Diffie, Bailey Whitfield

Diffie, Bailey Whitfield

(1944–  ) American

Mathematician, Computer Scientist

Bailey Whitfield Diffie created the system of public key cryptography that many computer users depend on today to protect their sensitive information (see encryption).

Diffie was born on June 5, 1944, in the borough of Queens, New York City. As a youngster he read about secret codes and became fascinated. Although he was an indiffer-ent high school student who barely qualified for graduation, Diffie scored so high on standardized tests that he won admission to the University of California, Berkeley, in 1962, where he studied mathematics for two years. However, in 1964 he transferred to the Massachusetts Institute of Tech-nology (MIT) and obtained his B.S. in mathematics in 1965.

After graduation Diffie took a job at Mitre Corporation, a defense contractor, where he plunged into computer pro-gramming, helping create Mathlab, a program that allowed mathematicians to not merely calculate with a computer, but also to manipulate mathematical symbols to solve equa-tions. (The program would eventually evolve into Macsyma, a software package used widely in the mathematical com-munity—see mathematics software.)

By the early 1970s Diffie had moved to the West Coast, working at the Stanford Artificial Intelligence Laboratory (SAIL), where he met Lawrence Roberts, head of informa-tion processing research for ARPA, the Defense Depart-ment’s research agency. Roberts’s main project was the creation of the ARPAnet, the computer network that would later evolve into the Internet.

Roberts was interested in providing security for the new network, and (along with AI researcher John McCarthy) he helped revive Diffie’s dormant interest in cryptogra-phy. By 1974 Diffie had learned that IBM was developing a more secure cipher system, the DES (Data Encryption Standard), under government supervision. However, Diffie soon became frustrated with the way the National Security Agency (NSA) doled out or withheld information on cryp-tography, making independent research in the field very difficult. Seeking to learn the state of the art, Diffie traveled widely, seeking out people who might have fresh thoughts on the subject.

Diffie found one such person in Martin Hellman, a Stan-ford professor who had also been struggling on his own to develop a better system of encryption. They decided to pool their ideas and efforts, and Diffie and Hellman came up with a new approach, which would become known as pub-lic key cryptography. It combined two important ideas that had already been discovered to an extent by other research-ers. The first idea was the “trap-door function”—a math-ematical operation that can be easily performed “forward” but that was very hard to work “backward.” Diffie realized, however, that a trap-door function could be devised that could be worked backward easily if the person had the appropriate key.

The second idea was that of key exchange. In classical cryptography, there is a single key used for both encryption and decryption. In such a case it is absolutely vital to keep the key secret from any third party, so arrangements have to be made in advance to transmit and protect the key.

Diffie, however, was able to work out the theory for a system that generates pairs of mathematically interrelated keys: a private key and a public key. Each participant publishes his or her public key, but keeps the correspond-ing private key secret. If one wants to send an encrypted message to someone, one uses that person’s public key (obtained from the electronic equivalent of a phone direc-tory). The resulting message can only be decrypted by the intended recipient, who uses the corresponding secret, private key.

The public key system can also be used as a form of “digital signature” for verifying the authenticity of a mes-sage. Here a person creates a message encrypted with his or her private key. Since such a message can only be decrypted using the corresponding public key, any other person can use that key (together with a trusted third-party key ser-vice) to verify that the message really came from its pur-ported author.

Diffie and Hellman’s 1976 paper in the IEEE Transac-tions on Information Theory began boldly with the statement that “we stand today on the brink of a revolution in cryp-tography.” This paper soon came to the attention of three researchers who would create a practical implementation called RSA (for Rivest, Shamir, and Adelman).

Through the 1980s Diffie, resisting urgent invitations from the NSA, served as manager of secure systems research for the phone company Northern Telecom, designing sys-tems for managing security keys for packet-switched data communications systems (such as the Internet).

In 1991 Diffie was appointed Distinguished Engineer for Sun Microsystems, a position that has left him free to deal with cryptography-related public policy issues. The best known of these issues has been the Clipper Chip, a proposal that all new computers be fitted with a hardware encryption device that would include a “back door” that would allow the government to decrypt data. Along with many civil libertarians and privacy activists, Diffie did not believe users should have to trust largely unaccountable government agencies for the preservation of their privacy. Their opposition was strong enough to scuttle the Clipper Chip proposal by the end of the 1990s. Another proposal, using public key cryptography but having a third-party “key escrow” agency hold the keys for possible criminal investigation, also fared poorly. In 1998 Diffie and Susan Landau wrote Privacy on the Line, a book about the politics of surveillance and encryption. The book was revised and expanded in 2007.

Diffie has received a number of awards for both technical excellence and contributions to civil liberties. These include the IEEE Information Theory Society Best Paper Award (1979), the IEEE Donald Fink Award (1981), the Electronic Frontier Foundation Pioneer Award (1994), and even the National Computer Systems Security Award (1996), given by the NIST and NSA.