arvind-newdirs - New Directions in Cryptography Invited...

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New Directions in Cryptography Invited Paper Whitfield Diffie and Martin E. Hellman Abstract Two kinds of contemporary developments in cryp- communications over an insecure channel order to use cryptog- tography 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 compu- tance is a common occurrence in business, however, and it is tation are beginning to provide the tools to solve cryptographic unrealistic to expect initial business contacts to be postponed problems of long standing. 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. Section III proposes two approaches to transmitting keying We stand today on the brink of a revolution in cryptography. information over public (i.e., insecure) channel without compro- The development of cheap digital hardware has freed it from mising the security of the system. In public key cryptosystem the design limitations of mechanical computing and brought enciphering and deciphering are governed by distinct keys, E the cost of high grade cryptographic devices down to where and D, such that computing D from E is computationally infeasi- they can be used in such commercial applications as remote ble (e.g., requiring 10 100 instructions). The enciphering key cash dispensers and computer terminals. In turn, such applica- E can thus be publicly disclosed without compromising the tions create a need for new types of cryptographic systems deciphering key D. Each user of the network can, therefore, which minimize the necessity of secure key distribution chan- place his enciphering key in a public directory. This enables nels and supply the equivalent of a written signature. At the any user of the system to send a message to any other user same time, theoretical developments in information theory and enciphered in such a way that only the intended receiver is computer science show promise of providing provably secure able to decipher it. As such, a public key cryptosystem is cryptosystems, changing this ancient art into a science. multiple access cipher. A private conversation can therefore be
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This note was uploaded on 10/18/2010 for the course MATH CS 301 taught by Professor Aliulger during the Fall '10 term at Koç University.

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arvind-newdirs - New Directions in Cryptography Invited...

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