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試題10

Perhaps the most obvious difference between private-key and public-key encryption is that the former assumes complete secrecy of all cry to graphic keys, whereas the latter requires secrecy for only the private key.Although this may seem like a minor distinction ,the ramifications are huge: in the private-key setting the communicating parties must somehow be able to share the (71) key without allowing any third party to learn it, whereas in the public-key setting the (72) key can be sent from one party to the other over a public channel without compromising security.For parties shouting across a room or, more realistically , communicating over a public network like a phone line or then ternet, public-key encryption is the only option.
Another important distinction is that private-key encryption sch emesuse the (73) key for both encryption and decryption, whereas public key encryption schemes use (74) keys for each operation.That is public-key encryption is inherently as ymmetri C．This asymmetry in the public-key setting means that the roles of sender and receiver are not interchangeable as they are in the private-key setting; a single key-pair allows communication in one direction only.(Bidirectional communication can be achieved in a number of ways; the point is that a single invocation of a public-key encryption scheme forces ad is tinction between one user who acts as a receiver and other users who act as senders.)。In addition, a single instance of a (75) encryption scheme enables multiple senders to communicate privately with a single receiver,in contrast to the private-key case where a secret key shared between two parties enables private communication only between those two parties.
(1) A．main
B．same
C．public
D．secret
(2) A．stream
B．different
C．public
D．secret
(3) A．different
B．same
C．public
D．private
(4) A．different
B．same
C．public
D．private
(5) A．private-key
B．public-key
C．stream
D．Hash

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