Internet Engineering Task Force (IETF)                     L. Velvindron
Request for Comments: 9155                       
Updates: 5246                                                K. Moriarty
Category: Standards Track                                            CIS
ISSN: 2070-1721                                               A. Ghedini
                                                         Cloudflare Inc.
                                                           December 2021

Deprecating MD5 and SHA-1 Signature Hashes in TLS 1.2 and DTLS 1.2

TLS 1.2とDTLS 1.2でのSHA-1シグネチャハッシュの非推奨



The MD5 and SHA-1 hashing algorithms are increasingly vulnerable to attack, and this document deprecates their use in TLS 1.2 and DTLS 1.2 digital signatures. However, this document does not deprecate SHA-1 with Hashed Message Authentication Code (HMAC), as used in record protection. This document updates RFC 5246.

MD5とSHA-1ハッシュアルゴリズムはますます攻撃に対してますます脆弱であり、この文書はTLS 1.2およびDTLS 1.2デジタル署名での使用を非推奨しています。ただし、この文書は、レコード保護で使用されているように、Hashed Message認証コード(HMAC)でSHA-1を非推奨しません。この文書はRFC 5246を更新します。

Status of This Memo


This is an Internet Standards Track document.


This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.

この文書はインターネットエンジニアリングタスクフォース(IETF)の製品です。IETFコミュニティのコンセンサスを表します。それはパブリックレビューを受け、インターネットエンジニアリングステアリンググループ(IESG)による出版の承認を受けました。インターネット規格に関する詳細情報は、RFC 7841のセクション2で利用できます。

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at


Copyright Notice


Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved.

Copyright(C)2021 IETFの信頼と文書著者として識別された人。全著作権所有。

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.

この文書は、この文書の公開日に有効なIETF文書(に関するBCP 78およびIETF信頼の法的規定の対象となります。この文書に関してあなたの権利と制限を説明するので、これらの文書をよくレビューしてください。この文書から抽出されたコードコンポーネントには、信託法定規定のセクション4。

Table of Contents


   1.  Introduction
     1.1.  Requirements Language
   2.  Signature Algorithms
   3.  Certificate Request
   4.  Server Key Exchange
   5.  Certificate Verify
   6.  IANA Considerations
   7.  Security Considerations
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Authors' Addresses
1. Introduction
1. はじめに
   The usage of MD5 and SHA-1 for signature hashing in (D)TLS 1.2 is
   specified in [RFC5246].  MD5 and SHA-1 have been proven to be
   insecure, subject to collision attacks [Wang].  In 2011, [RFC6151]
   detailed the security considerations, including collision attacks for
   MD5.  NIST formally deprecated use of SHA-1 in 2011
   [NISTSP800-131A-R2] and disallowed its use for digital signatures at
   the end of 2013, based on both the attack described in [Wang] and the
   potential for brute-force attack.  In 2016, researchers from the
   National Institute for Research in Digital Science and Technology
   (INRIA) identified a new class of transcript collision attacks on TLS
   (and other protocols) that relies on efficient collision-finding
   algorithms on the underlying hash constructions
   [Transcript-Collision].  Further, in 2017, researchers from Google
   and Centrum Wiskunde & Informatica (CWI) Amsterdam [SHA-1-Collision]
   proved SHA-1 collision attacks were practical.  This document updates
   [RFC5246] in such a way that MD5 and SHA-1 MUST NOT be used for
   digital signatures.  However, this document does not deprecate SHA-1
   with HMAC, as used in record protection.  Note that the CA/Browser
   Forum (CABF) has also deprecated use of SHA-1 for use in certificate
   signatures [CABF].
1.1. Requirements Language
1.1. 要件言語

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

この文書のキーワード "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", および "OPTIONAL" はBCP 14 [RFC2119] [RFC8174]で説明されているように、すべて大文字の場合にのみ解釈されます。

2. Signature Algorithms
2. 署名アルゴリズム

Clients MUST include the signature_algorithms extension. Clients MUST NOT include MD5 and SHA-1 in this extension.


3. Certificate Request
3. 証明書リクエスト

Servers SHOULD NOT include MD5 and SHA-1 in CertificateRequest messages.


4. Server Key Exchange
4. サーバー鍵交換機

Servers MUST NOT include MD5 and SHA-1 in ServerKeyExchange messages. If the client receives a ServerKeyExchange message indicating MD5 or SHA-1, then it MUST abort the connection with an illegal_parameter alert.


5. Certificate Verify
5. 証明書検証

Clients MUST NOT include MD5 and SHA-1 in CertificateVerify messages. If a server receives a CertificateVerify message with MD5 or SHA-1, it MUST abort the connection with an illegal_parameter alert.


6. IANA Considerations
6. IANAの考慮事項

IANA has updated the "TLS SignatureScheme" registry by changing the recommended status of SHA-1-based signature schemes to "N" (not recommended), as defined by [RFC8447]. The following entries have been updated; other entries in the registry remain the same.

[RFC8447]で定義されているように、SHA-1ベースの署名方式の推奨ステータスを「N」(推奨されない)に変更することで、IANAが「TLS SignaturesCheme」レジストリを更新しました。以下のエントリが更新されました。レジストリ内の他のエントリは同じままです。

      | Value  |  Description   | Recommended |      Reference      |
      | 0x0201 | rsa_pkcs1_sha1 |      N      | [RFC8446] [RFC9155] |
      | 0x0203 |   ecdsa_sha1   |      N      | [RFC8446] [RFC9155] |

Table 1


IANA has also updated the reference for the "TLS SignatureAlgorithm" and "TLS HashAlgorithm" registries to refer to this document in addition to RFCs 5246 and 8447.

IANAはまた、RFCS 5246および8447に加えて、「TLS SignatureAlgorithm」および「TLS Hashalgorithm」レジストリの参照を更新しました。

7. Security Considerations
7. セキュリティに関する考慮事項

Concerns with (D)TLS 1.2 implementations falling back to SHA-1 is an issue. This document updates the TLS 1.2 specification [RFC5246] to deprecate support for MD5 and SHA-1 for digital signatures. However, this document does not deprecate SHA-1 with HMAC, as used in record protection.

(D)TLS 1.2の実装はSHA-1に戻る問題です。この文書は、デジタル署名のためのMD5およびSHA-1のサポートを廃止するためにTLS 1.2仕様[RFC5246]を更新します。ただし、この文書は、レコード保護で使用されているように、HMACでSHA-1を非推奨しません。

8. References
8. 参考文献
8.1. Normative References
8.1. 引用文献

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <>.

[RFC2119] BRADNER、S、「RFCで使用するためのキーワード」、BCP 14、RFC 2119、DOI 10.17487 / RFC2119、1997年3月、<>。

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008, <>.

[RFC5246] Dierks、T.およびE. Rescorla、「トランスポート層セキュリティ(TLS)プロトコルバージョン1.2」、RFC 5246、DOI 10.17487 / RFC5246、2008年8月、< RFC5246>。

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <>.

[RFC8174] Leiba、B.、RFC 2119キーワードの「大文字の曖昧さ」、BCP 14、RFC 8174、DOI 10.17487 / RFC8174、2017年5月、<>。

[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, <>.

[RFC8446] RESCORLA、E。、「トランスポート層セキュリティ(TLS)プロトコルバージョン1.3」、RFC 8446、DOI 10.17487 / RFC8446、<>。

[RFC8447] Salowey, J. and S. Turner, "IANA Registry Updates for TLS and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018, <>.

[RFC8447] Salowey、J.およびS.ターナー、「TLSおよびDTLSのIANAレジストリアップデート」、RFC 8447、DOI 10.17487 / RFC8447、2018年8月、<>。

8.2. Informative References
8.2. 参考引用

[CABF] CA/Browser Forum, "Ballot 118 -- SHA-1 Sunset (passed)", October 2014, < sha-1-sunset/>.

[CABF] CA / Browserフォーラム、「Ballot 118 - Sha-1 Sunset(Passed)」、2014年10月、< Sha-1-サンセット/>。

[NISTSP800-131A-R2] Barker, E. and A. Roginsky, "Transitioning the Use of Cryptographic Algorithms and Key Lengths", NIST Special Publication 800-131A, Revision 2, DOI 10.6028/NIST.SP.800-131Ar2, March 2019, < NIST.SP.800-131Ar2.pdf>.

[NISTSP800-131A-R2] Barker、E、A. Roginsky、「暗号化アルゴリズムの使用とキー長の使用の移行」、NIST特別出版物800-131A、リビジョン2、DOI 10.6028 / NIST.SP.800-131AR2、3月2019年、< Nist.Sp.800-131ar2.pdf>。

[RFC6151] Turner, S. and L. Chen, "Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms", RFC 6151, DOI 10.17487/RFC6151, March 2011, <>.

[RFC6151]ターナー、S、およびL. Chen、「MD5メッセージダイジェストとHMAC-MD5アルゴリズムのためのセキュリティ上の考慮事項」、RFC 6151、DOI 10.17487 / RFC6151、2011年3月、<https:///>。

[SHA-1-Collision] Stevens, M., Bursztein, E., Karpman, P., Albertini, A., and Y. Markov, "The First Collision for Full SHA-1", 2017, <>.

[SHA-1-Collision]スティーブンズ、M.、Bursztein、E.、Karpman、P.、Albertini、A.、およびY。マルコフ、「Full Sha-1の最初の衝突」、2017、<HTTPS://>。

[Transcript-Collision] Bhargavan, K. and G. Leurent, "Transcript Collision Attacks: Breaking Authentication in TLS, IKE, and SSH", DOI 10.14722/ndss.2016.23418, February 2016, <>.

[Transcript-Collision] Bhargavan、K.およびG. Leurent、 "Transcript Collision Attacks:TLS、IKE、およびSSHの認証"、DOI 10.14722 / NDSS.2016.23418、2016年2月、< HAL-01244855 /文書>。

[Wang] Wang, X., Yin, Y., and H. Yu, "Finding Collisions in the Full SHA-1", DOI 10.1007/11535218_2, 2005, < crypto2005/36210017/36210017.pdf>.

[Wang] Wang、X.、YIN、Y、Y、Y、Y、「フルSHA-1の衝突の検索」、DOI 10.1007 / 11535218_2,2005、< crypto2005/ 36210017/36210017.pdf>。



The authors would like to thank Hubert Kario for his help in writing the initial draft version of this document. We are also grateful to Daniel Migault, Martin Thomson, Sean Turner, Christopher Wood, and David Cooper for their feedback.

この文書の初期ドラフト版を書くのに、Hubert KarioにHubert Karioに感謝します。私たちは、Daniel Migautt、Martin Thomson、Sean Turner、Christopher Wood、そしてDavid Cooperにフィードバックのために感謝しています。

Authors' Addresses


Loganaden Velvindron Rose Hill Mauritius

Loganaden Velvindron Cyberstorm.Mu Rose Hill Mauritius.

   Phone: +230 59762817

Kathleen Moriarty Center for Internet Security East Greenbush, NY United States of America

Kathleen MoriArtyインターネットセキュリティセンターイーストグリーンブッシュ、ニューヨーク州アメリカ合衆国


Alessandro Ghedini Cloudflare Inc.

アレッサンドロGhedini Cloudflare Inc.