<- Virtual Exhibitions in Informatics

Diffie-Hellman-Merkle Key Exchange

Diffie-Hellman key agreement was invented in 1976 during a collaboration between Whitfield Diffie and Martin Hellman and was the first practical method for establishing a shared secret over an unprotected communications channel.

This protocol was a huge step because now everybody could create a secret key over an unsecure line. The problem of key distribution, which became more and more unhandable, was theoretically solved.

The protocol looks as follows:

1) Alice chooses a secret a and publicates x=g^a mod p

2) Bob chooses a secret b and publicates y=g^b mod p

3) Alice calculates y^a = g^(ab) mod p

4) Bob calculates x^b=g^(ab) mod p

Both have the same secret g^(ab)

They published the protocol in their paper "New Directions in Cryptography"

A few years before (1974) Malcolm J. Williamson a staff member at GCHQ in the UK, created this protocol. But his work was classified as top secret and until 1997 nobody knew about his work.

Ralph C. Merkle


Ralph C. Merkle (born 2 February 1952) is a pioneer in public key cryptography, and more recently a researcher and speaker on nanotechnology and cryonics.

Merkle graduated from Livermore High School in 1970 and proceeded to study Computer Science at U.C. Berkeley, obtaining his B.A. in 1974, and his M.S. in 1977. In 1979 he was awarded a PhD in Electrical Engineering at Stanford; the thesis was entitled Secrecy, authentication and public key systems.

In industry, he was the manager of compiler development at Elxsi from 1980. In 1988, he became a research scientist at Xerox PARC, until 1999. Subsequently he worked as a nanotechnology theorist for Zyvex, returning to academia in 2003 as a distinguished professor at Georgia Tech.

Ralph Merkle is the great grandnephew of baseball star Fred Merkle (see History of baseball.)

Merkle devised an early scheme for communication over an insecure channel: Merkle's Puzzles. He also coinvented the Merkle-Hellman public key cryptosystem, and invented Merkle trees. While at Xerox PARC, Merkle designed the Khufu and Khafre block ciphers, and the Snefru hash function.

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