OK I have a probably naive cryptography question. It seems that one good way of transmitting secrets would be to do so with everyone thinking they are encrypted one way (or possibly not at all) when the truth is they are encrypted another way. I.e. a difficult problem to know when the message has been unencrypted. So basically there would be multiple ways to read the message which are plausible as the true unencrypted message. Is there any parallel to that sort of thing in modern cryptography?