Question 17 3 pts Mary receives from Bob, an extended message that contains the message along with a message authentication code (MAC). The message has Bob's medical preferences, A, B and C, should he have an accident and cannot communicate. Bob has an accident and is unconscious. Would Mary's claim that she can prove Bob's medical preferences are A, B and C, based on the message from Bob that has the MAC, be valid? - Yes the MAC proves the message is from Bob, that Bob's preferences in his message have not been changed and that his preferences were not forged. Yes - the digital signature included in the MAC is proof of authentication, integrity and non-repudiation No - the MAC would be sufficient to prove authentication and for integrity of the message but insufficient evidence for proof that the document could not forged. No the MAC is insufficient to prove authentication Question 18 3 pts Sherlock Holmes' arch criminal nemesis, Professor Moriarty, is undermining the famed detective by telling his client, Mr Hilton Cubitt of Riding Thorpe Manor that Sherlock knows nothing about cryptography. Professor Moriarty says he has proof - he has a letter that Sherlock had written to Watson that he had fooled Mr. Cubitt and taken fees for doing nothing. Mr. Cubitt asked to see the letter. Professor Moriarty said he had recovered the original letter from Sherlock's SHA256 hash of the letter, showing it to Mr. Cubitt. Mr Cubitt should be enraged, call Scotland Yard that Sherlock had perpetuated fraud on him and that he wanted all his fees back. Mr Cuibitt should believe Professor Moriarty because SHA256 proves authentication - that Sherlock did write the letter Mr Cubitt needs to be careful and check with Watson. He should not fully believe the Professor because the recovered original message from SHA256 was not signed so there is no proof of authentication. Mr Cubitt should relax and trust Sherlock. The Professor is lying - fake news - a document hash from SHA256 cannot be reversed back to the original document Question 19 2 pts Using UDP can avoid delays due to flow control and congestion control that may occur with using TCP. True False Question 20 If a web server and client are using persistent HTTP: 3 pts A new TCP connection is created and closed for every request/response. A new socket is created and closed for every request/response Web server spawns a new process for a new connection with every request/response. The client and server exchange HTTP messages via the same server socket throughout the duration of the persistent connection. Question 21 2 pts SMTP is primarily a push protocol where the sending email server pushes data to the receiving email server. True False