arc4random.c revision 1.3
1/* $NetBSD: arc4random.c,v 1.3 2015/07/10 14:20:34 christos Exp $ */ 2 3/* Portable arc4random.c based on arc4random.c from OpenBSD. 4 * Portable version by Chris Davis, adapted for Libevent by Nick Mathewson 5 * Copyright (c) 2010 Chris Davis, Niels Provos, and Nick Mathewson 6 * Copyright (c) 2010-2012 Niels Provos and Nick Mathewson 7 * 8 * Note that in Libevent, this file isn't compiled directly. Instead, 9 * it's included from evutil_rand.c 10 */ 11 12/* 13 * Copyright (c) 1996, David Mazieres <dm@uun.org> 14 * Copyright (c) 2008, Damien Miller <djm@openbsd.org> 15 * 16 * Permission to use, copy, modify, and distribute this software for any 17 * purpose with or without fee is hereby granted, provided that the above 18 * copyright notice and this permission notice appear in all copies. 19 * 20 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 21 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 22 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 23 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 24 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 25 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 26 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 27 */ 28 29/* 30 * Arc4 random number generator for OpenBSD. 31 * 32 * This code is derived from section 17.1 of Applied Cryptography, 33 * second edition, which describes a stream cipher allegedly 34 * compatible with RSA Labs "RC4" cipher (the actual description of 35 * which is a trade secret). The same algorithm is used as a stream 36 * cipher called "arcfour" in Tatu Ylonen's ssh package. 37 * 38 * Here the stream cipher has been modified always to include the time 39 * when initializing the state. That makes it impossible to 40 * regenerate the same random sequence twice, so this can't be used 41 * for encryption, but will generate good random numbers. 42 * 43 * RC4 is a registered trademark of RSA Laboratories. 44 */ 45 46#ifndef ARC4RANDOM_EXPORT 47#define ARC4RANDOM_EXPORT 48#endif 49 50#ifndef ARC4RANDOM_UINT32 51#define ARC4RANDOM_UINT32 uint32_t 52#endif 53 54#ifndef ARC4RANDOM_NO_INCLUDES 55#include "evconfig-private.h" 56#ifdef _WIN32 57#include <wincrypt.h> 58#include <process.h> 59#else 60#include <fcntl.h> 61#include <unistd.h> 62#include <sys/param.h> 63#include <sys/time.h> 64#ifdef EVENT__HAVE_SYS_SYSCTL_H 65#include <sys/sysctl.h> 66#endif 67#endif 68#include <limits.h> 69#include <stdlib.h> 70#include <string.h> 71#endif 72 73/* Add platform entropy 32 bytes (256 bits) at a time. */ 74#define ADD_ENTROPY 32 75 76/* Re-seed from the platform RNG after generating this many bytes. */ 77#define BYTES_BEFORE_RESEED 1600000 78 79struct arc4_stream { 80 unsigned char i; 81 unsigned char j; 82 unsigned char s[256]; 83}; 84 85#ifdef _WIN32 86#define getpid _getpid 87#define pid_t int 88#endif 89 90static int rs_initialized; 91static struct arc4_stream rs; 92static pid_t arc4_stir_pid; 93static int arc4_count; 94static int arc4_seeded_ok; 95 96static inline unsigned char arc4_getbyte(void); 97 98static inline void 99arc4_init(void) 100{ 101 int n; 102 103 for (n = 0; n < 256; n++) 104 rs.s[n] = n; 105 rs.i = 0; 106 rs.j = 0; 107} 108 109static inline void 110arc4_addrandom(const unsigned char *dat, int datlen) 111{ 112 int n; 113 unsigned char si; 114 115 rs.i--; 116 for (n = 0; n < 256; n++) { 117 rs.i = (rs.i + 1); 118 si = rs.s[rs.i]; 119 rs.j = (rs.j + si + dat[n % datlen]); 120 rs.s[rs.i] = rs.s[rs.j]; 121 rs.s[rs.j] = si; 122 } 123 rs.j = rs.i; 124} 125 126#ifndef _WIN32 127static ssize_t 128read_all(int fd, unsigned char *buf, size_t count) 129{ 130 size_t numread = 0; 131 ssize_t result; 132 133 while (numread < count) { 134 result = read(fd, buf+numread, count-numread); 135 if (result<0) 136 return -1; 137 else if (result == 0) 138 break; 139 numread += result; 140 } 141 142 return (ssize_t)numread; 143} 144#endif 145 146#ifdef _WIN32 147#define TRY_SEED_WIN32 148static int 149arc4_seed_win32(void) 150{ 151 /* This is adapted from Tor's crypto_seed_rng() */ 152 static int provider_set = 0; 153 static HCRYPTPROV provider; 154 unsigned char buf[ADD_ENTROPY]; 155 156 if (!provider_set) { 157 if (!CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL, 158 CRYPT_VERIFYCONTEXT)) { 159 if (GetLastError() != (DWORD)NTE_BAD_KEYSET) 160 return -1; 161 } 162 provider_set = 1; 163 } 164 if (!CryptGenRandom(provider, sizeof(buf), buf)) 165 return -1; 166 arc4_addrandom(buf, sizeof(buf)); 167 evutil_memclear_(buf, sizeof(buf)); 168 arc4_seeded_ok = 1; 169 return 0; 170} 171#endif 172 173#if defined(EVENT__HAVE_SYS_SYSCTL_H) && defined(EVENT__HAVE_SYSCTL) 174#if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_RANDOM && EVENT__HAVE_DECL_RANDOM_UUID 175#define TRY_SEED_SYSCTL_LINUX 176static int 177arc4_seed_sysctl_linux(void) 178{ 179 /* Based on code by William Ahern, this function tries to use the 180 * RANDOM_UUID sysctl to get entropy from the kernel. This can work 181 * even if /dev/urandom is inaccessible for some reason (e.g., we're 182 * running in a chroot). */ 183 int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID }; 184 unsigned char buf[ADD_ENTROPY]; 185 size_t len, n; 186 unsigned i; 187 int any_set; 188 189 memset(buf, 0, sizeof(buf)); 190 191 for (len = 0; len < sizeof(buf); len += n) { 192 n = sizeof(buf) - len; 193 194 if (0 != sysctl(mib, 3, &buf[len], &n, NULL, 0)) 195 return -1; 196 } 197 /* make sure that the buffer actually got set. */ 198 for (i=0,any_set=0; i<sizeof(buf); ++i) { 199 any_set |= buf[i]; 200 } 201 if (!any_set) 202 return -1; 203 204 arc4_addrandom(buf, sizeof(buf)); 205 evutil_memclear_(buf, sizeof(buf)); 206 arc4_seeded_ok = 1; 207 return 0; 208} 209#endif 210 211#if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_ARND 212#define TRY_SEED_SYSCTL_BSD 213static int 214arc4_seed_sysctl_bsd(void) 215{ 216 /* Based on code from William Ahern and from OpenBSD, this function 217 * tries to use the KERN_ARND syscall to get entropy from the kernel. 218 * This can work even if /dev/urandom is inaccessible for some reason 219 * (e.g., we're running in a chroot). */ 220 int mib[] = { CTL_KERN, KERN_ARND }; 221 unsigned char buf[ADD_ENTROPY]; 222 size_t len, n; 223 int i, any_set; 224 225 memset(buf, 0, sizeof(buf)); 226 227 len = sizeof(buf); 228 if (sysctl(mib, 2, buf, &len, NULL, 0) == -1) { 229 for (len = 0; len < sizeof(buf); len += sizeof(unsigned)) { 230 n = sizeof(unsigned); 231 if (n + len > sizeof(buf)) 232 n = len - sizeof(buf); 233 if (sysctl(mib, 2, &buf[len], &n, NULL, 0) == -1) 234 return -1; 235 } 236 } 237 /* make sure that the buffer actually got set. */ 238 for (i=any_set=0; i<sizeof(buf); ++i) { 239 any_set |= buf[i]; 240 } 241 if (!any_set) 242 return -1; 243 244 arc4_addrandom(buf, sizeof(buf)); 245 evutil_memclear_(buf, sizeof(buf)); 246 arc4_seeded_ok = 1; 247 return 0; 248} 249#endif 250#endif /* defined(EVENT__HAVE_SYS_SYSCTL_H) */ 251 252#ifdef __linux__ 253#define TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID 254static int 255arc4_seed_proc_sys_kernel_random_uuid(void) 256{ 257 /* Occasionally, somebody will make /proc/sys accessible in a chroot, 258 * but not /dev/urandom. Let's try /proc/sys/kernel/random/uuid. 259 * Its format is stupid, so we need to decode it from hex. 260 */ 261 int fd; 262 char buf[128]; 263 unsigned char entropy[64]; 264 int bytes, n, i, nybbles; 265 for (bytes = 0; bytes<ADD_ENTROPY; ) { 266 fd = evutil_open_closeonexec_("/proc/sys/kernel/random/uuid", O_RDONLY, 0); 267 if (fd < 0) 268 return -1; 269 n = read(fd, buf, sizeof(buf)); 270 close(fd); 271 if (n<=0) 272 return -1; 273 memset(entropy, 0, sizeof(entropy)); 274 for (i=nybbles=0; i<n; ++i) { 275 if (EVUTIL_ISXDIGIT_(buf[i])) { 276 int nyb = evutil_hex_char_to_int_(buf[i]); 277 if (nybbles & 1) { 278 entropy[nybbles/2] |= nyb; 279 } else { 280 entropy[nybbles/2] |= nyb<<4; 281 } 282 ++nybbles; 283 } 284 } 285 if (nybbles < 2) 286 return -1; 287 arc4_addrandom(entropy, nybbles/2); 288 bytes += nybbles/2; 289 } 290 evutil_memclear_(entropy, sizeof(entropy)); 291 evutil_memclear_(buf, sizeof(buf)); 292 arc4_seeded_ok = 1; 293 return 0; 294} 295#endif 296 297#ifndef _WIN32 298#define TRY_SEED_URANDOM 299static char *arc4random_urandom_filename = NULL; 300 301static int arc4_seed_urandom_helper_(const char *fname) 302{ 303 unsigned char buf[ADD_ENTROPY]; 304 int fd; 305 size_t n; 306 307 fd = evutil_open_closeonexec_(fname, O_RDONLY, 0); 308 if (fd<0) 309 return -1; 310 n = read_all(fd, buf, sizeof(buf)); 311 close(fd); 312 if (n != sizeof(buf)) 313 return -1; 314 arc4_addrandom(buf, sizeof(buf)); 315 evutil_memclear_(buf, sizeof(buf)); 316 arc4_seeded_ok = 1; 317 return 0; 318} 319 320static int 321arc4_seed_urandom(void) 322{ 323 /* This is adapted from Tor's crypto_seed_rng() */ 324 static const char *filenames[] = { 325 "/dev/srandom", "/dev/urandom", "/dev/random", NULL 326 }; 327 int i; 328 if (arc4random_urandom_filename) 329 return arc4_seed_urandom_helper_(arc4random_urandom_filename); 330 331 for (i = 0; filenames[i]; ++i) { 332 if (arc4_seed_urandom_helper_(filenames[i]) == 0) { 333 return 0; 334 } 335 } 336 337 return -1; 338} 339#endif 340 341static int 342arc4_seed(void) 343{ 344 int ok = 0; 345 /* We try every method that might work, and don't give up even if one 346 * does seem to work. There's no real harm in over-seeding, and if 347 * one of these sources turns out to be broken, that would be bad. */ 348#ifdef TRY_SEED_WIN32 349 if (0 == arc4_seed_win32()) 350 ok = 1; 351#endif 352#ifdef TRY_SEED_URANDOM 353 if (0 == arc4_seed_urandom()) 354 ok = 1; 355#endif 356#ifdef TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID 357 if (arc4random_urandom_filename == NULL && 358 0 == arc4_seed_proc_sys_kernel_random_uuid()) 359 ok = 1; 360#endif 361#ifdef TRY_SEED_SYSCTL_LINUX 362 /* Apparently Linux is deprecating sysctl, and spewing warning 363 * messages when you try to use it. */ 364 if (!ok && 0 == arc4_seed_sysctl_linux()) 365 ok = 1; 366#endif 367#ifdef TRY_SEED_SYSCTL_BSD 368 if (0 == arc4_seed_sysctl_bsd()) 369 ok = 1; 370#endif 371 return ok ? 0 : -1; 372} 373 374static int 375arc4_stir(void) 376{ 377 int i; 378 379 if (!rs_initialized) { 380 arc4_init(); 381 rs_initialized = 1; 382 } 383 384 arc4_seed(); 385 if (!arc4_seeded_ok) 386 return -1; 387 388 /* 389 * Discard early keystream, as per recommendations in 390 * "Weaknesses in the Key Scheduling Algorithm of RC4" by 391 * Scott Fluhrer, Itsik Mantin, and Adi Shamir. 392 * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps 393 * 394 * Ilya Mironov's "(Not So) Random Shuffles of RC4" suggests that 395 * we drop at least 2*256 bytes, with 12*256 as a conservative 396 * value. 397 * 398 * RFC4345 says to drop 6*256. 399 * 400 * At least some versions of this code drop 4*256, in a mistaken 401 * belief that "words" in the Fluhrer/Mantin/Shamir paper refers 402 * to processor words. 403 * 404 * We add another sect to the cargo cult, and choose 12*256. 405 */ 406 for (i = 0; i < 12*256; i++) 407 (void)arc4_getbyte(); 408 409 arc4_count = BYTES_BEFORE_RESEED; 410 411 return 0; 412} 413 414 415static void 416arc4_stir_if_needed(void) 417{ 418 pid_t pid = getpid(); 419 420 if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid) 421 { 422 arc4_stir_pid = pid; 423 arc4_stir(); 424 } 425} 426 427static inline unsigned char 428arc4_getbyte(void) 429{ 430 unsigned char si, sj; 431 432 rs.i = (rs.i + 1); 433 si = rs.s[rs.i]; 434 rs.j = (rs.j + si); 435 sj = rs.s[rs.j]; 436 rs.s[rs.i] = sj; 437 rs.s[rs.j] = si; 438 return (rs.s[(si + sj) & 0xff]); 439} 440 441static inline unsigned int 442arc4_getword(void) 443{ 444 unsigned int val; 445 446 val = arc4_getbyte() << 24; 447 val |= arc4_getbyte() << 16; 448 val |= arc4_getbyte() << 8; 449 val |= arc4_getbyte(); 450 451 return val; 452} 453 454#ifndef ARC4RANDOM_NOSTIR 455ARC4RANDOM_EXPORT int 456arc4random_stir(void) 457{ 458 int val; 459 ARC4_LOCK_(); 460 val = arc4_stir(); 461 ARC4_UNLOCK_(); 462 return val; 463} 464#endif 465 466#ifndef ARC4RANDOM_NOADDRANDOM 467ARC4RANDOM_EXPORT void 468arc4random_addrandom(const unsigned char *dat, int datlen) 469{ 470 int j; 471 ARC4_LOCK_(); 472 if (!rs_initialized) 473 arc4_stir(); 474 for (j = 0; j < datlen; j += 256) { 475 /* arc4_addrandom() ignores all but the first 256 bytes of 476 * its input. We want to make sure to look at ALL the 477 * data in 'dat', just in case the user is doing something 478 * crazy like passing us all the files in /var/log. */ 479 arc4_addrandom(dat + j, datlen - j); 480 } 481 ARC4_UNLOCK_(); 482} 483#endif 484 485#ifndef ARC4RANDOM_NORANDOM 486ARC4RANDOM_EXPORT ARC4RANDOM_UINT32 487arc4random(void) 488{ 489 ARC4RANDOM_UINT32 val; 490 ARC4_LOCK_(); 491 arc4_count -= 4; 492 arc4_stir_if_needed(); 493 val = arc4_getword(); 494 ARC4_UNLOCK_(); 495 return val; 496} 497#endif 498 499ARC4RANDOM_EXPORT void 500arc4random_buf(void *buf_, size_t n) 501{ 502 unsigned char *buf = buf_; 503 ARC4_LOCK_(); 504 arc4_stir_if_needed(); 505 while (n--) { 506 if (--arc4_count <= 0) 507 arc4_stir(); 508 buf[n] = arc4_getbyte(); 509 } 510 ARC4_UNLOCK_(); 511} 512 513#ifndef ARC4RANDOM_NOUNIFORM 514/* 515 * Calculate a uniformly distributed random number less than upper_bound 516 * avoiding "modulo bias". 517 * 518 * Uniformity is achieved by generating new random numbers until the one 519 * returned is outside the range [0, 2**32 % upper_bound). This 520 * guarantees the selected random number will be inside 521 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound) 522 * after reduction modulo upper_bound. 523 */ 524ARC4RANDOM_EXPORT unsigned int 525arc4random_uniform(unsigned int upper_bound) 526{ 527 ARC4RANDOM_UINT32 r, min; 528 529 if (upper_bound < 2) 530 return 0; 531 532#if (UINT_MAX > 0xffffffffUL) 533 min = 0x100000000UL % upper_bound; 534#else 535 /* Calculate (2**32 % upper_bound) avoiding 64-bit math */ 536 if (upper_bound > 0x80000000) 537 min = 1 + ~upper_bound; /* 2**32 - upper_bound */ 538 else { 539 /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */ 540 min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound; 541 } 542#endif 543 544 /* 545 * This could theoretically loop forever but each retry has 546 * p > 0.5 (worst case, usually far better) of selecting a 547 * number inside the range we need, so it should rarely need 548 * to re-roll. 549 */ 550 for (;;) { 551 r = arc4random(); 552 if (r >= min) 553 break; 554 } 555 556 return r % upper_bound; 557} 558#endif 559