Works?

    for(int i = 0; i < Length; i++) {
        CurrentByte = (PacketData[i] ^ DwordTableVal) & 0x0FF;
        DwordTableVal = (DwordTableVal >> 8) ^ Table[CurrentByte]; 
        ByteTableVal = ByteTable[(i & 0x0FF)];
        DecryptedData[i] = (ByteTableVal ^ PacketData[i]) ^ DecryptionFlagByte;
	}
}

void Flip4Byte(unsigned char * PacketData, unsigned char * DecryptedData)
{
	int c = 3;
    long * byte;
	byte = new long[4];

    for(int i = 0; i < 4; i++, c--) {
        byte[i] = PacketData[c];
        }

	for(int x = 0; x < 4; x++){ 
		DecryptedData[x] = byte[x]; 
	}
	delete[] byte;
}

void CalculateChecksum(unsigned char * PacketData, unsigned long DwordVal)
{
	int Counter = 0;
	long Byte1, Byte2, Byte3, Byte4; 
	Byte1 = Byte2 = Byte3 = Byte4 = 0;

	DwordVal = ~DwordVal;
	Byte1 = (DwordVal & 0x000000FF); 
	Byte2 = (DwordVal & 0x0000FF00) >> 8; 
	Byte3 = (DwordVal & 0x00FF0000) >> 16;
	Byte4 = (DwordVal & 0xFF000000) >> 24;
	
	PacketData[Counter++] = Byte4;
	PacketData[Counter++] = Byte3;
	PacketData[Counter++] = Byte2;
	PacketData[Counter++] = Byte1;
}

void EncryptData(unsigned char * PacketData, int Length, long FlagByte)
{
	long EncryptedByte = 0; 
	unsigned long DwordTableVal = 0;
	unsigned long DwordVal = 0xFFFFFFFF;
	int Counter = 4;

	for(int i = 0; i < Length; i++) {
		EncryptedByte = ((ByteTable[(Counter & 0x0FF)]) ^ FlagByte) ^ PacketData[Counter]; 
		PacketData[Counter++] = EncryptedByte;
		DwordTableVal = (EncryptedByte ^ DwordVal) & 0x0FF; 
		DwordVal = (DwordVal >> 8) ^ Table[DwordTableVal];
	}
	CalculateChecksum(PacketData, DwordVal);
}

unsigned long Table[] = { 
0x00000000,
0x77073096,
0xEE0E612C,
0x990951BA,
0x076DC419,
0x706AF48F,
0xE963A535,
0x9E6495A3,
0x0EDB8832,
0x79DCB8A4,
0xE0D5E91E,
0x97D2D988,
0x09B64C2B,
0x7EB17CBD,
0xE7B82D07,
0x90BF1D91,
0x1DB71064,
0x6AB020F2,
0xF3B97148,
0x84BE41DE,
0x1ADAD47D,
0x6DDDE4EB,
0xF4D4B551,
0x83D385C7,
0x136C9856,
0x646BA8C0,
0xFD62F97A,
0x8A65C9EC,
0x14015C4F,
0x63066CD9,
0xFA0F3D63,
0x8D080DF5,
0x3B6E20C8,
0x4C69105E,
0xD56041E4,
0xA2677172,
0x3C03E4D1,
0x4B04D447,
0xD20D85FD,
0xA50AB56B,
0x35B5A8FA,
0x42B2986C,
0xDBBBC9D6,
0xACBCF940,
0x32D86CE3,
0x45DF5C75,
0xDCD60DCF,
0xABD13D59,
0x26D930AC,
0x51DE003A,
0xC8D75180,
0xBFD06116,
0x21B4F4B5,
0x56B3C423,
0xCFBA9599,
0xB8BDA50F,
0x2802B89E,
0x5F058808,
0xC60CD9B2,
0xB10BE924,
0x2F6F7C87,
0x58684C11,
0xC1611DAB,
0xB6662D3D,
0x76DC4190,
0x01DB7106,
0x98D220BC,
0xEFD5102A,
0x71B18589,
0x06B6B51F,
0x9FBFE4A5,
0xE8B8D433,
0x7807C9A2,
0x0F00F934,
0x9609A88E,
0xE10E9818,
0x7F6A0DBB,
0x086D3D2D,
0x91646C97,
0xE6635C01,
0x6B6B51F4,
0x1C6C6162,
0x856530D8,
0xF262004E,
0x6C0695ED,
0x1B01A57B,
0x8208F4C1,
0xF50FC457,
0x65B0D9C6,
0x12B7E950,
0x8BBEB8EA,
0xFCB9887C,
0x62DD1DDF,
0x15DA2D49,
0x8CD37CF3,
0xFBD44C65,
0x4DB26158,
0x3AB551CE,
0xA3BC0074,
0xD4BB30E2,
0x4ADFA541,
0x3DD895D7,
0xA4D1C46D,
0xD3D6F4FB,
0x4369E96A,
0x346ED9FC,
0xAD678846,
0xDA60B8D0,
0x44042D73,
0x33031DE5,
0xAA0A4C5F,
0xDD0D7CC9,
0x5005713C,
0x270241AA,
0xBE0B1010,
0xC90C2086,
0x5768B525,
0x206F85B3,
0xB966D409,
0xCE61E49F,
0x5EDEF90E,
0x29D9C998,
0xB0D09822,
0xC7D7A8B4,
0x59B33D17,
0x2EB40D81,
0xB7BD5C3B,
0xC0BA6CAD,
0xEDB88320,
0x9ABFB3B6,
0x03B6E20C,
0x74B1D29A,
0xEAD54739,
0x9DD277AF,
0x04DB2615,
0x73DC1683,
0xE3630B12,
0x94643B84,
0x0D6D6A3E,
0x7A6A5AA8,
0xE40ECF0B,
0x9309FF9D,
0x0A00AE27,
0x7D079EB1,
0xF00F9344,
0x8708A3D2,
0x1E01F268,
0x6906C2FE,
0xF762575D,
0x806567CB,
0x196C3671,
0x6E6B06E7,
0xFED41B76,
0x89D32BE0,
0x10DA7A5A,
0x67DD4ACC,
0xF9B9DF6F,
0x8EBEEFF9,
0x17B7BE43,
0x60B08ED5,
0xD6D6A3E8,
0xA1D1937E,
0x38D8C2C4,
0x4FDFF252,
0xD1BB67F1 ,
0xA6BC5767,
0x3FB506DD,
0x48B2364B,
0xD80D2BDA,
0xAF0A1B4C,
0x36034AF6,
0x41047A60,
0xDF60EFC3,
0xA867DF55,
0x316E8EEF,
0x4669BE79,
0xCB61B38C,
0xBC66831A,
0x256FD2A0,
0x5268E236,
0xCC0C7795,
0xBB0B4703,
0x220216B9,
0x5505262F,
0xC5BA3BBE,
0xB2BD0B28,
0x2BB45A92,
0x5CB36A04,
0xC2D7FFA7,
0xB5D0CF31,
0x2CD99E8B,
0x5BDEAE1D,
0x9B64C2B0,
0xEC63F226,
0x756AA39C,
0x026D930A,
0x9C0906A9,
0xEB0E363F,
0x72076785,
0x05005713,
0x95BF4A82,
0xE2B87A14,
0x7BB12BAE,
0x0CB61B38,
0x92D28E9B,
0xE5D5BE0D,
0x7CDCEFB7,
0x0BDBDF21,
0x86D3D2D4,
0xF1D4E242,
0x68DDB3F8,
0x1FDA836E,
0x81BE16CD,
0xF6B9265B,
0x6FB077E1,
0x18B74777,
0x88085AE6,
0xFF0F6A70,
0x66063BCA,
0x11010B5C,
0x8F659EFF,
0xF862AE69,
0x616BFFD3,
0x166CCF45,
0xA00AE278,
0xD70DD2EE,
0x4E048354,
0x3903B3C2,
0xA7672661 ,
0xD06016F7,
0x4969474D,
0x3E6E77DB,
0xAED16A4A,
0xD9D65ADC,
0x40DF0B66,
0x37D83BF0,
0xA9BCAE53,
0xDEBB9EC5,
0x47B2CF7F,
0x30B5FFE9,
0xBDBDF21C,
0xCABAC28A,
0x53B39330,
0x24B4A3A6,
0xBAD03605,
0xCDD70693,
0x54DE5729,
0x23D967BF,
0xB3667A2E,
0xC4614AB8,
0x5D681B02,
0x2A6F2B94,
0xB40BBE37,
0xC30C8EA1,
0x5A05DF1B,
0x2D02EF8D,
0x00000000,
0x00007325,
0x00A550DC,
0x0044B4E0,
0x00A55124 ,
0x0044B890 
};

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

void Flip4Byte(unsigned char * PacketData, unsigned char * DecryptedData)
{
	int i, c;
	
    for(i = 0, c = 3; i < 4; i++, c--) {
        DecryptedData[i] = PacketData[c];
	}
}


//And
void CalculateChecksum(unsigned char * PacketData, unsigned long DwordVal)
{
	int Counter = 0;
	
	DwordVal = ~DwordVal;
	PacketData[Counter++] = (DwordVal & 0xFF000000) >> 24;
	PacketData[Counter++] = (DwordVal & 0x00FF0000) >> 16;
	PacketData[Counter++] = (DwordVal & 0x0000FF00) >> 8;
	PacketData[Counter] = (DwordVal & 0x000000FF);
}