randm.c

00001 /*****************************************************************************
00002 * randm.c - Random number generator program file.
00003 *
00004 * Copyright (c) 2003 by Marc Boucher, Services Informatiques (MBSI) inc.
00005 * Copyright (c) 1998 by Global Election Systems Inc.
00006 *
00007 * The authors hereby grant permission to use, copy, modify, distribute,
00008 * and license this software and its documentation for any purpose, provided
00009 * that existing copyright notices are retained in all copies and that this
00010 * notice and the following disclaimer are included verbatim in any 
00011 * distributions. No written agreement, license, or royalty fee is required
00012 * for any of the authorized uses.
00013 *
00014 * THIS SOFTWARE IS PROVIDED BY THE CONTRIBUTORS *AS IS* AND ANY EXPRESS OR
00015 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
00016 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 
00017 * IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
00018 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
00019 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
00020 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
00021 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
00022 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
00023 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00024 *
00025 ******************************************************************************
00026 * REVISION HISTORY
00027 *
00028 * 03-01-01 Marc Boucher <marc@mbsi.ca>
00029 *   Ported to lwIP.
00030 * 98-06-03 Guy Lancaster <lancasterg@acm.org>, Global Election Systems Inc.
00031 *   Extracted from avos.
00032 *****************************************************************************/
00033 
00034 #include "lwip/opt.h"
00035 
00036 #if PPP_SUPPORT /* don't build if not configured for use in lwipopts.h */
00037 
00038 #include "md5.h"
00039 #include "randm.h"
00040 
00041 #include "ppp.h"
00042 #include "pppdebug.h"
00043 
00044 #include <string.h>
00045 
00046 #if MD5_SUPPORT /* this module depends on MD5 */
00047 #define RANDPOOLSZ 16   /* Bytes stored in the pool of randomness. */
00048 
00049 /*****************************/
00050 /*** LOCAL DATA STRUCTURES ***/
00051 /*****************************/
00052 static char randPool[RANDPOOLSZ];   /* Pool of randomness. */
00053 static long randCount = 0;      /* Pseudo-random incrementer */
00054 
00055 
00056 /***********************************/
00057 /*** PUBLIC FUNCTION DEFINITIONS ***/
00058 /***********************************/
00059 /*
00060  * Initialize the random number generator.
00061  *
00062  * Since this is to be called on power up, we don't have much
00063  *  system randomess to work with.  Here all we use is the
00064  *  real-time clock.  We'll accumulate more randomness as soon
00065  *  as things start happening.
00066  */
00067 void
00068 avRandomInit()
00069 {
00070   avChurnRand(NULL, 0);
00071 }
00072 
00073 /*
00074  * Churn the randomness pool on a random event.  Call this early and often
00075  *  on random and semi-random system events to build randomness in time for
00076  *  usage.  For randomly timed events, pass a null pointer and a zero length
00077  *  and this will use the system timer and other sources to add randomness.
00078  *  If new random data is available, pass a pointer to that and it will be
00079  *  included.
00080  *
00081  * Ref: Applied Cryptography 2nd Ed. by Bruce Schneier p. 427
00082  */
00083 void
00084 avChurnRand(char *randData, u32_t randLen)
00085 {
00086   MD5_CTX md5;
00087 
00088   /* LWIP_DEBUGF(LOG_INFO, ("churnRand: %u@%P\n", randLen, randData)); */
00089   MD5Init(&md5);
00090   MD5Update(&md5, (u_char *)randPool, sizeof(randPool));
00091   if (randData) {
00092     MD5Update(&md5, (u_char *)randData, randLen);
00093   } else {
00094     struct {
00095       /* INCLUDE fields for any system sources of randomness */
00096       char foobar;
00097     } sysData;
00098 
00099     /* Load sysData fields here. */
00100     MD5Update(&md5, (u_char *)&sysData, sizeof(sysData));
00101   }
00102   MD5Final((u_char *)randPool, &md5);
00103 /*  LWIP_DEBUGF(LOG_INFO, ("churnRand: -> 0\n")); */
00104 }
00105 
00106 /*
00107  * Use the random pool to generate random data.  This degrades to pseudo
00108  *  random when used faster than randomness is supplied using churnRand().
00109  * Note: It's important that there be sufficient randomness in randPool
00110  *  before this is called for otherwise the range of the result may be
00111  *  narrow enough to make a search feasible.
00112  *
00113  * Ref: Applied Cryptography 2nd Ed. by Bruce Schneier p. 427
00114  *
00115  * XXX Why does he not just call churnRand() for each block?  Probably
00116  *  so that you don't ever publish the seed which could possibly help
00117  *  predict future values.
00118  * XXX Why don't we preserve md5 between blocks and just update it with
00119  *  randCount each time?  Probably there is a weakness but I wish that
00120  *  it was documented.
00121  */
00122 void
00123 avGenRand(char *buf, u32_t bufLen)
00124 {
00125   MD5_CTX md5;
00126   u_char tmp[16];
00127   u32_t n;
00128 
00129   while (bufLen > 0) {
00130     n = LWIP_MIN(bufLen, RANDPOOLSZ);
00131     MD5Init(&md5);
00132     MD5Update(&md5, (u_char *)randPool, sizeof(randPool));
00133     MD5Update(&md5, (u_char *)&randCount, sizeof(randCount));
00134     MD5Final(tmp, &md5);
00135     randCount++;
00136     MEMCPY(buf, tmp, n);
00137     buf += n;
00138     bufLen -= n;
00139   }
00140 }
00141 
00142 /*
00143  * Return a new random number.
00144  */
00145 u32_t
00146 avRandom()
00147 {
00148   u32_t newRand;
00149 
00150   avGenRand((char *)&newRand, sizeof(newRand));
00151 
00152   return newRand;
00153 }
00154 
00155 #else /* MD5_SUPPORT */
00156 
00157 /*****************************/
00158 /*** LOCAL DATA STRUCTURES ***/
00159 /*****************************/
00160 static int  avRandomized = 0;       /* Set when truely randomized. */
00161 static u32_t avRandomSeed = 0;      /* Seed used for random number generation. */
00162 
00163 
00164 /***********************************/
00165 /*** PUBLIC FUNCTION DEFINITIONS ***/
00166 /***********************************/
00167 /*
00168  * Initialize the random number generator.
00169  *
00170  * Here we attempt to compute a random number seed but even if
00171  * it isn't random, we'll randomize it later.
00172  *
00173  * The current method uses the fields from the real time clock,
00174  * the idle process counter, the millisecond counter, and the
00175  * hardware timer tick counter.  When this is invoked
00176  * in startup(), then the idle counter and timer values may
00177  * repeat after each boot and the real time clock may not be
00178  * operational.  Thus we call it again on the first random
00179  * event.
00180  */
00181 void
00182 avRandomInit()
00183 {
00184 #if 0
00185   /* Get a pointer into the last 4 bytes of clockBuf. */
00186   u32_t *lptr1 = (u32_t *)((char *)&clockBuf[3]);
00187 
00188   /*
00189    * Initialize our seed using the real-time clock, the idle
00190    * counter, the millisecond timer, and the hardware timer
00191    * tick counter.  The real-time clock and the hardware
00192    * tick counter are the best sources of randomness but
00193    * since the tick counter is only 16 bit (and truncated
00194    * at that), the idle counter and millisecond timer
00195    * (which may be small values) are added to help
00196    * randomize the lower 16 bits of the seed.
00197    */
00198   readClk();
00199   avRandomSeed += *(u32_t *)clockBuf + *lptr1 + OSIdleCtr
00200            + ppp_mtime() + ((u32_t)TM1 << 16) + TM1;
00201 #else
00202   avRandomSeed += sys_jiffies(); /* XXX */
00203 #endif
00204 
00205   /* Initialize the Borland random number generator. */
00206   srand((unsigned)avRandomSeed);
00207 }
00208 
00209 /*
00210  * Randomize our random seed value.  Here we use the fact that
00211  * this function is called at *truely random* times by the polling
00212  * and network functions.  Here we only get 16 bits of new random
00213  * value but we use the previous value to randomize the other 16
00214  * bits.
00215  */
00216 void
00217 avRandomize(void)
00218 {
00219   static u32_t last_jiffies;
00220 
00221   if (!avRandomized) {
00222     avRandomized = !0;
00223     avRandomInit();
00224     /* The initialization function also updates the seed. */
00225   } else {
00226     /* avRandomSeed += (avRandomSeed << 16) + TM1; */
00227     avRandomSeed += (sys_jiffies() - last_jiffies); /* XXX */
00228   }
00229   last_jiffies = sys_jiffies();
00230 }
00231 
00232 /*
00233  * Return a new random number.
00234  * Here we use the Borland rand() function to supply a pseudo random
00235  * number which we make truely random by combining it with our own
00236  * seed which is randomized by truely random events. 
00237  * Thus the numbers will be truely random unless there have been no
00238  * operator or network events in which case it will be pseudo random
00239  * seeded by the real time clock.
00240  */
00241 u32_t
00242 avRandom()
00243 {
00244   return ((((u32_t)rand() << 16) + rand()) + avRandomSeed);
00245 }
00246 
00247 #endif /* MD5_SUPPORT */
00248 
00249 #endif /* PPP_SUPPORT */