text: /*
   * magic.c - PPP Magic Number routines.
   *
   * Copyright (c) 1984-2000 Carnegie Mellon University. All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   *
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   *
   * 3. The name "Carnegie Mellon University" must not be used to
   *    endorse or promote products derived from this software without
   *    prior written permission. For permission or any legal
   *    details, please contact
   *      Office of Technology Transfer
   *      Carnegie Mellon University
   *      5000 Forbes Avenue
   *      Pittsburgh, PA  15213-3890
   *      (412) 268-4387, fax: (412) 268-7395
   *      tech-transfer@andrew.cmu.edu
   *
   * 4. Redistributions of any form whatsoever must retain the following
   *    acknowledgment:
   *    "This product includes software developed by Computing Services
   *     at Carnegie Mellon University (http://www.cmu.edu/computing/)."
   *
   * CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
   * THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
   * AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE
   * FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
   * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
   * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
   */
  /*****************************************************************************
  * 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 "netif/ppp/ppp_impl.h"
  #include "netif/ppp/magic.h"
  
  #if PPP_MD5_RANDM /* Using MD5 for better randomness if enabled */
  
  #if LWIP_INCLUDED_POLARSSL_MD5
  #include "netif/ppp/polarssl/md5.h"
  #else
  #include "polarssl/md5.h"
  #endif
  
  #define MD5_HASH_SIZE 16
  static char magic_randpool[MD5_HASH_SIZE];   /* Pool of randomness. */
  static long magic_randcount;      /* Pseudo-random incrementer */
  static u32_t magic_randomseed;    /* Seed used for random number generation. */
  
  /*
   * 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
   */
  static void magic_churnrand(char *rand_data, u32_t rand_len) {
    md5_context md5;
  
    /* LWIP_DEBUGF(LOG_INFO, ("magic_churnrand: %u@%P\n", rand_len, rand_data)); */
    md5_starts(&md5);
    md5_update(&md5, (u_char *)magic_randpool, sizeof(magic_randpool));
    if (rand_data) {
      md5_update(&md5, (u_char *)rand_data, rand_len);
    } else {
      struct {
        /* INCLUDE fields for any system sources of randomness */
        u32_t jiffies;
  #ifdef LWIP_RAND
        u32_t rand;
  #endif /* LWIP_RAND */
      } sys_data;
      magic_randomseed += sys_jiffies();
      sys_data.jiffies = magic_randomseed;
  #ifdef LWIP_RAND
      sys_data.rand = LWIP_RAND();
  #endif /* LWIP_RAND */
      /* Load sys_data fields here. */
      md5_update(&md5, (u_char *)&sys_data, sizeof(sys_data));
    }
    md5_finish(&md5, (u_char *)magic_randpool);
  /*  LWIP_DEBUGF(LOG_INFO, ("magic_churnrand: -> 0\n")); */
  }
  
  /*
   * Initialize the random number generator.
   */
  void magic_init(void) {
    magic_churnrand(NULL, 0);
  }
  
  /*
   * Randomize our random seed value.
   */
  void magic_randomize(void) {
    magic_churnrand(NULL, 0);
  }
  
  /*
   * magic_random_bytes - Fill a buffer with random bytes.
   *
   * Use the random pool to generate random data.  This degrades to pseudo
   *  random when used faster than randomness is supplied using magic_churnrand().
   * Note: It's important that there be sufficient randomness in magic_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 magic_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
   *  magic_randcount each time?  Probably there is a weakness but I wish that
   *  it was documented.
   */
  void magic_random_bytes(unsigned char *buf, u32_t buf_len) {
    md5_context md5;
    u_char tmp[MD5_HASH_SIZE];
    u32_t n;
  
    while (buf_len > 0) {
      md5_starts(&md5);
      md5_update(&md5, (u_char *)magic_randpool, sizeof(magic_randpool));
      md5_update(&md5, (u_char *)&magic_randcount, sizeof(magic_randcount));
      md5_finish(&md5, tmp);
      magic_randcount++;
      n = LWIP_MIN(buf_len, MD5_HASH_SIZE);
      MEMCPY(buf, tmp, n);
      buf += n;
      buf_len -= n;
    }
  }
  
  /*
   * Return a new random number.
   */
  u32_t magic(void) {
    u32_t new_rand;
  
    magic_random_bytes((unsigned char *)&new_rand, sizeof(new_rand));
  
    return new_rand;
  }
  
  #else /* PPP_MD5_RANDM */
  
  /*****************************/
  /*** LOCAL DATA STRUCTURES ***/
  /*****************************/
  #ifndef LWIP_RAND
  static int  magic_randomized;       /* Set when truely randomized. */
  #endif /* LWIP_RAND */
  static u32_t magic_randomseed;      /* 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 magic_init(void) {
    magic_randomseed += sys_jiffies();
  #ifndef LWIP_RAND
    /* Initialize the Borland random number generator. */
    srand((unsigned)magic_randomseed);
  #endif /* LWIP_RAND */
  }
  
  /*
   * magic_init - Initialize the magic number generator.
   *
   * 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 magic_randomize(void) {
  #ifndef LWIP_RAND
    if (!magic_randomized) {
      magic_randomized = !0;
      magic_init();
      /* The initialization function also updates the seed. */
    } else {
  #endif /* LWIP_RAND */
      magic_randomseed += sys_jiffies();
  #ifndef LWIP_RAND
    }
  #endif /* LWIP_RAND */
  }
  
  /*
   * 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 magic(void) {
  #ifdef LWIP_RAND
    return LWIP_RAND() + magic_randomseed;
  #else /* LWIP_RAND */
    return ((u32_t)rand() << 16) + (u32_t)rand() + magic_randomseed;
  #endif /* LWIP_RAND */
  }
  
  /*
   * magic_random_bytes - Fill a buffer with random bytes.
   */
  void magic_random_bytes(unsigned char *buf, u32_t buf_len) {
    u32_t new_rand, n;
  
    while (buf_len > 0) {
      new_rand = magic();
      n = LWIP_MIN(buf_len, sizeof(new_rand));
      MEMCPY(buf, &new_rand, n);
      buf += n;
      buf_len -= n;
    }
  }
  #endif /* PPP_MD5_RANDM */
  
  /*
   * Return a new random number between 0 and (2^pow)-1 included.
   */
  u32_t magic_pow(u8_t pow) {
    return magic() & ~(~0UL<<pow);
  }
  
  #endif /* PPP_SUPPORT */
  