SSH.NET/src/Renci.SshNet/Security/Cryptography/Ciphers/TwofishCipher.cs

using System;

namespace Renci.SshNet.Security.Cryptography.Ciphers
{
    /// <summary>
    /// Implements Twofish cipher algorithm
    /// </summary>
    public sealed class TwofishCipher : BlockCipher
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="TwofishCipher"/> class.
        /// </summary>
        /// <param name="key">The key.</param>
        /// <param name="mode">The mode.</param>
        /// <param name="padding">The padding.</param>
        /// <exception cref="ArgumentNullException"><paramref name="key"/> is null.</exception>
        /// <exception cref="ArgumentException">Keysize is not valid for this algorithm.</exception>
        public TwofishCipher(byte[] key, CipherMode mode, CipherPadding padding)
            : base(key, 16, mode, padding)
        {
            var keySize = key.Length * 8;

            if (!(keySize == 128 || keySize == 192 || keySize == 256))
                throw new ArgumentException(string.Format("KeySize '{0}' is not valid for this algorithm.", keySize));

            //  TODO:   Refactor this algorithm

            // calculate the MDS matrix
            var m1 = new int[2];
            var mX = new int[2];
            var mY = new int[2];

            for (var i = 0; i < MAX_KEY_BITS; i++)
            {
                var j = P[0 + i] & 0xff;
                m1[0] = j;
                mX[0] = Mx_X(j) & 0xff;
                mY[0] = Mx_Y(j) & 0xff;

                j = P[(1 * 256) + i] & 0xff;
                m1[1] = j;
                mX[1] = Mx_X(j) & 0xff;
                mY[1] = Mx_Y(j) & 0xff;

                gMDS0[i] = m1[P_00] | mX[P_00] << 8 | mY[P_00] << 16 | mY[P_00] << 24;

                gMDS1[i] = mY[P_10] | mY[P_10] << 8 | mX[P_10] << 16 | m1[P_10] << 24;

                gMDS2[i] = mX[P_20] | mY[P_20] << 8 | m1[P_20] << 16 | mY[P_20] << 24;

                gMDS3[i] = mX[P_30] | m1[P_30] << 8 | mY[P_30] << 16 | mX[P_30] << 24;
            }

            k64Cnt = key.Length / 8; // pre-padded ?
            SetKey(key);
        }

        /// <summary>
        /// Encrypts the specified region of the input byte array and copies the encrypted data to the specified region of the output byte array.
        /// </summary>
        /// <param name="inputBuffer">The input data to encrypt.</param>
        /// <param name="inputOffset">The offset into the input byte array from which to begin using data.</param>
        /// <param name="inputCount">The number of bytes in the input byte array to use as data.</param>
        /// <param name="outputBuffer">The output to which to write encrypted data.</param>
        /// <param name="outputOffset">The offset into the output byte array from which to begin writing data.</param>
        /// <returns>
        /// The number of bytes encrypted.
        /// </returns>
        public override int EncryptBlock(byte[] inputBuffer, int inputOffset, int inputCount, byte[] outputBuffer, int outputOffset)
        {
            int x0 = BytesTo32Bits(inputBuffer, inputOffset) ^ gSubKeys[INPUT_WHITEN];
            int x1 = BytesTo32Bits(inputBuffer, inputOffset + 4) ^ gSubKeys[INPUT_WHITEN + 1];
            int x2 = BytesTo32Bits(inputBuffer, inputOffset + 8) ^ gSubKeys[INPUT_WHITEN + 2];
            int x3 = BytesTo32Bits(inputBuffer, inputOffset + 12) ^ gSubKeys[INPUT_WHITEN + 3];

            int k = ROUND_SUBKEYS;
            int t0, t1;
            for (int r = 0; r < ROUNDS; r += 2)
            {
                t0 = Fe32_0(gSBox, x0);
                t1 = Fe32_3(gSBox, x1);
                x2 ^= t0 + t1 + gSubKeys[k++];
                x2 = (int)((uint)x2 >> 1) | x2 << 31;
                x3 = (x3 << 1 | (int)((uint)x3 >> 31)) ^ (t0 + 2 * t1 + gSubKeys[k++]);

                t0 = Fe32_0(gSBox, x2);
                t1 = Fe32_3(gSBox, x3);
                x0 ^= t0 + t1 + gSubKeys[k++];
                x0 = (int)((uint)x0 >> 1) | x0 << 31;
                x1 = (x1 << 1 | (int)((uint)x1 >> 31)) ^ (t0 + 2 * t1 + gSubKeys[k++]);
            }

            Bits32ToBytes(x2 ^ gSubKeys[OUTPUT_WHITEN], outputBuffer, outputOffset);
            Bits32ToBytes(x3 ^ gSubKeys[OUTPUT_WHITEN + 1], outputBuffer, outputOffset + 4);
            Bits32ToBytes(x0 ^ gSubKeys[OUTPUT_WHITEN + 2], outputBuffer, outputOffset + 8);
            Bits32ToBytes(x1 ^ gSubKeys[OUTPUT_WHITEN + 3], outputBuffer, outputOffset + 12);

            return BlockSize;
        }

        /// <summary>
        /// Decrypts the specified region of the input byte array and copies the decrypted data to the specified region of the output byte array.
        /// </summary>
        /// <param name="inputBuffer">The input data to decrypt.</param>
        /// <param name="inputOffset">The offset into the input byte array from which to begin using data.</param>
        /// <param name="inputCount">The number of bytes in the input byte array to use as data.</param>
        /// <param name="outputBuffer">The output to which to write decrypted data.</param>
        /// <param name="outputOffset">The offset into the output byte array from which to begin writing data.</param>
        /// <returns>
        /// The number of bytes decrypted.
        /// </returns>
        public override int DecryptBlock(byte[] inputBuffer, int inputOffset, int inputCount, byte[] outputBuffer, int outputOffset)
        {
            var x2 = BytesTo32Bits(inputBuffer, inputOffset) ^ gSubKeys[OUTPUT_WHITEN];
            var x3 = BytesTo32Bits(inputBuffer, inputOffset + 4) ^ gSubKeys[OUTPUT_WHITEN + 1];
            var x0 = BytesTo32Bits(inputBuffer, inputOffset + 8) ^ gSubKeys[OUTPUT_WHITEN + 2];
            var x1 = BytesTo32Bits(inputBuffer, inputOffset + 12) ^ gSubKeys[OUTPUT_WHITEN + 3];

            var k = ROUND_SUBKEYS + 2 * ROUNDS - 1;
            for (var r = 0; r < ROUNDS; r += 2)
            {
                var t0 = Fe32_0(gSBox, x2);
                var t1 = Fe32_3(gSBox, x3);
                x1 ^= t0 + 2 * t1 + gSubKeys[k--];
                x0 = (x0 << 1 | (int)((uint)x0 >> 31)) ^ (t0 + t1 + gSubKeys[k--]);
                x1 = (int)((uint)x1 >> 1) | x1 << 31;

                t0 = Fe32_0(gSBox, x0);
                t1 = Fe32_3(gSBox, x1);
                x3 ^= t0 + 2 * t1 + gSubKeys[k--];
                x2 = (x2 << 1 | (int)((uint)x2 >> 31)) ^ (t0 + t1 + gSubKeys[k--]);
                x3 = (int)((uint)x3 >> 1) | x3 << 31;
            }

            Bits32ToBytes(x0 ^ gSubKeys[INPUT_WHITEN], outputBuffer, outputOffset);
            Bits32ToBytes(x1 ^ gSubKeys[INPUT_WHITEN + 1], outputBuffer, outputOffset + 4);
            Bits32ToBytes(x2 ^ gSubKeys[INPUT_WHITEN + 2], outputBuffer, outputOffset + 8);
            Bits32ToBytes(x3 ^ gSubKeys[INPUT_WHITEN + 3], outputBuffer, outputOffset + 12);

            return BlockSize;
        }

        #region Static Definition Tables

        private static readonly byte[] P =  {
        //{  // p0
			(byte) 0xA9, (byte) 0x67, (byte) 0xB3, (byte) 0xE8,
			(byte) 0x04, (byte) 0xFD, (byte) 0xA3, (byte) 0x76,
			(byte) 0x9A, (byte) 0x92, (byte) 0x80, (byte) 0x78,
			(byte) 0xE4, (byte) 0xDD, (byte) 0xD1, (byte) 0x38,
			(byte) 0x0D, (byte) 0xC6, (byte) 0x35, (byte) 0x98,
			(byte) 0x18, (byte) 0xF7, (byte) 0xEC, (byte) 0x6C,
			(byte) 0x43, (byte) 0x75, (byte) 0x37, (byte) 0x26,
			(byte) 0xFA, (byte) 0x13, (byte) 0x94, (byte) 0x48,
			(byte) 0xF2, (byte) 0xD0, (byte) 0x8B, (byte) 0x30,
			(byte) 0x84, (byte) 0x54, (byte) 0xDF, (byte) 0x23,
			(byte) 0x19, (byte) 0x5B, (byte) 0x3D, (byte) 0x59,
			(byte) 0xF3, (byte) 0xAE, (byte) 0xA2, (byte) 0x82,
			(byte) 0x63, (byte) 0x01, (byte) 0x83, (byte) 0x2E,
			(byte) 0xD9, (byte) 0x51, (byte) 0x9B, (byte) 0x7C,
			(byte) 0xA6, (byte) 0xEB, (byte) 0xA5, (byte) 0xBE,
			(byte) 0x16, (byte) 0x0C, (byte) 0xE3, (byte) 0x61,
			(byte) 0xC0, (byte) 0x8C, (byte) 0x3A, (byte) 0xF5,
			(byte) 0x73, (byte) 0x2C, (byte) 0x25, (byte) 0x0B,
			(byte) 0xBB, (byte) 0x4E, (byte) 0x89, (byte) 0x6B,
			(byte) 0x53, (byte) 0x6A, (byte) 0xB4, (byte) 0xF1,
			(byte) 0xE1, (byte) 0xE6, (byte) 0xBD, (byte) 0x45,
			(byte) 0xE2, (byte) 0xF4, (byte) 0xB6, (byte) 0x66,
			(byte) 0xCC, (byte) 0x95, (byte) 0x03, (byte) 0x56,
			(byte) 0xD4, (byte) 0x1C, (byte) 0x1E, (byte) 0xD7,
			(byte) 0xFB, (byte) 0xC3, (byte) 0x8E, (byte) 0xB5,
			(byte) 0xE9, (byte) 0xCF, (byte) 0xBF, (byte) 0xBA,
			(byte) 0xEA, (byte) 0x77, (byte) 0x39, (byte) 0xAF,
			(byte) 0x33, (byte) 0xC9, (byte) 0x62, (byte) 0x71,
			(byte) 0x81, (byte) 0x79, (byte) 0x09, (byte) 0xAD,
			(byte) 0x24, (byte) 0xCD, (byte) 0xF9, (byte) 0xD8,
			(byte) 0xE5, (byte) 0xC5, (byte) 0xB9, (byte) 0x4D,
			(byte) 0x44, (byte) 0x08, (byte) 0x86, (byte) 0xE7,
			(byte) 0xA1, (byte) 0x1D, (byte) 0xAA, (byte) 0xED,
			(byte) 0x06, (byte) 0x70, (byte) 0xB2, (byte) 0xD2,
			(byte) 0x41, (byte) 0x7B, (byte) 0xA0, (byte) 0x11,
			(byte) 0x31, (byte) 0xC2, (byte) 0x27, (byte) 0x90,
			(byte) 0x20, (byte) 0xF6, (byte) 0x60, (byte) 0xFF,
			(byte) 0x96, (byte) 0x5C, (byte) 0xB1, (byte) 0xAB,
			(byte) 0x9E, (byte) 0x9C, (byte) 0x52, (byte) 0x1B,
			(byte) 0x5F, (byte) 0x93, (byte) 0x0A, (byte) 0xEF,
			(byte) 0x91, (byte) 0x85, (byte) 0x49, (byte) 0xEE,
			(byte) 0x2D, (byte) 0x4F, (byte) 0x8F, (byte) 0x3B,
			(byte) 0x47, (byte) 0x87, (byte) 0x6D, (byte) 0x46,
			(byte) 0xD6, (byte) 0x3E, (byte) 0x69, (byte) 0x64,
			(byte) 0x2A, (byte) 0xCE, (byte) 0xCB, (byte) 0x2F,
			(byte) 0xFC, (byte) 0x97, (byte) 0x05, (byte) 0x7A,
			(byte) 0xAC, (byte) 0x7F, (byte) 0xD5, (byte) 0x1A,
			(byte) 0x4B, (byte) 0x0E, (byte) 0xA7, (byte) 0x5A,
			(byte) 0x28, (byte) 0x14, (byte) 0x3F, (byte) 0x29,
			(byte) 0x88, (byte) 0x3C, (byte) 0x4C, (byte) 0x02,
			(byte) 0xB8, (byte) 0xDA, (byte) 0xB0, (byte) 0x17,
			(byte) 0x55, (byte) 0x1F, (byte) 0x8A, (byte) 0x7D,
			(byte) 0x57, (byte) 0xC7, (byte) 0x8D, (byte) 0x74,
			(byte) 0xB7, (byte) 0xC4, (byte) 0x9F, (byte) 0x72,
			(byte) 0x7E, (byte) 0x15, (byte) 0x22, (byte) 0x12,
			(byte) 0x58, (byte) 0x07, (byte) 0x99, (byte) 0x34,
			(byte) 0x6E, (byte) 0x50, (byte) 0xDE, (byte) 0x68,
			(byte) 0x65, (byte) 0xBC, (byte) 0xDB, (byte) 0xF8,
			(byte) 0xC8, (byte) 0xA8, (byte) 0x2B, (byte) 0x40,
			(byte) 0xDC, (byte) 0xFE, (byte) 0x32, (byte) 0xA4,
			(byte) 0xCA, (byte) 0x10, (byte) 0x21, (byte) 0xF0,
			(byte) 0xD3, (byte) 0x5D, (byte) 0x0F, (byte) 0x00,
			(byte) 0x6F, (byte) 0x9D, (byte) 0x36, (byte) 0x42,
			(byte) 0x4A, (byte) 0x5E, (byte) 0xC1, (byte) 0xE0,
        //                                    },
        //{  // p1
			(byte) 0x75, (byte) 0xF3, (byte) 0xC6, (byte) 0xF4,
			(byte) 0xDB, (byte) 0x7B, (byte) 0xFB, (byte) 0xC8,
			(byte) 0x4A, (byte) 0xD3, (byte) 0xE6, (byte) 0x6B,
			(byte) 0x45, (byte) 0x7D, (byte) 0xE8, (byte) 0x4B,
			(byte) 0xD6, (byte) 0x32, (byte) 0xD8, (byte) 0xFD,
			(byte) 0x37, (byte) 0x71, (byte) 0xF1, (byte) 0xE1,
			(byte) 0x30, (byte) 0x0F, (byte) 0xF8, (byte) 0x1B,
			(byte) 0x87, (byte) 0xFA, (byte) 0x06, (byte) 0x3F,
			(byte) 0x5E, (byte) 0xBA, (byte) 0xAE, (byte) 0x5B,
			(byte) 0x8A, (byte) 0x00, (byte) 0xBC, (byte) 0x9D,
			(byte) 0x6D, (byte) 0xC1, (byte) 0xB1, (byte) 0x0E,
			(byte) 0x80, (byte) 0x5D, (byte) 0xD2, (byte) 0xD5,
			(byte) 0xA0, (byte) 0x84, (byte) 0x07, (byte) 0x14,
			(byte) 0xB5, (byte) 0x90, (byte) 0x2C, (byte) 0xA3,
			(byte) 0xB2, (byte) 0x73, (byte) 0x4C, (byte) 0x54,
			(byte) 0x92, (byte) 0x74, (byte) 0x36, (byte) 0x51,
			(byte) 0x38, (byte) 0xB0, (byte) 0xBD, (byte) 0x5A,
			(byte) 0xFC, (byte) 0x60, (byte) 0x62, (byte) 0x96,
			(byte) 0x6C, (byte) 0x42, (byte) 0xF7, (byte) 0x10,
			(byte) 0x7C, (byte) 0x28, (byte) 0x27, (byte) 0x8C,
			(byte) 0x13, (byte) 0x95, (byte) 0x9C, (byte) 0xC7,
			(byte) 0x24, (byte) 0x46, (byte) 0x3B, (byte) 0x70,
			(byte) 0xCA, (byte) 0xE3, (byte) 0x85, (byte) 0xCB,
			(byte) 0x11, (byte) 0xD0, (byte) 0x93, (byte) 0xB8,
			(byte) 0xA6, (byte) 0x83, (byte) 0x20, (byte) 0xFF,
			(byte) 0x9F, (byte) 0x77, (byte) 0xC3, (byte) 0xCC,
			(byte) 0x03, (byte) 0x6F, (byte) 0x08, (byte) 0xBF,
			(byte) 0x40, (byte) 0xE7, (byte) 0x2B, (byte) 0xE2,
			(byte) 0x79, (byte) 0x0C, (byte) 0xAA, (byte) 0x82,
			(byte) 0x41, (byte) 0x3A, (byte) 0xEA, (byte) 0xB9,
			(byte) 0xE4, (byte) 0x9A, (byte) 0xA4, (byte) 0x97,
			(byte) 0x7E, (byte) 0xDA, (byte) 0x7A, (byte) 0x17,
			(byte) 0x66, (byte) 0x94, (byte) 0xA1, (byte) 0x1D,
			(byte) 0x3D, (byte) 0xF0, (byte) 0xDE, (byte) 0xB3,
			(byte) 0x0B, (byte) 0x72, (byte) 0xA7, (byte) 0x1C,
			(byte) 0xEF, (byte) 0xD1, (byte) 0x53, (byte) 0x3E,
			(byte) 0x8F, (byte) 0x33, (byte) 0x26, (byte) 0x5F,
			(byte) 0xEC, (byte) 0x76, (byte) 0x2A, (byte) 0x49,
			(byte) 0x81, (byte) 0x88, (byte) 0xEE, (byte) 0x21,
			(byte) 0xC4, (byte) 0x1A, (byte) 0xEB, (byte) 0xD9,
			(byte) 0xC5, (byte) 0x39, (byte) 0x99, (byte) 0xCD,
			(byte) 0xAD, (byte) 0x31, (byte) 0x8B, (byte) 0x01,
			(byte) 0x18, (byte) 0x23, (byte) 0xDD, (byte) 0x1F,
			(byte) 0x4E, (byte) 0x2D, (byte) 0xF9, (byte) 0x48,
			(byte) 0x4F, (byte) 0xF2, (byte) 0x65, (byte) 0x8E,
			(byte) 0x78, (byte) 0x5C, (byte) 0x58, (byte) 0x19,
			(byte) 0x8D, (byte) 0xE5, (byte) 0x98, (byte) 0x57,
			(byte) 0x67, (byte) 0x7F, (byte) 0x05, (byte) 0x64,
			(byte) 0xAF, (byte) 0x63, (byte) 0xB6, (byte) 0xFE,
			(byte) 0xF5, (byte) 0xB7, (byte) 0x3C, (byte) 0xA5,
			(byte) 0xCE, (byte) 0xE9, (byte) 0x68, (byte) 0x44,
			(byte) 0xE0, (byte) 0x4D, (byte) 0x43, (byte) 0x69,
			(byte) 0x29, (byte) 0x2E, (byte) 0xAC, (byte) 0x15,
			(byte) 0x59, (byte) 0xA8, (byte) 0x0A, (byte) 0x9E,
			(byte) 0x6E, (byte) 0x47, (byte) 0xDF, (byte) 0x34,
			(byte) 0x35, (byte) 0x6A, (byte) 0xCF, (byte) 0xDC,
			(byte) 0x22, (byte) 0xC9, (byte) 0xC0, (byte) 0x9B,
			(byte) 0x89, (byte) 0xD4, (byte) 0xED, (byte) 0xAB,
			(byte) 0x12, (byte) 0xA2, (byte) 0x0D, (byte) 0x52,
			(byte) 0xBB, (byte) 0x02, (byte) 0x2F, (byte) 0xA9,
			(byte) 0xD7, (byte) 0x61, (byte) 0x1E, (byte) 0xB4,
			(byte) 0x50, (byte) 0x04, (byte) 0xF6, (byte) 0xC2,
			(byte) 0x16, (byte) 0x25, (byte) 0x86, (byte) 0x56,
			(byte) 0x55, (byte) 0x09, (byte) 0xBE, (byte) 0x91
                                            //}
		};

        #endregion

        /**
		* Define the fixed p0/p1 permutations used in keyed S-box lookup.
		* By changing the following constant definitions, the S-boxes will
		* automatically Get changed in the Twofish engine.
		*/
        private const int P_00 = 1;
        private const int P_01 = 0;
        private const int P_02 = 0;
        private const int P_03 = P_01 ^ 1;
        private const int P_04 = 1;

        private const int P_10 = 0;
        private const int P_11 = 0;
        private const int P_12 = 1;
        private const int P_13 = P_11 ^ 1;
        private const int P_14 = 0;

        private const int P_20 = 1;
        private const int P_21 = 1;
        private const int P_22 = 0;
        private const int P_23 = P_21 ^ 1;
        private const int P_24 = 0;

        private const int P_30 = 0;
        private const int P_31 = 1;
        private const int P_32 = 1;
        private const int P_33 = P_31 ^ 1;
        private const int P_34 = 1;

        /* Primitive polynomial for GF(256) */
        private const int GF256_FDBK = 0x169;
        private const int GF256_FDBK_2 = GF256_FDBK / 2;
        private const int GF256_FDBK_4 = GF256_FDBK / 4;

        private const int RS_GF_FDBK = 0x14D; // field generator

        //====================================
        // Useful constants
        //====================================

        private const int ROUNDS = 16;
        private const int MAX_ROUNDS = 16;  // bytes = 128 bits
        private const int MAX_KEY_BITS = 256;

        private const int INPUT_WHITEN = 0;
        private const int OUTPUT_WHITEN = INPUT_WHITEN + 16 / 4; // 4
        private const int ROUND_SUBKEYS = OUTPUT_WHITEN + 16 / 4;// 8

        private const int TOTAL_SUBKEYS = ROUND_SUBKEYS + 2 * MAX_ROUNDS;// 40

        private const int SK_STEP = 0x02020202;
        private const int SK_BUMP = 0x01010101;
        private const int SK_ROTL = 9;

        private readonly int[] gMDS0 = new int[MAX_KEY_BITS];
        private readonly int[] gMDS1 = new int[MAX_KEY_BITS];
        private readonly int[] gMDS2 = new int[MAX_KEY_BITS];
        private readonly int[] gMDS3 = new int[MAX_KEY_BITS];

        /**
        * gSubKeys[] and gSBox[] are eventually used in the
        * encryption and decryption methods.
        */
        private int[] gSubKeys;
        private int[] gSBox;

        private int k64Cnt;

        private void SetKey(byte[] key)
        {
            var k32e = new int[MAX_KEY_BITS / 64]; // 4
            var k32o = new int[MAX_KEY_BITS / 64]; // 4

            var sBoxKeys = new int[MAX_KEY_BITS / 64]; // 4
            gSubKeys = new int[TOTAL_SUBKEYS];

            if (k64Cnt < 1)
            {
                throw new ArgumentException("Key size less than 64 bits");
            }

            if (k64Cnt > 4)
            {
                throw new ArgumentException("Key size larger than 256 bits");
            }

            /*
            * k64Cnt is the number of 8 byte blocks (64 chunks)
            * that are in the input key.  The input key is a
            * maximum of 32 bytes ( 256 bits ), so the range
            * for k64Cnt is 1..4
            */
            for (int i = 0; i < k64Cnt; i++)
            {
                var p = i * 8;

                k32e[i] = BytesTo32Bits(key, p);
                k32o[i] = BytesTo32Bits(key, p + 4);

                sBoxKeys[k64Cnt - 1 - i] = RS_MDS_Encode(k32e[i], k32o[i]);
            }

            for (int i = 0; i < TOTAL_SUBKEYS / 2; i++)
            {
                var q = i * SK_STEP;
                var A = F32(q, k32e);
                var B = F32(q + SK_BUMP, k32o);
                B = B << 8 | (int)((uint)B >> 24);
                A += B;
                gSubKeys[i * 2] = A;
                A += B;
                gSubKeys[i * 2 + 1] = A << SK_ROTL | (int)((uint)A >> (32 - SK_ROTL));
            }

            /*
            * fully expand the table for speed
            */
            var k0 = sBoxKeys[0];
            var k1 = sBoxKeys[1];
            var k2 = sBoxKeys[2];
            var k3 = sBoxKeys[3];
            gSBox = new int[4 * MAX_KEY_BITS];
            for (var i = 0; i < MAX_KEY_BITS; i++)
            {
                int b1, b2, b3;
                var b0 = b1 = b2 = b3 = i;
                switch (k64Cnt & 3)
                {
                    case 1:
                        gSBox[i * 2] = gMDS0[(P[P_01 * 256 + b0] & 0xff) ^ M_b0(k0)];
                        gSBox[i * 2 + 1] = gMDS1[(P[P_11 * 256 + b1] & 0xff) ^ M_b1(k0)];
                        gSBox[i * 2 + 0x200] = gMDS2[(P[P_21 * 256 + b2] & 0xff) ^ M_b2(k0)];
                        gSBox[i * 2 + 0x201] = gMDS3[(P[P_31 * 256 + b3] & 0xff) ^ M_b3(k0)];
                        break;
                    case 0: /* 256 bits of key */
                        b0 = (P[P_04 * 256 + b0] & 0xff) ^ M_b0(k3);
                        b1 = (P[P_14 * 256 + b1] & 0xff) ^ M_b1(k3);
                        b2 = (P[P_24 * 256 + b2] & 0xff) ^ M_b2(k3);
                        b3 = (P[P_34 * 256 + b3] & 0xff) ^ M_b3(k3);
                        goto case 3;
                    case 3:
                        b0 = (P[P_03 * 256 + b0] & 0xff) ^ M_b0(k2);
                        b1 = (P[P_13 * 256 + b1] & 0xff) ^ M_b1(k2);
                        b2 = (P[P_23 * 256 + b2] & 0xff) ^ M_b2(k2);
                        b3 = (P[P_33 * 256 + b3] & 0xff) ^ M_b3(k2);
                        goto case 2;
                    case 2:
                        gSBox[i * 2] = gMDS0[(P[P_01 * 256 + (P[P_02 * 256 + b0] & 0xff) ^ M_b0(k1)] & 0xff) ^ M_b0(k0)];
                        gSBox[i * 2 + 1] = gMDS1[(P[P_11 * 256 + (P[P_12 * 256 + b1] & 0xff) ^ M_b1(k1)] & 0xff) ^ M_b1(k0)];
                        gSBox[i * 2 + 0x200] = gMDS2[(P[P_21 * 256 + (P[P_22 * 256 + b2] & 0xff) ^ M_b2(k1)] & 0xff) ^ M_b2(k0)];
                        gSBox[i * 2 + 0x201] = gMDS3[(P[P_31 * 256 + (P[P_32 * 256 + b3] & 0xff) ^ M_b3(k1)] & 0xff) ^ M_b3(k0)];
                        break;
                }
            }

            /*
            * the function exits having setup the gSBox with the
            * input key material.
            */
        }

        /*
        * TODO:  This can be optimised and made cleaner by combining
        * the functionality in this function and applying it appropriately
        * to the creation of the subkeys during key setup.
        */
        private int F32(int x, int[] k32)
        {
            int b0 = M_b0(x);
            int b1 = M_b1(x);
            int b2 = M_b2(x);
            int b3 = M_b3(x);
            int k0 = k32[0];
            int k1 = k32[1];
            int k2 = k32[2];
            int k3 = k32[3];

            int result = 0;
            switch (k64Cnt & 3)
            {
                case 1:
                    result = gMDS0[(P[P_01 * 256 + b0] & 0xff) ^ M_b0(k0)] ^
                             gMDS1[(P[P_11 * 256 + b1] & 0xff) ^ M_b1(k0)] ^
                             gMDS2[(P[P_21 * 256 + b2] & 0xff) ^ M_b2(k0)] ^
                             gMDS3[(P[P_31 * 256 + b3] & 0xff) ^ M_b3(k0)];
                    break;
                case 0: /* 256 bits of key */
                    b0 = (P[P_04 * 256 + b0] & 0xff) ^ M_b0(k3);
                    b1 = (P[P_14 * 256 + b1] & 0xff) ^ M_b1(k3);
                    b2 = (P[P_24 * 256 + b2] & 0xff) ^ M_b2(k3);
                    b3 = (P[P_34 * 256 + b3] & 0xff) ^ M_b3(k3);
                    goto case 3;
                case 3:
                    b0 = (P[P_03 * 256 + b0] & 0xff) ^ M_b0(k2);
                    b1 = (P[P_13 * 256 + b1] & 0xff) ^ M_b1(k2);
                    b2 = (P[P_23 * 256 + b2] & 0xff) ^ M_b2(k2);
                    b3 = (P[P_33 * 256 + b3] & 0xff) ^ M_b3(k2);
                    goto case 2;
                case 2:
                    result =
                    gMDS0[(P[P_01 * 256 + (P[P_02 * 256 + b0] & 0xff) ^ M_b0(k1)] & 0xff) ^ M_b0(k0)] ^
                    gMDS1[(P[P_11 * 256 + (P[P_12 * 256 + b1] & 0xff) ^ M_b1(k1)] & 0xff) ^ M_b1(k0)] ^
                    gMDS2[(P[P_21 * 256 + (P[P_22 * 256 + b2] & 0xff) ^ M_b2(k1)] & 0xff) ^ M_b2(k0)] ^
                    gMDS3[(P[P_31 * 256 + (P[P_32 * 256 + b3] & 0xff) ^ M_b3(k1)] & 0xff) ^ M_b3(k0)];
                    break;
            }
            return result;
        }

        /**
        * Use (12, 8) Reed-Solomon code over GF(256) to produce
        * a key S-box 32-bit entity from 2 key material 32-bit
        * entities.
        *
        * @param    k0 first 32-bit entity
        * @param    k1 second 32-bit entity
        * @return     Remainder polynomial Generated using RS code
        */
        private static int RS_MDS_Encode(int k0, int k1)
        {
            int r = k1;
            // shift 1 byte at a time
            r = RS_rem(r);
            r = RS_rem(r);
            r = RS_rem(r);
            r = RS_rem(r);
            r ^= k0;
            r = RS_rem(r);
            r = RS_rem(r);
            r = RS_rem(r);
            r = RS_rem(r);

            return r;
        }

        /**
        * Reed-Solomon code parameters: (12,8) reversible code:
        * <p>
        * <pre>
        * G(x) = x^4 + (a+1/a)x^3 + ax^2 + (a+1/a)x + 1
        * </pre>
        * where a = primitive root of field generator 0x14D
        * </p>
        */
        private static int RS_rem(int x)
        {
            int b = (int)(((uint)x >> 24) & 0xff);
            int g2 = ((b << 1) ^
                    ((b & 0x80) != 0 ? RS_GF_FDBK : 0)) & 0xff;
            int g3 = ((int)((uint)b >> 1) ^
                    ((b & 0x01) != 0 ? (int)((uint)RS_GF_FDBK >> 1) : 0)) ^ g2;
            return ((x << 8) ^ (g3 << 24) ^ (g2 << 16) ^ (g3 << 8) ^ b);
        }

        private static int LFSR1(int x)
        {
            return (x >> 1) ^
                    (((x & 0x01) != 0) ? GF256_FDBK_2 : 0);
        }

        private static int LFSR2(int x)
        {
            return (x >> 2) ^
                    (((x & 0x02) != 0) ? GF256_FDBK_2 : 0) ^
                    (((x & 0x01) != 0) ? GF256_FDBK_4 : 0);
        }

        private static int Mx_X(int x)
        {
            return x ^ LFSR2(x);
        } // 5B

        private static int Mx_Y(int x)
        {
            return x ^ LFSR1(x) ^ LFSR2(x);
        } // EF

        private static int M_b0(int x)
        {
            return x & 0xff;
        }

        private static int M_b1(int x)
        {
            return (int)((uint)x >> 8) & 0xff;
        }

        private static int M_b2(int x)
        {
            return (int)((uint)x >> 16) & 0xff;
        }

        private static int M_b3(int x)
        {
            return (int)((uint)x >> 24) & 0xff;
        }

        private static int Fe32_0(int[] gSBox1, int x)
        {
            return gSBox1[0x000 + 2 * (x & 0xff)] ^
                gSBox1[0x001 + 2 * ((int)((uint)x >> 8) & 0xff)] ^
                gSBox1[0x200 + 2 * ((int)((uint)x >> 16) & 0xff)] ^
                gSBox1[0x201 + 2 * ((int)((uint)x >> 24) & 0xff)];
        }

        private static int Fe32_3(int[] gSBox1, int x)
        {
            return gSBox1[0x000 + 2 * ((int)((uint)x >> 24) & 0xff)] ^
                gSBox1[0x001 + 2 * (x & 0xff)] ^
                gSBox1[0x200 + 2 * ((int)((uint)x >> 8) & 0xff)] ^
                gSBox1[0x201 + 2 * ((int)((uint)x >> 16) & 0xff)];
        }

        private static int BytesTo32Bits(byte[] b, int p)
        {
            return ((b[p] & 0xff)) |
                ((b[p + 1] & 0xff) << 8) |
                ((b[p + 2] & 0xff) << 16) |
                ((b[p + 3] & 0xff) << 24);
        }

        private static void Bits32ToBytes(int inData, byte[] b, int offset)
        {
            b[offset] = (byte)inData;
            b[offset + 1] = (byte)(inData >> 8);
            b[offset + 2] = (byte)(inData >> 16);
            b[offset + 3] = (byte)(inData >> 24);
        }
    }
}