with the illegal_parameter 115 alert. 117 5. Certificate Verify 119 Clients MUST NOT include MD5 and SHA-1 in CertificateVerify messages. 120 If a server receives a CertificateVerify message with MD5 or SHA-1 it 121 MUST abort the connection with handshake_failure or 122 insufficient_security alert. 124 6. Updates to RFC5246 126 [RFC5246], The Transport Layer Security (TLS) Protocol Version 1.2, 127 suggests that implementations can assume support for MD5 and SHA-1 by 128 their peer. This update changes the suggestion to assume support for 129 SHA-256 instead, due to MD5 and SHA-1 being deprecated. 131 In Section 7.4.1.4.1: the text should be revised from: 133 OLD: 135 "Note: this is a change from TLS 1.1 where there are no explicit 136 rules, but as a practical matter one can assume that the peer 137 supports MD5 and SHA- 1." 139 NEW: 141 "Note: This is a change from TLS 1.1 where there are no explicit 142 rules, but as a practical matter one can assume that the peer 143 supports SHA-256." 145 7. Updates to RFC7525 147 [RFC7525], Recommendations for Secure Use of Transport Layer Security 148 (TLS) and Datagram Transport Layer Security (DTLS) recommends use of 149 SHA-256 as a minimum requirement. This update moves the minimum 150 recommendation to use stronger language deprecating use of both SHA-1 151 and MD5. The prior text did not explicitly include MD5 or SHA-1; and 152 this text adds guidance to ensure that these algorithms have been 153 deprecated. 155 Section 4.3: 157 OLD: 159 When using RSA, servers SHOULD authenticate using certificates with 160 at least a 2048-bit modulus for the public key. In addition, SHA-256 161 hash algorithm MUST be used (see [CAB-Baseline] for more details). 162 Clients SHOULD indicate to servers that they request SHA-256, by 163 using the "Signature Algorithms" extension defined in TLS 1.2. 165 NEW: 167 Servers SHOULD authenticate using certificates with at least a 168 2048-bit modulus for the public key. 170 In addition, the SHA-256 hash algorithm MUST be used; and SHA-1 or 171 MD5 MUST NOT be used (see [CAB-Baseline] for more details). Clients 172 MUST indicate to servers that they request SHA-256, by using the 173 "Signature Algorithms" extension defined in TLS 1.2. 175 8. IANA Considerations 177 The document updates the "TLS SignatureScheme" registry to change the 178 recommended status of SHA-1 based signature schemes to N (not 179 recommended) as defined by [RFC8447]. The following entries are to 180 be updated: 182 +--------+----------------+-------------+--------------------+ 183 | Value | Description | Recommended | Reference | 184 +--------+----------------+-------------+--------------------+ 185 | 0x0201 | rsa_pkcs1_sha1 | N | [RFC8446] [RFCTBD] | 186 | 0x0203 | ecdsa_sha1 | N | [RFC8446] [RFCTBD] | 187 +--------+----------------+-------------+--------------------+ 189 Other entries of the registry remain the same. 191 9. Security Considerations 193 Concerns with TLS 1.2 implementations falling back to SHA-1 is an 194 issue. This document updates the TLS 1.2 specification to deprecate 195 support for MD5 and SHA-1 for digital signatures. However, this 196 document does not deprecate SHA-1 in HMAC for record protection. 198 10. Acknowledgement 200 The authors would like to thank Hubert Kario for his help in writing 201 the initial draft. We are also grateful to Daniel Migault, Martin 202 Thomson and David Cooper for their feedback. 204 11. References 206 11.1. Normative References 208 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 209 Requirement Levels", BCP 14, RFC 2119, 210 DOI 10.17487/RFC2119, March 1997, 211 . 213 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 214 (TLS) Protocol Version 1.2", RFC 5246, 215 DOI 10.17487/RFC5246, August 2008, 216 . 218 [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, 219 "Recommendations for Secure Use of Transport Layer 220 Security (TLS) and Datagram Transport Layer Security 221 (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 222 2015, . 224 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 225 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 226 May 2017, . 228 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 229 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 230 . 232 [RFC8447] Salowey, J. and S. Turner, "IANA Registry Updates for TLS 233 and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018, 234 . 236 11.2. Informative References 238 [CAB-Baseline] 239 CA/Browser Forum, "Baseline Requirements for the Issuance 240 and Management of Publicly-Trusted Certificates Version 241 1.1.6", 2013, . 243 [NISTSP800-131A-R2] 244 Barker, E. and A. Roginsky, "Transitioning the Use of 245 Cryptographic Algorithms and Key Lengths", March 2019, 246 . 249 [RFC6151] Turner, S. and L. Chen, "Updated Security Considerations 250 for the MD5 Message-Digest and the HMAC-MD5 Algorithms", 251 RFC 6151, DOI 10.17487/RFC6151, March 2011, 252 . 254 [SHA-1-Collision] 255 Stevens, M., Bursztein, E., Karpman, P., Albertini, A., 256 and Y. Markov, "The first collision for full SHA-1", March 257 2019, . 259 [Transcript-Collision] 260 Bhargavan, K. and G. Leurent, "Transcript Collision 261 Attacks: Breaking Authentication in TLS, IKE, and SSH", 262 February 2016, . 265 [Wang] Wang, X., Yin, Y., and H. Yu, "Finding Collisions in the 266 Full SHA-1", 2005. 268 Authors' Addresses 270 Loganaden Velvindron 271 cyberstorm.mu 272 Rose Hill 273 MU 275 Phone: +230 59762817 276 Email: logan@cyberstorm.mu 278 Kathleen Moriarty 279 Dell Technologies 281 Email: Kathleen.Moriarty.ietf@gmail.com 282 Alessandro Ghedini 283 Cloudflare Inc. 285 Email: alessandro@cloudflare.com