< draft-ietf-curdle-rc4-die-die-die-04.txt   draft-ietf-curdle-rc4-die-die-die-05.txt >
Internet Engineering Task Force (IETF) L. Camara Internet Engineering Task Force (IETF) L. Camara
Internet-Draft December 12, 2017 Internet-Draft January 10, 2018
Obsoletes: 4345 Obsoletes: 4345
Updates: 3501, 4253, 6733 Updates: 4253
Intended Status: Best Current Practice Intended Status: Best Current Practice
Expires: June 15, 2018 Expires: July 14, 2018
Depreciating RC4 in all IETF Protocols
draft-ietf-curdle-rc4-die-die-die-04
[[RFC-Editor: Please replace all instances of xxxx in this document with Depreciating RC4 in Secure Shell (SSH)
the RFC number of draft-ietf-curdle-des-des-des-die-die-die.]] draft-ietf-curdle-rc4-die-die-die-05
[[RFC-Editor: please replace the second character of my surname by [[RFC-Editor: please replace the second character of my surname by
U+00E2 when publishing as RFC in the header and in all pages. U+00E2 when publishing as RFC in the header and in all pages.
Non-ASCII characters are allowed in RFCs as per RFC 7997.]] Non-ASCII characters are allowed in RFCs as per RFC 7997.]]
Abstract Abstract
RC4 is extremely weak as shown by RFC 6649 and RFC 7457, is This document depreciates RC4 in Secure Shell (SSH). Therefore, this
prohibited in TLS by RFC 7465, is prohibited in Kerberos by RFC xxxx document updates RFC 4253, and formally obsoletes and moves to
and it needs to be prohibited in all IETF protocols. This document Historic RFC 4345.
obsoletes RFC 4345 "Improved Arcfour Modes for the Secure Shell (SSH)
Transport Layer Protocol" (note Arcfour and RC4 are synonymous).
RFC 3501, RFC 4253, RFC 6649 and RFC 6733 are updated to note the
depreciation of RC4 in all IETF protocols.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 15, 2018. This Internet-Draft will expire on July 14, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Why obsolete RFC 4345 . . . . . . . . . . . . . . . . . . . . . 2 2. Why obsolete and move to Historic RFC 4345 . . . . . . . . . . 2
3. Updates to RFC 3501 . . . . . . . . . . . . . . . . . . . . . . 3 3. Updates to RFC 4253 . . . . . . . . . . . . . . . . . . . . . . 2
4. Updates to RFC 4253 . . . . . . . . . . . . . . . . . . . . . . 3 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 2
5. Updates to RFC 6733 . . . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 3
6. Action to be taken . . . . . . . . . . . . . . . . . . . . . . 4 6. Acknowlegdements . . . . . . . . . . . . . . . . . . . . . . . 3
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 3
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 7.1. Normative References . . . . . . . . . . . . . . . . . . . . 3
9. Acknowlegdements . . . . . . . . . . . . . . . . . . . . . . . 5 7.2. Informative References . . . . . . . . . . . . . . . . . . . 3
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 8. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 4
10.1. Normative References . . . . . . . . . . . . . . . . . . . . 5
10.2. Informative References . . . . . . . . . . . . . . . . . . . 6
11. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 6
Appendix A. Changelog . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction 1. Introduction
RC4 is extremely weak [RFC6649] [RFC7457] [RFCxxxx] and this document RC4 is extremely weak [RFC6649] [RFC7457] [RFC7465] and this document
depreciates its use in all IETF protocols, including Kerberos and depreciates its use in all IETF protocols, including Kerberos and
Secure Shell (SSH). The reasons for obsoleting RFC 4345 are Secure Shell (SSH). The reasons for obsoleting RFC 4345 are
discussed in Section 2. The updates to RFC 3501, RFC 4253 and discussed in Section 2. The updates to RFC 4253 and the reasons for
RFC 6733 and the reasons for doing them are specified in sections 3, doing them are specified in Section 3.
4, and 5, respectively.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in document are to be interpreted as described in
BCP 14 [RFC2119, RFC8174]. BCP 14 [RFC2119, RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Why obsolete RFC 4345 2. Why obsolete and move to Historic RFC 4345
RFC 4345 defines the "arcfour-128" and "arcfour-256" modes for Secure RFC 4345 defines the "arcfour-128" and "arcfour-256" modes for Secure
Shell (SSH), and is moved to Historic as RC4 is extremely Shell (SSH), and is obsoleted and moved to Historic as RC4 is
weak [RFC6649, RFC7457, RFCxxxx] and there is research that is at extremely weak [RFC6649, RFC7457] and there is research that is at
least 5 years old that totally breaks all practical usage of least 5 years old that totally breaks all practical usage of
RC4 [RFC6649]. RC4 [RFC6649].
3. Updates to RFC 3501 3. Updates to RFC 4253
The second paragraph of [RFC3501] required that implementations of
IMAP clients and servers implement a RC4 cipher suite in TLS
(contradicts [RFC7465]) and recommends implementing a weak cipher
suite (3DES is used in the suite). Unfortunately, at the time of
writing of RFC 3501, AES cipher suites were extremely new (the first
AES cipher suites were defined in RFC 3268, published in June 2002),
less than 1 year old and the strongest choice they have come up with
at the time was TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA.
As the document is over 14 years old, the second paragraph of
Section 11.1 of [RFC3501] is replaced with the following paragraph:
"""
IMAP client and server implementations were formerly required to
implement TLS_RSA_WITH_RC4_128_MD5 {TLS}, an extremely weak cipher
suite [RFC6151] [RFC6649] [RFC7457] [RFCxxxx] [RFCyyyy] that TLS
clients MUST NOT implement per [RFC7465]. Compatibility requirements
were removed in the grounds of security, and all clients and servers
SHOULD comply to [RFC7525].
"""
The TLS reference in [RFC3501] should be replaced with a reference to
RFC 5246, and references to RFC 6151, RFC 6649, RFC 7457, RFC 7465,
RFC xxxx and this document (as RFC yyyy) should be added.
4. Updates to RFC 4253
RFC 4253 is updated to note the depreciation of arcfour and 3des-cbc.
This document changes "OPTIONAL" to "NOT RECOMMENDED" for arcfour and
"REQUIRED" to "OPTIONAL" for 3des-cbc in the table of
Section 6.3 of [RFC4253] as 3DES is weak and maintaining the
requirement will compromise systems. [RFC4253] was published in
2006, 11 years ago, and states that """At some future time, it is
expected that another algorithm, one with better strength, will
become so prevalent and ubiquitous that the use of "3des-cbc" will be
deprecated by another STANDARDS ACTION."""
The "future time" referred to by [RFC4253] is set to 2017, the RFC 4253 is updated to note the depreciation of arcfour.
"STANDARDS ACTION" is set to the publication of this document and
the "algorithm" is set to the Advanced Encryption Standard (AES), as
AES is ubiquitous in Kerberos implementations (see Section 11).
The last sentence of the paragraph on RC4 (called "arcfour" The last sentence of the paragraph on RC4 (called "arcfour"
in [RFC4253]) in Section 6.3 of [RFC4253] should read: "Arcfour (and in [RFC4253]) in Section 6.3 of [RFC4253] should read: "Arcfour (and
RC4) are extremely weak [RFC6649] [RFC7457] [RFCxxxx] [RFCyyyy] and RC4) are extremely weak [RFC7457] and therefore it MUST NOT be used."
therefore their use is NOT RECOMMENDED."
References to RFC 6649, RFC 7457, RFC xxxx and this document (the
reference to this document is RFCyyyy in the above paragraph) should
be added to Section 6.3 of [RFC4253].
5. Updates to RFC 6733
Section 13.1 of [RFC6733] required that clients implement two RC4
cipher suites and a 3DES cipher suite (but recommends implementing an
AES cipher suite).
RFC 6733 was published in October 2012, and all paragraphs but the
last of Section 13.1 of [RFC6733] are to be replaced with:
"""
Diameter nodes were formerly required to implement insecure RC4
cipher suites and weak 3DES cipher suites. RC4 MUST NOT be used
because it is prohibited by RFC 7465.
Diameter nodes MUST comply to [RFC7525].
TLS_RSA_WITH_AES_128_CBC_SHA was not chosen to be absolutely required
as Diameter nodes may require all connections to use forward secrecy
by only implementing cipher suites with forward secrecy.
TLS_RSA_WITH_AES_128_CBC_SHA is not a forward secrecy cipher suite
because all connections can be decrypted once the private RSA key is
known by an attacker.
"""
6. Action to be taken
RC4 MUST NOT be used in new implementations of IETF protocols, and
RC4 MUST be eliminated as fast as possible from the existing Internet
infrastructure, as RC4 is insecure [RFC6649] [RFC7457] [RFCxxxx].
Vendors SHOULD take action to eradicate RC4 in all their software
and systems.
New IETF protocols MUST NOT allow RC4, and new versions of existing An informative reference to RFC 7457 is to be added to [RFC4253].
IETF protocols MUST either not allow RC4 or recommend not to use RC4
(for example, using "NOT RECOMMENDED" or "SHOULD NOT").
7. IANA Considerations 4. IANA Considerations
IANA may need to take action as the status for RC4 and 3DES IANA may need to take action as the status for RC4 and 3DES
algorithms for Secure Shell (SSH) is changed by this document algorithms for Secure Shell (SSH) is changed by this document
(see Section 4, that updates [RFC4253]). (see Section 3, that updates [RFC4253]).
8. Security Considerations 5. Security Considerations
This document depreciates RC4, that is obsolete cryptography, and This document depreciates RC4, that is obsolete cryptography, and
several attacks that render it useless have been published [RFC6649]. several attacks that render it useless have been published
Refer to Section 5 of [RFCxxxx] for further security considerations. published [RFC6649] [RFC7457] [RFC7465].
9. Acknowledgements
[[RFC-Editor: When possible, add native names according to the
conventions of RFC 7997.]]
Thanks to the following people:
* Sean Turner and Lily Chen for writing RFC 6151, that contains
updated security considerations for MD5 and HMAC-MD5.
* Love Hornquist Astrand and Tom Yu for writing RFC 6649, that
depreciates weak cryptographic algorithms in Kerberos.
* Yaron Sheffer, Ralph Holz and Peter Saint-Andre for writing
RFC 7457, that summarises known attacks against Transport Layer
Security (TLS), and RFC 7525, that provides recommendations for
the use of TLS and Datagram Transport Layer Security (DTLS).
* Andrei Popov for writing RFC 7465, that prohibits RC4 cipher
suites in Transport Layer Security (TLS).
* Julien Elie for sending me an email about the requirements to 6. Acknowledgements
implement RC4 cipher suites in RFC 3501 and RFC 6733.
Refer to the acknowledgements section of RFC 6649, RFC 7457 and Thanks to the numerous authors which have shown the weaknesses of
RFC xxxx for further acknowledgements. RC4 throughout the years.
10. References 7. References
10.1. Normative References 7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, May 2015.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in
RFC 2119 Key Words", BCP 14, RFC 8174, May 2017. RFC 2119 Key Words", BCP 14, RFC 8174, May 2017.
[RFCxxxx] Kaduk, B., and M. Short, "Deprecate 3DES and RC4 in 7.2. Informative References
Kerberos", draft-ietf-curdle-des-des-des-die-die-die-05,
Work in Progress.
10.2. Informative References
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - Version
4rev1", RFC 3501, March 2003.
[RFC4253] Ylonen, T., and C. Lonvick, Ed., "The Secure Shell (SSH) [RFC4253] Ylonen, T., and C. Lonvick, Ed., "The Secure Shell (SSH)
Transport Layer Protocol", RFC 4253, January 2006. Transport Layer Protocol", RFC 4253, January 2006.
[RFC4757] Jaganathan, K., Zhu, L., and J. Brezak, "The RC4-HMAC
Kerberos Encryption Types Used by Microsoft Windows",
RFC 4757, December 2006.
[RFC6151] Turner, S., and L. Chen, "Updated Security Considerations [RFC6151] Turner, S., and L. Chen, "Updated Security Considerations
for the MD5 Message-Digest and the HMAC-MD5 Algorithms", for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
RFC 6151, March 2011. RFC 6151, March 2011.
[RFC6733] Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn, [RFC6649] Hornquist Astrand, L. and T. Yu, "Deprecate DES, RC4-HMAC-
Ed., "Diameter Base Protocol", RFC 6733, October 2012. EXP, and Other Weak Cryptographic Algorithms in Kerberos",
BCP 179, RFC 6649, July 2012.
[RFC7457] Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing [RFC7457] Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing
Known Attacks on Transport Layer Security (TLS) and Known Attacks on Transport Layer Security (TLS) and
Datagram TLS (DTLS)", RFC 7457, February 2015. Datagram TLS (DTLS)", RFC 7457, February 2015.
[RFC7465] Popov, A., "Prohibiting RC4 Cipher Suites", RFC 7465, [RFC7465] Popov, A., "Prohibiting RC4 Cipher Suites", RFC 7465,
February 2015. 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.
[[RFC-Editor: please replace the 'i' in my name by U+00ED and the [[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 first 'a' in the surname by U+00E2, as non-ASCII characters are
allowed as per RFC 7997]] allowed as per RFC 7997]]
11. Author's Address 11. Author's Address
Luis Camara Luis Camara
EMail: <luis.camara@live.com.pt> EMail: <luis.camara@live.com.pt>
Appendix A. Changelog
[[RFC-Editor: please remove this section when publishing.]]
WG draft:
04 - Removed the updates to RFC 6649 per the mailing list comments.
03 - Style changes, removed SSL Labs paragraph in the
acknowledgements section and updated RFCxxxx reference to v05.
Now British English is used in all parts of the document,
except quotations.
02 - Addressed Todd Short's concerns.
01 - Massive simplification: removed informational updates, removed
all Pre-5378 Material, retracted all "Obsoletes:" except for
RFC 4345, removed Appendix A and renamed changelog to Appendix A.
00 - Dummy update to get the draft into the curdle WG.
Individual draft:
02 - Changed title to "Deprecating RC4 in all IETF Protocols", changed
the header of all pages to "Deprecating RC4 in all Protocols",
updated RFC 3501 and RFC 6733, simplified the reference to
draft-ietf-curdle-des-des-des-die-die-die to a simple "Work in
Progress" reference and fixed typos.
01 - Explained reasons for updating RFC 7905 and added an informative
reference to RFC 4757 to take away a missing reference warning.
00 - First version. [RFCxxxx] is a reference to
draft-ietf-curdle-des-des-des-die-die-die. The quote in
Section 11 is from version 03 of this draft (posted 2017-06-15)
 End of changes. 30 change blocks. 
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