Symmetric,orprivate-key,encryptionisbasedonasecretkeythatissharedbybothcommuncatingparties.The()partyusesthesecretkeyaspartofthemathematicaloperationtoencrypt()texttociphertext.Thereceivingpartyusesthesamesecretkeytodecrypttheciphertexttoplaintext.Asymmetric,orpublic-key,encryptionusestwodifferentkeysforeachuser:oneisa(_____)keyknownonlytothisoneuser;theotherisacorrespondingpublickey,whichisaccessibletoanyone.Theprivateandpublickeysaremathematicallyrelatedbytheencryptionalgorithm.Onekeyiausedforencyptionandtheotherfordecryption,dependingonthenatureofthecommunicationservicebeingimplemented.Inaddition,publickeyencryptiontechnoligiesallowdigital()tobeplacedonmessages.Adigitalsignatureusesthesender'sprivatekeytoencryptsomeportionofthemessage.Whenthemessageisreceived,thereceiverusesthesender's()keytpdecipherthedigitalsignaturetoverifythesender'sidentity. 横线处应选()。
A.plain
B.cipher
C.public
D.private
正确答案是D