private byte[] GetSecondSubKey(byte[] key)
        {
            var firstSubKey = GetFirstSubKey(key);
            var a           = (byte)(firstSubKey[0] ^ 0b10000000);
            var c           = Aes16Helper.RotNib(firstSubKey[1]);
            var b           = Aes16Helper.SubNib(c);
            var firstByte   = (byte)(a ^ b);
            var secondByte  = (byte)(firstByte ^ firstSubKey[1]);

            return(new[] { firstByte, secondByte });
        }
        private byte[] GetThirdSubKey(byte[] key)
        {
            var secondSubKey = GetSecondSubKey(key);
            var firstByte    = (byte)(secondSubKey[0] ^ 0b00110000 ^ Aes16Helper.SubNib(Aes16Helper.RotNib(secondSubKey[1])));
            var secondByte   = (byte)(firstByte ^ secondSubKey[1]);

            return(new[] { firstByte, secondByte });
        }