crypto/prng.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 in RFC3686 ctr mode
   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 <linux/err.h>
  17 #include <linux/init.h>
  18 #include <linux/module.h>
  19 #include <linux/mm.h>
  20 #include <linux/slab.h>
  21 #include <linux/fs.h>
  22 #include <linux/scatterlist.h>
  23 #include <linux/string.h>
  24 #include <linux/crypto.h>
  25 #include <linux/highmem.h>
  26 #include <linux/moduleparam.h>
  27 #include <linux/jiffies.h>
  28 #include <linux/timex.h>
  29 #include <linux/interrupt.h>
  30 #include <linux/miscdevice.h>
  31 #include "prng.h"
  32
  33 #define TEST_PRNG_ON_START 0
  34
  35 #define DEFAULT_PRNG_KEY "0123456789abcdef1011"
  36 #define DEFAULT_PRNG_KSZ 20
  37 #define DEFAULT_PRNG_IV "defaultv"
  38 #define DEFAULT_PRNG_IVSZ 8
  39 #define DEFAULT_BLK_SZ 16
  40 #define DEFAULT_V_SEED "zaybxcwdveuftgsh"
  41
  42 /*
  43  * Flags for the prng_context flags field
  44  */
  45
  46 #define PRNG_FIXED_SIZE 0x1
  47 #define PRNG_NEED_RESET 0x2
  48
  49 /*
  50  * Note: DT is our counter value
  51  *       I is our intermediate value
  52  *       V is our seed vector
  53  * See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf
  54  * for implementation details
  55  */
  56
  57
  58 struct prng_context {
  59         char *prng_key;
  60         char *prng_iv;
  61         spinlock_t prng_lock;
  62         unsigned char rand_data[DEFAULT_BLK_SZ];
  63         unsigned char last_rand_data[DEFAULT_BLK_SZ];
  64         unsigned char DT[DEFAULT_BLK_SZ];
  65         unsigned char I[DEFAULT_BLK_SZ];
  66         unsigned char V[DEFAULT_BLK_SZ];
  67         u32 rand_data_valid;
  68         struct crypto_blkcipher *tfm;
  69         u32 flags;
  70 };
  71
  72 static int dbg;
  73
  74 static void hexdump(char *note, unsigned char *buf, unsigned int len)
  75 {
  76         if (dbg) {
  77                 printk(KERN_CRIT "%s", note);
  78                 print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET,
  79                                 16, 1,
  80                                 buf, len, false);
  81         }
  82 }
  83
  84 #define dbgprint(format, args...) do {if(dbg) printk(format, ##args);} while(0)
  85
  86 static void xor_vectors(unsigned char *in1, unsigned char *in2,
  87                         unsigned char *out, unsigned int size)
  88 {
  89         int i;
  90
  91         for (i=0;i<size;i++)
  92                 out[i] = in1[i] ^ in2[i];
  93
  94 }
  95 /*
  96  * Returns DEFAULT_BLK_SZ bytes of random data per call
  97  * returns 0 if generation succeded, <0 if something went wrong
  98  */
  99 static int _get_more_prng_bytes(struct prng_context *ctx)
 100 {
 101         int i;
 102         struct blkcipher_desc desc;
 103         struct scatterlist sg_in, sg_out;
 104         int ret;
 105         unsigned char tmp[DEFAULT_BLK_SZ];
 106
 107         desc.tfm = ctx->tfm;
 108         desc.flags = 0;
 109
 110
 111         dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n",ctx);
 112
 113         hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ);
 114         hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ);
 115         hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ);
 116
 117         /*
 118          * This algorithm is a 3 stage state machine
 119          */
 120         for (i=0;i<3;i++) {
 121
 122                 desc.tfm = ctx->tfm;
 123                 desc.flags = 0;
 124                 switch (i) {
 125                         case 0:
 126                                 /*
 127                                  * Start by encrypting the counter value
 128                                  * This gives us an intermediate value I
 129                                  */
 130                                 memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ);
 131                                 sg_init_one(&sg_out, &ctx->I[0], DEFAULT_BLK_SZ);
 132                                 hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ);
 133                                 break;
 134                         case 1:
 135
 136                                 /*
 137                                  * Next xor I with our secret vector V
 138                                  * encrypt that result to obtain our
 139                                  * pseudo random data which we output
 140                                  */
 141                                 xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ);
 142                                 sg_init_one(&sg_out, &ctx->rand_data[0], DEFAULT_BLK_SZ);
 143                                 hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ);
 144                                 break;
 145                         case 2:
 146                                 /*
 147                                  * First check that we didn't produce the same random data
 148                                  * that we did last time around through this
 149                                  */
 150                                 if (!memcmp(ctx->rand_data, ctx->last_rand_data, DEFAULT_BLK_SZ)) {
 151                                         printk(KERN_ERR "ctx %p Failed repetition check!\n",
 152                                                 ctx);
 153                                         ctx->flags |= PRNG_NEED_RESET;
 154                                         return -1;
 155                                 }
 156                                 memcpy(ctx->last_rand_data, ctx->rand_data, DEFAULT_BLK_SZ);
 157
 158                                 /*
 159                                  * Lastly xor the random data with I
 160                                  * and encrypt that to obtain a new secret vector V
 161                                  */
 162                                 xor_vectors(ctx->rand_data, ctx->I, tmp, DEFAULT_BLK_SZ);
 163                                 sg_init_one(&sg_out, &ctx->V[0], DEFAULT_BLK_SZ);
 164                                 hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
 165                                 break;
 166                 }
 167
 168                 /* Initialize our input buffer */
 169                 sg_init_one(&sg_in, &tmp[0], DEFAULT_BLK_SZ);
 170
 171                 /* do the encryption */
 172                 ret = crypto_blkcipher_encrypt(&desc, &sg_out, &sg_in, DEFAULT_BLK_SZ);
 173
 174                 /* And check the result */
 175                 if (ret) {
 176                         dbgprint(KERN_CRIT "Encryption of new block failed for context %p\n",ctx);
 177                         ctx->rand_data_valid = DEFAULT_BLK_SZ;
 178                         return -1;
 179                 }
 180
 181         }
 182
 183         /*
 184          * Now update our DT value
 185          */
 186         for (i=DEFAULT_BLK_SZ-1;i>0;i--) {
 187                 ctx->DT[i] = ctx->DT[i-1];
 188         }
 189         ctx->DT[0] += 1;
 190
 191         dbgprint("Returning new block for context %p\n",ctx);
 192         ctx->rand_data_valid = 0;
 193
 194         hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ);
 195         hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ);
 196         hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ);
 197         hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ);
 198
 199         return 0;
 200 }
 201
 202 /* Our exported functions */
 203 int get_prng_bytes(char *buf, int nbytes, struct prng_context *ctx)
 204 {
 205         unsigned long flags;
 206         unsigned char *ptr = buf;
 207         unsigned int byte_count = (unsigned int)nbytes;
 208         int err;
 209
 210
 211         if (nbytes < 0)
 212                 return -EINVAL;
 213
 214         spin_lock_irqsave(&ctx->prng_lock, flags);
 215
 216         err = -EFAULT;
 217         if (ctx->flags & PRNG_NEED_RESET)
 218                 goto done;
 219
 220         /*
 221          * If the FIXED_SIZE flag is on, only return whole blocks of
 222          * pseudo random data
 223          */
 224         err = -EINVAL;
 225         if (ctx->flags & PRNG_FIXED_SIZE) {
 226                 if (nbytes < DEFAULT_BLK_SZ)
 227                         goto done;
 228                 byte_count = DEFAULT_BLK_SZ;
 229         }
 230
 231         err = byte_count;
 232
 233         dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",byte_count, ctx);
 234
 235
 236 remainder:
 237         if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
 238                 if (_get_more_prng_bytes(ctx) < 0) {
 239                         memset(buf, 0, nbytes);
 240                         err = -EFAULT;
 241                         goto done;
 242                 }
 243         }
 244
 245         /*
 246          * Copy up to the next whole block size
 247          */
 248         if (byte_count < DEFAULT_BLK_SZ) {
 249                 for (;ctx->rand_data_valid < DEFAULT_BLK_SZ; ctx->rand_data_valid++) {
 250                         *ptr = ctx->rand_data[ctx->rand_data_valid];
 251                         ptr++;
 252                         byte_count--;
 253                         if (byte_count == 0)
 254                                 goto done;
 255                 }
 256         }
 257
 258         /*
 259          * Now copy whole blocks
 260          */
 261         for(;byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) {
 262                 if (_get_more_prng_bytes(ctx) < 0) {
 263                         memset(buf, 0, nbytes);
 264                         err = -1;
 265                         goto done;
 266                 }
 267                 memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
 268                 ctx->rand_data_valid += DEFAULT_BLK_SZ;
 269                 ptr += DEFAULT_BLK_SZ;
 270         }
 271
 272         /*
 273          * Now copy any extra partial data
 274          */
 275         if (byte_count)
 276                 goto remainder;
 277
 278 done:
 279         spin_unlock_irqrestore(&ctx->prng_lock, flags);
 280         dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",err, ctx);
 281         return err;
 282 }
 283 EXPORT_SYMBOL_GPL(get_prng_bytes);
 284
 285 struct prng_context *alloc_prng_context(void)
 286 {
 287         struct prng_context *ctx=kzalloc(sizeof(struct prng_context), GFP_KERNEL);
 288
 289         spin_lock_init(&ctx->prng_lock);
 290
 291         if (reset_prng_context(ctx, NULL, NULL, NULL, NULL)) {
 292                 kfree(ctx);
 293                 ctx = NULL;
 294         }
 295
 296         dbgprint(KERN_CRIT "returning context %p\n",ctx);
 297         return ctx;
 298 }
 299
 300 EXPORT_SYMBOL_GPL(alloc_prng_context);
 301
 302 void free_prng_context(struct prng_context *ctx)
 303 {
 304         crypto_free_blkcipher(ctx->tfm);
 305         kfree(ctx);
 306 }
 307 EXPORT_SYMBOL_GPL(free_prng_context);
 308
 309 int reset_prng_context(struct prng_context *ctx,
 310                        unsigned char *key, unsigned char *iv,
 311                        unsigned char *V, unsigned char *DT)
 312 {
 313         int ret;
 314         int iv_len;
 315         int rc = -EFAULT;
 316
 317         spin_lock(&ctx->prng_lock);
 318         ctx->flags |= PRNG_NEED_RESET;
 319
 320         if (key)
 321                 memcpy(ctx->prng_key,key,strlen(ctx->prng_key));
 322         else
 323                 ctx->prng_key = DEFAULT_PRNG_KEY;
 324
 325         if (iv)
 326                 memcpy(ctx->prng_iv,iv, strlen(ctx->prng_iv));
 327         else
 328                 ctx->prng_iv = DEFAULT_PRNG_IV;
 329
 330         if (V)
 331                 memcpy(ctx->V,V,DEFAULT_BLK_SZ);
 332         else
 333                 memcpy(ctx->V,DEFAULT_V_SEED,DEFAULT_BLK_SZ);
 334
 335         if (DT)
 336                 memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
 337         else
 338                 memset(ctx->DT, 0, DEFAULT_BLK_SZ);
 339
 340         memset(ctx->rand_data,0,DEFAULT_BLK_SZ);
 341         memset(ctx->last_rand_data,0,DEFAULT_BLK_SZ);
 342
 343         if (ctx->tfm)
 344                 crypto_free_blkcipher(ctx->tfm);
 345
 346         ctx->tfm = crypto_alloc_blkcipher("rfc3686(ctr(aes))",0,0);
 347         if (!ctx->tfm) {
 348                 dbgprint(KERN_CRIT "Failed to alloc crypto tfm for context %p\n",ctx->tfm);
 349                 goto out;
 350         }
 351
 352         ctx->rand_data_valid = DEFAULT_BLK_SZ;
 353
 354         ret = crypto_blkcipher_setkey(ctx->tfm, ctx->prng_key, strlen(ctx->prng_key));
 355         if (ret) {
 356                 dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
 357                         crypto_blkcipher_get_flags(ctx->tfm));
 358                 crypto_free_blkcipher(ctx->tfm);
 359                 goto out;
 360         }
 361
 362         iv_len = crypto_blkcipher_ivsize(ctx->tfm);
 363         if (iv_len) {
 364                 crypto_blkcipher_set_iv(ctx->tfm, ctx->prng_iv, iv_len);
 365         }
 366         rc = 0;
 367         ctx->flags &= ~PRNG_NEED_RESET;
 368 out:
 369         spin_unlock(&ctx->prng_lock);
 370
 371         return rc;
 372
 373 }
 374 EXPORT_SYMBOL_GPL(reset_prng_context);
 375
 376 /* Module initalization */
 377 static int __init prng_mod_init(void)
 378 {
 379
 380 #ifdef TEST_PRNG_ON_START
 381         int i;
 382         unsigned char tmpbuf[DEFAULT_BLK_SZ];
 383
 384         struct prng_context *ctx = alloc_prng_context();
 385         if (ctx == NULL)
 386                 return -EFAULT;
 387         for (i=0;i<16;i++) {
 388                 if (get_prng_bytes(tmpbuf, DEFAULT_BLK_SZ, ctx) < 0) {
 389                         free_prng_context(ctx);
 390                         return -EFAULT;
 391                 }
 392         }
 393         free_prng_context(ctx);
 394 #endif
 395
 396         return 0;
 397 }
 398
 399 static void __exit prng_mod_fini(void)
 400 {
 401         return;
 402 }
 403
 404 MODULE_LICENSE("GPL");
 405 MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
 406 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
 407 module_param(dbg, int, 0);
 408 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
 409 module_init(prng_mod_init);
 410 module_exit(prng_mod_fini);