Diffie and Hellman created the Diffie-Hellman key exchange. The fact that it exists at alone got rid of a major a monopoly. Originally, the cryptography business was controlled by government entities and they gave the terms on which other individuals could have access to it. The key exchange allows for secret communication between two parties via a shared secret key over an insecure channel. This allows for symmetric encryption algorithms. The more important part is how the key exchange made the creation of secret keys able to be done publicly. Before it was required that centralized facilities to manufacture and distribute keys and have it be consistent with the military's top-down structure.
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