Video Over IP

APPENDIX B

Diffie-Hellman Key Exchange

In 1976, Whitfield Diffie and Martin Hellman published a paper¹ that first described one of the key underlying technologies for exchanging cryptographic keys between two parties that wish to communicate. This process, which has come to be known as the Diffie-Hellman Key Exchange, is now in common use in throughout the Internet, particularly since the key US patents covering this technology expired in 1997. Since this is such an important technology, let’s look at how it works.

Let’s say two users, whom we’ll call Bonnie and Clyde, are trying to exchange a secret message. Before they begin, they need to agree on two numbers: a prime number (p), and a second, smaller number called a generator (g).² For this ...