Shortcomings of Enc ■■■ Q: shortcomings of message encryption? 復大辱软件学院
16 Shortcomings of Enc… • Q: shortcomings of message encryption?
Shortcomings of Enc ■■■ Q: shortcomings of message encryption? Cost encrypt the whole message Not automatically 復大辱软件学院
17 Shortcomings of Enc… • Q: shortcomings of message encryption? • Cost – encrypt the whole message • Not automatically
efa Message Authentication Code(MAC) generated by an algorithm that creates a small fixed-sized block depending on both message and some key like encryption though need not be reversible appended to message as an authenticator receiver performs same computation on message and checks it matches the mac provides assurance that message is unaltered and comes from sender 復大辱软件学院
18 Message Authentication Code (MAC) • generated by an algorithm that creates a small fixed-sized block – depending on both message and some key – like encryption though need not be reversible • appended to message as an authenticator • receiver performs same computation on message and checks it matches the MAC • provides assurance that message is unaltered and comes from sender
MeSsage Authentication Code Source a- -Destination b-k M (a)Message authentication CRMn 19 復大辱软件学院
19 Message Authentication Code