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

* 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 "ppp.h"

#include "pppdebug.h"

#include <string.h>

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

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

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

/*** LOCAL DATA STRUCTURES ***/

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

static char randPool[RANDPOOLSZ];   /* Pool of randomness. */

static long randCount = 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

avRandomInit()

{

  avChurnRand(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

avChurnRand(char *randData, u32_t randLen)

{

  MD5_CTX md5;

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

  MD5Init(&md5);

  MD5Update(&md5, (u_char *)randPool, sizeof(randPool));

  if (randData) {

    MD5Update(&md5, (u_char *)randData, randLen);

  } else {

    struct {

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

      char foobar;

    } sysData;

    /* Load sysData fields here. */

    MD5Update(&md5, (u_char *)&sysData, sizeof(sysData));

  }

  MD5Final((u_char *)randPool, &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 randPool

 *  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

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

 *  it was documented.

 */

void

avGenRand(char *buf, u32_t bufLen)

{

  MD5_CTX md5;

  u_char tmp[16];

  u32_t n;

  while (bufLen > 0) {

    n = LWIP_MIN(bufLen, RANDPOOLSZ);

    MD5Init(&md5);

    MD5Update(&md5, (u_char *)randPool, sizeof(randPool));

    MD5Update(&md5, (u_char *)&randCount, sizeof(randCount));

    MD5Final(tmp, &md5);

    randCount++;

    MEMCPY(buf, tmp, n);

    buf += n;

    bufLen -= n;

  }

}

/*

 * Return a new random number.

 */

u32_t

avRandom()

{

  u32_t newRand;

  avGenRand((char *)&newRand, sizeof(newRand));

  return newRand;

}

#else /* MD5_SUPPORT */

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

/*** LOCAL DATA STRUCTURES ***/

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

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

static u32_t avRandomSeed = 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

avRandomInit()

{

#if 0

  /* Get a pointer into the last 4 bytes of clockBuf. */

  u32_t *lptr1 = (u32_t *)((char *)&clockBuf[3]);

  /*

   * Initialize our seed using the real-time clock, the idle

   * counter, the millisecond timer, and the hardware timer

   * tick counter.  The real-time clock and the hardware

   * tick counter are the best sources of randomness but

   * since the tick counter is only 16 bit (and truncated

   * at that), the idle counter and millisecond timer

   * (which may be small values) are added to help

   * randomize the lower 16 bits of the seed.

   */

  readClk();

  avRandomSeed += *(u32_t *)clockBuf + *lptr1 + OSIdleCtr

           + ppp_mtime() + ((u32_t)TM1 << 16) + TM1;

#else

  avRandomSeed += sys_jiffies(); /* XXX */

#endif

  /* Initialize the Borland random number generator. */

  srand((unsigned)avRandomSeed);

}

/*

 * 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

avRandomize(void)

{

  static u32_t last_jiffies;

  if (!avRandomized) {

    avRandomized = !0;

    avRandomInit();

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

  } else {

    /* avRandomSeed += (avRandomSeed << 16) + TM1; */

    avRandomSeed += (sys_jiffies() - last_jiffies); /* XXX */

  }

  last_jiffies = sys_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

avRandom()

{

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

}

#endif /* MD5_SUPPORT */

#endif /* PPP_SUPPORT */