Are there standards for public keys?

[benpate]

The answer may just be "yes" which would make this a short-lived issue, but here's the dilemma:

The very first hurdle in federating with any other app is negotiating and validating keys. But, it seems like different apps support varying encoding/encryption algorithms.

Is it possible, and is there any value in trying to document this along with the ActivityPub actions that an app supports?