n the following scenario, we will compare the security services that are given by digital signatures (DS) and message authentication codes (MAC). We assume that James can read all messages send from Chan to Badrul and the other way around, too. James has no knowledge of any keys but the public one in the case of DS. State whether and how (i) DS and (ii) MAC protect against each attack. The value auth(x) is calculated with DS and MAC’s algorithm, correspondingly.       i) (Message integrity) Chan sends a message x = “Transfer RM200 to Darren” in the clear and also sends auth(x) to Badrul. James intercepts the message and replaces “Darren” with “James”. Will Bob detect this?.      ii) (Replay) Chan sends a message x = “Transfer RM200 to James” in the clear and also sends auth(x) to Badrul. James observes the message and signature and sends them 100 times to Badrul. Will Badrul detect this?    iii) (Sender Authentication with the cheating third party) James claims that he sent some message x with a valid auth(x) to Badrul, but Chan claims the same. Can Badrul clear the question in either case?     iv) (Authentication with Badrul cheating) Badrul claims that he received a message x with a valid signature auth(x) from Chan (e.g., “Transfer RM200 from Chan to Badrul”) but Chan claims she has never sent it. Can Chan clear this question in either case

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