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1 office 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 }