I'm designing an identity-less, ephemeral messaging protocol where messages can be forged after-the-fact. The goal is protection against coercion or device seizure scenarios.

Core mechanism:

• Session keys derived via SPAKE2 from shared secret
• ChaCha20 encryption with deterministic nonces: sequence || timestamp
• HMAC authentication during conversation

Forgery capability: Anyone with session keys can create alternative messages using the same sequence/timestamp that decrypt to different content.

My question: Does this actually achieve cryptographic deniability? Are there ways someone could distinguish a real conversation transcript from a forged one?

I have a working prototype and want to validate that the approach is sound.

Edit: I totally meant to post this in a cryptography community, not cryptocurrency, haha. Sorry!

i’ve been working on this for a bit, finally got a proof of concept worked out with a desktop app. would love some feedback, mostly on the concept and protocol.

it hasn’t been security audited so don’t use it for anything crazy.

i started a (very niche) private messaging protocol & little CLI app demo. i’m no security expert, so any feedback or questions would be appreciated.

the gist is an ephemeral message exchange without identities. the goal is ultimate deniability.

the interesting (and weird) part is that messages are encrypted but not authenticated. this means an imposter could show up if they know the shared secret. otoh this means you can deny anything you say.