/**
* Generate a suitable blind factor for the public key the generator was initialised with.
*
* @return a random blind factor
*/
public BigInteger GenerateBlindingFactor()
{
if (key == null)
throw new InvalidOperationException("generator not initialised");
BigInteger m = key.Modulus;
int length = m.BitLength - 1; // must be less than m.BitLength
BigInteger factor;
BigInteger gcd;
do
{
factor = new BigInteger(length, random);
gcd = factor.Gcd(m);
}
while (factor.SignValue == 0 || factor.Equals(BigInteger.One) || !gcd.Equals(BigInteger.One));
return factor;
}
public BigInteger ModPow(BigInteger e, BigInteger m)
{
if (m.sign < 1)
throw new ArithmeticException("Modulus must be positive");
if (m.Equals(One))
return Zero;
if (e.sign == 0)
return One;
if (sign == 0)
return Zero;
bool negExp = e.sign < 0;
if (negExp)
e = e.Negate();
BigInteger result = this.Mod(m);
if (!e.Equals(One))
{
if ((m.magnitude[m.magnitude.Length - 1] & 1) == 0)
{
result = ModPowBarrett(result, e, m);
}
else
{
result = ModPowMonty(result, e, m, true);
}
}
if (negExp)
result = result.ModInverse(m);
return result;
}