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.

Copyright Notice

  Copyright (c) 2009 IETF Trust and the persons identified as the
  document authors.  All rights reserved.

  This document is subject to BCP 78 and the IETF Trust's Legal
  Provisions Relating to IETF Documents in effect on the date of
  publication of this document (http://trustee.ietf.org/license-info).
  Please review these documents carefully, as they describe your rights
  and restrictions with respect to this document.

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













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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



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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: [email protected]


























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