Org.BouncyCastle.Math.BigInteger.RabinMillerTest C# (CSharp) Method

		internal bool RabinMillerTest(
			int		certainty,
			Random	random)
		{
			Debug.Assert(certainty > 0);
			Debug.Assert(BitLength > 2);
			Debug.Assert(TestBit(0));

			// let n = 1 + d . 2^s
			BigInteger n = this;
			BigInteger nMinusOne = n.Subtract(One);
			int s = nMinusOne.GetLowestSetBit();
			BigInteger r = nMinusOne.ShiftRight(s);

			Debug.Assert(s >= 1);

			do
			{
				// TODO Make a method for random BigIntegers in range 0 < x < n)
				// - Method can be optimized by only replacing examined bits at each trial
				BigInteger a;
				do
				{
					a = new BigInteger(n.BitLength, random);
				}
				while (a.CompareTo(One) <= 0 || a.CompareTo(nMinusOne) >= 0);

				BigInteger y = a.ModPow(r, n);

				if (!y.Equals(One))
				{
					int j = 0;
					while (!y.Equals(nMinusOne))
					{
						if (++j == s)
							return false;

						y = y.ModPow(Two, n);

						if (y.Equals(One))
							return false;
					}
				}

				certainty -= 2; // composites pass for only 1/4 possible 'a'
			}
			while (certainty > 0);

			return true;
		}

        /*
         * Finds a pair of prime BigInteger's {p, q: p = 2q + 1}
         * 
         * (see: Handbook of Applied Cryptography 4.86)
         */
        internal static BigInteger[] GenerateSafePrimes(int size, int certainty, SecureRandom random)
        {
            BigInteger p, q;
            int qLength = size - 1;
            int minWeight = size >> 2;

            if (size <= 32)
            {
                for (;;)
                {
                    q = new BigInteger(qLength, 2, random);

                    p = q.ShiftLeft(1).Add(BigInteger.One);

                    if (!p.IsProbablePrime(certainty))
                        continue;

                    if (certainty > 2 && !q.IsProbablePrime(certainty - 2))
                        continue;

                    break;
                }
            }
            else
            {
                // Note: Modified from Java version for speed
                for (;;)
                {
                    q = new BigInteger(qLength, 0, random);

                retry:
                    for (int i = 0; i < primeLists.Length; ++i)
                    {
                        int test = q.Remainder(BigPrimeProducts[i]).IntValue;

                        if (i == 0)
                        {
                            int rem3 = test % 3;
                            if (rem3 != 2)
                            {
                                int diff = 2 * rem3 + 2;
                                q = q.Add(BigInteger.ValueOf(diff));
                                test = (test + diff) % primeProducts[i];
                            }
                        }

                        int[] primeList = primeLists[i];
                        for (int j = 0; j < primeList.Length; ++j)
                        {
                            int prime = primeList[j];
                            int qRem = test % prime;
                            if (qRem == 0 || qRem == (prime >> 1))
                            {
                                q = q.Add(Six);
                                goto retry;
                            }
                        }
                    }

                    if (q.BitLength != qLength)
                        continue;

                    if (!q.RabinMillerTest(2, random))
                        continue;

                    p = q.ShiftLeft(1).Add(BigInteger.One);

                    if (!p.RabinMillerTest(certainty, random))
                        continue;

                    if (certainty > 2 && !q.RabinMillerTest(certainty - 2, random))
                        continue;

                    /*
                     * Require a minimum weight of the NAF representation, since low-weight primes may be
                     * weak against a version of the number-field-sieve for the discrete-logarithm-problem.
                     * 
                     * See "The number field sieve for integers of low weight", Oliver Schirokauer.
                     */
                    if (WNafUtilities.GetNafWeight(p) < minWeight)
                        continue;

                    break;
                }
            }

            return new BigInteger[] { p, q };
        }