[Blink]

AES seems kind of stupid for a communications protocol. You have to transmit the key at some point, which automatically defeats the encryption. public-key crypto best fits this sort of thing.

On top of that, if you're *really* paranoid, and since you need to transfer a key safely anyway, use One Time Pad encryption, since it's uncrackable (no joke, it's mathematically impossible to crack). You need a good source of random data (radio noise works, or /dev/urandom), and you need a large pad so you won't run out of data for message encryption, and you meed a secure way to transfer the pad (MicroSD, inside of some random object, given in person).