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Network Working Group D. Shaw Request for Comments: 5581 June 2009 Updates: 4880 Category: Informational

                   The Camellia Cipher in OpenPGP

Status of This Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

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Abstract

 This document presents the necessary information to use the Camellia
 symmetric block cipher in the OpenPGP protocol.

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
 2.  Requirements Notation . . . . . . . . . . . . . . . . . . . . . 2
 3.  Camellia  . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
 4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 2
 5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 3
 6.  Normative References  . . . . . . . . . . . . . . . . . . . . . 3

Shaw Informational [Page 1]  RFC 5581 The Camellia Cipher in OpenPGP June 2009

1. Introduction

 The OpenPGP protocol [RFC4880] can support many different symmetric
 ciphers.  This document presents the necessary information to use the
 Camellia [RFC3713] symmetric cipher in the OpenPGP protocol.

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. Camellia

 Camellia is specified in [RFC3713].  It is a 128-bit symmetric block
 cipher (as are AES and Twofish in OpenPGP) that supports 128-bit,
 192-bit, and 256-bit keys.  This document defines the use of Camellia
 in OpenPGP.

   +---------------------+----------------------------------------+
   | Camellia Key Length | OpenPGP Symmetric-Key Algorithm Number |
   +---------------------+----------------------------------------+
   |         128         |                   11                   |
   |         192         |                   12                   |
   |         256         |                   13                   |
   +---------------------+----------------------------------------+

 OpenPGP applications MAY implement Camellia.  If implemented,
 Camellia may be used in any place in OpenPGP where a symmetric cipher
 is usable, and it is subject to the same usage requirements (such as
 its presence in the Preferred Symmetric Algorithms signature
 subpacket) as the other symmetric ciphers in OpenPGP.

 While the OpenPGP algorithm preferences system prevents
 interoperability problems with public key encrypted messages, if
 Camellia (or any other optional cipher) is used for encrypting
 private keys, there could be interoperability problems when migrating
 a private key from one system to another.  A similar issue can arise
 when using an optional cipher for symmetrically encrypted messages,
 as this OpenPGP message type does not use the algorithm preferences
 system.  Those using optional ciphers in this manner should take care
 they are using a cipher that their intended recipient can decrypt.

4. Security Considerations

 At publication time, there are no known weak keys for Camellia, and
 the Camellia algorithm is believed to be strong.  However, as with
 any technology involving cryptography, implementers should check the

Shaw Informational [Page 2]  RFC 5581 The Camellia Cipher in OpenPGP June 2009

 current literature, as well as the Camellia home page at
 http://info.isl.ntt.co.jp/camellia/ to determine if Camellia has been
 found to be vulnerable to attack.

5. IANA Considerations

 IANA assigned three algorithm numbers from the registry of OpenPGP
 Symmetric-Key Algorithms that was created by [RFC4880].

6. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.

 [RFC3713]  Matsui, M., Nakajima, J., and S. Moriai, "A Description of
            the Camellia Encryption Algorithm", RFC 3713, April 2004.

 [RFC4880]  Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R.
            Thayer, "OpenPGP Message Format", RFC 4880, November 2007.

Author's Address

 David Shaw

 EMail: dshaw@jabberwocky.com

Shaw Informational [Page 3]