New directions in cryptography. (English) Zbl 0435.94018

The authors discuss some of the recent results in communications theory that have arisen out of the need for security in the key distribution channels. They concentrate on the use of ciphers to restrict the extraction of information from a communication over an insecure. As is well known, the transmission and distribution is then likely to become a problem, in efficiency if not in security. The authors suggest various possible approaches to avoid these further problems that arise. The first they call a “public key distribution system”, which has the feature that an unauthorized “eavesdropper” will find it computationally infeasible to decipher the message since the enciphering and deciphering are governed by distinct keys. They propose a couple of techniques for implementing the system, but the reviewer was unconvinced. A further system is designed to treat a problem that arises in business transactions, that of transmitting a legally valid signature whose authenticity can be checked by anyone; this necessitates the signature’s being message-dependent. Finally, they treat the problem of “trap-doors” (a trap-door cipher is one that strongly resists decipherment by anyone unauthorized and not in possession of particular information used in the design of the cipher) and relate their concerns to various questions that arise in problems of computational complexity.


94A60 Cryptography
68Q25 Analysis of algorithms and problem complexity
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