context: using System;
  
  using Org.BouncyCastle.Crypto.Parameters;
  
  namespace Org.BouncyCastle.Crypto.Engines
  {
      /**
      * A class that provides Twofish encryption operations.
      *
      * This Java implementation is based on the Java reference
      * implementation provided by Bruce Schneier and developed
      * by Raif S. Naffah.
      */
      public sealed class TwofishEngine
  		: IBlockCipher
      {
          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  }
          };
  
          /**
          * 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    BLOCK_SIZE = 16;  // bytes = 128 bits
          private const int    MAX_KEY_BITS = 256;
  
          private const int    INPUT_WHITEN=0;
          private const int    OUTPUT_WHITEN=INPUT_WHITEN+BLOCK_SIZE/4; // 4
          private const int    ROUND_SUBKEYS=OUTPUT_WHITEN+BLOCK_SIZE/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 bool encrypting;
  
          private int[] gMDS0 = new int[MAX_KEY_BITS];
          private int[] gMDS1 = new int[MAX_KEY_BITS];
          private int[] gMDS2 = new int[MAX_KEY_BITS];
          private 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 byte[] workingKey;
  
          public TwofishEngine()
          {
              // calculate the MDS matrix
              int[] m1 = new int[2];
              int[] mX = new int[2];
              int[] mY = new int[2];
              int j;
  
              for (int i=0; i< MAX_KEY_BITS ; i++)
              {
                  j = P[0,i] & 0xff;
                  m1[0] = j;
                  mX[0] = Mx_X(j) & 0xff;
                  mY[0] = Mx_Y(j) & 0xff;
  
                  j = P[1,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;
              }
          }
  
          /**
          * initialise a Twofish cipher.
          *
          * @param forEncryption whether or not we are for encryption.
          * @param parameters the parameters required to set up the cipher.
          * @exception ArgumentException if the parameters argument is
          * inappropriate.
          */
          public void Init(
              bool              forEncryption,
              ICipherParameters parameters)
          {
              if (!(parameters is KeyParameter))
  				throw new ArgumentException("invalid parameter passed to Twofish init - " + parameters.GetType().ToString());
  
  			this.encrypting = forEncryption;
  			this.workingKey = ((KeyParameter)parameters).GetKey();
  			this.k64Cnt = (this.workingKey.Length / 8); // pre-padded ?
  			SetKey(this.workingKey);
          }
  
  		public string AlgorithmName
          {
              get { return "Twofish"; }
          }
  
  		public bool IsPartialBlockOkay
  		{
  			get { return false; }
  		}
  
  		public int ProcessBlock(
              byte[]	input,
              int		inOff,
              byte[]	output,
              int		outOff)
          {
              if (workingKey == null)
                  throw new InvalidOperationException("Twofish not initialised");
              if ((inOff + BLOCK_SIZE) > input.Length)
                  throw new DataLengthException("input buffer too short");
              if ((outOff + BLOCK_SIZE) > output.Length)
                  throw new DataLengthException("output buffer too short");
  
  			if (encrypting)
              {
                  EncryptBlock(input, inOff, output, outOff);
              }
              else
              {
                  DecryptBlock(input, inOff, output, outOff);
              }
  
              return BLOCK_SIZE;
          }
  
          public void Reset()
          {
              if (this.workingKey != null)
              {
                  SetKey(this.workingKey);
              }
          }
  
          public int GetBlockSize()
          {
              return BLOCK_SIZE;
          }
  
          //==================================
          // Private Implementation
          //==================================
  
          private void SetKey(byte[] key)
          {
              int[] k32e = new int[MAX_KEY_BITS/64]; // 4
              int[] k32o = new int[MAX_KEY_BITS/64]; // 4
  
              int[] 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,p=0; i<k64Cnt ; i++)
              {
                  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]);
              }
  
              int q,A,B;
              for (int i=0; i < TOTAL_SUBKEYS / 2 ; i++)
              {
                  q = i*SK_STEP;
                  A = F32(q,         k32e);
                  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
              */
              int k0 = sBoxKeys[0];
              int k1 = sBoxKeys[1];
              int k2 = sBoxKeys[2];
              int k3 = sBoxKeys[3];
              int b0, b1, b2, b3;
              gSBox = new int[4*MAX_KEY_BITS];
              for (int i=0; i<MAX_KEY_BITS; i++)
              {
                  b0 = b1 = b2 = b3 = i;
                  switch (k64Cnt & 3)
                  {
                      case 1:
                          gSBox[i*2]       = gMDS0[(P[P_01,b0] & 0xff) ^ M_b0(k0)];
                          gSBox[i*2+1]     = gMDS1[(P[P_11,b1] & 0xff) ^ M_b1(k0)];
                          gSBox[i*2+0x200] = gMDS2[(P[P_21,b2] & 0xff) ^ M_b2(k0)];
                          gSBox[i*2+0x201] = gMDS3[(P[P_31,b3] & 0xff) ^ M_b3(k0)];
                      break;
                      case 0: // 256 bits of key
  
gt:                         b0 = (P[P_04,b0] & 0xff) ^ M_b0(k3);