How would this work without breaking cryptography? The whole point of a good cipher is that the algorithm can be public and widely understood, and all that’s needed for it to be secure is for the private key to be private. A cipher that has some backdoor -master key- is by design insecure and no sane person should use it. Security through obscurity doesn’t work, trying to keep the algorithm private won’t work, someone sooner or later will break it.