Alice would like to send confidential and authenticated messages for Bob. Consider the following security protocol between Alice, Bob, using a trusted Server. Notation: E(M,K) encryption of message M with key K; D(M,K) decryption of message M with key K; Sign(M,K) signature of message M with key K, KD-X is the private key of X, KE-X is the public key of X, Ksession is a secret key, Id-X is the identity of X, h(M) is the hash value of message M, Timel is a time stamp, and l| denotes a concatenation of the messages. Assume, Alice and Bob know the Server's public key (KE-S) in a reliable manner. Message 1: AS: "Reqest signed public keys for A and B" Message 2: SBA: Sign(IKE-B | Id-B, KD-S) Sign(IKE-A Il Id-A], KD-S) Why did the Server sign both KE-B and KE-A