Introduction
What?
In November 1976, Stanford researchers Whitfield Diffie and Martin Hellman published a research paper titled “New Directions in Cryptography” that revolutionised cryptography forever. In their paper, they introduced the notion of public-key encryption and signatures, though they didn’t actually have any of those schemes; they simply had what they termed a public-key distribution scheme, a protocol that allows two parties to establish a shared secret by exchanging information visible to an eavesdropper. This protocol is now known as the Diffie–Hellman (DH) protocol.
Why?
Diffie–Hellman schemes are only secure when their parameters are well-chosen.