On Sep 13, 9:18 pm, Marco <[email protected]> wrote:
> How can i create a DETERMINISTIC, seeded random source?
>
> I tried various examples from the wiki, like the one below, and none
> of them generates the same block twice.
>
> What am I missing?
>
> const unsigned int SEEDSIZE = 16;
> byte pcbSeed[ SEEDSIZE ];
>
> const unsigned int BLOCKSIZE = 16 * 8;
> byte pcbScratch[ BLOCKSIZE ];
>
> //Set the seed to "xxxx...x"
> for(size_t i = 0; i < SEEDSIZE; ++i) {
> pcbSeed[i] = (byte)'x';
>
> }
>
> CryptoPP::RandomPool rng;
> // also tried
> // CryptoPP::AutoSeededX917RNG<CryptoPP::DES_EDE3> rng(true, false);
RandomPool is a PGP style pool, and its not deterministic. For example
RandomPool makes the following call:
time_t t = time(NULL);
...
AutoSeededX917RNG is not not deterministic either.
IncorporateEntropy() calls Reseed(), which looks like:
OS_GenerateRandomBlock(blocking, seed, seed.size());
if (length > 0)
{
SHA256 hash;
hash.Update(seed, seed.size());
hash.Update(input, length);
hash.TruncatedFinal(seed, UnsignedMin(hash.DigestSize(),
seed.size()));
}
OS_GenerateRandomBlock will use OS provided services, such as /dev/
[u]random or CryptGenRandom.
The source for RandPool can be found at
http://www.cryptopp.com/docs/ref/randpool_8cpp_source.html,
and AutoSeededX917RNG at http://www.cryptopp.com/docs/ref/osrng_8h_source.html.
LCGs are deterministic. http://www.cryptopp.com/docs/ref/class_l_c___r_n_g.html.
Jeff
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