12.
试题12从供选择的答案中,选出应填入下面叙述中_?_内的最确切的解答,把相应编号写在答卷的对应栏内。Inapublic-keycryptosystem,_A_encryptedwiththepublickeycanonlybedecipheredwiththeprivatekeyfromthesame_B_.Conversely,_A_encryptedwiththeprivatekeycanbedecryptedonlywiththepublickey.Userscanmaketheirpublickeys_C_availableorplacethematakeydistributioncenterorotherstoaccess.However,theprivatekeymustbe_D_safe.Inpublic-keysystemsthere’sno_E_tofindasafechannelforcommunicatingasharedsecretkey.A:①binarytext②hypertext③plaintext④supertextB:①length②pair③size④spaceC:①free②freely③locally④partlyD:①keep②keeped③keeping④keptE:①more②necessary③need④space[5分]