Therearetwogeneralapproachestoattackinga(1)encryptionscheme.Thefirstattackisknownascryptanalysis.Cryptanalyticattacksrelyonthenatureofthealgorithmplusperhapssomeknowledgeofthegeneralcharacteristicsofthe()orevensomesampleplaintext-ciphertextpairs.Thistypeof()exploitsthecharacteristicsofthealgorithmtoattempttodeduceaspecificplaintextortodeducethekeybeingused.Iftheattacksucceedsindeducingthekey,theeffectiscatastrophic:Allfutureandpastmessagesencryptedwiththatkeyarecompromised.Thesecondmethod,knownasthe()-forceattack,istotryeverypossiblekeyonapieceof()untilanintelligibletranslationintoplaintextisobtained.Onaverage,halfofallpossiblekeysmustbetriedtoachievesuccess. (1)处应选________.
A.stream B.symmetric C.asymmetric D.advanced正确答案B
