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RIOT/sys/crypto/chacha_prng.c 2.09 KB
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  /*
   * Copyright (C) 2015  René Kijewski  <rene.kijewski@fu-berlin.de>
   *
   * 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.
   */
  
  /*
   * Please notice:
   *  - I am not a cryptographer.
   *  - You should not use this code to run a nuclear power plant without a proper review.
   */
  
  #include "crypto/chacha.h"
  #include "mutex.h"
  
  #include <string.h>
  
  static chacha_ctx _chacha_prng_ctx = {
      .state = { RIOT_CHACHA_PRNG_DEFAULT },
      .rounds = 8,
  };
  static uint32_t _chacha_prng_data[64];
  static signed _chacha_prng_pos = 0;
  static mutex_t _chacha_prng_mutex = MUTEX_INIT;
  
  void chacha_prng_seed(const void *data, size_t bytes)
  {
      mutex_lock(&_chacha_prng_mutex);
  
      memcpy(_chacha_prng_ctx.state, data, bytes);
      _chacha_prng_pos = 0;
  
      mutex_unlock(&_chacha_prng_mutex);
  }
  
  uint32_t chacha_prng_next(void)
  {
      mutex_lock(&_chacha_prng_mutex);
  
      if (--_chacha_prng_pos < 0) {
          _chacha_prng_pos = 15;
          chacha_keystream_bytes(&_chacha_prng_ctx, _chacha_prng_data);
      }
      uint32_t result = _chacha_prng_data[_chacha_prng_pos];
  
      mutex_unlock(&_chacha_prng_mutex);
      return result;
  }