Therearetwogeneralapproachestoattackinga()encryptionscheme.Thefirstattackisknownascryptanalysis.Cryptanalyticattacksrelyonthenatureofthealgorithmplusperhapssomeknowledgeofthegeneralcharacteristicsofthe()orevensomesampleplaintext-ciphertextpairs.Thistypeof()exploitsthecharacteristicsofthealgorithmtoattempttodeduceaspecificplaintextortodeducethekeybeingused.Iftheattacksucceedsindeducingthekey,theeffectiscatastrophic:Allfutureandpastmessagesencryptedwiththatkeyarecompromised.Thesecondmethod,knownasthe(4)-forceattack,istotryeverypossiblekeyonapieceof()untilanintelligibletranslationintoplaintextisobtained.Onaverage,halfofallpossiblekeysmustbetriedtoachievesuccess. (4)处应选_______.
A.brute
B.perfect
C.atribue
D.research
正确答案是A