arc4random.c (12621B)
1 /* Portable arc4random.c based on arc4random.c from OpenBSD. 2 * Portable version by Chris Davis, adapted for Libevent by Nick Mathewson 3 * Copyright (c) 2010 Chris Davis, Niels Provos, and Nick Mathewson 4 * Copyright (c) 2010-2012 Niels Provos and Nick Mathewson 5 * 6 * Note that in Libevent, this file isn't compiled directly. Instead, 7 * it's included from evutil_rand.c 8 */ 9 10 /* 11 * Copyright (c) 1996, David Mazieres <dm@uun.org> 12 * Copyright (c) 2008, Damien Miller <djm@openbsd.org> 13 * 14 * Permission to use, copy, modify, and distribute this software for any 15 * purpose with or without fee is hereby granted, provided that the above 16 * copyright notice and this permission notice appear in all copies. 17 * 18 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 19 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 20 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 21 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 22 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 23 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 24 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 25 */ 26 27 /* 28 * Arc4 random number generator for OpenBSD. 29 * 30 * This code is derived from section 17.1 of Applied Cryptography, 31 * second edition, which describes a stream cipher allegedly 32 * compatible with RSA Labs "RC4" cipher (the actual description of 33 * which is a trade secret). The same algorithm is used as a stream 34 * cipher called "arcfour" in Tatu Ylonen's ssh package. 35 * 36 * Here the stream cipher has been modified always to include the time 37 * when initializing the state. That makes it impossible to 38 * regenerate the same random sequence twice, so this can't be used 39 * for encryption, but will generate good random numbers. 40 * 41 * RC4 is a registered trademark of RSA Laboratories. 42 */ 43 44 #ifndef ARC4RANDOM_EXPORT 45 #define ARC4RANDOM_EXPORT 46 #endif 47 48 #ifndef ARC4RANDOM_UINT32 49 #define ARC4RANDOM_UINT32 uint32_t 50 #endif 51 52 #ifndef ARC4RANDOM_NO_INCLUDES 53 #include "evconfig-private.h" 54 #ifdef _WIN32 55 #include <wincrypt.h> 56 #include <process.h> 57 #include <winerror.h> 58 #else 59 #include <fcntl.h> 60 #include <unistd.h> 61 #include <sys/param.h> 62 #include <sys/time.h> 63 #ifdef EVENT__HAVE_SYS_SYSCTL_H 64 #include <sys/sysctl.h> 65 #endif 66 #ifdef EVENT__HAVE_SYS_RANDOM_H 67 #include <sys/random.h> 68 #endif 69 #endif 70 #include <limits.h> 71 #include <stdlib.h> 72 #include <string.h> 73 #endif 74 75 /* Add platform entropy 32 bytes (256 bits) at a time. */ 76 #define ADD_ENTROPY 32 77 78 /* Re-seed from the platform RNG after generating this many bytes. */ 79 #define BYTES_BEFORE_RESEED 1600000 80 81 struct arc4_stream { 82 unsigned char i; 83 unsigned char j; 84 unsigned char s[256]; 85 }; 86 87 #ifdef _WIN32 88 #define getpid _getpid 89 #define pid_t int 90 #endif 91 92 static int rs_initialized; 93 static struct arc4_stream rs; 94 static pid_t arc4_stir_pid; 95 static int arc4_count; 96 97 static inline unsigned char arc4_getbyte(void); 98 99 static inline void 100 arc4_init(void) 101 { 102 int n; 103 104 for (n = 0; n < 256; n++) 105 rs.s[n] = n; 106 rs.i = 0; 107 rs.j = 0; 108 } 109 110 static inline void 111 arc4_addrandom(const unsigned char *dat, int datlen) 112 { 113 int n; 114 unsigned char si; 115 116 rs.i--; 117 for (n = 0; n < 256; n++) { 118 rs.i = (rs.i + 1); 119 si = rs.s[rs.i]; 120 rs.j = (rs.j + si + dat[n % datlen]); 121 rs.s[rs.i] = rs.s[rs.j]; 122 rs.s[rs.j] = si; 123 } 124 rs.j = rs.i; 125 } 126 127 #ifndef _WIN32 128 static ssize_t 129 read_all(int fd, unsigned char *buf, size_t count) 130 { 131 size_t numread = 0; 132 ssize_t result; 133 134 while (numread < count) { 135 result = read(fd, buf+numread, count-numread); 136 if (result<0) 137 return -1; 138 else if (result == 0) 139 break; 140 numread += result; 141 } 142 143 return (ssize_t)numread; 144 } 145 #endif 146 147 #ifdef _WIN32 148 #define TRY_SEED_WIN32 149 static int 150 arc4_seed_win32(void) 151 { 152 /* This is adapted from Tor's crypto_seed_rng() */ 153 static int provider_set = 0; 154 static HCRYPTPROV provider; 155 unsigned char buf[ADD_ENTROPY]; 156 157 if (!provider_set) { 158 if (!CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL, 159 CRYPT_VERIFYCONTEXT)) { 160 if (GetLastError() != (DWORD)NTE_BAD_KEYSET) 161 return -1; 162 } 163 provider_set = 1; 164 } 165 if (!CryptGenRandom(provider, sizeof(buf), buf)) 166 return -1; 167 arc4_addrandom(buf, sizeof(buf)); 168 evutil_memclear_(buf, sizeof(buf)); 169 return 0; 170 } 171 #endif 172 173 #if defined(EVENT__HAVE_GETRANDOM) 174 #define TRY_SEED_GETRANDOM 175 static int 176 arc4_seed_getrandom(void) 177 { 178 unsigned char buf[ADD_ENTROPY]; 179 size_t len, n; 180 unsigned i; 181 int any_set; 182 183 memset(buf, 0, sizeof(buf)); 184 185 for (len = 0; len < sizeof(buf); len += n) { 186 n = sizeof(buf) - len; 187 188 if (0 == getrandom(&buf[len], n, 0)) 189 return -1; 190 } 191 /* make sure that the buffer actually got set. */ 192 for (i=0,any_set=0; i<sizeof(buf); ++i) { 193 any_set |= buf[i]; 194 } 195 if (!any_set) 196 return -1; 197 198 arc4_addrandom(buf, sizeof(buf)); 199 evutil_memclear_(buf, sizeof(buf)); 200 return 0; 201 } 202 #endif /* EVENT__HAVE_GETRANDOM */ 203 204 #if defined(EVENT__HAVE_SYS_SYSCTL_H) && defined(EVENT__HAVE_SYSCTL) 205 #if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_ARND 206 #define TRY_SEED_SYSCTL_BSD 207 static int 208 arc4_seed_sysctl_bsd(void) 209 { 210 /* Based on code from William Ahern and from OpenBSD, this function 211 * tries to use the KERN_ARND syscall to get entropy from the kernel. 212 * This can work even if /dev/urandom is inaccessible for some reason 213 * (e.g., we're running in a chroot). */ 214 int mib[] = { CTL_KERN, KERN_ARND }; 215 unsigned char buf[ADD_ENTROPY]; 216 size_t len, n; 217 int i, any_set; 218 219 memset(buf, 0, sizeof(buf)); 220 221 len = sizeof(buf); 222 if (sysctl(mib, 2, buf, &len, NULL, 0) == -1) { 223 for (len = 0; len < sizeof(buf); len += sizeof(unsigned)) { 224 n = sizeof(unsigned); 225 if (n + len > sizeof(buf)) 226 n = len - sizeof(buf); 227 if (sysctl(mib, 2, &buf[len], &n, NULL, 0) == -1) 228 return -1; 229 } 230 } 231 /* make sure that the buffer actually got set. */ 232 for (i=any_set=0; i<sizeof(buf); ++i) { 233 any_set |= buf[i]; 234 } 235 if (!any_set) 236 return -1; 237 238 arc4_addrandom(buf, sizeof(buf)); 239 evutil_memclear_(buf, sizeof(buf)); 240 return 0; 241 } 242 #endif 243 #endif /* defined(EVENT__HAVE_SYS_SYSCTL_H) */ 244 245 #ifdef __linux__ 246 #define TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID 247 static int 248 arc4_seed_proc_sys_kernel_random_uuid(void) 249 { 250 /* Occasionally, somebody will make /proc/sys accessible in a chroot, 251 * but not /dev/urandom. Let's try /proc/sys/kernel/random/uuid. 252 * Its format is stupid, so we need to decode it from hex. 253 */ 254 int fd; 255 char buf[128]; 256 unsigned char entropy[64]; 257 int bytes, n, i, nybbles; 258 for (bytes = 0; bytes<ADD_ENTROPY; ) { 259 fd = evutil_open_closeonexec_("/proc/sys/kernel/random/uuid", O_RDONLY, 0); 260 if (fd < 0) 261 return -1; 262 n = read(fd, buf, sizeof(buf)); 263 close(fd); 264 if (n<=0) 265 return -1; 266 memset(entropy, 0, sizeof(entropy)); 267 for (i=nybbles=0; i<n; ++i) { 268 if (EVUTIL_ISXDIGIT_(buf[i])) { 269 int nyb = evutil_hex_char_to_int_(buf[i]); 270 if (nybbles & 1) { 271 entropy[nybbles/2] |= nyb; 272 } else { 273 entropy[nybbles/2] |= nyb<<4; 274 } 275 ++nybbles; 276 } 277 } 278 if (nybbles < 2) 279 return -1; 280 arc4_addrandom(entropy, nybbles/2); 281 bytes += nybbles/2; 282 } 283 evutil_memclear_(entropy, sizeof(entropy)); 284 evutil_memclear_(buf, sizeof(buf)); 285 return 0; 286 } 287 #endif 288 289 #ifndef _WIN32 290 #define TRY_SEED_URANDOM 291 static char *arc4random_urandom_filename = NULL; 292 293 static int arc4_seed_urandom_helper_(const char *fname) 294 { 295 unsigned char buf[ADD_ENTROPY]; 296 int fd; 297 size_t n; 298 299 fd = evutil_open_closeonexec_(fname, O_RDONLY, 0); 300 if (fd<0) 301 return -1; 302 n = read_all(fd, buf, sizeof(buf)); 303 close(fd); 304 if (n != sizeof(buf)) 305 return -1; 306 arc4_addrandom(buf, sizeof(buf)); 307 evutil_memclear_(buf, sizeof(buf)); 308 return 0; 309 } 310 311 static int 312 arc4_seed_urandom(void) 313 { 314 /* This is adapted from Tor's crypto_seed_rng() */ 315 static const char *filenames[] = { 316 "/dev/srandom", "/dev/urandom", "/dev/random", NULL 317 }; 318 int i; 319 if (arc4random_urandom_filename) 320 return arc4_seed_urandom_helper_(arc4random_urandom_filename); 321 322 for (i = 0; filenames[i]; ++i) { 323 if (arc4_seed_urandom_helper_(filenames[i]) == 0) { 324 return 0; 325 } 326 } 327 328 return -1; 329 } 330 #endif 331 332 static int 333 arc4_seed(void) 334 { 335 int ok = 0; 336 /* We try every method that might work, and don't give up even if one 337 * does seem to work. There's no real harm in over-seeding, and if 338 * one of these sources turns out to be broken, that would be bad. */ 339 #ifdef TRY_SEED_WIN32 340 if (0 == arc4_seed_win32()) 341 ok = 1; 342 #endif 343 #ifdef TRY_SEED_GETRANDOM 344 if (0 == arc4_seed_getrandom()) 345 ok = 1; 346 #endif 347 #ifdef TRY_SEED_URANDOM 348 if (0 == arc4_seed_urandom()) 349 ok = 1; 350 #endif 351 #ifdef TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID 352 if (arc4random_urandom_filename == NULL && 353 0 == arc4_seed_proc_sys_kernel_random_uuid()) 354 ok = 1; 355 #endif 356 #ifdef TRY_SEED_SYSCTL_BSD 357 if (0 == arc4_seed_sysctl_bsd()) 358 ok = 1; 359 #endif 360 return ok ? 0 : -1; 361 } 362 363 static int 364 arc4_stir(void) 365 { 366 int i; 367 368 if (!rs_initialized) { 369 arc4_init(); 370 rs_initialized = 1; 371 } 372 373 if (0 != arc4_seed()) 374 return -1; 375 376 /* 377 * Discard early keystream, as per recommendations in 378 * "Weaknesses in the Key Scheduling Algorithm of RC4" by 379 * Scott Fluhrer, Itsik Mantin, and Adi Shamir. 380 * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps 381 * 382 * Ilya Mironov's "(Not So) Random Shuffles of RC4" suggests that 383 * we drop at least 2*256 bytes, with 12*256 as a conservative 384 * value. 385 * 386 * RFC4345 says to drop 6*256. 387 * 388 * At least some versions of this code drop 4*256, in a mistaken 389 * belief that "words" in the Fluhrer/Mantin/Shamir paper refers 390 * to processor words. 391 * 392 * We add another sect to the cargo cult, and choose 12*256. 393 */ 394 for (i = 0; i < 12*256; i++) 395 (void)arc4_getbyte(); 396 397 arc4_count = BYTES_BEFORE_RESEED; 398 399 return 0; 400 } 401 402 403 static void 404 arc4_stir_if_needed(void) 405 { 406 pid_t pid = getpid(); 407 408 if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid) 409 { 410 arc4_stir_pid = pid; 411 arc4_stir(); 412 } 413 } 414 415 static inline unsigned char 416 arc4_getbyte(void) 417 { 418 unsigned char si, sj; 419 420 rs.i = (rs.i + 1); 421 si = rs.s[rs.i]; 422 rs.j = (rs.j + si); 423 sj = rs.s[rs.j]; 424 rs.s[rs.i] = sj; 425 rs.s[rs.j] = si; 426 return (rs.s[(si + sj) & 0xff]); 427 } 428 429 static inline unsigned int 430 arc4_getword(void) 431 { 432 unsigned int val; 433 434 val = arc4_getbyte() << 24; 435 val |= arc4_getbyte() << 16; 436 val |= arc4_getbyte() << 8; 437 val |= arc4_getbyte(); 438 439 return val; 440 } 441 442 #ifndef ARC4RANDOM_NOSTIR 443 ARC4RANDOM_EXPORT int 444 arc4random_stir(void) 445 { 446 int val; 447 ARC4_LOCK_(); 448 val = arc4_stir(); 449 ARC4_UNLOCK_(); 450 return val; 451 } 452 #endif 453 454 #ifndef ARC4RANDOM_NOADDRANDOM 455 ARC4RANDOM_EXPORT void 456 arc4random_addrandom(const unsigned char *dat, int datlen) 457 { 458 int j; 459 ARC4_LOCK_(); 460 if (!rs_initialized) 461 arc4_stir(); 462 for (j = 0; j < datlen; j += 256) { 463 /* arc4_addrandom() ignores all but the first 256 bytes of 464 * its input. We want to make sure to look at ALL the 465 * data in 'dat', just in case the user is doing something 466 * crazy like passing us all the files in /var/log. */ 467 arc4_addrandom(dat + j, datlen - j); 468 } 469 ARC4_UNLOCK_(); 470 } 471 #endif 472 473 #ifndef ARC4RANDOM_NORANDOM 474 ARC4RANDOM_EXPORT ARC4RANDOM_UINT32 475 arc4random(void) 476 { 477 ARC4RANDOM_UINT32 val; 478 ARC4_LOCK_(); 479 arc4_count -= 4; 480 arc4_stir_if_needed(); 481 val = arc4_getword(); 482 ARC4_UNLOCK_(); 483 return val; 484 } 485 #endif 486 487 ARC4RANDOM_EXPORT void 488 arc4random_buf(void *buf_, size_t n) 489 { 490 unsigned char *buf = buf_; 491 ARC4_LOCK_(); 492 arc4_stir_if_needed(); 493 while (n--) { 494 if (--arc4_count <= 0) 495 arc4_stir(); 496 buf[n] = arc4_getbyte(); 497 } 498 ARC4_UNLOCK_(); 499 } 500 501 #ifndef ARC4RANDOM_NOUNIFORM 502 /* 503 * Calculate a uniformly distributed random number less than upper_bound 504 * avoiding "modulo bias". 505 * 506 * Uniformity is achieved by generating new random numbers until the one 507 * returned is outside the range [0, 2**32 % upper_bound). This 508 * guarantees the selected random number will be inside 509 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound) 510 * after reduction modulo upper_bound. 511 */ 512 ARC4RANDOM_EXPORT unsigned int 513 arc4random_uniform(unsigned int upper_bound) 514 { 515 ARC4RANDOM_UINT32 r, min; 516 517 if (upper_bound < 2) 518 return 0; 519 520 #if (UINT_MAX > 0xffffffffUL) 521 min = 0x100000000UL % upper_bound; 522 #else 523 /* Calculate (2**32 % upper_bound) avoiding 64-bit math */ 524 if (upper_bound > 0x80000000) 525 min = 1 + ~upper_bound; /* 2**32 - upper_bound */ 526 else { 527 /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */ 528 min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound; 529 } 530 #endif 531 532 /* 533 * This could theoretically loop forever but each retry has 534 * p > 0.5 (worst case, usually far better) of selecting a 535 * number inside the range we need, so it should rarely need 536 * to re-roll. 537 */ 538 for (;;) { 539 r = arc4random(); 540 if (r >= min) 541 break; 542 } 543 544 return r % upper_bound; 545 } 546 #endif