Internet Engineering Task Force (IETF) A. Popov Request for Comments: 7465 Microsoft Corp. Updates: 5246, 4346, 2246 February 2015 Category: Standards Track ISSN: 2070-1721
Prohibiting RC4 Cipher Suites
This document requires that Transport Layer Security (TLS) clients and servers never negotiate the use of RC4 cipher suites when they establish connections. This applies to all TLS versions. This document updates RFCs 5246, 4346, and 2246.
Status of This Memo
This is an Internet Standards Track document.
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Popov Standards Track [Page 1]
RFC 7465 Prohibiting RC4 Cipher Suites February 2015
RC4 is a stream cipher that is described in [SCH]; it is widely supported, and often preferred by TLS servers. However, RC4 has long been known to have a variety of cryptographic weaknesses, e.g., see [PAU], [MAN], and [FLU]. Recent cryptanalysis results [ALF] exploit biases in the RC4 keystream to recover repeatedly encrypted plaintexts.
These recent results are on the verge of becoming practically exploitable; currently, they require 2^26 sessions or 13x2^30 encryptions. As a result, RC4 can no longer be seen as providing a sufficient level of security for TLS sessions.
This document requires that TLS ([RFC5246] [RFC4346] [RFC2246]) clients and servers never negotiate the use of RC4 cipher suites.
This document helps maintain the security guarantees of the TLS protocol by prohibiting the use of the RC4-based cipher suites (listed in Appendix A), which do not provide a sufficiently high level of security.