RFC 5581

RFC 5581: The Camellia Cipher in OpenPGP 🦋

okay so this RFC is by D. Shaw 💅 and it's Informational (so it's giving info, not a rule-book standard 🎀). It was published in June 2009, it Updates RFC 4880 (that's the OpenPGP message format spec), and it doesn't obsolete anything 🌸

Network Working Group, Request for Comments: 5581

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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

1. Introduction 🌈

okay so the OpenPGP protocol [RFC4880] can support loads of different symmetric ciphers 💖 This doc is the guide for using the Camellia [RFC3713] symmetric cipher inside OpenPGP, so it's basically the main character intro 👑

2. Requirements Notation 🎀

ngl this section is the fine print. 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's a 128-bit symmetric block cipher (same as AES and Twofish in OpenPGP, iconic 🔥) that supports 128-bit, 192-bit, and 256-bit keys. This document defines the use of Camellia in OpenPGP ✨

Here's the cute little lookup table for the algorithm numbers:

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

OpenPGP applications MAY implement Camellia 💜 If they do, 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. It's giving equal rights for all the ciphers 💅

⚠️ bestie, read this part: the OpenPGP algorithm preferences system stops interoperability problems with public key encrypted messages. BUT 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 come up when using an optional cipher for symmetrically encrypted messages, since this OpenPGP message type doesn't use the algorithm preferences system. So anyone using optional ciphers this way 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 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. This part is seriously important, so please actually go check 😭🔥

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 💖