Arthur de Jong

Open Source / Free Software developer

About gnupg-idea

Some people that need to inter-operate with PGP 2.x users need support for IDEA with GnuPG. These users have to find the correct IDEA source module, compile and the module install by hand.
IDEA is not available in GnuPG because it was previously restricted by patents held in Europe and the USA.

This package aims to make installing the IDEA module a little easier (my definition of easier anyway). After building, it provides a Debian package that you can install on your machine.

The steps to build and install this package are:

  • put the following line in your /etc/apt/sources.list:
    deb-src ./
  • apt-get update
  • apt-get --only-source build-dep gnupg-idea
  • apt-get --only-source -b source gnupg-idea
  • dpkg -i gnupg-idea_version_i386.deb

During the package build the IDEA source files are retrieved from the Internet. I cannot distribute the IDEA source with this package as the IDEA source code license does not allow distribution in The Netherlands.

The above steps can also be done by downloading this file, extract it and build the Debian package from that.

Another alternative is:

$ dget -u
$ cd gnupg-idea-3.3
$ sudo apt-get build-dep .
$ dpkg-buildpackage -b -uc
$ dpkg -i ../gnupg-idea_3.3_amd64.deb

Note about idea.c

I do not and cannot distribute the idea.c file needed because the license of the IDEA source does not permit distribution in Austria, France, Germany, Italy, Japan, The Netherlands, Spain, Sweden, Switzerland, the UK and the US.
Don't ask for it because I'm not going to give it to you.

Copyright notice


The gnupg-idea package (without the IDEA source code) is based on gpg-rsaidea-2.1 by Tom Lees and Josip Rodin.

Arthur de Jong stripped out the RSA stuff and pgp wrapper examples that are obsoleted by inclusion of RSA in gnupg and the pgpgpg package and added functions for downloading the idea source at build time.

Copyright © 1999 Josip Rodin
Copyright © 1999 Tom Lees
Copyright © 2002-2004 Arthur de Jong

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.


Version 1.11 of idea.c (the one that can be used for gnupg-idea) is distributed under a BSD-like license with an additional notice about distribution in certain countries.


Software patents are bad. The patent essentially caused this otherwise useful cipher to be useless to most people during it's useful lifetime.

The IDEA patent

IDEA has a horrible software patent on it. Luckily it has expired in most countries.


(The European patent covered Austria, France, Germany, Italy, The Netherlands, Spain, Sweden, Switzerland and The United Kingdom.)