They would need the secret key that only the bridge has, but yes. If someone broke into the server they could impersonate ActivityPub users. That's no different from any site though. Except that Nostr would make it hard or impossible to recover from a breach like that since compromising a key is permanent. 

 🤔 

 ok in reverse. if i have a my nsec on nostr and the bridge emulates an account on mastodon, my nsec on nostr side is always secure right? 

 technically the likelihood of a mastodon person to talk / interact / get data from a nostr person is lesser than than the other way round so as long as my nsec is secure i am fine. i practice safe nsec. hehe 

 Your nsec wouldn’t be compromised. The only risk is to the corresponding ActivityPub ID on the other end. 

 i wonder if we could run a personalized version of mostr bridge? but then i guess, that is what ditto is all about anyway 

 What attack vectors are there where this could happen and how secure is the mostr.pub server? The fact that it’s centralized like this is fairly concerning, ngl. 

 i think all of this concern are probably the reason why alex comes out with ditto, right?