Alice wants to send an email message m to Bob and ensure confidentiality, authentication, and integrity. So, Alice sends the following to Bob: KB+ ( KS) + KS (m + KA- (H(m))) where KB+ is Bob's public key, KA- is Alice's private key, and KS is their shared session key. What is the first thing that Bob has to do to start unpacking this message?

a. apply the shared session key to the 2nd part of the message to obtain the message and signed hash of the message

b. apply Bob's public key to the first part of the message to obtain the shared session key

c. apply Bob's private key to the first part of the message to obtain the shared session key

d. apply Alice's public key to the first part of the message to obtain the shared session key