void DL_GroupParameters_DSA::GenerateRandom(RandomNumberGenerator &rng, const NameValuePairs &alg)
{
Integer p, q, g;
if (alg.GetValue("Modulus", p) && alg.GetValue("SubgroupGenerator", g))
{
q = alg.GetValueWithDefault("SubgroupOrder", ComputeGroupOrder(p)/2);
Initialize(p, q, g);
}
else
{
int modulusSize = 1024, defaultSubgroupOrderSize;
alg.GetIntValue("ModulusSize", modulusSize) || alg.GetIntValue("KeySize", modulusSize);
switch (modulusSize)
{
case 1024:
defaultSubgroupOrderSize = 160;
break;
case 2048:
defaultSubgroupOrderSize = 224;
break;
case 3072:
defaultSubgroupOrderSize = 256;
break;
default:
throw InvalidArgument("DSA: not a valid prime length");
}
DL_GroupParameters_GFP::GenerateRandom(rng, CombinedNameValuePairs(alg, MakeParameters(Name::SubgroupOrderSize(), defaultSubgroupOrderSize, false)));
}
}
void DL_GroupParameters_DSA::GenerateRandom(RandomNumberGenerator &rng, const NameValuePairs &alg)
{
Integer p, q, g;
if (alg.GetValue("Modulus", p) && alg.GetValue("SubgroupGenerator", g))
{
q = alg.GetValueWithDefault("SubgroupOrder", ComputeGroupOrder(p)/2);
}
else
{
int modulusSize = 1024;
alg.GetIntValue("ModulusSize", modulusSize) || alg.GetIntValue("KeySize", modulusSize);
if (!DSA::IsValidPrimeLength(modulusSize))
throw InvalidArgument("DSA: not a valid prime length");
SecByteBlock seed(SHA::DIGESTSIZE);
Integer h;
int c;
do
{
rng.GenerateBlock(seed, SHA::DIGESTSIZE);
} while (!DSA::GeneratePrimes(seed, SHA::DIGESTSIZE*8, c, p, modulusSize, q));
do
{
h.Randomize(rng, 2, p-2);
g = a_exp_b_mod_c(h, (p-1)/q, p);
} while (g <= 1);
}
Initialize(p, q, g);
}