This is the same for any piece of crypto. If you've been provided someone else's encryption keys, and they're not either from the person themselves, or from a t

This is the same for any piece of crypto. If you've been provided someone else's encryption keys, and they're not either from the person themselves, or from a trustworthy intermediary, then your channel could be getting intercepted. It's a philosophical/conceptual problem with encryption, not one restricted to signal.