Internet Engineering Task Force (IETF) L. Hornquist Astrand
Request for Comments: 6649 Apple, Inc.
BCP: 179 T. Yu
Obsoletes: 1510 MIT Kerberos Consortium
Updates: 1964, 4120, 4121, 4757 July 2012
Category: Best Current Practice
Deprecate DES, RC4-HMAC-EXP, and Other Weak Cryptographic Algorithms
The Kerberos 5 network authentication protocol, originally specified
in RFC 1510, can use the Data Encryption Standard (DES) for
encryption. Almost 30 years after first publishing DES, the National
Institute of Standards and Technology (NIST) finally withdrew the
standard in 2005, reflecting a long-established consensus that DES is
insufficiently secure. By 2008, commercial hardware costing less
than USD 15,000 could break DES keys in less than a day on average.
DES is long past its sell-by date. Accordingly, this document
updates RFC 1964, RFC 4120, RFC 4121, and RFC 4757 to deprecate the
use of DES, RC4-HMAC-EXP, and other weak cryptographic algorithms in
Kerberos. Because RFC 1510 (obsoleted by RFC 4120) supports only
DES, this document recommends the reclassification of RFC 1510 as
Status of This Memo
This memo documents an Internet Best Current Practice.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
Hornquist Astrand & Yu Best Current Practice [Page 1]RFC 6649 Deprecate DES in Kerberos July 2012Copyright Notice
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Hornquist Astrand & Yu Best Current Practice [Page 2]RFC 6649 Deprecate DES in Kerberos July 20121. Introduction
The original specification of the Kerberos 5 network authentication
protocol [RFC1510] supports only the Data Encryption Standard (DES)
for encryption. For many years, the cryptographic community has
regarded DES as providing inadequate security, mostly because of its
small key size. Accordingly, this document recommends the
reclassification of [RFC1510] (obsoleted by [RFC4120]) as Historic
and updates current Kerberos-related specifications [RFC1964],
[RFC4120], and [RFC4121] to deprecate the use of DES and other weak
cryptographic algorithms in Kerberos, including some unkeyed
checksums and hashes, along with the weak 56-bit "export strength"
RC4 variant encryption type of [RFC4757].
2. Requirements Notation
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 [RFC2119].
3. Affected Specifications
The original IETF specification of Kerberos 5 [RFC1510] only supports
DES for encryption. [RFC4120] obsoletes [RFC1510] and updates the
Kerberos specification to include additional cryptographic
algorithms, but still permits the use of DES. [RFC3961] describes
the Kerberos cryptographic system and includes support for DES
encryption types, but it does not specify requirement levels for
The specification of the Kerberos Generic Security Services
Application Programming Interface (GSS-API) mechanism [RFC1964] and
its updated version [RFC4121] define checksum and encryption
mechanisms based on DES. With the existence of newer encryption