lib/liblwip/netif/ppp/randm.c

   1 /*****************************************************************************
   2 * randm.c - Random number generator program file.
   3 *
   4 * Copyright (c) 2003 by Marc Boucher, Services Informatiques (MBSI) inc.
   5 * Copyright (c) 1998 by Global Election Systems Inc.
   6 *
   7 * The authors hereby grant permission to use, copy, modify, distribute,
   8 * and license this software and its documentation for any purpose, provided
   9 * that existing copyright notices are retained in all copies and that this
  10 * notice and the following disclaimer are included verbatim in any
  11 * distributions. No written agreement, license, or royalty fee is required
  12 * for any of the authorized uses.
  13 *
  14 * THIS SOFTWARE IS PROVIDED BY THE CONTRIBUTORS *AS IS* AND ANY EXPRESS OR
  15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  17 * IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24 *
  25 ******************************************************************************
  26 * REVISION HISTORY
  27 *
  28 * 03-01-01 Marc Boucher <marc@mbsi.ca>
  29 *   Ported to lwIP.
  30 * 98-06-03 Guy Lancaster <lancasterg@acm.org>, Global Election Systems Inc.
  31 *   Extracted from avos.
  32 *****************************************************************************/
  33
  34 #include "lwip/opt.h"
  35
  36 #if PPP_SUPPORT /* don't build if not configured for use in lwipopts.h */
  37
  38 #include "md5.h"
  39 #include "randm.h"
  40
  41 #include "ppp.h"
  42 #include "pppdebug.h"
  43
  44 #include <string.h>
  45
  46 #if MD5_SUPPORT /* this module depends on MD5 */
  47 #define RANDPOOLSZ 16   /* Bytes stored in the pool of randomness. */
  48
  49 /*****************************/
  50 /*** LOCAL DATA STRUCTURES ***/
  51 /*****************************/
  52 static char randPool[RANDPOOLSZ];   /* Pool of randomness. */
  53 static long randCount = 0;      /* Pseudo-random incrementer */
  54
  55
  56 /***********************************/
  57 /*** PUBLIC FUNCTION DEFINITIONS ***/
  58 /***********************************/
  59 /*
  60  * Initialize the random number generator.
  61  *
  62  * Since this is to be called on power up, we don't have much
  63  *  system randomess to work with.  Here all we use is the
  64  *  real-time clock.  We'll accumulate more randomness as soon
  65  *  as things start happening.
  66  */
  67 void
  68 avRandomInit()
  69 {
  70   avChurnRand(NULL, 0);
  71 }
  72
  73 /*
  74  * Churn the randomness pool on a random event.  Call this early and often
  75  *  on random and semi-random system events to build randomness in time for
  76  *  usage.  For randomly timed events, pass a null pointer and a zero length
  77  *  and this will use the system timer and other sources to add randomness.
  78  *  If new random data is available, pass a pointer to that and it will be
  79  *  included.
  80  *
  81  * Ref: Applied Cryptography 2nd Ed. by Bruce Schneier p. 427
  82  */
  83 void
  84 avChurnRand(char *randData, u32_t randLen)
  85 {
  86   MD5_CTX md5;
  87
  88   /* LWIP_DEBUGF(LOG_INFO, ("churnRand: %u@%P\n", randLen, randData)); */
  89   MD5Init(&md5);
  90   MD5Update(&md5, (u_char *)randPool, sizeof(randPool));
  91   if (randData) {
  92     MD5Update(&md5, (u_char *)randData, randLen);
  93   } else {
  94     struct {
  95       /* INCLUDE fields for any system sources of randomness */
  96       char foobar;
  97     } sysData;
  98
  99     /* Load sysData fields here. */
 100     MD5Update(&md5, (u_char *)&sysData, sizeof(sysData));
 101   }
 102   MD5Final((u_char *)randPool, &md5);
 103 /*  LWIP_DEBUGF(LOG_INFO, ("churnRand: -> 0\n")); */
 104 }
 105
 106 /*
 107  * Use the random pool to generate random data.  This degrades to pseudo
 108  *  random when used faster than randomness is supplied using churnRand().
 109  * Note: It's important that there be sufficient randomness in randPool
 110  *  before this is called for otherwise the range of the result may be
 111  *  narrow enough to make a search feasible.
 112  *
 113  * Ref: Applied Cryptography 2nd Ed. by Bruce Schneier p. 427
 114  *
 115  * XXX Why does he not just call churnRand() for each block?  Probably
 116  *  so that you don't ever publish the seed which could possibly help
 117  *  predict future values.
 118  * XXX Why don't we preserve md5 between blocks and just update it with
 119  *  randCount each time?  Probably there is a weakness but I wish that
 120  *  it was documented.
 121  */
 122 void
 123 avGenRand(char *buf, u32_t bufLen)
 124 {
 125   MD5_CTX md5;
 126   u_char tmp[16];
 127   u32_t n;
 128
 129   while (bufLen > 0) {
 130     n = LWIP_MIN(bufLen, RANDPOOLSZ);
 131     MD5Init(&md5);
 132     MD5Update(&md5, (u_char *)randPool, sizeof(randPool));
 133     MD5Update(&md5, (u_char *)&randCount, sizeof(randCount));
 134     MD5Final(tmp, &md5);
 135     randCount++;
 136     MEMCPY(buf, tmp, n);
 137     buf += n;
 138     bufLen -= n;
 139   }
 140 }
 141
 142 /*
 143  * Return a new random number.
 144  */
 145 u32_t
 146 avRandom()
 147 {
 148   u32_t newRand;
 149
 150   avGenRand((char *)&newRand, sizeof(newRand));
 151
 152   return newRand;
 153 }
 154
 155 #else /* MD5_SUPPORT */
 156
 157 /*****************************/
 158 /*** LOCAL DATA STRUCTURES ***/
 159 /*****************************/
 160 static int  avRandomized = 0;       /* Set when truely randomized. */
 161 static u32_t avRandomSeed = 0;      /* Seed used for random number generation. */
 162
 163
 164 /***********************************/
 165 /*** PUBLIC FUNCTION DEFINITIONS ***/
 166 /***********************************/
 167 /*
 168  * Initialize the random number generator.
 169  *
 170  * Here we attempt to compute a random number seed but even if
 171  * it isn't random, we'll randomize it later.
 172  *
 173  * The current method uses the fields from the real time clock,
 174  * the idle process counter, the millisecond counter, and the
 175  * hardware timer tick counter.  When this is invoked
 176  * in startup(), then the idle counter and timer values may
 177  * repeat after each boot and the real time clock may not be
 178  * operational.  Thus we call it again on the first random
 179  * event.
 180  */
 181 void
 182 avRandomInit()
 183 {
 184 #if 0
 185   /* Get a pointer into the last 4 bytes of clockBuf. */
 186   u32_t *lptr1 = (u32_t *)((char *)&clockBuf[3]);
 187
 188   /*
 189    * Initialize our seed using the real-time clock, the idle
 190    * counter, the millisecond timer, and the hardware timer
 191    * tick counter.  The real-time clock and the hardware
 192    * tick counter are the best sources of randomness but
 193    * since the tick counter is only 16 bit (and truncated
 194    * at that), the idle counter and millisecond timer
 195    * (which may be small values) are added to help
 196    * randomize the lower 16 bits of the seed.
 197    */
 198   readClk();
 199   avRandomSeed += *(u32_t *)clockBuf + *lptr1 + OSIdleCtr
 200            + ppp_mtime() + ((u32_t)TM1 << 16) + TM1;
 201 #else
 202   avRandomSeed += sys_jiffies(); /* XXX */
 203 #endif
 204
 205   /* Initialize the Borland random number generator. */
 206   srand((unsigned)avRandomSeed);
 207 }
 208
 209 /*
 210  * Randomize our random seed value.  Here we use the fact that
 211  * this function is called at *truely random* times by the polling
 212  * and network functions.  Here we only get 16 bits of new random
 213  * value but we use the previous value to randomize the other 16
 214  * bits.
 215  */
 216 void
 217 avRandomize(void)
 218 {
 219   static u32_t last_jiffies;
 220
 221   if (!avRandomized) {
 222     avRandomized = !0;
 223     avRandomInit();
 224     /* The initialization function also updates the seed. */
 225   } else {
 226     /* avRandomSeed += (avRandomSeed << 16) + TM1; */
 227     avRandomSeed += (sys_jiffies() - last_jiffies); /* XXX */
 228   }
 229   last_jiffies = sys_jiffies();
 230 }
 231
 232 /*
 233  * Return a new random number.
 234  * Here we use the Borland rand() function to supply a pseudo random
 235  * number which we make truely random by combining it with our own
 236  * seed which is randomized by truely random events.
 237  * Thus the numbers will be truely random unless there have been no
 238  * operator or network events in which case it will be pseudo random
 239  * seeded by the real time clock.
 240  */
 241 u32_t
 242 avRandom()
 243 {
 244   return ((((u32_t)rand() << 16) + rand()) + avRandomSeed);
 245 }
 246
 247 #endif /* MD5_SUPPORT */
 248
 249 #endif /* PPP_SUPPORT */