RFC 5469

DES and IDEA Cipher Suites for Transport Layer Security (TLS)

📅 published February 2009, from ietf

RFC 5469: DES and IDEA Cipher Suites for Transport Layer Security (TLS) 🎀

okay bestie, let's get into it 💅 this is RFC 5469, titled "DES and IDEA Cipher Suites for Transport Layer Security (TLS)." It's an Informational doc from February 2009, written by P. Eronen, Ed. at Nokia. The header doesn't list anything it obsoletes or updates.

Status of This Memo

okay so this memo is for information only ✨ It gives info to the Internet community and does not specify an Internet standard of any kind. Distribution of this memo is unlimited 🌸

Copyright Notice

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) as they stand on the date this document was published. Please read these carefully, because they spell out your rights and restrictions for this document 📜

Abstract

okay the tea ☕ TLS versions 1.0 (RFC 2246) and 1.1 (RFC 4346) include cipher suites built on DES (Data Encryption Standard) and IDEA (International Data Encryption Algorithm). DES (in single-DES mode) and IDEA are no longer recommended for general use in TLS, and they've been removed from TLS version 1.2 (RFC 5246). This doc specifies these cipher suites for completeness and explains why using them is no longer recommended 🥺

1. Introduction ✨

TLS versions 1.0 [TLS10] and 1.1 [TLS11] include cipher suites based on DES and IDEA, same as the abstract said 💜 DES (in single-DES mode) and IDEA are no longer recommended for general use in TLS, and they've been removed from TLS version 1.2 [TLS12].

This doc specifies these cipher suites for completeness and explains why we shouldn't be using them anymore 🫶

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 [REQ]. These are the official requirement words, so they carry real weight here 🔥

2. DES Cipher Suites 🍓

DES (Data Encryption Standard) is a block cipher that was first approved as a US federal standard in 1976. It's specified in [DES] 🧚

For TLS key generation purposes, DES is treated as having a 64-bit key. But it only gives 56 bits of protection, because 8 of those 64 bits aren't used by the algorithm 🙈 DES uses a 64-bit block size.

The following cipher suites have been defined for using DES in Cipher Block Chaining (CBC) mode in TLS:

   CipherSuite TLS_RSA_WITH_DES_CBC_SHA            = { 0x00,0x09 };
   CipherSuite TLS_DH_DSS_WITH_DES_CBC_SHA         = { 0x00,0x0C };
   CipherSuite TLS_DH_RSA_WITH_DES_CBC_SHA         = { 0x00,0x0F };
   CipherSuite TLS_DHE_DSS_WITH_DES_CBC_SHA        = { 0x00,0x12 };
   CipherSuite TLS_DHE_RSA_WITH_DES_CBC_SHA        = { 0x00,0x15 };
   CipherSuite TLS_DH_anon_WITH_DES_CBC_SHA        = { 0x00,0x1A };

The key exchange algorithms (RSA, DH_DSS, DH_RSA, DHE_DSS, DHE_RSA, and DH_anon) and the MAC (Message Authentication Code) algorithm (SHA) are defined in the base TLS specification 💅

3. IDEA Cipher Suite 🦋

IDEA (International Data Encryption Algorithm) is a block cipher designed by Xuejia Lai and James Massey [IDEA] [SCH]. It uses a 128-bit key and operates on 64-bit blocks ✨

The following cipher suite has been defined for using IDEA in CBC mode in TLS:

   CipherSuite TLS_RSA_WITH_IDEA_CBC_SHA           = { 0x00,0x07 };

The key exchange algorithm (RSA) and the MAC algorithm (SHA) are defined in the base TLS specification 🌈

4. Security Considerations 🚨

this section is the main character moment, so pay attention 👑

4.1. DES Cipher Suites

DES has an effective key strength of 56 bits, and it's been known to be vulnerable to practical brute force attacks for over 20 years [DH] 😭 A fairly recent 2006 paper by Kumar, et al. [COPA] describes a system that does an exhaustive key search in less than nine days on average, and it costs less than 10,000 USD to build. Yikes 💀

Given all that, the single-DES cipher suites SHOULD NOT be implemented by TLS libraries. If a TLS library does implement these cipher suites, it SHOULD NOT enable them by default. Experience has also shown that rarely used code is a source of security and interoperability problems, so existing implementations SHOULD consider removing these cipher suites 🫠

4.2. IDEA Cipher Suite

IDEA has a 128-bit key, so it's not vulnerable to an exhaustive key search. Lowkey respect 🙌 However, the IDEA cipher suite for TLS hasn't really seen widespread use. Most implementations either don't support it, don't enable it by default, or don't negotiate it when other algorithms (such as AES, 3DES, or RC4) are available 🥹

Experience has shown that rarely used code is a source of security and interoperability problems. Given this, the IDEA cipher suite SHOULD NOT be implemented by TLS libraries and SHOULD be removed from existing implementations 🧹

5. IANA Considerations 🌸

IANA has already allocated values for the cipher suites described in this document in the TLS Cipher Suite Registry, which is defined in [TLS11]. IANA has updated the references of these cipher suites to point to this document:

   Value         Description                             Reference
   -----------   --------------------------------------  ---------
   0x00,0x07     TLS_RSA_WITH_IDEA_CBC_SHA               [RFC5469]
   0x00,0x09     TLS_RSA_WITH_DES_CBC_SHA                [RFC5469]
   0x00,0x0C     TLS_DH_DSS_WITH_DES_CBC_SHA             [RFC5469]
   0x00,0x0F     TLS_DH_RSA_WITH_DES_CBC_SHA             [RFC5469]
   0x00,0x12     TLS_DHE_DSS_WITH_DES_CBC_SHA            [RFC5469]
   0x00,0x15     TLS_DHE_RSA_WITH_DES_CBC_SHA            [RFC5469]
   0x00,0x1A     TLS_DH_anon_WITH_DES_CBC_SHA            [RFC5469]

This document doesn't create any new registries for IANA to maintain, and it doesn't require any new assignments from existing registries 🎀

6. Acknowledgments 🫶

The editor would like to thank Steven Bellovin, Uri Blumenthal, Michael D'Errico, Paul Hoffman, Simon Josefsson, Bodo Moeller, Tom Petch, Martin Rex, and Len Sassaman for their contributions to preparing this document. Iconic cast 👑

7. References 📚

7.1. Normative References

[DES] National Institute of Standards and Technology, "Data Encryption Standard (DES)", FIPS PUB 46-3, October 1999.

[IDEA] Lai, X., "On the Design and Security of Block Ciphers", ETH Series in Information Processing, v. 1, Konstanz: Hartung-Gorre Verlag, 1992.

[REQ] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.

[SCH] Schneier, B., "Applied Cryptography: Protocols, Algorithms, and Source Code in C", 2nd ed., John Wiley & Sons, Inc., 1996.

[TLS10] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999.

[TLS11] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.1", RFC 4346, April 2006.

[TLS12] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008.

7.2. Informative References

[COPA] Kumar, S., Paar, C., Pelzl, J., Pfeiffer, G., and M. Schimmler, "Breaking Ciphers with COPACOBANA - A Cost-Optimized Parallel Code Breaker", Workshop on Cryptographic Hardware and Embedded Systems (CHES 2006), Yokohama, Japan, October 2006.

[DH] Diffie, W. and M. Hellman, "Exhaustive Cryptanalysis of the NBS Data Encryption Standard", IEEE Computer, Volume 10, Issue 6, June 1977.

Author's Address 📮

Pasi Eronen (editor) Nokia Research Center P.O. Box 407 FIN-00045 Nokia Group Finland

EMail: pasi.eronen@nokia.com

📦 where this page comes from

ietf: rfc5469 2009-02
💖 girlified by claude-haiku-5-5 on 2026-10-17: a language model's rewrite of the original, under its terms