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/urandom" 58 #define THREAD_LOCK() \ 59 do { \ 60 if (__isthreaded) \ 61 _pthread_mutex_lock(&arc4random_mtx); \ 62 } while (0) 63 64 #define THREAD_UNLOCK() \ 65 do { \ 66 if (__isthreaded) \ 67 _pthread_mutex_unlock(&arc4random_mtx); \ 68 } while (0) 69 70 static struct arc4_stream rs; 71 static int rs_initialized; 72 static int rs_stired; 73 static int arc4_count; 74 75 static inline u_int8_t arc4_getbyte(void); 76 static void arc4_stir(void); 77 78 static inline void 79 arc4_init(void) 80 { 81 int n; 82 83 for (n = 0; n < 256; n++) 84 rs.s[n] = n; 85 rs.i = 0; 86 rs.j = 0; 87 } 88 89 static inline void 90 arc4_addrandom(u_char *dat, int datlen) 91 { 92 int n; 93 u_int8_t si; 94 95 rs.i--; 96 for (n = 0; n < 256; n++) { 97 rs.i = (rs.i + 1); 98 si = rs.s[rs.i]; 99 rs.j = (rs.j + si + dat[n % datlen]); 100 rs.s[rs.i] = rs.s[rs.j]; 101 rs.s[rs.j] = si; 102 } 103 rs.j = rs.i; 104 } 105 106 static void 107 arc4_stir(void) 108 { 109 int fd, n; 110 struct { 111 struct timeval tv; 112 pid_t pid; 113 u_int8_t rnd[128 - sizeof(struct timeval) - sizeof(pid_t)]; 114 } rdat; 115 116 gettimeofday(&rdat.tv, NULL); 117 rdat.pid = getpid(); 118 fd = _open(RANDOMDEV, O_RDONLY, 0); 119 if (fd >= 0) { 120 (void) _read(fd, rdat.rnd, sizeof(rdat.rnd)); 121 _close(fd); 122 } 123 /* fd < 0? Ah, what the heck. We'll just take whatever was on the 124 * stack... */ 125 126 arc4_addrandom((void *) &rdat, sizeof(rdat)); 127 128 /* 129 * Throw away the first N bytes of output, as suggested in the 130 * paper "Weaknesses in the Key Scheduling Algorithm of RC4" 131 * by Fluher, Mantin, and Shamir. N=1024 is based on 132 * suggestions in the paper "(Not So) Random Shuffles of RC4" 133 * by Ilya Mironov. 134 */ 135 for (n = 0; n < 1024; n++) 136 (void) arc4_getbyte(); 137 arc4_count = 1600000; 138 } 139 140 static inline u_int8_t 141 arc4_getbyte(void) 142 { 143 u_int8_t si, sj; 144 145 rs.i = (rs.i + 1); 146 si = rs.s[rs.i]; 147 rs.j = (rs.j + si); 148 sj = rs.s[rs.j]; 149 rs.s[rs.i] = sj; 150 rs.s[rs.j] = si; 151 152 return (rs.s[(si + sj) & 0xff]); 153 } 154 155 static inline u_int32_t 156 arc4_getword(void) 157 { 158 u_int32_t val; 159 160 val = arc4_getbyte() << 24; 161 val |= arc4_getbyte() << 16; 162 val |= arc4_getbyte() << 8; 163 val |= arc4_getbyte(); 164 165 return (val); 166 } 167 168 static void 169 arc4_check_init(void) 170 { 171 if (!rs_initialized) { 172 arc4_init(); 173 rs_initialized = 1; 174 } 175 } 176 177 static inline void 178 arc4_check_stir(void) 179 { 180 if (!rs_stired || arc4_count <= 0) { 181 arc4_stir(); 182 rs_stired = 1; 183 } 184 } 185 186 void 187 arc4random_stir(void) 188 { 189 THREAD_LOCK(); 190 arc4_check_init(); 191 arc4_stir(); 192 THREAD_UNLOCK(); 193 } 194 195 void 196 arc4random_addrandom(u_char *dat, int datlen) 197 { 198 THREAD_LOCK(); 199 arc4_check_init(); 200 arc4_check_stir(); 201 arc4_addrandom(dat, datlen); 202 THREAD_UNLOCK(); 203 } 204 205 u_int32_t 206 arc4random(void) 207 { 208 u_int32_t rnd; 209 210 THREAD_LOCK(); 211 arc4_check_init(); 212 arc4_check_stir(); 213 rnd = arc4_getword(); 214 arc4_count -= 4; 215 THREAD_UNLOCK(); 216 217 return (rnd); 218 } 219 220 void 221 arc4random_buf(void *_buf, size_t n) 222 { 223 u_char *buf = (u_char *)_buf; 224 225 THREAD_LOCK(); 226 arc4_check_init(); 227 while (n--) { 228 arc4_check_stir(); 229 buf[n] = arc4_getbyte(); 230 arc4_count--; 231 } 232 THREAD_UNLOCK(); 233 } 234 235 /* 236 * Calculate a uniformly distributed random number less than upper_bound 237 * avoiding "modulo bias". 238 * 239 * Uniformity is achieved by generating new random numbers until the one 240 * returned is outside the range [0, 2**32 % upper_bound). This 241 * guarantees the selected random number will be inside 242 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound) 243 * after reduction modulo upper_bound. 244 */ 245 u_int32_t 246 arc4random_uniform(u_int32_t upper_bound) 247 { 248 u_int32_t r, min; 249 250 if (upper_bound < 2) 251 return (0); 252 253 #if (ULONG_MAX > 0xffffffffUL) 254 min = 0x100000000UL % upper_bound; 255 #else 256 /* Calculate (2**32 % upper_bound) avoiding 64-bit math */ 257 if (upper_bound > 0x80000000) 258 min = 1 + ~upper_bound; /* 2**32 - upper_bound */ 259 else { 260 /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */ 261 min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound; 262 } 263 #endif 264 265 /* 266 * This could theoretically loop forever but each retry has 267 * p > 0.5 (worst case, usually far better) of selecting a 268 * number inside the range we need, so it should rarely need 269 * to re-roll. 270 */ 271 for (;;) { 272 r = arc4random(); 273 if (r >= min) 274 break; 275 } 276 277 return (r % upper_bound); 278 } 279 280 #if 0 281 /*-------- Test code for i386 --------*/ 282 #include <stdio.h> 283 #include <machine/pctr.h> 284 int 285 main(int argc, char **argv) 286 { 287 const int iter = 1000000; 288 int i; 289 pctrval v; 290 291 v = rdtsc(); 292 for (i = 0; i < iter; i++) 293 arc4random(); 294 v = rdtsc() - v; 295 v /= iter; 296 297 printf("%qd cycles\n", v); 298 } 299 #endif 300