Abstract Two kinds of contemporary developments in cryp- communications over an insecure channel order to use cryptogtography are examined. Widening applications of teleprocess- raphy to insure privacy, however, it currently necessary for the ing have given rise to a need for new types of cryptographic communicating parties to share a key which is known to no systems, which minimize the need for secure key distribution one else. This is done by sending the key in advance over some channels and supply the equivalent of a written signature. This secure channel such a private courier or registered mail. A paper suggests ways to solve these currently open problems. private conversation between two people with no prior acquain-It also discusses how the theories of communication and computation are beginning to provide the tools to solve cryptographic problems of long standing. tance is a common occurrence in business, however, and it is unrealistic to expect initial business contacts to be postponed long enough for keys to be transmitted by some physical means. The cost and delay imposed by this key distribution problem is a major barrier to the transfer of business communications 1 INTRODUCTION to large teleprocessing networks.