/**
		* 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;
		}
Example #2
0
        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;
        }