Signing/encryption with arbitrary keypair

[MichaelMure]

Just a note on the subject:

It would be neat to have the pubsub support signing/encryption with arbitrary keys and not only the node keys.

My usecase is a web-of-trust of identities. The user generate a keypair and sign/encrypt for other identity keypairs. If the pubsub support arbitrary keypair it's easier for me to check that a message come from the good sender.