// initializes the private variables (throws CryptographicException)
private void Initialize(BigInteger p, BigInteger g, BigInteger x, int secretLen, bool checkInput)
{
if (!p.IsProbablePrime() || g <= 0 || g >= p || (x != null && (x <= 0 || x > p - 2)))
throw new CryptographicException();
// default is to generate a number as large as the prime this
// is usually overkill, but it's the most secure thing we can
// do if the user doesn't specify a desired secret length ...
if (secretLen == 0)
secretLen = p.BitCount();
m_P = p;
m_G = g;
if (x == null) {
BigInteger pm1 = m_P - 1;
for(m_X = BigInteger.GenerateRandom(secretLen); m_X >= pm1 || m_X == 0; m_X = BigInteger.GenerateRandom(secretLen)) {}
} else {
m_X = x;
}
}
private void ExpectPrime (BigInteger bi)
{
Assertion.AssertEquals (true, bi.IsProbablePrime ());
}
private void GenerateParams (int keyLength)
{
byte[] seed = new byte[20];
byte[] part1 = new byte[20];
byte[] part2 = new byte[20];
byte[] u = new byte[20];
// TODO: a prime generator should be made for this
SHA1 sha = SHA1.Create ();
int n = (keyLength - 1) / 160;
byte[] w = new byte [keyLength / 8];
bool primesFound = false;
while (!primesFound) {
do {
Random.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 ());
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 x = new BigInteger (w);
BigInteger c = x % (q * 2);
p = x - (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 = BigInteger.GenerateRandom (keyLength);
if ((h <= 1) || (h >= (p - 1)))
continue;
g = h.ModPow (pMinusOneOverQ, p);
if (g <= 1)
continue;
break;
}
this.seed = new BigInteger (seed);
j = (p - 1) / q;
}
private void ExpectComposite (BigInteger bi)
{
Assertion.AssertEquals (false, bi.IsProbablePrime ());
}
private void ExpectPrime (BigInteger bi)
{
Assert.AreEqual (true, bi.IsProbablePrime ());
}
