单选题 71-75 (1) isthescienceofhidinginformation.Whereasthegoalofcryptographyistomakedataunreadablebyathirdparty.thegoalofsteganographyistohidethedatafromathirdparty.Inthisarticle,Iwilldiscusswhatsteganographyis,whatpurposesitserves,andwillprovideanexampleusingavailablesoftware. Therearealargenumberofsteganographic (2) thatmostofusarefamiliarwith(especiallyifyouwatchalotofspymovies),rangingfrominvisibleinkandmicrodotstosecretingahiddenmessageinthesecondletterofeachwordofalargebodyoftextandspreadspectrumradiocommunication.Withcomputersandnetworks,therearemanyotherwaysofhidinginformations,suchas: Covertchannels(c,g,Lokiandsomedistributeddenial-of-servicetoolsusetheInternetControl (3) Protocol,orICMP,asthecommunicationchannelbetweenthe“badguy”andacompromicyedsystem) HiddentextwithinWebpages Hidingfilesin“plainsight”(c,g.whatbetterplaceto“hide”afilethanwithanimportantsoundingnameinthec:/winntsystem32directory) Nullciphers(c,g,usingthefirstletterofeachwordtoformahiddenmessageinanotherwiseinnocuoustext) steganographytoday,however,issignificantlymore (4) thantheexampleaboutsuggest,allowingausertohidelargeamountsofinformationwithinimageandaudio.Theseformsofsteganographyoftenareusedinconjunctionwithcryptographysotheinformationisdoubleprotected;firstitisencryptedandthenhiddensothatanadvertisementfirst.findtheinformation(anoftendifficulttaskinandofitself)andthedecryptedit. Thesimplestapproachtohidingdatawithinanimagefileiscalled (5) signatureinsertion.Inthismethod,wecantakethebinaryrepresentationofthehiddendataandthebitofeachbytewithinthecovertimage.Ifweareusing24-bitcolortheamountandwillbeminimumandindiscriminatetothehumaneye.