linux/crypto/ansi_cprng.c
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   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
  46struct 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
  58static int dbg;
  59
  60static 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 {\
  71if (dbg)\
  72        printk(format, ##args);\
  73} while (0)
  74
  75static 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 */
  88static 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 */
 182static 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
 216remainder:
 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) {
 229empty_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
 264done:
 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
 271static void free_prng_context(struct prng_context *ctx)
 272{
 273        crypto_free_cipher(ctx->tfm);
 274}
 275
 276static 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;
 328out:
 329        spin_unlock(&ctx->prng_lock);
 330
 331        return rc;
 332
 333}
 334
 335static 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
 344static void cprng_exit(struct crypto_tfm *tfm)
 345{
 346        free_prng_context(crypto_tfm_ctx(tfm));
 347}
 348
 349static 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 */
 363static 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
 382static 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 */
 404static 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;
 415out:
 416        return 0;
 417}
 418
 419static void __exit prng_mod_fini(void)
 420{
 421        crypto_unregister_alg(&rng_alg);
 422        return;
 423}
 424
 425MODULE_LICENSE("GPL");
 426MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
 427MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
 428module_param(dbg, int, 0);
 429MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
 430module_init(prng_mod_init);
 431module_exit(prng_mod_fini);
 432MODULE_ALIAS("stdrng");
 433