The Carnac protocol - or how to read the contents of a sealed envelope

Johnny Carson as long time host of the Tonight show often appeared in the spoof role of Carnac the Magni cent, a mentalist who could magically read the contents of a sealed envelope. This is in fact a well known stock-in-trade trick of the mentalist's craft, known as billet reading . Here we propose a cryptographic solution to the problem of billet reading, apparently allowing a ciphertext to be decrypted without direct knowledge of the ciphertext, and present both a compelling use case and a practical implementation.