firmware/random.c (d48e86e) - flaneth · BlinkenArea

random.c

/* flaneth - flash and ethernet
   Copyright (C) 2007-2012 Stefan Schuermans <stefan@schuermans.info>
   Copyleft: GNU public license V2 - http://www.gnu.org/copyleft/gpl.html
   a BlinkenArea project - http://www.blinkenarea.org/ */

#include <stdlib.h>

#include "random.h"

// number of complete bytes a call to random( ) returns
#if RANDOM_MAX < 0xFF
#error random number generator is not able to return a random byte
#elif RANDOM_MAX < 0xFFFF
#define RANDOM_BYTES 1
#elif RANDOM_MAX < 0xFFFFFF
#define RANDOM_BYTES 2
#elif RANDOM_MAX < 0xFFFFFFFF
#define RANDOM_BYTES 3
#else
#define RANDOM_BYTES 4
#endif

// entropy collected so far
unsigned long RandomEntropy = 0;        // the entropy itself
unsigned char RandomEntropyCnt  // number of times entropy was collected so
                                // far
    = sizeof(unsigned long) * 8 - 5;    // (use first entropy (few is better
                                        // than none))

// provide some entropy
void RandomProvideEntropy(unsigned char Entropy)        // (extern)
{
  // collect entropy
  RandomEntropy = RandomEntropy << 1 ^ (unsigned int)Entropy;
  RandomEntropyCnt++;
}

// task function to do the work - call from main loop
void RandomTask(void)   // (extern)
{
  // enough entropy was collected
  if (RandomEntropyCnt >= sizeof(unsigned long) * 8)    // one time entropy
                                                        // for every bit of
                                                        // RandomEntropy
  {
    RandomEntropyCnt = 0;
    // re-seed random number generator
    srandom(RandomEntropy);
  }
}

// get random data
void RandomGetData(unsigned char *pData, unsigned char Length)  // (extern)
{
  unsigned long r;
  unsigned char i;

// return random data
  for (; Length >= RANDOM_BYTES; Length -= RANDOM_BYTES) {
    r = random();
    for (i = 0; i < RANDOM_BYTES; i++) {
      *pData = (unsigned char)r;
      pData++;
      r >>= 8;
    }
  }
  if (Length > 0) {
    r = random();
    for (i = 0; i < Length; i++) {
      *pData = (unsigned char)r;
      pData++;
      r >>= 8;
    }
  }
}

flaneth

header fix