Subversion Repositories openrisc

/*****************************************************************************

* randm.c - Random number generator program file.

*

* Copyright (c) 2003 by Marc Boucher, Services Informatiques (MBSI) inc.

* Copyright (c) 1998 by Global Election Systems Inc.

*

* The authors hereby grant permission to use, copy, modify, distribute,

* and license this software and its documentation for any purpose, provided

* that existing copyright notices are retained in all copies and that this

* notice and the following disclaimer are included verbatim in any

* distributions. No written agreement, license, or royalty fee is required

* for any of the authorized uses.

*

* THIS SOFTWARE IS PROVIDED BY THE CONTRIBUTORS *AS IS* AND ANY EXPRESS OR

* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

* IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,

* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

*

******************************************************************************

* REVISION HISTORY

*

* 03-01-01 Marc Boucher <marc@mbsi.ca>

*   Ported to lwIP.

* 98-06-03 Guy Lancaster <lancasterg@acm.org>, Global Election Systems Inc.

*   Extracted from avos.

*****************************************************************************/

#include "lwip/opt.h"

#if PPP_SUPPORT /* don't build if not configured for use in lwipopts.h */

#include "md5.h"

#include "randm.h"

#include "timesys.h"

#include "netif/ppp/ppp.h"

#include "pppdebug.h"

#if MD5_SUPPORT /* this module depends on MD5 */

#define RAND_POOL_SIZE 16 /* Bytes stored in the pool of randomness. */

/*****************************/

/*** LOCAL DATA STRUCTURES ***/

/*****************************/

static char rand_pool[RAND_POOL_SIZE];  /* Pool of randomness. */

static long rand_count = 0;             /* Pseudo-random incrementer */

/***********************************/

/*** PUBLIC FUNCTION DEFINITIONS ***/

/***********************************/

/*

 * Initialize the random number generator.

 *

 * Since this is to be called on power up, we don't have much

 *  system randomess to work with.  Here all we use is the

 *  real-time clock.  We'll accumulate more randomness as soon

 *  as things start happening.

 */

void

randm_init()

{

  randm_churn(NULL, 0);

}

/*

 * Churn the randomness pool on a random event.  Call this early and often

 *  on random and semi-random system events to build randomness in time for

 *  usage.  For randomly timed events, pass a null pointer and a zero length

 *  and this will use the system timer and other sources to add randomness.

 *  If new random data is available, pass a pointer to that and it will be

 *  included.

 *

 * Ref: Applied Cryptography 2nd Ed. by Bruce Schneier p. 427

 */

void

randm_churn(char *data, u32_t len)

{

  md5_ctx md5;

  /* ppp_trace(LOG_INFO, "churnRand: %u@%P\n", len, data); */

  md5_init(&md5);

  md5_update(&md5, (u8_t *) rand_pool, sizeof(rand_pool));

  if (data) {

    md5_update(&md5, (u8_t *) data, len);

  } else {

    struct {

      /* INCLUDE fields for any system sources of randomness */

      char foobar;

    } sys_data;

    /* Load sys_data fields here. */

    md5_update(&md5, (u8_t *) &sys_data, sizeof(sys_data));

  }

  md5_final((u8_t *) rand_pool, &md5);

/*  ppp_trace(LOG_INFO, "churnRand: -> 0\n"); */

}

/*

 * Use the random pool to generate random data.  This degrades to pseudo

 *  random when used faster than randomness is supplied using churnRand().

 * Note: It's important that there be sufficient randomness in rand_pool

 *  before this is called for otherwise the range of the result may be

 *  narrow enough to make a search feasible.

 *

 * Ref: Applied Cryptography 2nd Ed. by Bruce Schneier p. 427

 *

 * XXX Why does he not just call churnRand() for each block?  Probably

 *  so that you don't ever publish the seed which could possibly help

 *  predict future values.

 * XXX Why don't we preserve md5 between blocks and just update it with

 *  rand_count each time?  Probably there is a weakness but I wish that

 *  it was documented.

 */

void

randm_gen_rand(char *buf, u32_t len)

{

  md5_ctx md5;

  u8_t tmp[16];

  u32_t n;

  while (len > 0) {

    n = LWIP_MIN(len, RAND_POOL_SIZE);

    md5_init(&md5);

    md5_update(&md5, (u8_t *) rand_pool, sizeof(rand_pool));

    md5_update(&md5, (u8_t *) &rand_count, sizeof(rand_count));

    md5_final(tmp, &md5);

    rand_count++;

    MEMCPY(buf, tmp, n);

    buf += n;

    len -= n;

  }

}

/*

 * Return a new random number.

 */

u32_t

randm_rand()

{

  u32_t rand;

  randm_gen_rand((char *) &rand, sizeof(rand));

  return rand;

}

#else /* MD5_SUPPORT */

/*****************************/

/*** LOCAL DATA STRUCTURES ***/

/*****************************/

static int randomized = 0;  /* Set when truely randomized. */

static u32_t seed = 0;      /* Seed used for random number generation. */

/***********************************/

/*** PUBLIC FUNCTION DEFINITIONS ***/

/***********************************/

/*

 * Initialize the random number generator.

 *

 * Here we attempt to compute a random number seed but even if

 * it isn't random, we'll randomize it later.

 *

 * The current method uses the fields from the real time clock,

 * the idle process counter, the millisecond counter, and the

 * hardware timer tick counter.  When this is invoked

 * in startup(), then the idle counter and timer values may

 * repeat after each boot and the real time clock may not be

 * operational.  Thus we call it again on the first random

 * event.

 */

void

randm_init()

{

  /* XXX week but probably enough */

  seed += ppp_jiffies();

  /* Initialize the Borland random number generator. */

  srand(seed);

}

/*

 * Randomize our random seed value.  Here we use the fact that

 * this function is called at *truely random* times by the polling

 * and network functions.  Here we only get 16 bits of new random

 * value but we use the previous value to randomize the other 16

 * bits.

 */

void

randm_randomize(void)

{

  static u32_t last_jiffies;

  if (!randomized) {

    randomized = 1;

    randm_init();

    /* The initialization function also updates the seed. */

  } else {

    /* XXX week but probably enough */

    seed += (seed << 16) + (ppp_jiffies() - last_jiffies); /* XXX */

  }

  last_jiffies = ppp_jiffies();

}

/*

 * Return a new random number.

 * Here we use the Borland rand() function to supply a pseudo random

 * number which we make truely random by combining it with our own

 * seed which is randomized by truely random events.

 * Thus the numbers will be truely random unless there have been no

 * operator or network events in which case it will be pseudo random

 * seeded by the real time clock.

 */

u32_t

randm_rand()

{

  return ((((u32_t) rand() << 16) + rand()) + seed);

}

#endif /* MD5_SUPPORT */

#endif /* PPP_SUPPORT */