There are two separate Advanced Encryption Standard (AES) Encryption Keys used for Tunneling. One Key is used for encrypting outgoing data and the other Key is used for decrypting incoming data.

These AES Keys are a fixed 16 bytes in length. Any Keys entered that are less than 16 bytes long are padded with zeroes. Key data can be entered in as ASCII, Hexadecimal, Decimal, or a mixture of all three.

Note that the Keys are shared secret keys so they must be known by both sides of the connection and kept secret.

Tunneling using AES Encryption uses a non-standard protocol and because it uses shared keys, it is not very secure. A better, standard based, and more secure alternative is to use Tunneling over SSH.