1 /* 2 * Random number generator 3 * Copyright (c) 2010-2011, Jouni Malinen <j (at) w1.fi> 4 * 5 * This software may be distributed under the terms of the BSD license. 6 * See README for more details. 7 * 8 * This random number generator is used to provide additional entropy to the 9 * one provided by the operating system (os_get_random()) for session key 10 * generation. The os_get_random() output is expected to be secure and the 11 * implementation here is expected to provide only limited protection against 12 * cases where os_get_random() cannot provide strong randomness. This 13 * implementation shall not be assumed to be secure as the sole source of 14 * randomness. The random_get_bytes() function mixes in randomness from 15 * os_get_random() and as such, calls to os_get_random() can be replaced with 16 * calls to random_get_bytes() without reducing security. 17 * 18 * The design here follows partially the design used in the Linux 19 * drivers/char/random.c, but the implementation here is simpler and not as 20 * strong. This is a compromise to reduce duplicated CPU effort and to avoid 21 * extra code/memory size. As pointed out above, os_get_random() needs to be 22 * guaranteed to be secure for any of the security assumptions to hold. 23 */ 24 25 #include "utils/includes.h" 26 #ifdef __linux__ 27 #include <fcntl.h> 28 #endif /* __linux__ */ 29 30 #include "utils/common.h" 31 #include "utils/eloop.h" 32 #include "crypto/crypto.h" 33 #include "sha1.h" 34 #include "random.h" 35 36 #define POOL_WORDS 32 37 #define POOL_WORDS_MASK (POOL_WORDS - 1) 38 #define POOL_TAP1 26 39 #define POOL_TAP2 20 40 #define POOL_TAP3 14 41 #define POOL_TAP4 7 42 #define POOL_TAP5 1 43 #define EXTRACT_LEN 16 44 #define MIN_READY_MARK 2 45 46 static u32 pool[POOL_WORDS]; 47 static unsigned int input_rotate = 0; 48 static unsigned int pool_pos = 0; 49 static u8 dummy_key[20]; 50 #ifdef __linux__ 51 static size_t dummy_key_avail = 0; 52 static int random_fd = -1; 53 #endif /* __linux__ */ 54 static unsigned int own_pool_ready = 0; 55 #define RANDOM_ENTROPY_SIZE 20 56 static char *random_entropy_file = NULL; 57 static int random_entropy_file_read = 0; 58 59 #define MIN_COLLECT_ENTROPY 1000 60 static unsigned int entropy = 0; 61 static unsigned int total_collected = 0; 62 63 64 static void random_write_entropy(void); 65 66 67 static u32 __ROL32(u32 x, u32 y) 68 { 69 return (x << (y & 31)) | (x >> (32 - (y & 31))); 70 } 71 72 73 static void random_mix_pool(const void *buf, size_t len) 74 { 75 static const u32 twist[8] = { 76 0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158, 77 0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 78 }; 79 const u8 *pos = buf; 80 u32 w; 81 82 wpa_hexdump_key(MSG_EXCESSIVE, "random_mix_pool", buf, len); 83 84 while (len--) { 85 w = __ROL32(*pos++, input_rotate & 31); 86 input_rotate += pool_pos ? 7 : 14; 87 pool_pos = (pool_pos - 1) & POOL_WORDS_MASK; 88 w ^= pool[pool_pos]; 89 w ^= pool[(pool_pos + POOL_TAP1) & POOL_WORDS_MASK]; 90 w ^= pool[(pool_pos + POOL_TAP2) & POOL_WORDS_MASK]; 91 w ^= pool[(pool_pos + POOL_TAP3) & POOL_WORDS_MASK]; 92 w ^= pool[(pool_pos + POOL_TAP4) & POOL_WORDS_MASK]; 93 w ^= pool[(pool_pos + POOL_TAP5) & POOL_WORDS_MASK]; 94 pool[pool_pos] = (w >> 3) ^ twist[w & 7]; 95 } 96 } 97 98 99 static void random_extract(u8 *out) 100 { 101 unsigned int i; 102 u8 hash[SHA1_MAC_LEN]; 103 u32 *hash_ptr; 104 u32 buf[POOL_WORDS / 2]; 105 106 /* First, add hash back to pool to make backtracking more difficult. */ 107 hmac_sha1(dummy_key, sizeof(dummy_key), (const u8 *) pool, 108 sizeof(pool), hash); 109 random_mix_pool(hash, sizeof(hash)); 110 /* Hash half the pool to extra data */ 111 for (i = 0; i < POOL_WORDS / 2; i++) 112 buf[i] = pool[(pool_pos - i) & POOL_WORDS_MASK]; 113 hmac_sha1(dummy_key, sizeof(dummy_key), (const u8 *) buf, 114 sizeof(buf), hash); 115 /* 116 * Fold the hash to further reduce any potential output pattern. 117 * Though, compromise this to reduce CPU use for the most common output 118 * length (32) and return 16 bytes from instead of only half. 119 */ 120 hash_ptr = (u32 *) hash; 121 hash_ptr[0] ^= hash_ptr[4]; 122 os_memcpy(out, hash, EXTRACT_LEN); 123 } 124 125 126 void random_add_randomness(const void *buf, size_t len) 127 { 128 struct os_time t; 129 static unsigned int count = 0; 130 131 count++; 132 if (entropy > MIN_COLLECT_ENTROPY && (count & 0x3ff) != 0) { 133 /* 134 * No need to add more entropy at this point, so save CPU and 135 * skip the update. 136 */ 137 return; 138 } 139 wpa_printf(MSG_EXCESSIVE, "Add randomness: count=%u entropy=%u", 140 count, entropy); 141 142 os_get_time(&t); 143 wpa_hexdump_key(MSG_EXCESSIVE, "random pool", 144 (const u8 *) pool, sizeof(pool)); 145 random_mix_pool(&t, sizeof(t)); 146 random_mix_pool(buf, len); 147 wpa_hexdump_key(MSG_EXCESSIVE, "random pool", 148 (const u8 *) pool, sizeof(pool)); 149 entropy++; 150 total_collected++; 151 } 152 153 154 int random_get_bytes(void *buf, size_t len) 155 { 156 int ret; 157 u8 *bytes = buf; 158 size_t left; 159 160 wpa_printf(MSG_MSGDUMP, "Get randomness: len=%u entropy=%u", 161 (unsigned int) len, entropy); 162 163 /* Start with assumed strong randomness from OS */ 164 ret = os_get_random(buf, len); 165 wpa_hexdump_key(MSG_EXCESSIVE, "random from os_get_random", 166 buf, len); 167 168 /* Mix in additional entropy extracted from the internal pool */ 169 left = len; 170 while (left) { 171 size_t siz, i; 172 u8 tmp[EXTRACT_LEN]; 173 random_extract(tmp); 174 wpa_hexdump_key(MSG_EXCESSIVE, "random from internal pool", 175 tmp, sizeof(tmp)); 176 siz = left > EXTRACT_LEN ? EXTRACT_LEN : left; 177 for (i = 0; i < siz; i++) 178 *bytes++ ^= tmp[i]; 179 left -= siz; 180 } 181 182 #ifdef CONFIG_FIPS 183 /* Mix in additional entropy from the crypto module */ 184 left = len; 185 while (left) { 186 size_t siz, i; 187 u8 tmp[EXTRACT_LEN]; 188 if (crypto_get_random(tmp, sizeof(tmp)) < 0) { 189 wpa_printf(MSG_ERROR, "random: No entropy available " 190 "for generating strong random bytes"); 191 return -1; 192 } 193 wpa_hexdump_key(MSG_EXCESSIVE, "random from crypto module", 194 tmp, sizeof(tmp)); 195 siz = left > EXTRACT_LEN ? EXTRACT_LEN : left; 196 for (i = 0; i < siz; i++) 197 *bytes++ ^= tmp[i]; 198 left -= siz; 199 } 200 #endif /* CONFIG_FIPS */ 201 202 wpa_hexdump_key(MSG_EXCESSIVE, "mixed random", buf, len); 203 204 if (entropy < len) 205 entropy = 0; 206 else 207 entropy -= len; 208 209 return ret; 210 } 211 212 213 int random_pool_ready(void) 214 { 215 #ifdef __linux__ 216 int fd; 217 ssize_t res; 218 219 /* 220 * Make sure that there is reasonable entropy available before allowing 221 * some key derivation operations to proceed. 222 */ 223 224 if (dummy_key_avail == sizeof(dummy_key)) 225 return 1; /* Already initialized - good to continue */ 226 227 /* 228 * Try to fetch some more data from the kernel high quality 229 * /dev/random. There may not be enough data available at this point, 230 * so use non-blocking read to avoid blocking the application 231 * completely. 232 */ 233 fd = open("/dev/random", O_RDONLY | O_NONBLOCK); 234 if (fd < 0) { 235 wpa_printf(MSG_ERROR, "random: Cannot open /dev/random: %s", 236 strerror(errno)); 237 return -1; 238 } 239 240 res = read(fd, dummy_key + dummy_key_avail, 241 sizeof(dummy_key) - dummy_key_avail); 242 if (res < 0) { 243 wpa_printf(MSG_ERROR, "random: Cannot read from /dev/random: " 244 "%s", strerror(errno)); 245 res = 0; 246 } 247 wpa_printf(MSG_DEBUG, "random: Got %u/%u bytes from " 248 "/dev/random", (unsigned) res, 249 (unsigned) (sizeof(dummy_key) - dummy_key_avail)); 250 dummy_key_avail += res; 251 close(fd); 252 253 if (dummy_key_avail == sizeof(dummy_key)) { 254 if (own_pool_ready < MIN_READY_MARK) 255 own_pool_ready = MIN_READY_MARK; 256 random_write_entropy(); 257 return 1; 258 } 259 260 wpa_printf(MSG_INFO, "random: Only %u/%u bytes of strong " 261 "random data available from /dev/random", 262 (unsigned) dummy_key_avail, (unsigned) sizeof(dummy_key)); 263 264 if (own_pool_ready >= MIN_READY_MARK || 265 total_collected + 10 * own_pool_ready > MIN_COLLECT_ENTROPY) { 266 wpa_printf(MSG_INFO, "random: Allow operation to proceed " 267 "based on internal entropy"); 268 return 1; 269 } 270 271 wpa_printf(MSG_INFO, "random: Not enough entropy pool available for " 272 "secure operations"); 273 return 0; 274 #else /* __linux__ */ 275 /* TODO: could do similar checks on non-Linux platforms */ 276 return 1; 277 #endif /* __linux__ */ 278 } 279 280 281 void random_mark_pool_ready(void) 282 { 283 own_pool_ready++; 284 wpa_printf(MSG_DEBUG, "random: Mark internal entropy pool to be " 285 "ready (count=%u/%u)", own_pool_ready, MIN_READY_MARK); 286 random_write_entropy(); 287 } 288 289 290 #ifdef __linux__ 291 292 static void random_close_fd(void) 293 { 294 if (random_fd >= 0) { 295 eloop_unregister_read_sock(random_fd); 296 close(random_fd); 297 random_fd = -1; 298 } 299 } 300 301 302 static void random_read_fd(int sock, void *eloop_ctx, void *sock_ctx) 303 { 304 ssize_t res; 305 306 if (dummy_key_avail == sizeof(dummy_key)) { 307 random_close_fd(); 308 return; 309 } 310 311 res = read(sock, dummy_key + dummy_key_avail, 312 sizeof(dummy_key) - dummy_key_avail); 313 if (res < 0) { 314 wpa_printf(MSG_ERROR, "random: Cannot read from /dev/random: " 315 "%s", strerror(errno)); 316 return; 317 } 318 319 wpa_printf(MSG_DEBUG, "random: Got %u/%u bytes from /dev/random", 320 (unsigned) res, 321 (unsigned) (sizeof(dummy_key) - dummy_key_avail)); 322 dummy_key_avail += res; 323 324 if (dummy_key_avail == sizeof(dummy_key)) { 325 random_close_fd(); 326 if (own_pool_ready < MIN_READY_MARK) 327 own_pool_ready = MIN_READY_MARK; 328 random_write_entropy(); 329 } 330 } 331 332 #endif /* __linux__ */ 333 334 335 static void random_read_entropy(void) 336 { 337 char *buf; 338 size_t len; 339 340 if (!random_entropy_file) 341 return; 342 343 buf = os_readfile(random_entropy_file, &len); 344 if (buf == NULL) 345 return; /* entropy file not yet available */ 346 347 if (len != 1 + RANDOM_ENTROPY_SIZE) { 348 wpa_printf(MSG_DEBUG, "random: Invalid entropy file %s", 349 random_entropy_file); 350 os_free(buf); 351 return; 352 } 353 354 own_pool_ready = (u8) buf[0]; 355 random_add_randomness(buf + 1, RANDOM_ENTROPY_SIZE); 356 random_entropy_file_read = 1; 357 os_free(buf); 358 wpa_printf(MSG_DEBUG, "random: Added entropy from %s " 359 "(own_pool_ready=%u)", 360 random_entropy_file, own_pool_ready); 361 } 362 363 364 static void random_write_entropy(void) 365 { 366 char buf[RANDOM_ENTROPY_SIZE]; 367 FILE *f; 368 u8 opr; 369 int fail = 0; 370 371 if (!random_entropy_file) 372 return; 373 374 if (random_get_bytes(buf, RANDOM_ENTROPY_SIZE) < 0) 375 return; 376 377 f = fopen(random_entropy_file, "wb"); 378 if (f == NULL) { 379 wpa_printf(MSG_ERROR, "random: Could not open entropy file %s " 380 "for writing", random_entropy_file); 381 return; 382 } 383 384 opr = own_pool_ready > 0xff ? 0xff : own_pool_ready; 385 if (fwrite(&opr, 1, 1, f) != 1 || 386 fwrite(buf, RANDOM_ENTROPY_SIZE, 1, f) != 1) 387 fail = 1; 388 fclose(f); 389 if (fail) { 390 wpa_printf(MSG_ERROR, "random: Could not write entropy data " 391 "to %s", random_entropy_file); 392 return; 393 } 394 395 wpa_printf(MSG_DEBUG, "random: Updated entropy file %s " 396 "(own_pool_ready=%u)", 397 random_entropy_file, own_pool_ready); 398 } 399 400 401 void random_init(const char *entropy_file) 402 { 403 os_free(random_entropy_file); 404 if (entropy_file) 405 random_entropy_file = os_strdup(entropy_file); 406 else 407 random_entropy_file = NULL; 408 random_read_entropy(); 409 410 #ifdef __linux__ 411 if (random_fd >= 0) 412 return; 413 414 random_fd = open("/dev/random", O_RDONLY | O_NONBLOCK); 415 if (random_fd < 0) { 416 wpa_printf(MSG_ERROR, "random: Cannot open /dev/random: %s", 417 strerror(errno)); 418 return; 419 } 420 wpa_printf(MSG_DEBUG, "random: Trying to read entropy from " 421 "/dev/random"); 422 423 eloop_register_read_sock(random_fd, random_read_fd, NULL, NULL); 424 #endif /* __linux__ */ 425 426 random_write_entropy(); 427 } 428 429 430 void random_deinit(void) 431 { 432 #ifdef __linux__ 433 random_close_fd(); 434 #endif /* __linux__ */ 435 random_write_entropy(); 436 os_free(random_entropy_file); 437 random_entropy_file = NULL; 438 } 439
