Devil's Fork

Then J.D. took a breath and erased all the arrows he drew.

  “In a MIM attack, a hacker steps in between Bob and Alice—“ He wrote “Hacker” in between “Alice” and “Bob” on the whiteboard. “Now let’s say that, again, Alice wants to send a message to Bob. So she asks Bob to send her his key. But, this time when Bob sends his key, the Hacker intercepts it before it gets to Alice.” J.D. now drew an arrow from “Bob” to “Hacker” and labeled it “Bob’s Key”.

  “The Hacker has Bob’s key. Now the hacker sends his own key to Alice. Alice thinks that this is Bob’s key, so she encrypts her message with this key the same way as before.” He drew an arrow from “Hacker” to “Alice” and labeled it “Hacker’s Key.”

  “Then she sends the message to Bob. But—“ he put emphasis on the word “but” as he drew an arrow from “Alice” to “Hacker”. “But the hacker intercepts this message. Since the message is encrypted in the hacker’s key, he can decipher it and read it. Then he can encrypt it with Bob’s key, since he received it earlier, and send the message to Bob. Bob will decrypt it with his key and read it.” He now drew an arrow from “Hacker” to “Bob”.