well, tests pass now
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Internet Engineering Task Force (IETF) L. Velvindron
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Request for Comments: 8758 cyberstorm.mu
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BCP: 227 April 2020
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Updates: 4253
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Category: Best Current Practice
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ISSN: 2070-1721
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Deprecating RC4 in Secure Shell (SSH)
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Abstract
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This document deprecates RC4 in Secure Shell (SSH). Therefore, this
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document formally moves RFC 4345 to Historic status.
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Status of This Memo
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This memo documents an Internet Best Current Practice.
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This document is a product of the Internet Engineering Task Force
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(IETF). It represents the consensus of the IETF community. It has
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received public review and has been approved for publication by the
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Internet Engineering Steering Group (IESG). Further information on
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BCPs is available in Section 2 of RFC 7841.
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Information about the current status of this document, any errata,
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and how to provide feedback on it may be obtained at
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https://www.rfc-editor.org/info/rfc8758.
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Copyright Notice
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Copyright (c) 2020 IETF Trust and the persons identified as the
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document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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Provisions Relating to IETF Documents
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(https://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
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include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
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described in the Simplified BSD License.
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Table of Contents
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1. Introduction
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1.1. Requirements Language
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2. Updates to RFC 4253
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3. IANA Considerations
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4. Security Considerations
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5. References
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5.1. Normative References
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5.2. Informative References
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Acknowledgements
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Author's Address
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1. Introduction
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The usage of RC4 suites (also designated as "arcfour") for SSH is
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specified in [RFC4253] and [RFC4345]. [RFC4253] specifies the
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allocation of the "arcfour" cipher for SSH. [RFC4345] specifies and
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allocates the "arcfour128" and "arcfour256" ciphers for SSH. RC4
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encryption has known weaknesses [RFC7465] [RFC8429]; therefore, this
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document starts the deprecation process for their use in Secure Shell
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(SSH) [RFC4253]. Accordingly, [RFC4253] is updated to note the
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deprecation of the RC4 ciphers, and [RFC4345] is moved to Historic
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status, as all ciphers it specifies MUST NOT be used.
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1.1. Requirements Language
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
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"OPTIONAL" in this document are to be interpreted as described in
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BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
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capitals, as shown here.
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2. Updates to RFC 4253
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[RFC4253] is updated to prohibit arcfour's use in SSH. [RFC4253],
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Section 6.3 allocates the "arcfour" cipher by defining a list of
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defined ciphers in which the "arcfour" cipher appears as optional, as
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shown in Table 1.
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+---------+----------+----------------------------------------------+
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| arcfour | OPTIONAL | the ARCFOUR stream cipher |
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| | | with a 128-bit key |
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+---------+----------+----------------------------------------------+
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Table 1
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This document updates the status of the "arcfour" ciphers in the list
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found in [RFC4253], Section 6.3 by moving it from OPTIONAL to MUST
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NOT.
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+---------+----------+----------------------------------------------+
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| arcfour | MUST NOT | the ARCFOUR stream cipher |
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| | | with a 128-bit key |
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+---------+----------+----------------------------------------------+
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Table 2
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[RFC4253] defines the "arcfour" ciphers with the following text:
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| The "arcfour" cipher is the Arcfour stream cipher with 128-bit
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| keys. The Arcfour cipher is believed to be compatible with the
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| RC4 cipher [SCHNEIER]. Arcfour (and RC4) has problems with weak
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| keys, and should be used with caution.
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This document updates [RFC4253], Section 6.3 by replacing the text
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above with the following text:
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| The "arcfour" cipher is the Arcfour stream cipher with 128-bit
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| keys. The Arcfour cipher is compatible with the RC4 cipher
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| [SCHNEIER]. Arcfour (and RC4) has known weaknesses [RFC7465]
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| [RFC8429] and MUST NOT be used.
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3. IANA Considerations
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The IANA has updated the "Encryption Algorithm Names" subregistry in
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the "Secure Shell (SSH) Protocol Parameters" registry [IANA]. The
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registration procedure is IETF review, which is achieved by this
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document. The registry has been updated as follows:
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+---------------------------+-----------+----------+
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| Encryption Algorithm Name | Reference | Note |
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+===========================+===========+==========+
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| arcfour | RFC 8758 | HISTORIC |
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+---------------------------+-----------+----------+
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| arcfour128 | RFC 8758 | HISTORIC |
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+---------------------------+-----------+----------+
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| arcfour256 | RFC 8758 | HISTORIC |
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+---------------------------+-----------+----------+
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Table 3
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4. Security Considerations
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This document only prohibits the use of RC4 in SSH; it introduces no
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new security considerations.
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5. References
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5.1. Normative References
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
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Requirement Levels", BCP 14, RFC 2119,
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DOI 10.17487/RFC2119, March 1997,
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<https://www.rfc-editor.org/info/rfc2119>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
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2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
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May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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5.2. Informative References
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[IANA] "Secure Shell (SSH) Protocol Parameters",
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<https://www.iana.org/assignments/ssh-parameters>.
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[RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
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Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
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January 2006, <https://www.rfc-editor.org/info/rfc4253>.
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[RFC4345] Harris, B., "Improved Arcfour Modes for the Secure Shell
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(SSH) Transport Layer Protocol", RFC 4345,
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DOI 10.17487/RFC4345, January 2006,
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<https://www.rfc-editor.org/info/rfc4345>.
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[RFC7465] Popov, A., "Prohibiting RC4 Cipher Suites", RFC 7465,
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DOI 10.17487/RFC7465, February 2015,
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<https://www.rfc-editor.org/info/rfc7465>.
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[RFC8429] Kaduk, B. and M. Short, "Deprecate Triple-DES (3DES) and
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RC4 in Kerberos", BCP 218, RFC 8429, DOI 10.17487/RFC8429,
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October 2018, <https://www.rfc-editor.org/info/rfc8429>.
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[SCHNEIER] Schneier, B., "Applied Cryptography Second Edition:
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Protocols, Algorithms, and Source in Code in C", John
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Wiley and Sons New York, NY, 1996.
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Acknowledgements
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The author would like to thank Eric Rescorla, Daniel Migault, and
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Rich Salz.
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Author's Address
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Loganaden Velvindron
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cyberstorm.mu
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Mauritius
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Email: logan@cyberstorm.mu
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