If you read this and intend to make security design decisions based on it (as opposed to reading it just for fun), please read more about the subject from other sources as well. A few statements in it are a bit contradictory, like claiming DH is safe from MITM while at the same time in other words acknowledging e.g. that identity cannot be proven with it. I don't mean to bash the author as primers are a good way to get people interested in stuff, but small oversights can sometimes cause big problems.