idea.c

/* $Id$
 *
 * The basic IDEA transformation
 * 
 * Please be aware that IDEA IS PATENT ENCUMBERED; see the note below.
 *                      -------------------------
 *
 * This implementation is taken from pgp, see note below.
 *
 * Only primitive operations are done here, chaining modes etc
 * are implemented in a higher level program.
 *
 **********************************************************************
 *
 *    idea.c - C source code for IDEA block cipher.
 *      IDEA (International Data Encryption Algorithm), formerly known as 
 *      IPES (Improved Proposed Encryption Standard).
 *      Algorithm developed by Xuejia Lai and James L. Massey, of ETH Zurich.
 *      This implementation modified and derived from original C code 
 *      developed by Xuejia Lai.  
 *      Zero-based indexing added, names changed from IPES to IDEA.
 *      CFB functions added.  Random number routines added.
 *
 *      Extensively optimized and restructured by Colin Plumb.
 *
 ***********************************************************************
 *
 * Some changes including endianness cleanup done by Niels Möller.
 *
 */
 
/*
 IDEA is patent encumbered; the following information was copied from the
 idea.c extension for the GNU Privacy Guard.

 The IDEA algorithm is patented by Ascom Systec Ltd. of CH-5506 Maegenwil,
 Switzerland, who allow it to be used on a royalty-free basis for certain
 non-profit applications.  Commercial users must obtain a license from the
 company in order to use IDEA.	IDEA may be used on a royalty-free basis under
 the following conditions:

 Free use for private purposes:

 The free use of software containing the algorithm is strictly limited to non
 revenue generating data transfer between private individuals, ie not serving
 commercial purposes.  Requests by freeware developers to obtain a
 royalty-free license to spread an application program containing the
 algorithm for non-commercial purposes must be directed to Ascom.

 Special offer for shareware developers:

 There is a special waiver for shareware developers.  Such waiver eliminates
 the upfront fees as well as royalties for the first US$10,000 gross sales of
 a product containing the algorithm if and only if:

 1. The product is being sold for a minimum of US$10 and a maximum of US$50.
 2. The source code for the shareware is available to the public.

 Special conditions for research projects:

 The use of the algorithm in research projects is free provided that it serves
 the purpose of such project and within the project duration.  Any use of the
 algorithm after the termination of a project including activities resulting
 from a project and for purposes not directly related to the project requires
 a license.

 Ascom Tech requires the following notice to be included for freeware
 products:

 This software product contains the IDEA algorithm as described and claimed in