Suppose we are using a three$-$message mutual authentication protocol, and Alice initiates contact with Bob. Suppose we wish Bob to be a stateless server, and therefore it is inconvenient to require him to remember the challenge he sent to Alice. R is the challenge, then is the following protocol secure$?$ And why? Here K$\_$bob is Bob$$s secret key and K$\_$alice$-$bob is the secret key between Alice and Bob. Both are for symmetric ciphers. Assume that the crypto is safe so that you cannot derive K$\_$bob with R and K$\_$bob$($R $).$