The protocol enables two users to establish a secret key using a public-key scheme based on discrete logarithms

The answer in the space provided is the Diffie-Hellman Key Exchange. This is entitled to be the first published key algorithm in which has a limit in which the exchange occurs in secret values and that its purpose was to enable two users to have an exchange of key in a secure manner in means of using it for a subsequent symmetric encryption in terms of messages.

a few, because i should have plenty.

answer(a) occurs after your prediction;