C# BigInteger.Mod方法代码示例

        /// <summary>Choose a random prime value for use with RSA</summary>
        /// <param name="bitlength">the bit-length of the returned prime</param>
        /// <param name="e">the RSA public exponent</param>
        /// <returns>a prime p, with (p-1) relatively prime to e</returns>
        protected virtual BigInteger ChooseRandomPrime(int bitlength, BigInteger e)
        {
            for (;;)
            {
                BigInteger p = new BigInteger(bitlength, 1, param.Random);

                if (p.Mod(e).Equals(BigInteger.One))
                    continue;

                if (!p.IsProbablePrime(param.Certainty))
                    continue;

                if (!e.Gcd(p.Subtract(BigInteger.One)).Equals(BigInteger.One))
                    continue;

                return p;
            }
        }

        /**
         * generate suitable parameters for DSA, in line with
         * <i>FIPS 186-3 A.1 Generation of the FFC Primes p and q</i>.
         */
        protected virtual DsaParameters GenerateParameters_FIPS186_3()
        {
// A.1.1.2 Generation of the Probable Primes p and q Using an Approved Hash Function
            IDigest d = digest;
            int outlen = d.GetDigestSize() * 8;

// 1. Check that the (L, N) pair is in the list of acceptable (L, N pairs) (see Section 4.2). If
//    the pair is not in the list, then return INVALID.
            // Note: checked at initialisation
            
// 2. If (seedlen < N), then return INVALID.
            // FIXME This should be configurable (must be >= N)
            int seedlen = N;
            byte[] seed = new byte[seedlen / 8];

// 3. n = ceiling(L ⁄ outlen) – 1.
            int n = (L - 1) / outlen;

// 4. b = L – 1 – (n ∗ outlen).
            int b = (L - 1) % outlen;

            byte[] output = new byte[d.GetDigestSize()];
            for (;;)
            {
// 5. Get an arbitrary sequence of seedlen bits as the domain_parameter_seed.
                random.NextBytes(seed);

// 6. U = Hash (domain_parameter_seed) mod 2^(N–1).
                Hash(d, seed, output);
                BigInteger U = new BigInteger(1, output).Mod(BigInteger.One.ShiftLeft(N - 1));

// 7. q = 2^(N–1) + U + 1 – ( U mod 2).
                BigInteger q = BigInteger.One.ShiftLeft(N - 1).Add(U).Add(BigInteger.One).Subtract(
                    U.Mod(BigInteger.Two));

// 8. Test whether or not q is prime as specified in Appendix C.3.
                // TODO Review C.3 for primality checking
                if (!q.IsProbablePrime(certainty))
                {
// 9. If q is not a prime, then go to step 5.
                    continue;
                }

// 10. offset = 1.
                // Note: 'offset' value managed incrementally
                byte[] offset = Arrays.Clone(seed);

// 11. For counter = 0 to (4L – 1) do
                int counterLimit = 4 * L;
                for (int counter = 0; counter < counterLimit; ++counter)
                {
// 11.1 For j = 0 to n do
//      Vj = Hash ((domain_parameter_seed + offset + j) mod 2^seedlen).
// 11.2 W = V0 + (V1 ∗ 2^outlen) + ... + (V^(n–1) ∗ 2^((n–1) ∗ outlen)) + ((Vn mod 2^b) ∗ 2^(n ∗ outlen)).
                    // TODO Assemble w as a byte array
                    BigInteger W = BigInteger.Zero;
                    for (int j = 0, exp = 0; j <= n; ++j, exp += outlen)
                    {
                        Inc(offset);
                        Hash(d, offset, output);

                        BigInteger Vj = new BigInteger(1, output);
                        if (j == n)
                        {
                            Vj = Vj.Mod(BigInteger.One.ShiftLeft(b));
                        }

                        W = W.Add(Vj.ShiftLeft(exp));
                    }

// 11.3 X = W + 2^(L–1). Comment: 0 ≤ W < 2L–1; hence, 2L–1 ≤ X < 2L.
                    BigInteger X = W.Add(BigInteger.One.ShiftLeft(L - 1));

// 11.4 c = X mod 2q.
                    BigInteger c = X.Mod(q.ShiftLeft(1));

// 11.5 p = X - (c - 1). Comment: p ≡ 1 (mod 2q).
                    BigInteger p = X.Subtract(c.Subtract(BigInteger.One));

                    // 11.6 If (p < 2^(L - 1)), then go to step 11.9
                    if (p.BitLength != L)
                        continue;

// 11.7 Test whether or not p is prime as specified in Appendix C.3.
                    // TODO Review C.3 for primality checking
                    if (p.IsProbablePrime(certainty))
                    {
// 11.8 If p is determined to be prime, then return VALID and the values of p, q and
//      (optionally) the values of domain_parameter_seed and counter.
                        // TODO Make configurable (8-bit unsigned)?

                        if (usageIndex >= 0)
                        {
                            BigInteger g = CalculateGenerator_FIPS186_3_Verifiable(d, p, q, seed, usageIndex);
                            if (g != null)
                                return new DsaParameters(p, q, g, new DsaValidationParameters(seed, counter, usageIndex));
//.........这里部分代码省略.........

		/**
		* @exception InvalidCipherTextException if the decrypted block is not a valid ISO 9796 bit string
		*/
		private byte[] DecodeBlock(
			byte[]	input,
			int		inOff,
			int		inLen)
		{
			byte[]  block = engine.ProcessBlock(input, inOff, inLen);
			int     r = 1;
			int     t = (bitSize + 13) / 16;

			BigInteger iS = new BigInteger(1, block);
			BigInteger iR;
			if (iS.Mod(Sixteen).Equals(Six))
			{
				iR = iS;
			}
			else
			{
				iR = modulus.Subtract(iS);

				if (!iR.Mod(Sixteen).Equals(Six))
					throw new InvalidCipherTextException("resulting integer iS or (modulus - iS) is not congruent to 6 mod 16");
			}

			block = iR.ToByteArrayUnsigned();

			if ((block[block.Length - 1] & 0x0f) != 0x6)
				throw new InvalidCipherTextException("invalid forcing byte in block");

			block[block.Length - 1] =
				(byte)(((ushort)(block[block.Length - 1] & 0xff) >> 4)
				| ((inverse[(block[block.Length - 2] & 0xff) >> 4]) << 4));

			block[0] = (byte)((shadows[(uint) (block[1] & 0xff) >> 4] << 4)
				| shadows[block[1] & 0x0f]);

			bool boundaryFound = false;
			int boundary = 0;

			for (int i = block.Length - 1; i >= block.Length - 2 * t; i -= 2)
			{
				int val = ((shadows[(uint) (block[i] & 0xff) >> 4] << 4)
					| shadows[block[i] & 0x0f]);

				if (((block[i - 1] ^ val) & 0xff) != 0)
				{
					if (!boundaryFound)
					{
						boundaryFound = true;
						r = (block[i - 1] ^ val) & 0xff;
						boundary = i - 1;
					}
					else
					{
						throw new InvalidCipherTextException("invalid tsums in block");
					}
				}
			}

			block[boundary] = 0;

			byte[] nblock = new byte[(block.Length - boundary) / 2];

			for (int i = 0; i < nblock.Length; i++)
			{
				nblock[i] = block[2 * i + boundary + 1];
			}

			padBits = r - 1;

			return nblock;
		}

        protected virtual DsaParameters GenerateParameters_FIPS186_2()
        {
            byte[] seed = new byte[20];
            byte[] part1 = new byte[20];
            byte[] part2 = new byte[20];
            byte[] u = new byte[20];
            int n = (L - 1) / 160;
            byte[] w = new byte[L / 8];

            if (!(digest is Sha1Digest))
                throw new InvalidOperationException("can only use SHA-1 for generating FIPS 186-2 parameters");

            for (;;)
            {
                random.NextBytes(seed);

                Hash(digest, seed, part1);
                Array.Copy(seed, 0, part2, 0, seed.Length);
                Inc(part2);
                Hash(digest, part2, part2);

                for (int i = 0; i != u.Length; i++)
                {
                    u[i] = (byte)(part1[i] ^ part2[i]);
                }

                u[0] |= (byte)0x80;
                u[19] |= (byte)0x01;

                BigInteger q = new BigInteger(1, u);

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

                byte[] offset = Arrays.Clone(seed);
                Inc(offset);

                for (int counter = 0; counter < 4096; ++counter)
                {
                    for (int k = 0; k < n; k++)
                    {
                        Inc(offset);
                        Hash(digest, offset, part1);
                        Array.Copy(part1, 0, w, w.Length - (k + 1) * part1.Length, part1.Length);
                    }

                    Inc(offset);
                    Hash(digest, offset, 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(1, w);

                    BigInteger c = x.Mod(q.ShiftLeft(1));

                    BigInteger p = x.Subtract(c.Subtract(BigInteger.One));

                    if (p.BitLength != L)
                        continue;

                    if (p.IsProbablePrime(certainty))
                    {
                        BigInteger g = CalculateGenerator_FIPS186_2(p, q, random);

                        return new DsaParameters(p, q, g, new DsaValidationParameters(seed, counter));
                    }
                }
            }
        }