Definition: Diffie-Hellman

A cryptographic key exchange method developed by Whitfield Diffie and Martin Hellman in 1976. Also known as the "Diffie-Hellman-Merkle" method and "exponential key agreement." Diffie-Hellman enables parties at both ends to derive a shared, secret key from a common starting point without the key ever being transmitted from one side to the other.

Although Diffie-Hellman is an asymmetric algorithm, it does not use public and private keys like the popular RSA method. Its logarithms and modular arithmetic are complicated mathematics; however, the example below is simplified to explain the concept, and the numbers are minuscule compared to a real exchange. See elliptic curve cryptography, RSA and key management.

Very Clever Math

Both sides use a common public number, but each side uses a different random number as a power to raise the common number, and the results are sent to each other. The receiving party raises the received number to the same power used before, and the results wind up the same on both sides.