In this attack, Trudy intercepts Alice’s message “I am Alice” and records the message and the value of R. Trudy then sends the same message and R value to Bob. When Bob sends the challenge E(R,K(ab)) to Trudy, she can simply forward this message to Alice, who will encrypt it and return the result to Trudy. Trudy can then forward the encrypted message back to Bob, who will accept it as proof of Alice’s identity.