Internet Engineering Task Force (IETF) L. Camara Internet-Draft January 10, 2018 Obsoletes: 4345 Updates: 4253 Intended Status: Best Current Practice Expires: July 14, 2018 Depreciating RC4 in Secure Shell (SSH) draft-ietf-curdle-rc4-die-die-die-05 [[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 depreciates 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 14, 2018 [Page 1] Internet-Draft Depreciating 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 . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction RC4 is extremely weak [RFC6649] [RFC7457] [RFC7465] and this document depreciates its use in all IETF protocols, including Kerberos and Secure Shell (SSH). The reasons for obsoleting RFC 4345 are discussed in Section 2. The updates to RFC 4253 and the reasons for doing them are specified in Section 3. 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 Secure Shell (SSH), and is obsoleted and moved to Historic as RC4 is extremely weak [RFC6649, RFC7457] and there is research that is at least 5 years old that totally breaks all practical usage of RC4 [RFC6649]. 3. Updates to RFC 4253 RFC 4253 is updated to note the depreciation of arcfour. The last sentence of the paragraph on RC4 (called "arcfour" in [RFC4253]) in Section 6.3 of [RFC4253] should read: "Arcfour (and RC4) are extremely weak [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 14, 2018 [Page 2] Internet-Draft Depreciating RC4 in Secure Shell January 2018 5. Security Considerations This document depreciates RC4, that is obsolete cryptography, and several attacks that render it useless have been published published [RFC6649] [RFC7457] [RFC7465]. 6. Acknowledgements Thanks to the numerous authors which have shown the weaknesses of RC4 throughout the years. 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. [RFC6151] Turner, S., and L. Chen, "Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms", RFC 6151, March 2011. [RFC6649] Hornquist Astrand, L. and T. Yu, "Deprecate DES, RC4-HMAC- EXP, and Other Weak Cryptographic Algorithms in Kerberos", BCP 179, RFC 6649, July 2012. [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. [RFC7465] Popov, A., "Prohibiting RC4 Cipher Suites", RFC 7465, February 2015. [RFCxxxx] Kaduk, B., and M. Short, "Deprecate 3DES and RC4 in Kerberos", draft-ietf-curdle-des-des-des-die-die-die-05, Work in Progress. Camara Expires July 14, 2018 [Page 3] Internet-Draft Depreciating RC4 in Secure Shell January 2018 [[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]] 11. Author's Address Luis Camara EMail: Camara Expires July 14, 2018 [Page 4]