1 /* 2 * Copyright (c) 1996, David Mazieres <dm@uun.org> 3 * Copyright (c) 2008, Damien Miller <djm@openbsd.org> 4 * 5 * Permission to use, copy, modify, and distribute this software for any 6 * purpose with or without fee is hereby granted, provided that the above 7 * copyright notice and this permission notice appear in all copies. 8 * 9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16 */ 17 18 /* 19 * Arc4 random number generator for OpenBSD. 20 * 21 * This code is derived from section 17.1 of Applied Cryptography, 22 * second edition, which describes a stream cipher allegedly 23 * compatible with RSA Labs "RC4" cipher (the actual description of 24 * which is a trade secret). The same algorithm is used as a stream 25 * cipher called "arcfour" in Tatu Ylonen's ssh package. 26 * 27 * Here the stream cipher has been modified always to include the time 28 * when initializing the state. That makes it impossible to 29 * regenerate the same random sequence twice, so this can't be used 30 * for encryption, but will generate good random numbers. 31 * 32 * RC4 is a registered trademark of RSA Laboratories. 33 */ 34 35 #include <sys/cdefs.h> 36 __FBSDID("$FreeBSD$"); 37 38 #include "namespace.h" 39 #include <sys/types.h> 40 #include <sys/time.h> 41 #include <stdlib.h> 42 #include <fcntl.h> 43 #include <unistd.h> 44 #include <pthread.h> 45 46 #include "libc_private.h" 47 #include "un-namespace.h" 48 49 struct arc4_stream { 50 u_int8_t i; 51 u_int8_t j; 52 u_int8_t s[256]; 53 }; 54 55 static pthread_mutex_t arc4random_mtx = PTHREAD_MUTEX_INITIALIZER; 56 57 #define RANDOMDEV "/dev/random" 58 #define KEYSIZE 128 59 #define THREAD_LOCK() \ 60 do { \ 61 if (__isthreaded) \ 62 _pthread_mutex_lock(&arc4random_mtx); \ 63 } while (0) 64 65 #define THREAD_UNLOCK() \ 66 do { \ 67 if (__isthreaded) \ 68 _pthread_mutex_unlock(&arc4random_mtx); \ 69 } while (0) 70 71 static struct arc4_stream rs; 72 static int rs_initialized; 73 static int rs_stired; 74 static int arc4_count; 75 76 static inline u_int8_t arc4_getbyte(void); 77 static void arc4_stir(void); 78 79 static inline void 80 arc4_init(void) 81 { 82 int n; 83 84 for (n = 0; n < 256; n++) 85 rs.s[n] = n; 86 rs.i = 0; 87 rs.j = 0; 88 } 89 90 static inline void 91 arc4_addrandom(u_char *dat, int datlen) 92 { 93 int n; 94 u_int8_t si; 95 96 rs.i--; 97 for (n = 0; n < 256; n++) { 98 rs.i = (rs.i + 1); 99 si = rs.s[rs.i]; 100 rs.j = (rs.j + si + dat[n % datlen]); 101 rs.s[rs.i] = rs.s[rs.j]; 102 rs.s[rs.j] = si; 103 } 104 rs.j = rs.i; 105 } 106 107 static void 108 arc4_stir(void) 109 { 110 int done, fd, n; 111 struct { 112 struct timeval tv; 113 pid_t pid; 114 u_int8_t rnd[KEYSIZE]; 115 } rdat; 116 117 fd = _open(RANDOMDEV, O_RDONLY, 0); 118 done = 0; 119 if (fd >= 0) { 120 if (_read(fd, &rdat, KEYSIZE) == KEYSIZE) 121 done = 1; 122 (void)_close(fd); 123 } 124 if (!done) { 125 (void)gettimeofday(&rdat.tv, NULL); 126 rdat.pid = getpid(); 127 /* We'll just take whatever was on the stack too... */ 128 } 129 130 arc4_addrandom((u_char *)&rdat, KEYSIZE); 131 132 /* 133 * Throw away the first N bytes of output, as suggested in the 134 * paper "Weaknesses in the Key Scheduling Algorithm of RC4" 135 * by Fluher, Mantin, and Shamir. N=1024 is based on 136 * suggestions in the paper "(Not So) Random Shuffles of RC4" 137 * by Ilya Mironov. 138 */ 139 for (n = 0; n < 1024; n++) 140 (void) arc4_getbyte(); 141 arc4_count = 1600000; 142 } 143 144 static inline u_int8_t 145 arc4_getbyte(void) 146 { 147 u_int8_t si, sj; 148 149 rs.i = (rs.i + 1); 150 si = rs.s[rs.i]; 151 rs.j = (rs.j + si); 152 sj = rs.s[rs.j]; 153 rs.s[rs.i] = sj; 154 rs.s[rs.j] = si; 155 156 return (rs.s[(si + sj) & 0xff]); 157 } 158 159 static inline u_int32_t 160 arc4_getword(void) 161 { 162 u_int32_t val; 163 164 val = arc4_getbyte() << 24; 165 val |= arc4_getbyte() << 16; 166 val |= arc4_getbyte() << 8; 167 val |= arc4_getbyte(); 168 169 return (val); 170 } 171 172 static void 173 arc4_check_init(void) 174 { 175 if (!rs_initialized) { 176 arc4_init(); 177 rs_initialized = 1; 178 } 179 } 180 181 static inline void 182 arc4_check_stir(void) 183 { 184 if (!rs_stired || arc4_count <= 0) { 185 arc4_stir(); 186 rs_stired = 1; 187 } 188 } 189 190 void 191 arc4random_stir(void) 192 { 193 THREAD_LOCK(); 194 arc4_check_init(); 195 arc4_stir(); 196 rs_stired = 1; 197 THREAD_UNLOCK(); 198 } 199 200 void 201 arc4random_addrandom(u_char *dat, int datlen) 202 { 203 THREAD_LOCK(); 204 arc4_check_init(); 205 arc4_check_stir(); 206 arc4_addrandom(dat, datlen); 207 THREAD_UNLOCK(); 208 } 209 210 u_int32_t 211 arc4random(void) 212 { 213 u_int32_t rnd; 214 215 THREAD_LOCK(); 216 arc4_check_init(); 217 arc4_check_stir(); 218 rnd = arc4_getword(); 219 arc4_count -= 4; 220 THREAD_UNLOCK(); 221 222 return (rnd); 223 } 224 225 void 226 arc4random_buf(void *_buf, size_t n) 227 { 228 u_char *buf = (u_char *)_buf; 229 230 THREAD_LOCK(); 231 arc4_check_init(); 232 while (n--) { 233 arc4_check_stir(); 234 buf[n] = arc4_getbyte(); 235 arc4_count--; 236 } 237 THREAD_UNLOCK(); 238 } 239 240 /* 241 * Calculate a uniformly distributed random number less than upper_bound 242 * avoiding "modulo bias". 243 * 244 * Uniformity is achieved by generating new random numbers until the one 245 * returned is outside the range [0, 2**32 % upper_bound). This 246 * guarantees the selected random number will be inside 247 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound) 248 * after reduction modulo upper_bound. 249 */ 250 u_int32_t 251 arc4random_uniform(u_int32_t upper_bound) 252 { 253 u_int32_t r, min; 254 255 if (upper_bound < 2) 256 return (0); 257 258 #if (ULONG_MAX > 0xffffffffUL) 259 min = 0x100000000UL % upper_bound; 260 #else 261 /* Calculate (2**32 % upper_bound) avoiding 64-bit math */ 262 if (upper_bound > 0x80000000) 263 min = 1 + ~upper_bound; /* 2**32 - upper_bound */ 264 else { 265 /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */ 266 min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound; 267 } 268 #endif 269 270 /* 271 * This could theoretically loop forever but each retry has 272 * p > 0.5 (worst case, usually far better) of selecting a 273 * number inside the range we need, so it should rarely need 274 * to re-roll. 275 */ 276 for (;;) { 277 r = arc4random(); 278 if (r >= min) 279 break; 280 } 281 282 return (r % upper_bound); 283 } 284 285 #if 0 286 /*-------- Test code for i386 --------*/ 287 #include <stdio.h> 288 #include <machine/pctr.h> 289 int 290 main(int argc, char **argv) 291 { 292 const int iter = 1000000; 293 int i; 294 pctrval v; 295 296 v = rdtsc(); 297 for (i = 0; i < iter; i++) 298 arc4random(); 299 v = rdtsc() - v; 300 v /= iter; 301 302 printf("%qd cycles\n", v); 303 } 304 #endif 305