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 #include "internal.h" 24 25 #define DEFAULT_PRNG_KEY "0123456789abcdef" 26 #define DEFAULT_PRNG_KSZ 16 27 #define DEFAULT_BLK_SZ 16 28 #define DEFAULT_V_SEED "zaybxcwdveuftgsh" 29 30 /* 31 * Flags for the prng_context flags field 32 */ 33 34 #define PRNG_FIXED_SIZE 0x1 35 #define PRNG_NEED_RESET 0x2 36 37 /* 38 * Note: DT is our counter value 39 * I is our intermediate value 40 * V is our seed vector 41 * See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf 42 * for implementation details 43 */ 44 45 46 struct prng_context { 47 spinlock_t prng_lock; 48 unsigned char rand_data[DEFAULT_BLK_SZ]; 49 unsigned char last_rand_data[DEFAULT_BLK_SZ]; 50 unsigned char DT[DEFAULT_BLK_SZ]; 51 unsigned char I[DEFAULT_BLK_SZ]; 52 unsigned char V[DEFAULT_BLK_SZ]; 53 u32 rand_data_valid; 54 struct crypto_cipher *tfm; 55 u32 flags; 56 }; 57 58 static int dbg; 59 60 static void hexdump(char *note, unsigned char *buf, unsigned int len) 61 { 62 if (dbg) { 63 printk(KERN_CRIT "%s", note); 64 print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET, 65 16, 1, 66 buf, len, false); 67 } 68 } 69 70 #define dbgprint(format, args...) do {\ 71 if (dbg)\ 72 printk(format, ##args);\ 73 } while (0) 74 75 static void xor_vectors(unsigned char *in1, unsigned char *in2, 76 unsigned char *out, unsigned int size) 77 { 78 int i; 79 80 for (i = 0; i < size; i++) 81 out[i] = in1[i] ^ in2[i]; 82 83 } 84 /* 85 * Returns DEFAULT_BLK_SZ bytes of random data per call 86 * returns 0 if generation succeded, <0 if something went wrong 87 */ 88 static int _get_more_prng_bytes(struct prng_context *ctx) 89 { 90 int i; 91 unsigned char tmp[DEFAULT_BLK_SZ]; 92 unsigned char *output = NULL; 93 94 95 dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n", 96 ctx); 97 98 hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ); 99 hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ); 100 hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ); 101 102 /* 103 * This algorithm is a 3 stage state machine 104 */ 105 for (i = 0; i < 3; i++) { 106 107 switch (i) { 108 case 0: 109 /* 110 * Start by encrypting the counter value 111 * This gives us an intermediate value I 112 */ 113 memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ); 114 output = ctx->I; 115 hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ); 116 break; 117 case 1: 118 119 /* 120 * Next xor I with our secret vector V 121 * encrypt that result to obtain our 122 * pseudo random data which we output 123 */ 124 xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ); 125 hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ); 126 output = ctx->rand_data; 127 break; 128 case 2: 129 /* 130 * First check that we didn't produce the same 131 * random data that we did last time around through this 132 */ 133 if (!memcmp(ctx->rand_data, ctx->last_rand_data, 134 DEFAULT_BLK_SZ)) { 135 printk(KERN_ERR 136 "ctx %p Failed repetition check!\n", 137 ctx); 138 ctx->flags |= PRNG_NEED_RESET; 139 return -EINVAL; 140 } 141 memcpy(ctx->last_rand_data, ctx->rand_data, 142 DEFAULT_BLK_SZ); 143 144 /* 145 * Lastly xor the random data with I 146 * and encrypt that to obtain a new secret vector V 147 */ 148 xor_vectors(ctx->rand_data, ctx->I, tmp, 149 DEFAULT_BLK_SZ); 150 output = ctx->V; 151 hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ); 152 break; 153 } 154 155 156 /* do the encryption */ 157 crypto_cipher_encrypt_one(ctx->tfm, output, tmp); 158 159 } 160 161 /* 162 * Now update our DT value 163 */ 164 for (i = 0; i < DEFAULT_BLK_SZ; i++) { 165 ctx->DT[i] += 1; 166 if (ctx->DT[i] != 0) 167 break; 168 } 169 170 dbgprint("Returning new block for context %p\n", ctx); 171 ctx->rand_data_valid = 0; 172 173 hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ); 174 hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ); 175 hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ); 176 hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ); 177 178 return 0; 179 } 180 181 /* Our exported functions */ 182 static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx) 183 { 184 unsigned long flags; 185 unsigned char *ptr = buf; 186 unsigned int byte_count = (unsigned int)nbytes; 187 int err; 188 189 190 if (nbytes < 0) 191 return -EINVAL; 192 193 spin_lock_irqsave(&ctx->prng_lock, flags); 194 195 err = -EINVAL; 196 if (ctx->flags & PRNG_NEED_RESET) 197 goto done; 198 199 /* 200 * If the FIXED_SIZE flag is on, only return whole blocks of 201 * pseudo random data 202 */ 203 err = -EINVAL; 204 if (ctx->flags & PRNG_FIXED_SIZE) { 205 if (nbytes < DEFAULT_BLK_SZ) 206 goto done; 207 byte_count = DEFAULT_BLK_SZ; 208 } 209 210 err = byte_count; 211 212 dbgprint(KERN_CRIT "getting %d random bytes for context %p\n", 213 byte_count, ctx); 214 215 216 remainder: 217 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) { 218 if (_get_more_prng_bytes(ctx) < 0) { 219 memset(buf, 0, nbytes); 220 err = -EINVAL; 221 goto done; 222 } 223 } 224 225 /* 226 * Copy up to the next whole block size 227 */ 228 if (byte_count < DEFAULT_BLK_SZ) { 229 for (; ctx->rand_data_valid < DEFAULT_BLK_SZ; 230 ctx->rand_data_valid++) { 231 *ptr = ctx->rand_data[ctx->rand_data_valid]; 232 ptr++; 233 byte_count--; 234 if (byte_count == 0) 235 goto done; 236 } 237 } 238 239 /* 240 * Now copy whole blocks 241 */ 242 for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) { 243 if (_get_more_prng_bytes(ctx) < 0) { 244 memset(buf, 0, nbytes); 245 err = -EINVAL; 246 goto done; 247 } 248 memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ); 249 ctx->rand_data_valid += DEFAULT_BLK_SZ; 250 ptr += DEFAULT_BLK_SZ; 251 } 252 253 /* 254 * Now copy any extra partial data 255 */ 256 if (byte_count) 257 goto remainder; 258 259 done: 260 spin_unlock_irqrestore(&ctx->prng_lock, flags); 261 dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n", 262 err, ctx); 263 return err; 264 } 265 266 static void free_prng_context(struct prng_context *ctx) 267 { 268 crypto_free_cipher(ctx->tfm); 269 } 270 271 static int reset_prng_context(struct prng_context *ctx, 272 unsigned char *key, size_t klen, 273 unsigned char *V, unsigned char *DT) 274 { 275 int ret; 276 int rc = -EINVAL; 277 unsigned char *prng_key; 278 279 spin_lock(&ctx->prng_lock); 280 ctx->flags |= PRNG_NEED_RESET; 281 282 prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY; 283 284 if (!key) 285 klen = DEFAULT_PRNG_KSZ; 286 287 if (V) 288 memcpy(ctx->V, V, DEFAULT_BLK_SZ); 289 else 290 memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ); 291 292 if (DT) 293 memcpy(ctx->DT, DT, DEFAULT_BLK_SZ); 294 else 295 memset(ctx->DT, 0, DEFAULT_BLK_SZ); 296 297 memset(ctx->rand_data, 0, DEFAULT_BLK_SZ); 298 memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ); 299 300 if (ctx->tfm) 301 crypto_free_cipher(ctx->tfm); 302 303 ctx->tfm = crypto_alloc_cipher("aes", 0, 0); 304 if (IS_ERR(ctx->tfm)) { 305 dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n", 306 ctx); 307 ctx->tfm = NULL; 308 goto out; 309 } 310 311 ctx->rand_data_valid = DEFAULT_BLK_SZ; 312 313 ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen); 314 if (ret) { 315 dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n", 316 crypto_cipher_get_flags(ctx->tfm)); 317 crypto_free_cipher(ctx->tfm); 318 goto out; 319 } 320 321 rc = 0; 322 ctx->flags &= ~PRNG_NEED_RESET; 323 out: 324 spin_unlock(&ctx->prng_lock); 325 326 return rc; 327 328 } 329 330 static int cprng_init(struct crypto_tfm *tfm) 331 { 332 struct prng_context *ctx = crypto_tfm_ctx(tfm); 333 334 spin_lock_init(&ctx->prng_lock); 335 336 return reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL); 337 } 338 339 static void cprng_exit(struct crypto_tfm *tfm) 340 { 341 free_prng_context(crypto_tfm_ctx(tfm)); 342 } 343 344 static int cprng_get_random(struct crypto_rng *tfm, u8 *rdata, 345 unsigned int dlen) 346 { 347 struct prng_context *prng = crypto_rng_ctx(tfm); 348 349 return get_prng_bytes(rdata, dlen, prng); 350 } 351 352 static int cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen) 353 { 354 struct prng_context *prng = crypto_rng_ctx(tfm); 355 u8 *key = seed + DEFAULT_PRNG_KSZ; 356 357 if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ) 358 return -EINVAL; 359 360 reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, NULL); 361 362 if (prng->flags & PRNG_NEED_RESET) 363 return -EINVAL; 364 return 0; 365 } 366 367 static struct crypto_alg rng_alg = { 368 .cra_name = "stdrng", 369 .cra_driver_name = "ansi_cprng", 370 .cra_priority = 100, 371 .cra_flags = CRYPTO_ALG_TYPE_RNG, 372 .cra_ctxsize = sizeof(struct prng_context), 373 .cra_type = &crypto_rng_type, 374 .cra_module = THIS_MODULE, 375 .cra_list = LIST_HEAD_INIT(rng_alg.cra_list), 376 .cra_init = cprng_init, 377 .cra_exit = cprng_exit, 378 .cra_u = { 379 .rng = { 380 .rng_make_random = cprng_get_random, 381 .rng_reset = cprng_reset, 382 .seedsize = DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ, 383 } 384 } 385 }; 386 387 388 /* Module initalization */ 389 static int __init prng_mod_init(void) 390 { 391 int ret = 0; 392 393 if (fips_enabled) 394 rng_alg.cra_priority += 200; 395 396 ret = crypto_register_alg(&rng_alg); 397 398 if (ret) 399 goto out; 400 out: 401 return 0; 402 } 403 404 static void __exit prng_mod_fini(void) 405 { 406 crypto_unregister_alg(&rng_alg); 407 return; 408 } 409 410 MODULE_LICENSE("GPL"); 411 MODULE_DESCRIPTION("Software Pseudo Random Number Generator"); 412 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>"); 413 module_param(dbg, int, 0); 414 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)"); 415 module_init(prng_mod_init); 416 module_exit(prng_mod_fini); 417 MODULE_ALIAS("stdrng"); 418