Question: W. Diffie and M. E. Hellman. "New Directions in Cryptography."/EEE Transactions on Information Theory IT-22 (November 1976). The paper that laid the theoretical groundwork for the so-called public key encryption schemes. As explained in the body of the chapter, ordinary encryption schemes such as the DES [15.3] require the encryption key to be kept secret. By contrast, the public key schemes use two different keys, one for encryption and one for decryption, and only the decryption key need be kept secret (and it is not possible to deduce the decryption key from the encryption key). In such schemes, therefore, anyone can generate encrypted messages, but no one-not even the message originator-is able to decrypt those messages except their intended recipient.