using System;

using Org.BouncyCastle.Crypto.Parameters;

namespace Org.BouncyCastle.Crypto.Engines
{
    /**
    * a class that provides a basic SKIPJACK engine.
    */
    public class SkipjackEngine
		: IBlockCipher
    {
        const int BLOCK_SIZE = 8;

        static readonly short [] ftable =
        {
            0xa3, 0xd7, 0x09, 0x83, 0xf8, 0x48, 0xf6, 0xf4, 0xb3, 0x21, 0x15, 0x78, 0x99, 0xb1, 0xaf, 0xf9,
            0xe7, 0x2d, 0x4d, 0x8a, 0xce, 0x4c, 0xca, 0x2e, 0x52, 0x95, 0xd9, 0x1e, 0x4e, 0x38, 0x44, 0x28,
            0x0a, 0xdf, 0x02, 0xa0, 0x17, 0xf1, 0x60, 0x68, 0x12, 0xb7, 0x7a, 0xc3, 0xe9, 0xfa, 0x3d, 0x53,
            0x96, 0x84, 0x6b, 0xba, 0xf2, 0x63, 0x9a, 0x19, 0x7c, 0xae, 0xe5, 0xf5, 0xf7, 0x16, 0x6a, 0xa2,
            0x39, 0xb6, 0x7b, 0x0f, 0xc1, 0x93, 0x81, 0x1b, 0xee, 0xb4, 0x1a, 0xea, 0xd0, 0x91, 0x2f, 0xb8,
            0x55, 0xb9, 0xda, 0x85, 0x3f, 0x41, 0xbf, 0xe0, 0x5a, 0x58, 0x80, 0x5f, 0x66, 0x0b, 0xd8, 0x90,
            0x35, 0xd5, 0xc0, 0xa7, 0x33, 0x06, 0x65, 0x69, 0x45, 0x00, 0x94, 0x56, 0x6d, 0x98, 0x9b, 0x76,
            0x97, 0xfc, 0xb2, 0xc2, 0xb0, 0xfe, 0xdb, 0x20, 0xe1, 0xeb, 0xd6, 0xe4, 0xdd, 0x47, 0x4a, 0x1d,
            0x42, 0xed, 0x9e, 0x6e, 0x49, 0x3c, 0xcd, 0x43, 0x27, 0xd2, 0x07, 0xd4, 0xde, 0xc7, 0x67, 0x18,
            0x89, 0xcb, 0x30, 0x1f, 0x8d, 0xc6, 0x8f, 0xaa, 0xc8, 0x74, 0xdc, 0xc9, 0x5d, 0x5c, 0x31, 0xa4,
            0x70, 0x88, 0x61, 0x2c, 0x9f, 0x0d, 0x2b, 0x87, 0x50, 0x82, 0x54, 0x64, 0x26, 0x7d, 0x03, 0x40,
            0x34, 0x4b, 0x1c, 0x73, 0xd1, 0xc4, 0xfd, 0x3b, 0xcc, 0xfb, 0x7f, 0xab, 0xe6, 0x3e, 0x5b, 0xa5,
            0xad, 0x04, 0x23, 0x9c, 0x14, 0x51, 0x22, 0xf0, 0x29, 0x79, 0x71, 0x7e, 0xff, 0x8c, 0x0e, 0xe2,
            0x0c, 0xef, 0xbc, 0x72, 0x75, 0x6f, 0x37, 0xa1, 0xec, 0xd3, 0x8e, 0x62, 0x8b, 0x86, 0x10, 0xe8,
            0x08, 0x77, 0x11, 0xbe, 0x92, 0x4f, 0x24, 0xc5, 0x32, 0x36, 0x9d, 0xcf, 0xf3, 0xa6, 0xbb, 0xac,
            0x5e, 0x6c, 0xa9, 0x13, 0x57, 0x25, 0xb5, 0xe3, 0xbd, 0xa8, 0x3a, 0x01, 0x05, 0x59, 0x2a, 0x46
        };

        private int[] key0, key1, key2, key3;
        private bool encrypting;

        /**
        * initialise a SKIPJACK 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 SKIPJACK init - " + parameters.GetType().ToString());

			byte[] keyBytes = ((KeyParameter)parameters).GetKey();

            this.encrypting = forEncryption;
            this.key0 = new int[32];
            this.key1 = new int[32];
            this.key2 = new int[32];
            this.key3 = new int[32];

            //
            // expand the key to 128 bytes in 4 parts (saving us a modulo, multiply
            // and an addition).
            //
            for (int i = 0; i < 32; i ++)
            {
                key0[i] = keyBytes[(i * 4) % 10] & 0xff;
                key1[i] = keyBytes[(i * 4 + 1) % 10] & 0xff;
                key2[i] = keyBytes[(i * 4 + 2) % 10] & 0xff;
                key3[i] = keyBytes[(i * 4 + 3) % 10] & 0xff;
            }
        }

        public string AlgorithmName
        {
            get { return "SKIPJACK"; }
        }

		public bool IsPartialBlockOkay
		{
			get { return false; }
		}

		public int GetBlockSize()
        {
            return BLOCK_SIZE;
        }

        public int ProcessBlock(
            byte[]	input,
            int		inOff,
            byte[]	output,
            int		outOff)
        {
            if (key1 == null)
                throw new InvalidOperationException("SKIPJACK 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;
        }

		public void Reset()
        {
        }

        /**
        * The G permutation
        */
        private int G(
            int     k,
            int     w)
        {
            int g1, g2, g3, g4, g5, g6;

            g1 = (w >> 8) & 0xff;
            g2 = w & 0xff;

            g3 = ftable[g2 ^ key0[k]] ^ g1;
            g4 = ftable[g3 ^ key1[k]] ^ g2;
            g5 = ftable[g4 ^ key2[k]] ^ g3;
            g6 = ftable[g5 ^ key3[k]] ^ g4;

            return ((g5 << 8) + g6);
        }

        public int EncryptBlock(
            byte[]      input,
            int         inOff,
            byte[]      outBytes,
            int         outOff)
        {
            int w1 = (input[inOff + 0] << 8) + (input[inOff + 1] & 0xff);
            int w2 = (input[inOff + 2] << 8) + (input[inOff + 3] & 0xff);
            int w3 = (input[inOff + 4] << 8) + (input[inOff + 5] & 0xff);
            int w4 = (input[inOff + 6] << 8) + (input[inOff + 7] & 0xff);

            int k = 0;

            for (int t = 0; t < 2; t++)
            {
                for(int i = 0; i < 8; i++)
                {
                    int tmp = w4;
                    w4 = w3;
                    w3 = w2;
                    w2 = G(k, w1);
                    w1 = w2 ^ tmp ^ (k + 1);
                    k++;
                }

                for(int i = 0; i < 8; i++)
                {
                    int tmp = w4;
                    w4 = w3;
                    w3 = w1 ^ w2 ^ (k + 1);
                    w2 = G(k, w1);
                    w1 = tmp;
                    k++;
                }
            }

            outBytes[outOff + 0] = (byte)((w1 >> 8));
            outBytes[outOff + 1] = (byte)(w1);
            outBytes[outOff + 2] = (byte)((w2 >> 8));
            outBytes[outOff + 3] = (byte)(w2);
            outBytes[outOff + 4] = (byte)((w3 >> 8));
            outBytes[outOff + 5] = (byte)(w3);
            outBytes[outOff + 6] = (byte)((w4 >> 8));
            outBytes[outOff + 7] = (byte)(w4);

            return BLOCK_SIZE;
        }

        /**
        * the inverse of the G permutation.
        */
        private int H(
            int     k,
            int     w)
        {
            int h1, h2, h3, h4, h5, h6;

            h1 = w & 0xff;
            h2 = (w >> 8) & 0xff;

            h3 = ftable[h2 ^ key3[k]] ^ h1;
            h4 = ftable[h3 ^ key2[k]] ^ h2;
            h5 = ftable[h4 ^ key1[k]] ^ h3;
            h6 = ftable[h5 ^ key0[k]] ^ h4;

            return ((h6 << 8) + h5);
        }

        public int DecryptBlock(
            byte[]      input,
            int         inOff,
            byte[]      outBytes,
            int         outOff)
        {
            int w2 = (input[inOff + 0] << 8) + (input[inOff + 1] & 0xff);
            int w1 = (input[inOff + 2] << 8) + (input[inOff + 3] & 0xff);
            int w4 = (input[inOff + 4] << 8) + (input[inOff + 5] & 0xff);
            int w3 = (input[inOff + 6] << 8) + (input[inOff + 7] & 0xff);

            int k = 31;

            for (int t = 0; t < 2; t++)
            {
                for(int i = 0; i < 8; i++)
                {
                    int tmp = w4;
                    w4 = w3;
                    w3 = w2;
                    w2 = H(k, w1);
                    w1 = w2 ^ tmp ^ (k + 1);
                    k--;
                }

                for(int i = 0; i < 8; i++)
                {
                    int tmp = w4;
                    w4 = w3;
                    w3 = w1 ^ w2 ^ (k + 1);
                    w2 = H(k, w1);
                    w1 = tmp;
                    k--;
                }
            }

            outBytes[outOff + 0] = (byte)((w2 >> 8));
            outBytes[outOff + 1] = (byte)(w2);
            outBytes[outOff + 2] = (byte)((w1 >> 8));
            outBytes[outOff + 3] = (byte)(w1);
            outBytes[outOff + 4] = (byte)((w4 >> 8));
            outBytes[outOff + 5] = (byte)(w4);
            outBytes[outOff + 6] = (byte)((w3 >> 8));
            outBytes[outOff + 7] = (byte)(w3);

            return BLOCK_SIZE;
        }
    }

}
