context: using System;
  
  using Org.BouncyCastle.Crypto.Parameters;
  
  namespace Org.BouncyCastle.Crypto.Engines
  {
      /**
      * an implementation of RC2 as described in RFC 2268
      *      "A Description of the RC2(r) Encryption Algorithm" R. Rivest.
      */
      public class RC2Engine
  		: IBlockCipher
      {
          //
          // the values we use for key expansion (based on the digits of PI)
          //
          private static byte[] piTable =
          {
              (byte)0xd9, (byte)0x78, (byte)0xf9, (byte)0xc4, (byte)0x19, (byte)0xdd, (byte)0xb5, (byte)0xed,
              (byte)0x28, (byte)0xe9, (byte)0xfd, (byte)0x79, (byte)0x4a, (byte)0xa0, (byte)0xd8, (byte)0x9d,
              (byte)0xc6, (byte)0x7e, (byte)0x37, (byte)0x83, (byte)0x2b, (byte)0x76, (byte)0x53, (byte)0x8e,
              (byte)0x62, (byte)0x4c, (byte)0x64, (byte)0x88, (byte)0x44, (byte)0x8b, (byte)0xfb, (byte)0xa2,
              (byte)0x17, (byte)0x9a, (byte)0x59, (byte)0xf5, (byte)0x87, (byte)0xb3, (byte)0x4f, (byte)0x13,
              (byte)0x61, (byte)0x45, (byte)0x6d, (byte)0x8d, (byte)0x9, (byte)0x81, (byte)0x7d, (byte)0x32,
              (byte)0xbd, (byte)0x8f, (byte)0x40, (byte)0xeb, (byte)0x86, (byte)0xb7, (byte)0x7b, (byte)0xb,
              (byte)0xf0, (byte)0x95, (byte)0x21, (byte)0x22, (byte)0x5c, (byte)0x6b, (byte)0x4e, (byte)0x82,
              (byte)0x54, (byte)0xd6, (byte)0x65, (byte)0x93, (byte)0xce, (byte)0x60, (byte)0xb2, (byte)0x1c,
              (byte)0x73, (byte)0x56, (byte)0xc0, (byte)0x14, (byte)0xa7, (byte)0x8c, (byte)0xf1, (byte)0xdc,
              (byte)0x12, (byte)0x75, (byte)0xca, (byte)0x1f, (byte)0x3b, (byte)0xbe, (byte)0xe4, (byte)0xd1,
              (byte)0x42, (byte)0x3d, (byte)0xd4, (byte)0x30, (byte)0xa3, (byte)0x3c, (byte)0xb6, (byte)0x26,
              (byte)0x6f, (byte)0xbf, (byte)0xe, (byte)0xda, (byte)0x46, (byte)0x69, (byte)0x7, (byte)0x57,
              (byte)0x27, (byte)0xf2, (byte)0x1d, (byte)0x9b, (byte)0xbc, (byte)0x94, (byte)0x43, (byte)0x3,
              (byte)0xf8, (byte)0x11, (byte)0xc7, (byte)0xf6, (byte)0x90, (byte)0xef, (byte)0x3e, (byte)0xe7,
              (byte)0x6, (byte)0xc3, (byte)0xd5, (byte)0x2f, (byte)0xc8, (byte)0x66, (byte)0x1e, (byte)0xd7,
              (byte)0x8, (byte)0xe8, (byte)0xea, (byte)0xde, (byte)0x80, (byte)0x52, (byte)0xee, (byte)0xf7,
              (byte)0x84, (byte)0xaa, (byte)0x72, (byte)0xac, (byte)0x35, (byte)0x4d, (byte)0x6a, (byte)0x2a,
              (byte)0x96, (byte)0x1a, (byte)0xd2, (byte)0x71, (byte)0x5a, (byte)0x15, (byte)0x49, (byte)0x74,
              (byte)0x4b, (byte)0x9f, (byte)0xd0, (byte)0x5e, (byte)0x4, (byte)0x18, (byte)0xa4, (byte)0xec,
              (byte)0xc2, (byte)0xe0, (byte)0x41, (byte)0x6e, (byte)0xf, (byte)0x51, (byte)0xcb, (byte)0xcc,
              (byte)0x24, (byte)0x91, (byte)0xaf, (byte)0x50, (byte)0xa1, (byte)0xf4, (byte)0x70, (byte)0x39,
              (byte)0x99, (byte)0x7c, (byte)0x3a, (byte)0x85, (byte)0x23, (byte)0xb8, (byte)0xb4, (byte)0x7a,
              (byte)0xfc, (byte)0x2, (byte)0x36, (byte)0x5b, (byte)0x25, (byte)0x55, (byte)0x97, (byte)0x31,
              (byte)0x2d, (byte)0x5d, (byte)0xfa, (byte)0x98, (byte)0xe3, (byte)0x8a, (byte)0x92, (byte)0xae,
              (byte)0x5, (byte)0xdf, (byte)0x29, (byte)0x10, (byte)0x67, (byte)0x6c, (byte)0xba, (byte)0xc9,
              (byte)0xd3, (byte)0x0, (byte)0xe6, (byte)0xcf, (byte)0xe1, (byte)0x9e, (byte)0xa8, (byte)0x2c,
              (byte)0x63, (byte)0x16, (byte)0x1, (byte)0x3f, (byte)0x58, (byte)0xe2, (byte)0x89, (byte)0xa9,
              (byte)0xd, (byte)0x38, (byte)0x34, (byte)0x1b, (byte)0xab, (byte)0x33, (byte)0xff, (byte)0xb0,
              (byte)0xbb, (byte)0x48, (byte)0xc, (byte)0x5f, (byte)0xb9, (byte)0xb1, (byte)0xcd, (byte)0x2e,
              (byte)0xc5, (byte)0xf3, (byte)0xdb, (byte)0x47, (byte)0xe5, (byte)0xa5, (byte)0x9c, (byte)0x77,
              (byte)0xa, (byte)0xa6, (byte)0x20, (byte)0x68, (byte)0xfe, (byte)0x7f, (byte)0xc1, (byte)0xad
          };
  
          private const int BLOCK_SIZE = 8;
  
          private int[]   workingKey;
          private bool encrypting;
  
          private int[] GenerateWorkingKey(
              byte[]      key,
              int         bits)
          {
              int     x;
              int[]   xKey = new int[128];
  
              for (int i = 0; i != key.Length; i++)
              {
                  xKey[i] = key[i] & 0xff;
              }
  
              // Phase 1: Expand input key to 128 bytes
              int len = key.Length;
  
              if (len < 128)
              {
                  int     index = 0;
  
                  x = xKey[len - 1];
  
                  do
                  {
                      x = piTable[(x + xKey[index++]) & 255] & 0xff;
                      xKey[len++] = x;
                  }
                  while (len < 128);
              }
  
              // Phase 2 - reduce effective key size to "bits"
              len = (bits + 7) >> 3;
              x = piTable[xKey[128 - len] & (255 >> (7 & -bits))] & 0xff;
              xKey[128 - len] = x;
  
              for (int i = 128 - len - 1; i >= 0; i--)
              {
                      x = piTable[x ^ xKey[i + len]] & 0xff;
                      xKey[i] = x;
              }
  
              // Phase 3 - copy to newKey in little-endian order
              int[] newKey = new int[64];
  
              for (int i = 0; i != newKey.Length; i++)
              {
                  newKey[i] = (xKey[2 * i] + (xKey[2 * i + 1] << 8));
              }
  
              return newKey;
          }
  
          /**
          * initialise a RC2 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)
          {
              this.encrypting = forEncryption;
  
  			if (parameters is RC2Parameters)
              {
                  RC2Parameters param = (RC2Parameters) parameters;
  
  				workingKey = GenerateWorkingKey(param.GetKey(), param.EffectiveKeyBits);
              }
              else if (parameters is KeyParameter)
              {
  				KeyParameter param = (KeyParameter) parameters;
  				byte[] key = param.GetKey();
  
  				workingKey = GenerateWorkingKey(key, key.Length * 8);
              }
              else
              {
                  throw new ArgumentException("invalid parameter passed to RC2 init - " + parameters.GetType().Name);
              }
          }
  
  		public void Reset()
          {
          }
  
  		public string AlgorithmName
          {
              get { return "RC2"; }
          }
  
  		public bool IsPartialBlockOkay
  		{
  			get { return false; }
  		}
  
  		public int GetBlockSize()
          {
              return BLOCK_SIZE;
          }
  
          public  int ProcessBlock(
              byte[]	input,
              int		inOff,
              byte[]	output,
              int		outOff)
          {
              if (workingKey == null)
                  throw new InvalidOperationException("RC2 engine 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;
          }
  
          /**
          * return the result rotating the 16 bit number in x left by y
          */
          private int RotateWordLeft(
              int x,
              int y)
          {
              x &= 0xffff;
              return (x << y) | (x >> (16 - y));
          }
  
          private void EncryptBlock(
              byte[]  input,
              int     inOff,
              byte[]  outBytes,
              int     outOff)
          {
              int x76, x54, x32, x10;
  
              x76 = ((input[inOff + 7] & 0xff) << 8) + (input[inOff + 6] & 0xff);
              x54 = ((input[inOff + 5] & 0xff) << 8) + (input[inOff + 4] & 0xff);
              x32 = ((input[inOff + 3] & 0xff) << 8) + (input[inOff + 2] & 0xff);
              x10 = ((input[inOff + 1] & 0xff) << 8) + (input[inOff + 0] & 0xff);
  
              for (int i = 0; i <= 16; i += 4)
              {
                      x10 = RotateWordLeft(x10 + (x32 & ~x76) + (x54 & x76) + workingKey[i  ], 1);
                      x32 = RotateWordLeft(x32 + (x54 & ~x10) + (x76 & x10) + workingKey[i+1], 2);
                      x54 = RotateWordLeft(x54 + (x76 & ~x32) + (x10 & x32) + workingKey[i+2], 3);
                      x76 = RotateWordLeft(x76 + (x10 & ~x54) + (x32 & x54) + workingKey[i+3], 5);
              }
  
              x10 += workingKey[x76 & 63];
              x32 += workingKey[x10 & 63];
              x54 += workingKey[x32 & 63];
              x76 += workingKey[x54 & 63];
  
              for (int i = 20; i <= 40; i += 4)
              {
                      x10 = RotateWordLeft(x10 + (x32 & ~x76) + (x54 & x76) + workingKey[i  ], 1);
                      x32 = RotateWordLeft(x32 + (x54 & ~x10) + (x76 & x10) + workingKey[i+1], 2);
                      x54 = RotateWordLeft(x54 + (x76 & ~x32) + (x10 & x32) + workingKey[i+2], 3);
                      x76 = RotateWordLeft(x76 + (x10 & ~x54) + (x32 & x54) + workingKey[i+3], 5);
              }
  
              x10 += workingKey[x76 & 63];
              x32 += workingKey[x10 & 63];
              x54 += workingKey[x32 & 63];
              x76 += workingKey[x54 & 63];
  
              for (int i = 44; i < 64; i += 4)
              {
                      x10 = RotateWordLeft(x10 + (x32 & ~x76) + (x54 & x76) + workingKey[i  ], 1);
                      x32 = RotateWordLeft(x32 + (x54 & ~x10) + (x76 & x10) + workingKey[i+1], 2);
                      x54 = RotateWordLeft(x54 + (x76 & ~x32) + (x10 & x32) + workingKey[i+2], 3);
                      x76 = RotateWordLeft(x76 + (x10 & ~x54) + (x32 & x54) + workingKey[i+3], 5);
              }
  
              outBytes[outOff + 0] = (byte)x10;
              outBytes[outOff + 1] = (byte)(x10 >> 8);
              outBytes[outOff + 2] = (byte)x32;
              outBytes[outOff + 3] = (byte)(x32 >> 8);
              outBytes[outOff + 4] = (byte)x54;
              outBytes[outOff + 5] = (byte)(x54 >> 8);
              outBytes[outOff + 6] = (byte)x76;
              outBytes[outOff + 7] = (byte)(x76 >> 8);
          }
  
          private void DecryptBlock(
              byte[]  input,
              int     inOff,
              byte[]  outBytes,
              int     outOff)
          {
              int x76, x54, x32, x10;
  
              x76 = ((input[inOff + 7] & 0xff) << 8) + (input[inOff + 6] & 0xff);
              x54 = ((input[inOff + 5] & 0xff) << 8) + (input[inOff + 4] & 0xff);
              x32 = ((input[inOff + 3] & 0xff) << 8) + (input[inOff + 2] & 0xff);
              x10 = ((input[inOff + 1] & 0xff) << 8) + (input[inOff + 0] & 0xff);
  
              for (int i = 60; i >= 44; i -= 4)
              {
                  x76 = RotateWordLeft(x76, 11) - ((x10 & ~x54) + (x32 & x54) + workingKey[i+3]);
                  x54 = RotateWordLeft(x54, 13) - ((x76 & ~x32) + (x10 & x32) + workingKey[i+2]);
                  x32 = RotateWordLeft(x32, 14) - ((x54 & ~x10) + (x76 & x10) + workingKey[i+1]);
                  x10 = RotateWordLeft(x10, 15) - ((x32 & ~x76) + (x54 & x76) + workingKey[i  ]);
              }
  
              x76 -= workingKey[x54 & 63];
              x54 -= workingKey[x32 & 63];
              x32 -= workingKey[x10 & 63];
  
gt:             x10 -= workingKey[x76 & 63];