1 /* 2 * PRNG: Pseudo Random Number Generator 3 * Based on NIST Recommended PRNG From ANSI X9.31 Appendix A.2.4 using 4 * AES 128 cipher 5 * 6 * (C) Neil Horman <nhorman@tuxdriver.com> 7 * 8 * This program is free software; you can redistribute it and/or modify it 9 * under the terms of the GNU General Public License as published by the 10 * Free Software Foundation; either version 2 of the License, or (at your 11 * any later version. 12 * 13 * 14 */ 15 16 #include <crypto/internal/rng.h> 17 #include <linux/err.h> 18 #include <linux/init.h> 19 #include <linux/module.h> 20 #include <linux/moduleparam.h> 21 #include <linux/string.h> 22 23 #define DEFAULT_PRNG_KEY "0123456789abcdef" 24 #define DEFAULT_PRNG_KSZ 16 25 #define DEFAULT_BLK_SZ 16 26 #define DEFAULT_V_SEED "zaybxcwdveuftgsh" 27 28 /* 29 * Flags for the prng_context flags field 30 */ 31 32 #define PRNG_FIXED_SIZE 0x1 33 #define PRNG_NEED_RESET 0x2 34 35 /* 36 * Note: DT is our counter value 37 * I is our intermediate value 38 * V is our seed vector 39 * See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf 40 * for implementation details 41 */ 42 43 44 struct prng_context { 45 spinlock_t prng_lock; 46 unsigned char rand_data[DEFAULT_BLK_SZ]; 47 unsigned char last_rand_data[DEFAULT_BLK_SZ]; 48 unsigned char DT[DEFAULT_BLK_SZ]; 49 unsigned char I[DEFAULT_BLK_SZ]; 50 unsigned char V[DEFAULT_BLK_SZ]; 51 u32 rand_data_valid; 52 struct crypto_cipher *tfm; 53 u32 flags; 54 }; 55 56 static int dbg; 57 58 static void hexdump(char *note, unsigned char *buf, unsigned int len) 59 { 60 if (dbg) { 61 printk(KERN_CRIT "%s", note); 62 print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET, 63 16, 1, 64 buf, len, false); 65 } 66 } 67 68 #define dbgprint(format, args...) do {\ 69 if (dbg)\ 70 printk(format, ##args);\ 71 } while (0) 72 73 static void xor_vectors(unsigned char *in1, unsigned char *in2, 74 unsigned char *out, unsigned int size) 75 { 76 int i; 77 78 for (i = 0; i < size; i++) 79 out[i] = in1[i] ^ in2[i]; 80 81 } 82 /* 83 * Returns DEFAULT_BLK_SZ bytes of random data per call 84 * returns 0 if generation succeeded, <0 if something went wrong 85 */ 86 static int _get_more_prng_bytes(struct prng_context *ctx, int cont_test) 87 { 88 int i; 89 unsigned char tmp[DEFAULT_BLK_SZ]; 90 unsigned char *output = NULL; 91 92 93 dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n", 94 ctx); 95 96 hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ); 97 hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ); 98 hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ); 99 100 /* 101 * This algorithm is a 3 stage state machine 102 */ 103 for (i = 0; i < 3; i++) { 104 105 switch (i) { 106 case 0: 107 /* 108 * Start by encrypting the counter value 109 * This gives us an intermediate value I 110 */ 111 memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ); 112 output = ctx->I; 113 hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ); 114 break; 115 case 1: 116 117 /* 118 * Next xor I with our secret vector V 119 * encrypt that result to obtain our 120 * pseudo random data which we output 121 */ 122 xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ); 123 hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ); 124 output = ctx->rand_data; 125 break; 126 case 2: 127 /* 128 * First check that we didn't produce the same 129 * random data that we did last time around through this 130 */ 131 if (!memcmp(ctx->rand_data, ctx->last_rand_data, 132 DEFAULT_BLK_SZ)) { 133 if (cont_test) { 134 panic("cprng %p Failed repetition check!\n", 135 ctx); 136 } 137 138 printk(KERN_ERR 139 "ctx %p Failed repetition check!\n", 140 ctx); 141 142 ctx->flags |= PRNG_NEED_RESET; 143 return -EINVAL; 144 } 145 memcpy(ctx->last_rand_data, ctx->rand_data, 146 DEFAULT_BLK_SZ); 147 148 /* 149 * Lastly xor the random data with I 150 * and encrypt that to obtain a new secret vector V 151 */ 152 xor_vectors(ctx->rand_data, ctx->I, tmp, 153 DEFAULT_BLK_SZ); 154 output = ctx->V; 155 hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ); 156 break; 157 } 158 159 160 /* do the encryption */ 161 crypto_cipher_encrypt_one(ctx->tfm, output, tmp); 162 163 } 164 165 /* 166 * Now update our DT value 167 */ 168 for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) { 169 ctx->DT[i] += 1; 170 if (ctx->DT[i] != 0) 171 break; 172 } 173 174 dbgprint("Returning new block for context %p\n", ctx); 175 ctx->rand_data_valid = 0; 176 177 hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ); 178 hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ); 179 hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ); 180 hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ); 181 182 return 0; 183 } 184 185 /* Our exported functions */ 186 static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx, 187 int do_cont_test) 188 { 189 unsigned char *ptr = buf; 190 unsigned int byte_count = (unsigned int)nbytes; 191 int err; 192 193 194 spin_lock_bh(&ctx->prng_lock); 195 196 err = -EINVAL; 197 if (ctx->flags & PRNG_NEED_RESET) 198 goto done; 199 200 /* 201 * If the FIXED_SIZE flag is on, only return whole blocks of 202 * pseudo random data 203 */ 204 err = -EINVAL; 205 if (ctx->flags & PRNG_FIXED_SIZE) { 206 if (nbytes < DEFAULT_BLK_SZ) 207 goto done; 208 byte_count = DEFAULT_BLK_SZ; 209 } 210 211 /* 212 * Return 0 in case of success as mandated by the kernel 213 * crypto API interface definition. 214 */ 215 err = 0; 216 217 dbgprint(KERN_CRIT "getting %d random bytes for context %p\n", 218 byte_count, ctx); 219 220 221 remainder: 222 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) { 223 if (_get_more_prng_bytes(ctx, do_cont_test) < 0) { 224 memset(buf, 0, nbytes); 225 err = -EINVAL; 226 goto done; 227 } 228 } 229 230 /* 231 * Copy any data less than an entire block 232 */ 233 if (byte_count < DEFAULT_BLK_SZ) { 234 empty_rbuf: 235 while (ctx->rand_data_valid < DEFAULT_BLK_SZ) { 236 *ptr = ctx->rand_data[ctx->rand_data_valid]; 237 ptr++; 238 byte_count--; 239 ctx->rand_data_valid++; 240 if (byte_count == 0) 241 goto done; 242 } 243 } 244 245 /* 246 * Now copy whole blocks 247 */ 248 for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) { 249 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) { 250 if (_get_more_prng_bytes(ctx, do_cont_test) < 0) { 251 memset(buf, 0, nbytes); 252 err = -EINVAL; 253 goto done; 254 } 255 } 256 if (ctx->rand_data_valid > 0) 257 goto empty_rbuf; 258 memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ); 259 ctx->rand_data_valid += DEFAULT_BLK_SZ; 260 ptr += DEFAULT_BLK_SZ; 261 } 262 263 /* 264 * Now go back and get any remaining partial block 265 */ 266 if (byte_count) 267 goto remainder; 268 269 done: 270 spin_unlock_bh(&ctx->prng_lock); 271 dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n", 272 err, ctx); 273 return err; 274 } 275 276 static void free_prng_context(struct prng_context *ctx) 277 { 278 crypto_free_cipher(ctx->tfm); 279 } 280 281 static int reset_prng_context(struct prng_context *ctx, 282 const unsigned char *key, size_t klen, 283 const unsigned char *V, const unsigned char *DT) 284 { 285 int ret; 286 const unsigned char *prng_key; 287 288 spin_lock_bh(&ctx->prng_lock); 289 ctx->flags |= PRNG_NEED_RESET; 290 291 prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY; 292 293 if (!key) 294 klen = DEFAULT_PRNG_KSZ; 295 296 if (V) 297 memcpy(ctx->V, V, DEFAULT_BLK_SZ); 298 else 299 memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ); 300 301 if (DT) 302 memcpy(ctx->DT, DT, DEFAULT_BLK_SZ); 303 else 304 memset(ctx->DT, 0, DEFAULT_BLK_SZ); 305 306 memset(ctx->rand_data, 0, DEFAULT_BLK_SZ); 307 memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ); 308 309 ctx->rand_data_valid = DEFAULT_BLK_SZ; 310 311 ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen); 312 if (ret) { 313 dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n", 314 crypto_cipher_get_flags(ctx->tfm)); 315 goto out; 316 } 317 318 ret = 0; 319 ctx->flags &= ~PRNG_NEED_RESET; 320 out: 321 spin_unlock_bh(&ctx->prng_lock); 322 return ret; 323 } 324 325 static int cprng_init(struct crypto_tfm *tfm) 326 { 327 struct prng_context *ctx = crypto_tfm_ctx(tfm); 328 329 spin_lock_init(&ctx->prng_lock); 330 ctx->tfm = crypto_alloc_cipher("aes", 0, 0); 331 if (IS_ERR(ctx->tfm)) { 332 dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n", 333 ctx); 334 return PTR_ERR(ctx->tfm); 335 } 336 337 if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0) 338 return -EINVAL; 339 340 /* 341 * after allocation, we should always force the user to reset 342 * so they don't inadvertently use the insecure default values 343 * without specifying them intentially 344 */ 345 ctx->flags |= PRNG_NEED_RESET; 346 return 0; 347 } 348 349 static void cprng_exit(struct crypto_tfm *tfm) 350 { 351 free_prng_context(crypto_tfm_ctx(tfm)); 352 } 353 354 static int cprng_get_random(struct crypto_rng *tfm, 355 const u8 *src, unsigned int slen, 356 u8 *rdata, unsigned int dlen) 357 { 358 struct prng_context *prng = crypto_rng_ctx(tfm); 359 360 return get_prng_bytes(rdata, dlen, prng, 0); 361 } 362 363 /* 364 * This is the cprng_registered reset method the seed value is 365 * interpreted as the tuple { V KEY DT} 366 * V and KEY are required during reset, and DT is optional, detected 367 * as being present by testing the length of the seed 368 */ 369 static int cprng_reset(struct crypto_rng *tfm, 370 const u8 *seed, unsigned int slen) 371 { 372 struct prng_context *prng = crypto_rng_ctx(tfm); 373 const u8 *key = seed + DEFAULT_BLK_SZ; 374 const u8 *dt = NULL; 375 376 if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ) 377 return -EINVAL; 378 379 if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ)) 380 dt = key + DEFAULT_PRNG_KSZ; 381 382 reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt); 383 384 if (prng->flags & PRNG_NEED_RESET) 385 return -EINVAL; 386 return 0; 387 } 388 389 #ifdef CONFIG_CRYPTO_FIPS 390 static int fips_cprng_get_random(struct crypto_rng *tfm, 391 const u8 *src, unsigned int slen, 392 u8 *rdata, unsigned int dlen) 393 { 394 struct prng_context *prng = crypto_rng_ctx(tfm); 395 396 return get_prng_bytes(rdata, dlen, prng, 1); 397 } 398 399 static int fips_cprng_reset(struct crypto_rng *tfm, 400 const u8 *seed, unsigned int slen) 401 { 402 u8 rdata[DEFAULT_BLK_SZ]; 403 const u8 *key = seed + DEFAULT_BLK_SZ; 404 int rc; 405 406 struct prng_context *prng = crypto_rng_ctx(tfm); 407 408 if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ) 409 return -EINVAL; 410 411 /* fips strictly requires seed != key */ 412 if (!memcmp(seed, key, DEFAULT_PRNG_KSZ)) 413 return -EINVAL; 414 415 rc = cprng_reset(tfm, seed, slen); 416 417 if (!rc) 418 goto out; 419 420 /* this primes our continuity test */ 421 rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0); 422 prng->rand_data_valid = DEFAULT_BLK_SZ; 423 424 out: 425 return rc; 426 } 427 #endif 428 429 static struct rng_alg rng_algs[] = { { 430 .generate = cprng_get_random, 431 .seed = cprng_reset, 432 .seedsize = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ, 433 .base = { 434 .cra_name = "stdrng", 435 .cra_driver_name = "ansi_cprng", 436 .cra_priority = 100, 437 .cra_ctxsize = sizeof(struct prng_context), 438 .cra_module = THIS_MODULE, 439 .cra_init = cprng_init, 440 .cra_exit = cprng_exit, 441 } 442 #ifdef CONFIG_CRYPTO_FIPS 443 }, { 444 .generate = fips_cprng_get_random, 445 .seed = fips_cprng_reset, 446 .seedsize = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ, 447 .base = { 448 .cra_name = "fips(ansi_cprng)", 449 .cra_driver_name = "fips_ansi_cprng", 450 .cra_priority = 300, 451 .cra_ctxsize = sizeof(struct prng_context), 452 .cra_module = THIS_MODULE, 453 .cra_init = cprng_init, 454 .cra_exit = cprng_exit, 455 } 456 #endif 457 } }; 458 459 /* Module initalization */ 460 static int __init prng_mod_init(void) 461 { 462 return crypto_register_rngs(rng_algs, ARRAY_SIZE(rng_algs)); 463 } 464 465 static void __exit prng_mod_fini(void) 466 { 467 crypto_unregister_rngs(rng_algs, ARRAY_SIZE(rng_algs)); 468 } 469 470 MODULE_LICENSE("GPL"); 471 MODULE_DESCRIPTION("Software Pseudo Random Number Generator"); 472 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>"); 473 module_param(dbg, int, 0); 474 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)"); 475 subsys_initcall(prng_mod_init); 476 module_exit(prng_mod_fini); 477 MODULE_ALIAS_CRYPTO("stdrng"); 478 MODULE_ALIAS_CRYPTO("ansi_cprng"); 479