Documentation/crypto/descore-readme.rst

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.. SPDX-License-Identifier: GPL-2.0
.. include:: <isonum.txt>

===========================================
Fast & Portable DES encryption & decryption
===========================================

.. note::

   Below is the original README file from the descore.shar package,
   converted to ReST format.

------------------------------------------------------------------------------

des - fast & portable DES encryption & decryption.

Copyright |copy| 1992  Dana L. How

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU Library General Public License as published by
the Free Software Foundation; either version 2 of the License, 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 Library General Public License for more details.

You should have received a copy of the GNU Library General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

Author's address: how@isl.stanford.edu

.. README,v 1.15 1992/05/20 00:25:32 how E

==>> To compile after untarring/unsharring, just ``make`` <<==

This package was designed with the following goals:

1.	Highest possible encryption/decryption PERFORMANCE.
2.	PORTABILITY to any byte-addressable host with a 32bit unsigned C type
3.	Plug-compatible replacement for KERBEROS's low-level routines.

This second release includes a number of performance enhancements for
register-starved machines.  My discussions with Richard Outerbridge,
71755.204@compuserve.com, sparked a number of these enhancements.

To more rapidly understand the code in this package, inspect desSmallFips.i
(created by typing ``make``) BEFORE you tackle desCode.h.  The latter is set
up in a parameterized fashion so it can easily be modified by speed-daemon
hackers in pursuit of that last microsecond.  You will find it more
illuminating to inspect one specific implementation,
and then move on to the common abstract skeleton with this one in mind.


performance comparison to other available des code which i could
compile on a SPARCStation 1 (cc -O4, gcc -O2):

this code (byte-order independent):

  - 30us per encryption (options: 64k tables, no IP/FP)
  - 33us per encryption (options: 64k tables, FIPS standard bit ordering)
  - 45us per encryption (options:  2k tables, no IP/FP)
  - 48us per encryption (options:  2k tables, FIPS standard bit ordering)
  - 275us to set a new key (uses 1k of key tables)

	this has the quickest encryption/decryption routines i've seen.
	since i was interested in fast des filters rather than crypt(3)
	and password cracking, i haven't really bothered yet to speed up

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