boringssl/crypto/rand/deterministic.c

/* Copyright (c) 2016, Google Inc.
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

#include <openssl/rand.h>

#if defined(BORINGSSL_UNSAFE_DETERMINISTIC_MODE)

#include <string.h>

#include <openssl/chacha.h>

#include "internal.h"


/* g_num_calls is the number of calls to |CRYPTO_sysrand| that have occured.
 *
 * TODO(davidben): This is intentionally not thread-safe. If the fuzzer mode is
 * ever used in a multi-threaded program, replace this with a thread-local. (A
 * mutex would not be deterministic.) */
static uint64_t g_num_calls = 0;

void RAND_reset_for_fuzzing(void) { g_num_calls = 0; }

void CRYPTO_sysrand(uint8_t *out, size_t requested) {
  static const uint8_t kZeroKey[32];

  uint8_t nonce[12];
  OPENSSL_memset(nonce, 0, sizeof(nonce));
  OPENSSL_memcpy(nonce, &g_num_calls, sizeof(g_num_calls));

  OPENSSL_memset(out, 0, requested);
  CRYPTO_chacha_20(out, out, requested, kZeroKey, nonce, 0);
  g_num_calls++;
}

#endif  /* BORINGSSL_UNSAFE_DETERMINISTIC_MODE */