3. (16 points) The figure attached below, Figure 8.21 on page 629 in the text, shows the operations that Alice must perform to provide confidentiality, authentication, and integrity when sending a message to Bob over the network. Both Alice and Bob use public key cryptography and each has a public and private key as described in the text. Consider the case of Alice sending a message, m, to Bob, and answer the following questions. a) (2 points)Who can know Alice's public key? b) (2 points)Who can know Alice's private key? c) 2 points)What key would Alice use to digitally sign a message to Bob? d) (2 points)Is this message now confidential or can anybody view the contents? e (2 points)What key would Bob use to verify the signature? f (4 points) In the figure below, why do we use a session key (Ks) instead of relying only on public key cryptography