sure!

during or after a conversation, anyone with the keys can create fake transcripts by creating messages with the same metadata, same nonce, different content.

because of this, no transcript can be proven to be the correct transcript. the trade-off is you don’t get forward secrecy on the per-message level, but you get it per-conversation.

another detail is that there is no identity, so all the above aside, there’s also no way to prove who sent which message.

ooh, i’ll have to think through it, but it sounds like that’d add message integrity without sacrificing deniability. also wouldn’t be much to add. appreciate the feedback!

you’re not wrong, but that’s just the trade off that has to be made, i think. it’s the only way i can think to do it, at least. need -some- authentication for practical usability.

your gpg example removes the deniability since it proves who wrote the message.

interesting point! i chose symmetric shared key because it means you can’t prove who sent what message.

the shared secret does add some authentication, which i think is necessary. the goal is it only creates enough to be practical (a random person can’t eavesdrop), but not enough to prove things. messages themselves still aren’t authenticated by any one person.

also, i’m new to lemmy, so if there are any communities i should cross post this to that may be interested, please let me know!