private DSA_Secret_Key GenerateParams(int keyLength)
{
byte[] seed = new byte[20];
byte[] part1 = new byte[20];
byte[] part2 = new byte[20];
byte[] u = new byte[20];
RandomNumberGenerator rng = RandomNumberGenerator.Create();
BigInteger p = new BigInteger(); // prime
BigInteger q = new BigInteger(); // group order
BigInteger g; // group generator
DSA_Secret_Key dskKey = new DSA_Secret_Key();
SHA1 sha = SHA1.Create();
int n = (keyLength - 1) / 160;
byte[] w = new byte [keyLength / 8];
bool primesFound = false;
while (!primesFound) {
do {
rng.GetBytes(seed);
part1 = sha.ComputeHash(seed);
Array.Copy(seed, 0, part2, 0, seed.Length);
add(part2, seed, 1);
part2 = sha.ComputeHash(part2);
for (int i = 0; i != u.Length; i++)
u[i] = (byte)(part1[i] ^ part2[i]);
// first bit must be set (to respect key length)
u[0] |= (byte)0x80;
// last bit must be set (prime are all odds - except 2)
u[19] |= (byte)0x01;
q = new BigInteger(u);
} while (!q.isProbablePrime());
int counter = 0;
int offset = 2;
while (counter < 4096) {
for (int k = 0; k < n; k++) {
add(part1, seed, offset + k);
part1 = sha.ComputeHash(part1);
Array.Copy(part1, 0, w, w.Length - (k + 1) * part1.Length, part1.Length);
}
add(part1, seed, offset + n);
part1 = sha.ComputeHash(part1);
Array.Copy(part1, part1.Length - ((w.Length - (n) * part1.Length)), w, 0, w.Length - n * part1.Length);
w[0] |= (byte)0x80;
BigInteger xx = new BigInteger (w);
BigInteger c = xx % (q * 2);
p = xx - (c - 1);
if (p.testBit((uint)(keyLength - 1))) {
if (p.isProbablePrime()) {
primesFound = true;
break;
}
}
counter += 1;
offset += n + 1;
}
}
// calculate the generator g
BigInteger pMinusOneOverQ = (p - 1) / q;
for (;;) {
BigInteger h = new BigInteger();
h = BigInteger.genRandom(keyLength);
if ((h <= 1) || (h >= (p - 1)))
continue;
g = h.modPow(pMinusOneOverQ, p);
if (g <= 1)
continue;
break;
}
dskKey.p = p;
dskKey.q = q;
dskKey.g = g;
return dskKey;
}
