Secret Key Cryptography

Full Title or Meme

In Secret Key Cryptography two parties that wish to communicate have some method for creating pre-shared secrets which can be used to hide subsequent communications from others.

Context

At least since the time of Julius Cesar there have been methods know to hide messages from prying eyes.

Problem

A shared secret is not really a secret any longer as either side gets to decide when to release the key and expose the communications, or allow fraudulent messages to be created, even long in the past.