Therearetwogeneralapproachestoattackinga()encryptionscheme.Thefirstattackisknownascryptanalysis.Cryptanalyticattacksrelyonthenatureofthealgorithmplusperhapssomeknowledgeofthegeneralcharacteristicsofthe()orevensomesampleplaintext-ciphertextpairs.Thistypeof(3)exploitsthecharacteristicsofthealgorithmtoattempttodeduceaspecificplaintextortodeducethekeybeingused.Iftheattacksucceedsindeducingthekey,theeffectiscatastrophic:Allfutureandpastmessagesencryptedwiththatkeyarecompromised.Thesecondmethod,knownasthe()-forceattack,istotryeverypossiblekeyonapieceof()untilanintelligibletranslationintoplaintextisobtained.Onaverage,halfofallpossiblekeysmustbetriedtoachievesuccess. (3)应选__________.
A.message
B.knowledge
C.algorithm
D.attack
正确答案是D