1 /*
2 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
3 * Use is subject to license terms.
4 */
5
6 /* $OpenBSD: arc4random.c,v 1.6 2001/06/05 05:05:38 pvalchev Exp $ */
7
8 /*
9 * Arc4 random number generator for OpenBSD.
10 * Copyright 1996 David Mazieres <dm@lcs.mit.edu>.
11 *
12 * Modification and redistribution in source and binary forms is
13 * permitted provided that due credit is given to the author and the
14 * OpenBSD project by leaving this copyright notice intact.
15 */
16
17 /*
18 * This code is derived from section 17.1 of Applied Cryptography,
19 * second edition, which describes a stream cipher allegedly
20 * compatible with RSA Labs "RC4" cipher (the actual description of
21 * which is a trade secret). The same algorithm is used as a stream
22 * cipher called "arcfour" in Tatu Ylonen's ssh package.
23 *
24 * Here the stream cipher has been modified always to include the time
25 * when initializing the state. That makes it impossible to
26 * regenerate the same random sequence twice, so this can't be used
27 * for encryption, but will generate good random numbers.
28 *
29 * RC4 is a registered trademark of RSA Laboratories.
30 */
31
32 #include <fcntl.h>
33 #include <stdlib.h>
34 #include <unistd.h>
35 #include <sys/types.h>
36 #include <sys/param.h>
37 #include <sys/time.h>
38
39 #ifdef __GNUC__
40 #define inline __inline
41 #else /* !__GNUC__ */
42 #define inline
43 #endif /* !__GNUC__ */
44
45 struct arc4_stream {
46 uint8_t i;
47 uint8_t j;
48 uint8_t s[256];
49 };
50
51 int rs_initialized;
52 static struct arc4_stream rs;
53
54 static inline void
arc4_init(as)55 arc4_init(as)
56 struct arc4_stream *as;
57 {
58 int n;
59
60 for (n = 0; n < 256; n++)
61 as->s[n] = n;
62 as->i = 0;
63 as->j = 0;
64 }
65
66 static inline void
arc4_addrandom(as,dat,datlen)67 arc4_addrandom(as, dat, datlen)
68 struct arc4_stream *as;
69 u_char *dat;
70 size_t datlen;
71 {
72 int n;
73 uint8_t si;
74
75 as->i--;
76 for (n = 0; n < 256; n++) {
77 as->i = (as->i + 1);
78 si = as->s[as->i];
79 as->j = (as->j + si + dat[n % datlen]);
80 as->s[as->i] = as->s[as->j];
81 as->s[as->j] = si;
82 }
83 as->j = as->i;
84 }
85
86 static void
arc4_stir(as)87 arc4_stir(as)
88 struct arc4_stream *as;
89 {
90 int fd;
91 struct {
92 struct timeval tv;
93 uint rnd[(128 - sizeof(struct timeval)) / sizeof(uint)];
94 } rdat;
95
96 (void) gettimeofday(&rdat.tv, NULL);
97 fd = open("/dev/urandom", O_RDONLY);
98 if (fd != -1) {
99 (void) read(fd, rdat.rnd, sizeof(rdat.rnd));
100 (void) close(fd);
101 }
102 /* fd < 0 ? Ah, what the heck. We'll just take
103 * whatever was on the stack... */
104
105 arc4_addrandom(as, (void *) &rdat, sizeof(rdat));
106 }
107
108 static inline uint8_t
arc4_getbyte(as)109 arc4_getbyte(as)
110 struct arc4_stream *as;
111 {
112 uint8_t si, sj;
113
114 as->i = (as->i + 1);
115 si = as->s[as->i];
116 as->j = (as->j + si);
117 sj = as->s[as->j];
118 as->s[as->i] = sj;
119 as->s[as->j] = si;
120 return (as->s[(si + sj) & 0xff]);
121 }
122
123 static inline uint32_t
arc4_getword(as)124 arc4_getword(as)
125 struct arc4_stream *as;
126 {
127 uint32_t val;
128 val = arc4_getbyte(as) << 24;
129 val |= arc4_getbyte(as) << 16;
130 val |= arc4_getbyte(as) << 8;
131 val |= arc4_getbyte(as);
132 return val;
133 }
134
135 void
arc4random_stir()136 arc4random_stir()
137 {
138 if (!rs_initialized) {
139 arc4_init(&rs);
140 rs_initialized = 1;
141 }
142 arc4_stir(&rs);
143 }
144
145 void
arc4random_addrandom(dat,datlen)146 arc4random_addrandom(dat, datlen)
147 u_char *dat;
148 size_t datlen;
149 {
150 if (!rs_initialized)
151 arc4random_stir();
152 arc4_addrandom(&rs, dat, datlen);
153 }
154
155 uint32_t
arc4random()156 arc4random()
157 {
158 if (!rs_initialized)
159 arc4random_stir();
160 return arc4_getword(&rs);
161 }
162
163 #if 0
164 /*-------- Test code for i386 --------*/
165 #include <stdio.h>
166 #include <machine/pctr.h>
167 int
168 main(int argc, char **argv)
169 {
170 const int iter = 1000000;
171 int i;
172 pctrval v;
173
174 v = rdtsc();
175 for (i = 0; i < iter; i++)
176 arc4random();
177 v = rdtsc() - v;
178 v /= iter;
179
180 printf("%qd cycles\n", v);
181 }
182 #endif
183