Q7: In this problem we will compare the security services that are provided by digital signatures (DS) and message authentication codes (MAC). We assume that Oscar is able to observe all messages sent from Alice to Bob and vice versa. Oscar has no knowledge of any secret keys but the public one in case of digital siganture. The value auth(x) is computed with a DS or a MAC algorithm, respectively. State whether and how (i) DS and (ii) MAC protect against cach attack. (5 points each). 1. (Message integrity) Alice sends a message x = Transfer $1000 to Mark in the clear and also sends auth(x) to Bob. Oscar intercepts the message and replaces Mark with Oscar. Will Bob detect this in either case (using MAC or DS)? 2. (Replay) Alice sends a message x = Transfer $1000 to Oscar in the clear and also sends auth(x) to Bob. Oscar observes the message and signature and sends them 100 times to Bob. Will Bob detect this