CSABlockDecryptor.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace CSA
{
    class CSABlockDecryptor
    {
        private byte[] _data;

        private const int _DVBCSA_KEYSBUFF_SIZE = 56;
        private const uint _DVBCSA_CWBITS_SIZE = 64;
        private const uint _DVBCSA_DATA_SIZE = 8;

        private CSAKeyStruct _ks;
        private int _len;

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


        public CSABlockDecryptor(CSAKeyStruct ks, byte[] data_in, int len)
        {
            _data = data_in;

            _ks = ks;

            _len = len;
        }

        public void CSABlockDecrypt(int startOffset)
        {
            int i = _DVBCSA_KEYSBUFF_SIZE - 1;

            while (i >= 0)
            {
                byte L;
                byte S;

                S = _dvbcsa_block_sbox[_ks.sch[i] ^ _data[startOffset + 6]];

                L = (byte)(_data[startOffset + 7] ^ S);

                _data[startOffset + 7] = _data[startOffset + 6];
                _data[startOffset + 6] = (byte)(_data[startOffset + 5] ^ _csa_block_perm[S]);
                _data[startOffset + 5] = _data[startOffset + 4];
                _data[startOffset + 4] = (byte)(_data[startOffset + 3] ^ L);
                _data[startOffset + 3] = (byte)(_data[startOffset + 2] ^ L);
                _data[startOffset + 2] = (byte)(_data[startOffset + 1] ^ L);
                _data[startOffset + 1] = _data[startOffset + 0];

                _data[startOffset + 0] = L;

                i--;
            }
        }


        public void CSAXor64(int offset)
        {
            int i;

            for (i = 0; i < 8; i++)
                _data[offset + i - 8] ^= _data[offset + i];
        }
    }
}