Class: RFuzz::FuzzRnd

Inherits:
Object
  • Object
show all
Defined in:
ext/fuzzrnd/fuzzrnd.c

Instance Method Summary collapse

Constructor Details

#seed ⇒ Object

Seeds the global ArcFour random generator with the given seed. The same seeds should produce the exact same stream of random data so that you can get large amounts of randomness but replay possible interactions using just an initial key.

This function also doubles as the FuzzRnd.initialize method since they do nearly the same thing.

Taken from www.mozilla.org/projects/security/pki/nss/draft-kaukonen-cipher-arcfour-03.txt sample code, but compared with the output of the ArcFour implementation in the Phelix test code to make sure it is the same initialization. The main difference is that this init takes an arbitrary keysize while the original Phelix ArcFour only took a 32bit key.

Returns itself so you can seed and then get data easily.



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# File 'ext/fuzzrnd/fuzzrnd.c', line 99

VALUE FuzzRnd_seed(VALUE self, VALUE data) {

  unsigned int t, u;
  unsigned int keyindex;
  unsigned int stateindex;
  unsigned char *state;
  unsigned int counter;
  char *key = NULL;
  size_t key_len = 0;

  REQUIRE_TYPE(data, T_STRING);

  key = RSTRING(data)->ptr;
  key_len = RSTRING(data)->len;

  state = ArcFour.sbox;
  ArcFour.i = 0;
  ArcFour.j = 0;

  for (counter = 0; counter < 256; counter++)
    state[counter] = counter;

  keyindex = 0;
  stateindex = 0;
  for (counter = 0; counter < 256; counter++)
  {
    t = state[counter];
    stateindex = (stateindex + key[keyindex] + t) & 0xff;
    u = state[stateindex];
    state[stateindex] = t;
    state[counter] = u;
    if (++keyindex >= key_len)
      keyindex = 0;
  }

  return self;
}

Instance Method Details

#seed ⇒ Object

Returns a String of random bytes of length that you can use for generating randomness. It uses the ArcFour cipher to make the randomness, so the same seeds produce the same random bits, and the randomness is reasonably high quality.

Don’t use this for secure random generation. It probably would work if you seeded from a /dev/random that worked, but don’t blame me if you get hacked.

The main motiviation for using ArcFour without automated reseed is to produce lots of random bytes quickly, make them high enough quality for good random tests, and to make sure that we can replay possible sequences if there’s a sequence that we want to test.



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# File 'ext/fuzzrnd/fuzzrnd.c', line 48

VALUE FuzzRnd_data(VALUE self, VALUE length)
{

  uint32_t n;
  unsigned char a,b;
  size_t len = 0;
  VALUE data;
  char *p = NULL;

  REQUIRE_TYPE(length, T_FIXNUM);

  len = FIX2INT(length);
  data = rb_str_buf_new(len);
  p = RSTRING(data)->ptr;
  rb_str_resize(data, len);

  for (n=0;n<len;n++)             /* run the ArcFour algorithm as long as it needs */
  {
    ArcFour.i++;
    a     =         ArcFour.sbox[ArcFour.i];
    ArcFour.j = (unsigned char) (ArcFour.j + a);     /* avoid MSVC picky compiler warning */
    b     =         ArcFour.sbox[ArcFour.j];
    ArcFour.sbox[ArcFour.i] = b;
    ArcFour.sbox[ArcFour.j] = a;
    p[n]  = ArcFour.sbox[(a+b) & 0xFF];
  }

  return data;
}

#seed ⇒ Object

Seeds the global ArcFour random generator with the given seed. The same seeds should produce the exact same stream of random data so that you can get large amounts of randomness but replay possible interactions using just an initial key.

This function also doubles as the FuzzRnd.initialize method since they do nearly the same thing.

Taken from www.mozilla.org/projects/security/pki/nss/draft-kaukonen-cipher-arcfour-03.txt sample code, but compared with the output of the ArcFour implementation in the Phelix test code to make sure it is the same initialization. The main difference is that this init takes an arbitrary keysize while the original Phelix ArcFour only took a 32bit key.

Returns itself so you can seed and then get data easily.



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# File 'ext/fuzzrnd/fuzzrnd.c', line 99

VALUE FuzzRnd_seed(VALUE self, VALUE data) {

  unsigned int t, u;
  unsigned int keyindex;
  unsigned int stateindex;
  unsigned char *state;
  unsigned int counter;
  char *key = NULL;
  size_t key_len = 0;

  REQUIRE_TYPE(data, T_STRING);

  key = RSTRING(data)->ptr;
  key_len = RSTRING(data)->len;

  state = ArcFour.sbox;
  ArcFour.i = 0;
  ArcFour.j = 0;

  for (counter = 0; counter < 256; counter++)
    state[counter] = counter;

  keyindex = 0;
  stateindex = 0;
  for (counter = 0; counter < 256; counter++)
  {
    t = state[counter];
    stateindex = (stateindex + key[keyindex] + t) & 0xff;
    u = state[stateindex];
    state[stateindex] = t;
    state[counter] = u;
    if (++keyindex >= key_len)
      keyindex = 0;
  }

  return self;
}