Public key

A public key cryptosystem is one in which different keys are used to encrypt and decrypt any item. The keys in the pair are termed the 'public' key, and the 'private' key (from their now-common use, in which one key of the pair is widely distributed, and the other is tightly held).

They are now widely used on the Internet, to sign information (e.g. in the Domain Name System), and in other ways (e.g. to securely exchange keys for use with another cryptosystem).

History

The concept of public key cryptography was first invented by James Ellis, then of UK's Government Communications Headquarters, in 1970. He had come up with only the basic idea; another person there, Clifford Cocks, came up with a cryptosystem which implemented it.

However, their ideas were kept classified - a step which did no good, as in 1976, the basic idea was independently rediscovered by Whitfield Diffie and Martin Hellman (who devised a secure method, usable by two remote entities, for creating key pairs, 'at a distance'). Shortly thereafter, in 1977, Ron Rivest, Adi Shamir and Leonard Adleman devised a cryptosystem which implemented the public key idea.