trezor-firmware/crypto/rand.c

/**
 * Copyright (c) 2013-2014 Tomas Dzetkulic
 * Copyright (c) 2013-2014 Pavol Rusnak
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES
 * OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */

#include "rand.h"

#ifdef USE_INSECURE_PRNG

#pragma message( \
    "NOT SUITABLE FOR PRODUCTION USE! Replace random32() function with your own secure code.")

// The following code is not supposed to be used in a production environment.
// It's included only to make the library testable.
// The message above tries to prevent any accidental use outside of the test
// environment.
//
// You are supposed to replace the random8() and random32() function with your
// own secure code. There is also a possibility to replace the random_buffer()
// function as it is defined as a weak symbol.

static uint32_t seed = 0;

void random_reseed(const uint32_t value) { seed = value; }

uint32_t random32(void) {
  // Linear congruential generator from Numerical Recipes
  // https://en.wikipedia.org/wiki/Linear_congruential_generator
  seed = 1664525 * seed + 1013904223;
  return seed;
}

#endif /* USE_INSECURE_PRNG */

//
// The following code is platform independent
//

void __attribute__((weak)) random_buffer(uint8_t *buf, size_t len) {
  uint32_t r = 0;
  for (size_t i = 0; i < len; i++) {
    if (i % 4 == 0) {
      r = random32();
    }
    buf[i] = (r >> ((i % 4) * 8)) & 0xFF;
  }
}

void random_xor(uint8_t *buf, size_t len) {
  uint8_t r[4] = {0};
  for (size_t i = 0; i < len; i++) {
    if (i % sizeof(r) == 0) {
      random_buffer(r, sizeof(r));
    }
    buf[i] ^= r[i % sizeof(r)];
  }
}

uint32_t random_uniform(uint32_t n) {
  uint32_t x = 0, max = 0xFFFFFFFF - (0xFFFFFFFF % n);
  while ((x = random32()) >= max)
    ;
  return x / (max / n);
}

void random_permute(char *str, size_t len) {
  for (int i = len - 1; i >= 1; i--) {
    int j = random_uniform(i + 1);
    char t = str[j];
    str[j] = str[i];
    str[i] = t;
  }
}