crypto/ansi_cprng.c

   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 = DEFAULT_BLK_SZ - 1; i >= 0; 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 any data less than an entire block
 227          */
 228         if (byte_count < DEFAULT_BLK_SZ) {
 229 empty_rbuf:
 230                 for (; ctx->rand_data_valid < DEFAULT_BLK_SZ;
 231                         ctx->rand_data_valid++) {
 232                         *ptr = ctx->rand_data[ctx->rand_data_valid];
 233                         ptr++;
 234                         byte_count--;
 235                         if (byte_count == 0)
 236                                 goto done;
 237                 }
 238         }
 239
 240         /*
 241          * Now copy whole blocks
 242          */
 243         for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) {
 244                 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
 245                         if (_get_more_prng_bytes(ctx) < 0) {
 246                                 memset(buf, 0, nbytes);
 247                                 err = -EINVAL;
 248                                 goto done;
 249                         }
 250                 }
 251                 if (ctx->rand_data_valid > 0)
 252                         goto empty_rbuf;
 253                 memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
 254                 ctx->rand_data_valid += DEFAULT_BLK_SZ;
 255                 ptr += DEFAULT_BLK_SZ;
 256         }
 257
 258         /*
 259          * Now go back and get any remaining partial block
 260          */
 261         if (byte_count)
 262                 goto remainder;
 263
 264 done:
 265         spin_unlock_irqrestore(&ctx->prng_lock, flags);
 266         dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",
 267                 err, ctx);
 268         return err;
 269 }
 270
 271 static void free_prng_context(struct prng_context *ctx)
 272 {
 273         crypto_free_cipher(ctx->tfm);
 274 }
 275
 276 static int reset_prng_context(struct prng_context *ctx,
 277                               unsigned char *key, size_t klen,
 278                               unsigned char *V, unsigned char *DT)
 279 {
 280         int ret;
 281         int rc = -EINVAL;
 282         unsigned char *prng_key;
 283
 284         spin_lock(&ctx->prng_lock);
 285         ctx->flags |= PRNG_NEED_RESET;
 286
 287         prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;
 288
 289         if (!key)
 290                 klen = DEFAULT_PRNG_KSZ;
 291
 292         if (V)
 293                 memcpy(ctx->V, V, DEFAULT_BLK_SZ);
 294         else
 295                 memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ);
 296
 297         if (DT)
 298                 memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
 299         else
 300                 memset(ctx->DT, 0, DEFAULT_BLK_SZ);
 301
 302         memset(ctx->rand_data, 0, DEFAULT_BLK_SZ);
 303         memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ);
 304
 305         if (ctx->tfm)
 306                 crypto_free_cipher(ctx->tfm);
 307
 308         ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
 309         if (IS_ERR(ctx->tfm)) {
 310                 dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n",
 311                         ctx);
 312                 ctx->tfm = NULL;
 313                 goto out;
 314         }
 315
 316         ctx->rand_data_valid = DEFAULT_BLK_SZ;
 317
 318         ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen);
 319         if (ret) {
 320                 dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
 321                         crypto_cipher_get_flags(ctx->tfm));
 322                 crypto_free_cipher(ctx->tfm);
 323                 goto out;
 324         }
 325
 326         rc = 0;
 327         ctx->flags &= ~PRNG_NEED_RESET;
 328 out:
 329         spin_unlock(&ctx->prng_lock);
 330
 331         return rc;
 332
 333 }
 334
 335 static int cprng_init(struct crypto_tfm *tfm)
 336 {
 337         struct prng_context *ctx = crypto_tfm_ctx(tfm);
 338
 339         spin_lock_init(&ctx->prng_lock);
 340
 341         return reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL);
 342 }
 343
 344 static void cprng_exit(struct crypto_tfm *tfm)
 345 {
 346         free_prng_context(crypto_tfm_ctx(tfm));
 347 }
 348
 349 static int cprng_get_random(struct crypto_rng *tfm, u8 *rdata,
 350                             unsigned int dlen)
 351 {
 352         struct prng_context *prng = crypto_rng_ctx(tfm);
 353
 354         return get_prng_bytes(rdata, dlen, prng);
 355 }
 356
 357 /*
 358  *  This is the cprng_registered reset method the seed value is
 359  *  interpreted as the tuple { V KEY DT}
 360  *  V and KEY are required during reset, and DT is optional, detected
 361  *  as being present by testing the length of the seed
 362  */
 363 static int cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
 364 {
 365         struct prng_context *prng = crypto_rng_ctx(tfm);
 366         u8 *key = seed + DEFAULT_BLK_SZ;
 367         u8 *dt = NULL;
 368
 369         if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
 370                 return -EINVAL;
 371
 372         if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
 373                 dt = key + DEFAULT_PRNG_KSZ;
 374
 375         reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);
 376
 377         if (prng->flags & PRNG_NEED_RESET)
 378                 return -EINVAL;
 379         return 0;
 380 }
 381
 382 static struct crypto_alg rng_alg = {
 383         .cra_name               = "stdrng",
 384         .cra_driver_name        = "ansi_cprng",
 385         .cra_priority           = 100,
 386         .cra_flags              = CRYPTO_ALG_TYPE_RNG,
 387         .cra_ctxsize            = sizeof(struct prng_context),
 388         .cra_type               = &crypto_rng_type,
 389         .cra_module             = THIS_MODULE,
 390         .cra_list               = LIST_HEAD_INIT(rng_alg.cra_list),
 391         .cra_init               = cprng_init,
 392         .cra_exit               = cprng_exit,
 393         .cra_u                  = {
 394                 .rng = {
 395                         .rng_make_random        = cprng_get_random,
 396                         .rng_reset              = cprng_reset,
 397                         .seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
 398                 }
 399         }
 400 };
 401
 402
 403 /* Module initalization */
 404 static int __init prng_mod_init(void)
 405 {
 406         int ret = 0;
 407
 408         if (fips_enabled)
 409                 rng_alg.cra_priority += 200;
 410
 411         ret = crypto_register_alg(&rng_alg);
 412
 413         if (ret)
 414                 goto out;
 415 out:
 416         return 0;
 417 }
 418
 419 static void __exit prng_mod_fini(void)
 420 {
 421         crypto_unregister_alg(&rng_alg);
 422         return;
 423 }
 424
 425 MODULE_LICENSE("GPL");
 426 MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
 427 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
 428 module_param(dbg, int, 0);
 429 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
 430 module_init(prng_mod_init);
 431 module_exit(prng_mod_fini);
 432 MODULE_ALIAS("stdrng");