weakprng.c

wm PNE 3.3 source code, running at more than vxworks6.x version.

/* $Header: /usr/cvsroot/target/src/wrn/wm/common/lib/weakprng.c,v 1.3 2003/01/16 18:18:58 josh Exp $ */

/*
 * Copyright (C) 1999-2005 Wind River Systems, Inc.
 * All rights reserved.  Provided under license only.
 * Distribution or other use of this software is only
 * permitted pursuant to the terms of a license agreement
 * from Wind River Systems (and is otherwise prohibited).
 * Refer to that license agreement for terms of use.
 */


/****************************************************************************
 *  Copyright 1998 Integrated Systems, Inc.
 *  All rights reserved.
 ****************************************************************************/

/* 
 * $Log: weakprng.c,v $
 * Revision 1.3  2003/01/16 18:18:58  josh
 * directory structure shifting
 *
 * Revision 1.2  2001/11/06 22:15:56  tneale
 * Fixed for newest file layout
 *
 * Revision 1.1.1.1  2001/11/05 17:48:40  tneale
 * Tornado shuffle
 *
 * Revision 1.9  2001/01/19 22:21:33  paul
 * Update copyright.
 *
 * Revision 1.8  2000/03/17 00:17:00  meister
 * Update copyright message
 *
 * Revision 1.7  1998/03/06 20:30:45  sra
 * Fiddle seeding algorithm per Phil's recommendation.
 *
 * Revision 1.6  1998/02/25 22:08:28  mrf
 * Correct copyright dates.
 *
 * Revision 1.5  1998/02/25 15:17:07  mrf
 * Fix msvc5 compiler warnings.
 *
 * Revision 1.4  1998/02/25 04:43:28  sra
 * Update copyrights.
 *
 * Revision 1.3  1998/02/21 23:38:34  sra
 * Minor changes to WeakPRNG module.
 *
 * Revision 1.1  1998/02/21 22:05:36  mrf
 * Added weak random number generator.
 *
 */

/* [clearcase]
modification history
-------------------
01b,20apr05,job  update copyright notices
01a,11dec03,job  fix copyright statements
*/


#ifndef EPILOGUE_INSTALL_H
#include <wrn/wm/common/install.h>
#endif

#ifndef COMMON_CONFIG_H
#include <wrn/wm/common/config.h>
#endif

#ifndef	COMMON_GLUE_H
#include <wrn/wm/common/glue.h>
#endif

#ifndef COMMON_WEAKPRNG_H
#include <wrn/wm/common/weakprng.h>
#endif

/*
 * This file implements a cryptographically WEAK random number generator 
 * suitable only for dithering protocol responses to avoid collisions or
 * other situations where the purpose of the "random" number is to avoid
 * simultaneity or repeated use of the same values.  For any cryptographic
 * purposes, the cryptographically strong random number generator (found
 * in common/lib/prng.c) should be used instead.
 *
 * This weak generator is useful for dithering for those protocols which
 * require it (such as DHCP, RIP, IGMP, Router Discovery and IPv6 Neighbor
 * Discovery). It has relatively low processing overhead (compared to the 
 * strong random number generator), and it is seeded automatically by 
 * Attache.  
 *
 * It is the purpose of this weak random number generator, not to produce
 * truly random numbers, but to produce numbers which are likely to be 
 * different for different hosts on a given link.  In order to obtain
 * this result, it is important that different hosts use different seeds.
 * Attache seeds (and re-seeds) the generator in several places with values
 * that are likely to be unique for this host.  Seeds include the GLUE_NOW() 
 * value at the end of the attache_init() call, the hardware address or 
 * IPv6 address token provided in the net_if structure during each if_attach() 
 * call, if any, and the IP addresses provided to route_add_address() each 
 * time it is called.  Successive seeds do not reset the generator.  If a
 * customer has additional seed information that may help to improve the
 * uniqueness of the generated values for a particular host (e.g. a box
 * serial number), he can also input those seeds using the seed call below.
 */

static bits32_t ep_weak_prng_value;

/* ep_seed_weak_prng --
 *	Seeds the weak random number generator with (hopefully unique
 *	for this host) seed data.  Data is provided as a buffer of
 *	unsigned bytes and a length (in bytes).  We run the generator
 *	as part of the seeding process to reduce the chance of losing
 *	this seed if the generator is seeded again before it is used.
 */
void
ep_seed_weak_prng(bits8_t *seed_string, size_t len)
{
  int i;

  for (i = 0; i < (int) len; i++) {
    ep_weak_prng_value ^= ((bits32_t) (seed_string[i])) << (8 * (i & 3));
    if ((i & 3) == 3)
      ep_weak_prng(0xFFFFFFFFL);
  }
  ep_weak_prng(0xFFFFFFFFL);
}

/* ep_weak_prng --
 *	Returns a "random" 32_bit integer less than or equal to 'max'.
 *
 * 	The algorithm is a linear congruential random number generator,
 * 	equivilent to the ANSI C rand() function but with constants that
 * 	provide better results than those used in the BSD rand() function.
 *
 * 	These constants are from Knuth, chap 3, pp 102 & 170.  Don't change
 * 	them unless you really understand the underlying math.
 */
bits32_t
ep_weak_prng(bits32_t max)
{
  ep_weak_prng_value = (ep_weak_prng_value + 1) * 16664525L;

  return ++max ? ep_weak_prng_value % max : ep_weak_prng_value;
}