arc4random.c revision 1.34
1 /* $NetBSD: arc4random.c,v 1.34 2024/01/20 14:52:47 christos Exp $ */ 2 3 /*- 4 * Copyright (c) 2014 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Taylor R. Campbell. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29 * POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32 /* 33 * Legacy arc4random(3) API from OpenBSD reimplemented using the 34 * ChaCha20 PRF, with per-thread state. 35 * 36 * Security model: 37 * - An attacker who sees some outputs cannot predict past or future 38 * outputs. 39 * - An attacker who sees the PRNG state cannot predict past outputs. 40 * - An attacker who sees a child's PRNG state cannot predict past or 41 * future outputs in the parent, or in other children. 42 * 43 * The arc4random(3) API may abort the process if: 44 * 45 * (a) the crypto self-test fails, 46 * (b) pthread_atfork or thr_keycreate fail, or 47 * (c) sysctl(KERN_ARND) fails when reseeding the PRNG. 48 * 49 * The crypto self-test, pthread_atfork, and thr_keycreate occur only 50 * once, on the first use of any of the arc4random(3) API. KERN_ARND 51 * is unlikely to fail later unless the kernel is seriously broken. 52 */ 53 54 #include <sys/cdefs.h> 55 __RCSID("$NetBSD: arc4random.c,v 1.34 2024/01/20 14:52:47 christos Exp $"); 56 57 #include "namespace.h" 58 #include "reentrant.h" 59 60 #include <sys/bitops.h> 61 #include <sys/endian.h> 62 #include <sys/errno.h> 63 #include <sys/mman.h> 64 #include <sys/sysctl.h> 65 66 #include <assert.h> 67 #include <sha2.h> 68 #include <stdbool.h> 69 #include <stdint.h> 70 #include <stdlib.h> 71 #include <string.h> 72 #include <unistd.h> 73 74 #ifdef __weak_alias 75 __weak_alias(arc4random,_arc4random) 76 __weak_alias(arc4random_addrandom,_arc4random_addrandom) 77 __weak_alias(arc4random_buf,_arc4random_buf) 78 __weak_alias(arc4random_stir,_arc4random_stir) 79 __weak_alias(arc4random_uniform,_arc4random_uniform) 80 #endif 81 82 /* 83 * For standard ChaCha, use le32dec/le32enc. We don't need that for 84 * the purposes of a nondeterministic random number generator -- we 85 * don't need to be bit-for-bit compatible over any wire. 86 */ 87 88 static inline uint32_t 89 crypto_le32dec(const void *p) 90 { 91 uint32_t v; 92 93 (void)memcpy(&v, p, sizeof v); 94 95 return v; 96 } 97 98 static inline void 99 crypto_le32enc(void *p, uint32_t v) 100 { 101 102 (void)memcpy(p, &v, sizeof v); 103 } 104 105 /* ChaCha core */ 106 107 #define crypto_core_OUTPUTBYTES 64 108 #define crypto_core_INPUTBYTES 16 109 #define crypto_core_KEYBYTES 32 110 #define crypto_core_CONSTBYTES 16 111 112 #define crypto_core_ROUNDS 20 113 114 static uint32_t 115 rotate(uint32_t u, unsigned c) 116 { 117 118 return (u << c) | (u >> (32 - c)); 119 } 120 121 #define QUARTERROUND(a, b, c, d) do { \ 122 (a) += (b); (d) ^= (a); (d) = rotate((d), 16); \ 123 (c) += (d); (b) ^= (c); (b) = rotate((b), 12); \ 124 (a) += (b); (d) ^= (a); (d) = rotate((d), 8); \ 125 (c) += (d); (b) ^= (c); (b) = rotate((b), 7); \ 126 } while (0) 127 128 static const uint8_t crypto_core_constant32[16] = "expand 32-byte k"; 129 130 static void 131 crypto_core(uint8_t *out, const uint8_t *in, const uint8_t *k, 132 const uint8_t *c) 133 { 134 uint32_t x0,x1,x2,x3,x4,x5,x6,x7,x8,x9,x10,x11,x12,x13,x14,x15; 135 uint32_t j0,j1,j2,j3,j4,j5,j6,j7,j8,j9,j10,j11,j12,j13,j14,j15; 136 int i; 137 138 j0 = x0 = crypto_le32dec(c + 0); 139 j1 = x1 = crypto_le32dec(c + 4); 140 j2 = x2 = crypto_le32dec(c + 8); 141 j3 = x3 = crypto_le32dec(c + 12); 142 j4 = x4 = crypto_le32dec(k + 0); 143 j5 = x5 = crypto_le32dec(k + 4); 144 j6 = x6 = crypto_le32dec(k + 8); 145 j7 = x7 = crypto_le32dec(k + 12); 146 j8 = x8 = crypto_le32dec(k + 16); 147 j9 = x9 = crypto_le32dec(k + 20); 148 j10 = x10 = crypto_le32dec(k + 24); 149 j11 = x11 = crypto_le32dec(k + 28); 150 j12 = x12 = crypto_le32dec(in + 0); 151 j13 = x13 = crypto_le32dec(in + 4); 152 j14 = x14 = crypto_le32dec(in + 8); 153 j15 = x15 = crypto_le32dec(in + 12); 154 155 for (i = crypto_core_ROUNDS; i > 0; i -= 2) { 156 QUARTERROUND( x0, x4, x8,x12); 157 QUARTERROUND( x1, x5, x9,x13); 158 QUARTERROUND( x2, x6,x10,x14); 159 QUARTERROUND( x3, x7,x11,x15); 160 QUARTERROUND( x0, x5,x10,x15); 161 QUARTERROUND( x1, x6,x11,x12); 162 QUARTERROUND( x2, x7, x8,x13); 163 QUARTERROUND( x3, x4, x9,x14); 164 } 165 166 crypto_le32enc(out + 0, x0 + j0); 167 crypto_le32enc(out + 4, x1 + j1); 168 crypto_le32enc(out + 8, x2 + j2); 169 crypto_le32enc(out + 12, x3 + j3); 170 crypto_le32enc(out + 16, x4 + j4); 171 crypto_le32enc(out + 20, x5 + j5); 172 crypto_le32enc(out + 24, x6 + j6); 173 crypto_le32enc(out + 28, x7 + j7); 174 crypto_le32enc(out + 32, x8 + j8); 175 crypto_le32enc(out + 36, x9 + j9); 176 crypto_le32enc(out + 40, x10 + j10); 177 crypto_le32enc(out + 44, x11 + j11); 178 crypto_le32enc(out + 48, x12 + j12); 179 crypto_le32enc(out + 52, x13 + j13); 180 crypto_le32enc(out + 56, x14 + j14); 181 crypto_le32enc(out + 60, x15 + j15); 182 } 183 184 /* ChaCha self-test */ 185 186 #ifdef _DIAGNOSTIC 187 188 /* 189 * Test vector for ChaCha20 from 190 * <http://tools.ietf.org/html/draft-strombergson-chacha-test-vectors-00>, 191 * test vectors for ChaCha12 and ChaCha8 and for big-endian machines 192 * generated by the same crypto_core code with crypto_core_ROUNDS and 193 * crypto_le32enc/dec varied. 194 */ 195 196 static const uint8_t crypto_core_selftest_vector[64] = { 197 #if _BYTE_ORDER == _LITTLE_ENDIAN 198 # if crypto_core_ROUNDS == 8 199 0x3e,0x00,0xef,0x2f,0x89,0x5f,0x40,0xd6, 200 0x7f,0x5b,0xb8,0xe8,0x1f,0x09,0xa5,0xa1, 201 0x2c,0x84,0x0e,0xc3,0xce,0x9a,0x7f,0x3b, 202 0x18,0x1b,0xe1,0x88,0xef,0x71,0x1a,0x1e, 203 0x98,0x4c,0xe1,0x72,0xb9,0x21,0x6f,0x41, 204 0x9f,0x44,0x53,0x67,0x45,0x6d,0x56,0x19, 205 0x31,0x4a,0x42,0xa3,0xda,0x86,0xb0,0x01, 206 0x38,0x7b,0xfd,0xb8,0x0e,0x0c,0xfe,0x42, 207 # elif crypto_core_ROUNDS == 12 208 0x9b,0xf4,0x9a,0x6a,0x07,0x55,0xf9,0x53, 209 0x81,0x1f,0xce,0x12,0x5f,0x26,0x83,0xd5, 210 0x04,0x29,0xc3,0xbb,0x49,0xe0,0x74,0x14, 211 0x7e,0x00,0x89,0xa5,0x2e,0xae,0x15,0x5f, 212 0x05,0x64,0xf8,0x79,0xd2,0x7a,0xe3,0xc0, 213 0x2c,0xe8,0x28,0x34,0xac,0xfa,0x8c,0x79, 214 0x3a,0x62,0x9f,0x2c,0xa0,0xde,0x69,0x19, 215 0x61,0x0b,0xe8,0x2f,0x41,0x13,0x26,0xbe, 216 # elif crypto_core_ROUNDS == 20 217 0x76,0xb8,0xe0,0xad,0xa0,0xf1,0x3d,0x90, 218 0x40,0x5d,0x6a,0xe5,0x53,0x86,0xbd,0x28, 219 0xbd,0xd2,0x19,0xb8,0xa0,0x8d,0xed,0x1a, 220 0xa8,0x36,0xef,0xcc,0x8b,0x77,0x0d,0xc7, 221 0xda,0x41,0x59,0x7c,0x51,0x57,0x48,0x8d, 222 0x77,0x24,0xe0,0x3f,0xb8,0xd8,0x4a,0x37, 223 0x6a,0x43,0xb8,0xf4,0x15,0x18,0xa1,0x1c, 224 0xc3,0x87,0xb6,0x69,0xb2,0xee,0x65,0x86, 225 # else 226 # error crypto_core_ROUNDS must be 8, 12, or 20. 227 # endif 228 #elif _BYTE_ORDER == _BIG_ENDIAN 229 # if crypto_core_ROUNDS == 8 230 0x9a,0x13,0x07,0xe3,0x38,0x18,0x9e,0x99, 231 0x15,0x37,0x16,0x4d,0x04,0xe6,0x48,0x9a, 232 0x07,0xd6,0xe8,0x7a,0x02,0xf9,0xf5,0xc7, 233 0x3f,0xa9,0xc2,0x0a,0xe1,0xc6,0x62,0xea, 234 0x80,0xaf,0xb6,0x51,0xca,0x52,0x43,0x87, 235 0xe3,0xa6,0xa6,0x61,0x11,0xf5,0xe6,0xcf, 236 0x09,0x0f,0xdc,0x9d,0xc3,0xc3,0xbb,0x43, 237 0xd7,0xfa,0x70,0x42,0xbf,0xa5,0xee,0xa2, 238 # elif crypto_core_ROUNDS == 12 239 0xcf,0x6c,0x16,0x48,0xbf,0xf4,0xba,0x85, 240 0x32,0x69,0xd3,0x98,0xc8,0x7d,0xcd,0x3f, 241 0xdc,0x76,0x6b,0xa2,0x7b,0xcb,0x17,0x4d, 242 0x05,0xda,0xdd,0xd8,0x62,0x54,0xbf,0xe0, 243 0x65,0xed,0x0e,0xf4,0x01,0x7e,0x3c,0x05, 244 0x35,0xb2,0x7a,0x60,0xf3,0x8f,0x12,0x33, 245 0x24,0x60,0xcd,0x85,0xfe,0x4c,0xf3,0x39, 246 0xb1,0x0e,0x3e,0xe0,0xba,0xa6,0x2f,0xa9, 247 # elif crypto_core_ROUNDS == 20 248 0x83,0x8b,0xf8,0x75,0xf7,0xde,0x9d,0x8c, 249 0x33,0x14,0x72,0x28,0xd1,0xbe,0x88,0xe5, 250 0x94,0xb5,0xed,0xb8,0x56,0xb5,0x9e,0x0c, 251 0x64,0x6a,0xaf,0xd9,0xa7,0x49,0x10,0x59, 252 0xba,0x3a,0x82,0xf8,0x4a,0x70,0x9c,0x00, 253 0x82,0x2c,0xae,0xc6,0xd7,0x1c,0x2e,0xda, 254 0x2a,0xfb,0x61,0x70,0x2b,0xd1,0xbf,0x8b, 255 0x95,0xbc,0x23,0xb6,0x4b,0x60,0x02,0xec, 256 # else 257 # error crypto_core_ROUNDS must be 8, 12, or 20. 258 # endif 259 #else 260 # error Byte order must be little-endian or big-endian. 261 #endif 262 }; 263 264 static int 265 crypto_core_selftest(void) 266 { 267 const uint8_t nonce[crypto_core_INPUTBYTES] = {0}; 268 const uint8_t key[crypto_core_KEYBYTES] = {0}; 269 uint8_t block[64]; 270 unsigned i; 271 272 crypto_core(block, nonce, key, crypto_core_constant32); 273 for (i = 0; i < 64; i++) { 274 if (block[i] != crypto_core_selftest_vector[i]) 275 return EIO; 276 } 277 278 return 0; 279 } 280 281 #else /* !_DIAGNOSTIC */ 282 283 static int 284 crypto_core_selftest(void) 285 { 286 287 return 0; 288 } 289 290 #endif 291 292 /* PRNG */ 293 294 /* 295 * For a state s, rather than use ChaCha20 as a stream cipher to 296 * generate the concatenation ChaCha20_s(0) || ChaCha20_s(1) || ..., we 297 * split ChaCha20_s(0) into s' || x and yield x for the first request, 298 * split ChaCha20_s'(0) into s'' || y and yield y for the second 299 * request, &c. This provides backtracking resistance: an attacker who 300 * finds s'' can't recover s' or x. 301 */ 302 303 #define crypto_prng_SEEDBYTES crypto_core_KEYBYTES 304 #define crypto_prng_MAXOUTPUTBYTES \ 305 (crypto_core_OUTPUTBYTES - crypto_prng_SEEDBYTES) 306 307 struct crypto_prng { 308 uint8_t state[crypto_prng_SEEDBYTES]; 309 }; 310 311 static void 312 crypto_prng_seed(struct crypto_prng *prng, const void *seed) 313 { 314 315 (void)memcpy(prng->state, seed, crypto_prng_SEEDBYTES); 316 } 317 318 static void 319 crypto_prng_buf(struct crypto_prng *prng, void *buf, size_t n) 320 { 321 const uint8_t nonce[crypto_core_INPUTBYTES] = {0}; 322 uint8_t output[crypto_core_OUTPUTBYTES]; 323 324 _DIAGASSERT(n <= crypto_prng_MAXOUTPUTBYTES); 325 __CTASSERT(sizeof prng->state + crypto_prng_MAXOUTPUTBYTES 326 <= sizeof output); 327 328 crypto_core(output, nonce, prng->state, crypto_core_constant32); 329 (void)memcpy(prng->state, output, sizeof prng->state); 330 (void)memcpy(buf, output + sizeof prng->state, n); 331 (void)explicit_memset(output, 0, sizeof output); 332 } 333 334 /* One-time stream: expand short single-use secret into long secret */ 335 336 #define crypto_onetimestream_SEEDBYTES crypto_core_KEYBYTES 337 338 static void 339 crypto_onetimestream(const void *seed, void *buf, size_t n) 340 { 341 uint32_t nonce[crypto_core_INPUTBYTES / sizeof(uint32_t)] = {0}; 342 uint8_t block[crypto_core_OUTPUTBYTES]; 343 uint8_t *p8, *p32; 344 const uint8_t *nonce8 = (const uint8_t *)(void *)nonce; 345 size_t ni, nb, nf; 346 347 /* 348 * Guarantee we can generate up to n bytes. We have 349 * 2^(8*INPUTBYTES) possible inputs yielding output of 350 * OUTPUTBYTES*2^(8*INPUTBYTES) bytes. It suffices to require 351 * that sizeof n > (1/CHAR_BIT) log_2 n be less than 352 * (1/CHAR_BIT) log_2 of the total output stream length. We 353 * have 354 * 355 * log_2 (o 2^(8 i)) = log_2 o + log_2 2^(8 i) 356 * = log_2 o + 8 i. 357 */ 358 #ifndef __lint__ 359 __CTASSERT(CHAR_BIT * sizeof n <= (ilog2(crypto_core_OUTPUTBYTES) + 360 8 * crypto_core_INPUTBYTES)); 361 #endif 362 363 p8 = buf; 364 p32 = (uint8_t *)roundup2((uintptr_t)p8, 4); 365 ni = p32 - p8; 366 if (n < ni) 367 ni = n; 368 nb = (n - ni) / sizeof block; 369 nf = (n - ni) % sizeof block; 370 371 _DIAGASSERT(((uintptr_t)p32 & 3) == 0); 372 _DIAGASSERT(ni <= n); 373 _DIAGASSERT(nb <= (n / sizeof block)); 374 _DIAGASSERT(nf <= n); 375 _DIAGASSERT(n == (ni + (nb * sizeof block) + nf)); 376 _DIAGASSERT(ni < 4); 377 _DIAGASSERT(nf < sizeof block); 378 379 if (ni) { 380 crypto_core(block, nonce8, seed, crypto_core_constant32); 381 nonce[0]++; 382 (void)memcpy(p8, block, ni); 383 } 384 while (nb--) { 385 crypto_core(p32, nonce8, seed, crypto_core_constant32); 386 if (++nonce[0] == 0) 387 nonce[1]++; 388 p32 += crypto_core_OUTPUTBYTES; 389 } 390 if (nf) { 391 crypto_core(block, nonce8, seed, crypto_core_constant32); 392 if (++nonce[0] == 0) 393 nonce[1]++; 394 (void)memcpy(p32, block, nf); 395 } 396 397 if (ni | nf) 398 (void)explicit_memset(block, 0, sizeof block); 399 } 400 401 /* arc4random state: per-thread, per-process (zeroed in child on fork) */ 402 403 struct arc4random_prng { 404 struct crypto_prng arc4_prng; 405 bool arc4_seeded; 406 }; 407 408 static void 409 arc4random_prng_addrandom(struct arc4random_prng *prng, const void *data, 410 size_t datalen) 411 { 412 const int mib[] = { CTL_KERN, KERN_ARND }; 413 SHA256_CTX ctx; 414 uint8_t buf[crypto_prng_SEEDBYTES]; 415 size_t buflen = sizeof buf; 416 417 __CTASSERT(sizeof buf == SHA256_DIGEST_LENGTH); 418 419 SHA256_Init(&ctx); 420 421 crypto_prng_buf(&prng->arc4_prng, buf, sizeof buf); 422 SHA256_Update(&ctx, buf, sizeof buf); 423 424 if (sysctl(mib, (u_int)__arraycount(mib), buf, &buflen, NULL, 0) == -1) 425 abort(); 426 if (buflen != sizeof buf) 427 abort(); 428 SHA256_Update(&ctx, buf, sizeof buf); 429 430 if (data != NULL) 431 SHA256_Update(&ctx, data, datalen); 432 433 SHA256_Final(buf, &ctx); 434 (void)explicit_memset(&ctx, 0, sizeof ctx); 435 436 /* reseed(SHA256(prng() || sysctl(KERN_ARND) || data)) */ 437 crypto_prng_seed(&prng->arc4_prng, buf); 438 (void)explicit_memset(buf, 0, sizeof buf); 439 prng->arc4_seeded = true; 440 } 441 442 #ifdef _REENTRANT 443 static struct arc4random_prng * 444 arc4random_prng_create(void) 445 { 446 struct arc4random_prng *prng; 447 const size_t size = roundup(sizeof(*prng), sysconf(_SC_PAGESIZE)); 448 449 prng = mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 450 0); 451 if (prng == MAP_FAILED) 452 goto fail0; 453 if (minherit(prng, size, MAP_INHERIT_ZERO) == -1) 454 goto fail1; 455 456 return prng; 457 458 fail1: (void)munmap(prng, size); 459 fail0: return NULL; 460 } 461 #endif 462 463 #ifdef _REENTRANT 464 static void 465 arc4random_prng_destroy(struct arc4random_prng *prng) 466 { 467 const size_t size = roundup(sizeof(*prng), sysconf(_SC_PAGESIZE)); 468 469 (void)explicit_memset(prng, 0, sizeof(*prng)); 470 (void)munmap(prng, size); 471 } 472 #endif 473 474 /* Library state */ 475 476 static struct arc4random_global { 477 #ifdef _REENTRANT 478 mutex_t lock; 479 thread_key_t thread_key; 480 #endif 481 struct arc4random_prng prng; 482 bool initialized; 483 } arc4random_global = { 484 #ifdef _REENTRANT 485 .lock = MUTEX_INITIALIZER, 486 #endif 487 .initialized = false, 488 }; 489 490 static void 491 arc4random_atfork_prepare(void) 492 { 493 494 mutex_lock(&arc4random_global.lock); 495 (void)explicit_memset(&arc4random_global.prng, 0, 496 sizeof arc4random_global.prng); 497 } 498 499 static void 500 arc4random_atfork_parent(void) 501 { 502 503 mutex_unlock(&arc4random_global.lock); 504 } 505 506 static void 507 arc4random_atfork_child(void) 508 { 509 510 mutex_unlock(&arc4random_global.lock); 511 } 512 513 #ifdef _REENTRANT 514 static void 515 arc4random_tsd_destructor(void *p) 516 { 517 struct arc4random_prng *const prng = p; 518 519 arc4random_prng_destroy(prng); 520 } 521 #endif 522 523 static void 524 arc4random_initialize(void) 525 { 526 527 mutex_lock(&arc4random_global.lock); 528 if (!arc4random_global.initialized) { 529 if (crypto_core_selftest() != 0) 530 abort(); 531 if (pthread_atfork(&arc4random_atfork_prepare, 532 &arc4random_atfork_parent, &arc4random_atfork_child) 533 != 0) 534 abort(); 535 #ifdef _REENTRANT 536 if (thr_keycreate(&arc4random_global.thread_key, 537 &arc4random_tsd_destructor) != 0) 538 abort(); 539 #endif 540 arc4random_global.initialized = true; 541 } 542 mutex_unlock(&arc4random_global.lock); 543 } 544 545 static struct arc4random_prng * 546 arc4random_prng_get(void) 547 { 548 struct arc4random_prng *prng = NULL; 549 550 /* Make sure the library is initialized. */ 551 if (__predict_false(!arc4random_global.initialized)) 552 arc4random_initialize(); 553 554 #ifdef _REENTRANT 555 /* Get or create the per-thread PRNG state. */ 556 prng = thr_getspecific(arc4random_global.thread_key); 557 if (__predict_false(prng == NULL)) { 558 prng = arc4random_prng_create(); 559 thr_setspecific(arc4random_global.thread_key, prng); 560 } 561 #endif 562 563 /* If we can't create it, fall back to the global PRNG. */ 564 if (__predict_false(prng == NULL)) { 565 mutex_lock(&arc4random_global.lock); 566 prng = &arc4random_global.prng; 567 } 568 569 /* Guarantee the PRNG is seeded. */ 570 if (__predict_false(!prng->arc4_seeded)) 571 arc4random_prng_addrandom(prng, NULL, 0); 572 573 return prng; 574 } 575 576 static void 577 arc4random_prng_put(struct arc4random_prng *prng) 578 { 579 580 /* If we had fallen back to the global PRNG, unlock it. */ 581 if (__predict_false(prng == &arc4random_global.prng)) 582 mutex_unlock(&arc4random_global.lock); 583 } 584 585 /* Public API */ 586 587 uint32_t 588 arc4random(void) 589 { 590 struct arc4random_prng *prng; 591 uint32_t v; 592 593 prng = arc4random_prng_get(); 594 crypto_prng_buf(&prng->arc4_prng, &v, sizeof v); 595 arc4random_prng_put(prng); 596 597 return v; 598 } 599 600 void 601 arc4random_buf(void *buf, size_t len) 602 { 603 struct arc4random_prng *prng; 604 605 if (len <= crypto_prng_MAXOUTPUTBYTES) { 606 prng = arc4random_prng_get(); 607 crypto_prng_buf(&prng->arc4_prng, buf, len); 608 arc4random_prng_put(prng); 609 } else { 610 uint8_t seed[crypto_onetimestream_SEEDBYTES]; 611 612 prng = arc4random_prng_get(); 613 crypto_prng_buf(&prng->arc4_prng, seed, sizeof seed); 614 arc4random_prng_put(prng); 615 616 crypto_onetimestream(seed, buf, len); 617 (void)explicit_memset(seed, 0, sizeof seed); 618 } 619 } 620 621 uint32_t 622 arc4random_uniform(uint32_t bound) 623 { 624 struct arc4random_prng *prng; 625 uint32_t minimum, r; 626 627 /* 628 * We want a uniform random choice in [0, n), and arc4random() 629 * makes a uniform random choice in [0, 2^32). If we reduce 630 * that modulo n, values in [0, 2^32 mod n) will be represented 631 * slightly more than values in [2^32 mod n, n). Instead we 632 * choose only from [2^32 mod n, 2^32) by rejecting samples in 633 * [0, 2^32 mod n), to avoid counting the extra representative 634 * of [0, 2^32 mod n). To compute 2^32 mod n, note that 635 * 636 * 2^32 mod n = 2^32 mod n - 0 637 * = 2^32 mod n - n mod n 638 * = (2^32 - n) mod n, 639 * 640 * the last of which is what we compute in 32-bit arithmetic. 641 */ 642 minimum = (-bound % bound); 643 644 prng = arc4random_prng_get(); 645 do crypto_prng_buf(&prng->arc4_prng, &r, sizeof r); 646 while (__predict_false(r < minimum)); 647 arc4random_prng_put(prng); 648 649 return (r % bound); 650 } 651 652 void 653 arc4random_stir(void) 654 { 655 struct arc4random_prng *prng; 656 657 prng = arc4random_prng_get(); 658 arc4random_prng_addrandom(prng, NULL, 0); 659 arc4random_prng_put(prng); 660 } 661 662 /* 663 * Silly signature here is for hysterical raisins. Should instead be 664 * const void *data and size_t datalen. 665 */ 666 void 667 arc4random_addrandom(u_char *data, int datalen) 668 { 669 struct arc4random_prng *prng; 670 671 _DIAGASSERT(0 <= datalen); 672 673 prng = arc4random_prng_get(); 674 arc4random_prng_addrandom(prng, data, datalen); 675 arc4random_prng_put(prng); 676 } 677 678 #ifdef _ARC4RANDOM_TEST 679 680 #include <sys/wait.h> 681 682 #include <err.h> 683 #include <stdio.h> 684 685 int 686 main(int argc __unused, char **argv __unused) 687 { 688 unsigned char gubbish[] = "random gubbish"; 689 const uint8_t zero64[64] = {0}; 690 uint8_t buf[2048]; 691 unsigned i, a, n; 692 693 /* Test arc4random: should not be deterministic. */ 694 if (printf("arc4random: %08"PRIx32"\n", arc4random()) < 0) 695 err(1, "printf"); 696 697 /* Test stirring: should definitely not be deterministic. */ 698 arc4random_stir(); 699 700 /* Test small buffer. */ 701 arc4random_buf(buf, 8); 702 if (printf("arc4randombuf small:") < 0) 703 err(1, "printf"); 704 for (i = 0; i < 8; i++) 705 if (printf(" %02x", buf[i]) < 0) 706 err(1, "printf"); 707 if (printf("\n") < 0) 708 err(1, "printf"); 709 710 /* Test addrandom: should not make the rest deterministic. */ 711 arc4random_addrandom(gubbish, sizeof gubbish); 712 713 /* Test large buffer. */ 714 arc4random_buf(buf, sizeof buf); 715 if (printf("arc4randombuf_large:") < 0) 716 err(1, "printf"); 717 for (i = 0; i < sizeof buf; i++) 718 if (printf(" %02x", buf[i]) < 0) 719 err(1, "printf"); 720 if (printf("\n") < 0) 721 err(1, "printf"); 722 723 /* Test misaligned small and large. */ 724 for (a = 0; a < 64; a++) { 725 for (n = a; n < sizeof buf; n++) { 726 (void)memset(buf, 0, sizeof buf); 727 arc4random_buf(buf, n - a); 728 if (memcmp(buf + n - a, zero64, a) != 0) 729 errx(1, "arc4random buffer overflow 0"); 730 731 (void)memset(buf, 0, sizeof buf); 732 arc4random_buf(buf + a, n - a); 733 if (memcmp(buf, zero64, a) != 0) 734 errx(1, "arc4random buffer overflow 1"); 735 736 if ((2*a) <= n) { 737 (void)memset(buf, 0, sizeof buf); 738 arc4random_buf(buf + a, n - a - a); 739 if (memcmp(buf + n - a, zero64, a) != 0) 740 errx(1, 741 "arc4random buffer overflow 2"); 742 } 743 } 744 } 745 746 /* Test fork-safety. */ 747 { 748 pid_t pid, rpid; 749 int status; 750 751 pid = fork(); 752 switch (pid) { 753 case -1: 754 err(1, "fork"); 755 case 0: 756 _exit(arc4random_prng_get()->arc4_seeded); 757 default: 758 rpid = waitpid(pid, &status, 0); 759 if (rpid == -1) 760 err(1, "waitpid"); 761 if (rpid != pid) 762 errx(1, "waitpid returned wrong pid" 763 ": %"PRIdMAX" != %"PRIdMAX, 764 (intmax_t)rpid, 765 (intmax_t)pid); 766 if (WIFEXITED(status)) { 767 if (WEXITSTATUS(status) != 0) 768 errx(1, "child exited with %d", 769 WEXITSTATUS(status)); 770 } else if (WIFSIGNALED(status)) { 771 errx(1, "child terminated on signal %d", 772 WTERMSIG(status)); 773 } else { 774 errx(1, "child died mysteriously: %d", status); 775 } 776 } 777 } 778 779 /* XXX Test multithreaded fork safety...? */ 780 781 return 0; 782 } 783 #endif 784
Indexes created Mon Sep 22 21:09:42 GMT 2025