(Solved): (10 points) Alice is sending an email to Bob. The email message (could include attachments of files ...

(10 points) Alice is sending an email to Bob. The email message (could include attachments of files up to

Bytes) should be encrypted. Normally the email delivery do not employ mutual authentication. Instead it just uses one way communication. Based on the above requirements, please Design a one message security protocol between the email sending server (Alice's side) and the email receiving server (Bob's side). Note that we assume that the two email servers have the public key of each other before hand. Explain how did the receiver authenticate the sender and obtain the plaintext email message.