Therearetwogeneralapproachestoattackinga()encryptionscheme.Thefirstattackisknownascryptanalysis.Cryptanalyticattacksrelyonthenatureofthealgorithmplusperhapssomeknowledgeofthegeneralcharacteristicsofthe()orevensomesampleplaintext-ciphertextpairs.Thistypeof()exploitsthecharacteristicsofthealgorithmtoattempttodeduceaspecificplaintextortodeducethekeybeingused.Iftheattacksucceedsindeducingthekey,theeffectiscatastrophic:Allfutureandpastmessagesencryptedwiththatkeyarecompromised.Thesecondmethod,knownasthe()-forceattack,istotryeverypossiblekeyonapieceof(5)untilanintelligibletranslationintoplaintextisobtained.Onaverage,halfofallpossiblekeysmustbetriedtoachievesuccess. (5)处应选_______.
A.plaintext
B.ciphertext
C.sample
D.code
正确答案是D