Let M be a confidential email that Alice wants to send to Bob, PUB be Bob's encryption public key, and PRA be Alice's private key for signing. Which of the following options would be the best choice for protecting all three - confidentiality, message integrity and message authentication - of sent emails? Justify your answers in the spaces provided. (Hint: assume the possibility of 'man-in-the-middle' attack when considering each option.) 1) Send EPUB(M),EPRA(M) 2) Send EPUn(M),EPRA(EPUn(M)) 3) Send EPUn(K),EPRA(EPUn(M)),EK(M) where k is a new symmetric key chosen for this email and Es represents encryption under k with a symmetric-key stream cipher