Internet Engineering Task Force (IETF) L. Camara Internet-Draft January 26, 2018 Obsoletes: 4345 (if approved) Updates: 4253 (if approved) Intended Status: Best Current Practice Expires: July 30, 2018 Deprecating RC4 in Secure Shell (SSH) draft-ietf-curdle-rc4-die-die-die-06 [[RFC-Editor: please replace the second character of my surname by U+00E2 when publishing as RFC in the header and in all pages. Non-ASCII characters are allowed in RFCs as per RFC 7997.]] Abstract This document deprecates RC4 in Secure Shell (SSH). Therefore, this document updates RFC 4253, and formally obsoletes and moves to Historic RFC 4345. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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Camara Expires July 30, 2018 [Page 1] Internet-Draft Deprecating RC4 in Secure Shell January 2018 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Why obsolete and move to Historic RFC 4345 . . . . . . . . . . 2 3. Updates to RFC 4253 . . . . . . . . . . . . . . . . . . . . . . 2 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 2 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 3 6. Acknowlegdements . . . . . . . . . . . . . . . . . . . . . . . 3 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 3 7.1. Normative References . . . . . . . . . . . . . . . . . . . . 3 7.2. Informative References . . . . . . . . . . . . . . . . . . . 3 8. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction RC4 is broken [RFC7457] and this document deprecates its use in Secure Shell (SSH). The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD 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. 2. Why obsolete and move to Historic RFC 4345 RFC 4345 defines the "arcfour-128" and "arcfour-256" modes for SSH, and is obsoleted and moved to Historic as RC4 is broken [RFC7457]. The modes defined by RFC 4345 MUST NOT be used. 3. Updates to RFC 4253 RFC 4253 is updated to prohibit arcfour's use in SSH. The last sentence of the paragraph on RC4 (called "arcfour" in [RFC4253]) in Section 6.3 of [RFC4253] should read: "Arcfour (also known as RC4) is broken [RFC7457] and therefore it MUST NOT be used." An informative reference to RFC 7457 is to be added to [RFC4253]. 4. IANA Considerations IANA may need to take action as the status for RC4 and 3DES algorithms for Secure Shell (SSH) is changed by this document (see Section 3, that updates [RFC4253]). Camara Expires July 30, 2018 [Page 2] Internet-Draft Deprecating RC4 in Secure Shell January 2018 5. Security Considerations This document only prohibits the use of RC4 in SSH, and introduces no new security considerations. 6. Acknowledgements Thanks to the numerous authors which have shown the weaknesses of RC4 throughout the years, and to the several people which have commented on the CURDLE mailing list about this document. 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, May 2017. 7.2. Informative References [RFC4253] Ylonen, T., and C. Lonvick, Ed., "The Secure Shell (SSH) Transport Layer Protocol", RFC 4253, January 2006. [RFC7457] Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing Known Attacks on Transport Layer Security (TLS) and Datagram TLS (DTLS)", RFC 7457, February 2015. [[RFC-Editor: please replace the 'i' in my name by U+00ED and the first 'a' in the surname by U+00E2, as non-ASCII characters are allowed as per RFC 7997]] 8. Author's Address Luis Camara EMail: Camara Expires July 30, 2018 [Page 3]