<<One of our customer is interested in the Firebird 3 feature of a "over the wire" connection encryption. This customer however prefers the AES-protocol instead of the default plug in with arc4.
I searched over the internet but I could not find any AES plugin (I could finally it only for encryption of database but not connection).
Does anynow knows if a 3rd party offers an AES plugin?>>

As far as I am aware the only current commercially available plugins for Firebird are for encryption.
If your customer is interested in such a plugin, we could probably develop one for them.

Regards
Paul