Also, ZuccNet is using RSA-2048-OAEP to encrypt each message: https://github.com/tomquirk/zuccnet/blob/master/src/util/cry...

This is not forward secure. It will also only work for messages under 256 bytes. I don't know what happens in this code if you exceed that message length.

You want to use ephemeral session keys here. Read the Secret Conversations whitepaper as an example.