Code:
List<Byte> Pt_split(string plain)
        {
            List<Byte> pb = new List<Byte>();
            // Byte p;
            string p;
            int temp = 0;
            if (plain.Length % 2 != 0)
                plain = '0' + plain;

            for (int i = 0; i < plain.Length / 2; i++)
            {
                p = plain.Substring(temp, 2);
...