I had an idea about my device: offer plans to build it yourself. Buy your components, and build it. Reading about Anom today makes me upset that simple multiplication on a device could have prevented all this. Seeing also that so much money is put into security... I don't understand why nobody has built such thing yet.
My device has the convenience to work immediately with no previous data/key shared between the protagonists, with an en/decryption key by key (you can chat live and decrypt any word real time). But a scheme with shared data/key and the whole message encrypted and  then decrypted is much simpler to realize and as safe (just less cool)