Internet Engineering Task Force L. Camara
Internet-Draft
Obsoletes: 4325 (if approved) L. Velvindron
Updates: 4253 (if approved) August 9, 2018
Intended status: Best Current Practice
Expires: February 10, 2019
Deprecating RC4 in Secure Shell (SSH)
draft-ietf-curdle-rc4-die-die-die-08
Abstract
This document deprecates RC4 in Secure Shell (SSH). Therefore, this
document updates [RFC4253], and formally obsoletes and moves to
Historic [RFC4345].
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Updates to RFC 4253 . . . . . . . . . . . . . . . . . . . . . 2
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.1. Normative References . . . . . . . . . . . . . . . . . . 4
6.2. Informative References . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
The usage of RC4 suites ( also designated as arcfour ) for SSH are
specified in [RFC4253] and [RFC4345]. [RFC4253] specifies the
allocation of the "arcfour" cipher for SSH. [RFC4345] specifies and
allocates the the "arcfour-128" and "arcfour-256" ciphers for SSH.
RC4 encryption is steadily weakening in cryptographic strength
[RFC7465] [I-D.ietf-curdle-des-des-des-die-die-die], and the
deprecation process should be begun for their use in Secure Shell
(SSH) [RFC4253]. Accordingly, [RFC4253] is updated to note the
deprecation of the RC4 ciphers and [RFC4345] is moved to Historic as
all ciphers it specifies MUST NOT be used.
1.1. Requirements Language
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 RFC 2119 [RFC2119].
2. Updates to RFC 4253
[RFC4253] is updated to prohibit arcfour's use in SSH. [RFC4253]
allocates the "arcfour" cipher in Section 6.3 by defining a list of
defined ciphers where the "arcfour" cipher appears as optional as
mentioned below:
+---------------+-----------------+---------------------------------+
| arcfour | OPTIONAL | the ARCFOUR stream cipher with |
| | | a 128-bit key |
+---------------+-----------------+---------------------------------+
The current document updates the status of the "arcfour" ciphers in
the list of [RFC4253] Section 6.3 by moving it from OPTIONAL to MUST
NOT.
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+----------+-----------+--------------------------------------------+
| arcfour | MUST NOT | the ARCFOUR stream cipher with a 128-bit |
| | | key |
+----------+-----------+--------------------------------------------+
[RFC4253] defines the "arcfour" ciphers with the text mentioned
below:
The "arcfour" cipher is the Arcfour stream cipher with 128-bit keys.
The Arcfour cipher is believed to be compatible with the RC4 cipher
[SCHNEIER]. Arcfour (and RC4) has problems with weak keys, and
should be used with caution.
The current document updates [RFC4253] Section 6.3 by replacing the
text above with the following text:
The "arcfour" cipher is the Arcfour stream cipher with 128-bit keys.
The Arcfour cipher is believed to be compatible with the RC4 cipher
[SCHNEIER]. Arcfour (and RC4) is steadily weakening in cryptographic
strength [RFC7465] [I-D.ietf-curdle-des-des-des-die-die-die], and
MUST NOT be used.
3. IANA Considerations
The IANA is requested to update the Encryption Algorithm Name
Registry of the Secure Shell (SSH) Protocol Parameters [IANA]. The
Registration procedure is IETF Review which is achieved by this
document. The registry should be updated as follows:
+-------------+------------------------------------+
| Encryption | Algorithm Name Reference Note |
+-------------+------------------------------------+
| arcfour | [RFC-TBD] |
| arcfour128 | [RFC-TBD] |
| arcfour256 | [RFC-TBD] |
+-------------+------------------------------------+
Where TBD is the RFC number assigned to the document.
All drafts are required to have an IANA considerations section (see
Guidelines for Writing an IANA Considerations Section in RFCs
[RFC5226] for a guide). If the draft does not require IANA to do
anything, the section contains an explicit statement that this is the
case (as above). If there are no requirements for IANA, the section
will be removed during conversion into an RFC by the RFC Editor.
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4. Acknowledgements
The authors would like to thank Daniel Migault
5. Security Considerations
This document only prohibits the use of RC4 in SSH, and introduces no
new security considerations.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[SCHNEIER]
Schneier, B., "Applied Cryptography Second Edition:
protocols algorithms and source in code in C", , 1996,
<SCHNEIER>.
6.2. Informative References
[I-D.ietf-curdle-des-des-des-die-die-die]
Kaduk, B. and M. Short, "Deprecate 3DES and RC4 in
Kerberos", draft-ietf-curdle-des-des-des-die-die-die-05
(work in progress), September 2017.
[RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
January 2006, <https://www.rfc-editor.org/info/rfc4253>.
[RFC4345] Harris, B., "Improved Arcfour Modes for the Secure Shell
(SSH) Transport Layer Protocol", RFC 4345,
DOI 10.17487/RFC4345, January 2006,
<https://www.rfc-editor.org/info/rfc4345>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
[RFC7465] Popov, A., "Prohibiting RC4 Cipher Suites", RFC 7465,
DOI 10.17487/RFC7465, February 2015,
<https://www.rfc-editor.org/info/rfc7465>.
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Authors' Addresses
Luis Camara
Email: luis.camara@live.com.pt
Loganaden Velvindron
Mauritius
Email: logan@hackers.mu
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