c) Consider the following protocol: Step 1: AB:{NA,A}pk(B) Step 2: BA:{A,{NA,NB}inv(pk(B))}pk(A) Step 3: AB:{NB}pk(B) Briefly explain whether this protocol is secure (i.e., establishes a mutually authenticated and secure channel) or not. - If it is secure, give an informal justification why it is secure. - If an attack is possible, briefly explain the attack