<- Virtual Exhibitions in Informatics

Public-Key Cryptography

A important work in the field of public-key cryptography was made by Whitfield Diffie, Martin Hellman and Ralph Merkle. In Summer 1975 Diffie and Hellman published the new idea of a public-key cryptosystem. The main difference to symmetric systems is, that two keys are needed. A private (secret) key and a public key. The public key should be used for encryption, while the private key (only known to one person) is used to decrypt the messages.

The idea of a public-key cryptosystem was born, but Diffie, Hellman and Merkle had not found a method, which could work in a public-key system. They called such function, which was easy to compute in one direction, but hard to compute in the other, trapdoor or one-way functions. And so the hunt for such a function has begun.

In 1969 James Ellis, staff member at GCHQ in the UK, had the same ideas but was not allowed to publicate his knowledge because his work was classified as top secret.

Whitfield Diffie


Bailey Whitfield 'Whit' Diffie (born June 5, 1944) is a US cryptographer and one of the pioneers of public-key cryptography.

He received a Bachelor of Science degree in mathematics from the Massachusetts Institute of Technology in 1965.

Diffie and Martin Hellman's paper New Directions in Cryptography was published in 1976. It introduced a radically new method of distributing cryptographic keys, which went far toward solving one of the fundamental problems of cryptography, key distribution. It has become known as Diffie-Hellman key exchange.

In 1991 he joined Sun Microsystems' SunLabs-West research facility (in Mountain View, California) as a Distinguished Engineer, working primarily on public policy aspects of cryptography. As of January 2004 Diffie remains with Sun, serving as its Chief Security Officer, and as a Vice President and Sun Fellow.

Martin Hellman


Martin E. Hellman (born October 2, 1945) is a cryptologist, famous for his invention of public key cryptography in cooperation with Whitfield Diffie and Ralph Merkle.

He earned his Bachelor's degree from New York University in 1966, and at Stanford University he earned a Master's degree in 1967 and a Ph.D. in 1969, all in electrical engineering.

From 1968-1969 he worked at IBM's Watson Research Center where he encountered Horst Feistel. From 1969-1971 he was an assistant professor at MIT. He return to Stanford in 1971, becoming Professor Emeritus in 1996, although he has now retired from research and most of his university activities.

Further Links