package/ead/src/tinysrp/t_truerand.c

   1 /*
   2  *      Physically random numbers (very nearly uniform)
   3  *      D. P. Mitchell
   4  *      Modified by Matt Blaze 7/95
   5  */
   6 /*
   7  * The authors of this software are Don Mitchell and Matt Blaze.
   8  *              Copyright (c) 1995 by AT&T.
   9  * Permission to use, copy, and modify this software without fee
  10  * is hereby granted, provided that this entire notice is included in
  11  * all copies of any software which is or includes a copy or
  12  * modification of this software and in all copies of the supporting
  13  * documentation for such software.
  14  *
  15  * This software may be subject to United States export controls.
  16  *
  17  * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
  18  * WARRANTY.  IN PARTICULAR, NEITHER THE AUTHORS NOR AT&T MAKE ANY
  19  * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
  20  * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
  21  */
  22
  23 /*
  24  * WARNING: depending on the particular platform, raw_truerand()
  25  * output may be biased or correlated.  In general, you can expect
  26  * about 16 bits of "pseudo-entropy" out of each 32 bit word returned
  27  * by truerand(), but it may not be uniformly diffused.  You should
  28  * raw_therefore run the output through some post-whitening function
  29  * (like MD5 or DES or whatever) before using it to generate key
  30  * material.  (RSAREF's random package does this for you when you feed
  31  * raw_truerand() bits to the seed input function.)
  32  *
  33  * The application interface, for 8, 16, and 32 bit properly "whitened"
  34  * random numbers, can be found in trand8(), trand16(), and trand32().
  35  * Use those instead of calling raw_truerand() directly.
  36  *
  37  * The basic idea here is that between clock "skew" and various
  38  * hard-to-predict OS event arrivals, counting a tight loop will yield
  39  * a little (maybe a third of a bit or so) of "good" randomness per
  40  * interval clock tick.  This seems to work well even on unloaded
  41  * machines.  If there is a human operator at the machine, you should
  42  * augment truerand with other measure, like keyboard event timing.
  43  * On server machines (e.g., when you need to generate a
  44  * Diffie-Hellman secret) truerand alone may be good enough.
  45  *
  46  * Test these assumptions on your own platform before fielding a
  47  * system based on this software or these techniques.
  48  *
  49  * This software seems to work well (at 10 or so bits per
  50  * raw_truerand() call) on a Sun Sparc-20 under SunOS 4.1.3 and on a
  51  * P100 under BSDI 2.0.  You're on your own elsewhere.
  52  *
  53  */
  54
  55 #include "t_defines.h"
  56
  57 #include <signal.h>
  58 #include <setjmp.h>
  59 #include <sys/time.h>
  60 #include <math.h>
  61 #include <stdio.h>
  62
  63 #ifdef OLD_TRUERAND
  64 static jmp_buf env;
  65 #endif
  66 static unsigned volatile count
  67 #ifndef OLD_TRUERAND
  68   , done = 0
  69 #endif
  70 ;
  71
  72 static unsigned ocount;
  73 static unsigned buffer;
  74
  75 static void
  76 tick()
  77 {
  78         struct itimerval it, oit;
  79
  80         it.it_interval.tv_sec = 0;
  81         it.it_interval.tv_usec = 0;
  82         it.it_value.tv_sec = 0;
  83         it.it_value.tv_usec = 16665;
  84         if (setitimer(ITIMER_REAL, &it, &oit) < 0)
  85                 perror("tick");
  86 }
  87
  88 static void
  89 interrupt()
  90 {
  91         if (count) {
  92 #ifdef OLD_TRUERAND
  93                 longjmp(env, 1);
  94 #else
  95                 ++done;
  96                 return;
  97 #endif
  98         }
  99
 100         (void) signal(SIGALRM, interrupt);
 101         tick();
 102 }
 103
 104 static unsigned long
 105 roulette()
 106 {
 107 #ifdef OLD_TRUERAND
 108         if (setjmp(env)) {
 109                 count ^= (count>>3) ^ (count>>6) ^ ocount;
 110                 count &= 0x7;
 111                 ocount=count;
 112                 buffer = (buffer<<3) ^ count;
 113                 return buffer;
 114         }
 115 #else
 116         done = 0;
 117 #endif
 118         (void) signal(SIGALRM, interrupt);
 119         count = 0;
 120         tick();
 121 #ifdef OLD_TRUERAND
 122         for (;;)
 123 #else
 124         while(done == 0)
 125 #endif
 126                 count++;        /* about 1 MHz on VAX 11/780 */
 127 #ifndef OLD_TRUERAND
 128         count ^= (count>>3) ^ (count>>6) ^ ocount;
 129         count &= 0x7;
 130         ocount=count;
 131         buffer = (buffer<<3) ^ count;
 132         return buffer;
 133 #endif
 134 }
 135
 136 unsigned long
 137 raw_truerand()
 138 {
 139         count=0;
 140         (void) roulette();
 141         (void) roulette();
 142         (void) roulette();
 143         (void) roulette();
 144         (void) roulette();
 145         (void) roulette();
 146         (void) roulette();
 147         (void) roulette();
 148         (void) roulette();
 149         (void) roulette();
 150         return roulette();
 151 }