Steganography

Summary

Generallyspeaking,steganographicinformationlookslikesomethingelse,suchasashoppinglist,anarticle,apictureorother"disguise"(cover)Message.

Thesteganographicinformationisusuallyencryptedbysometraditionalmethods,andthena"covertext"ismodifiedinsomewaytoincludetheencryptedmessage,formingtheso-called"secrettext""(Stegotext).Forexample,thesize,spacing,font,orothercharacteristicsofthecovertextcanbemodifiedtoincludehiddeninformation.Onlywhentherecipientknowsthehidingtechnologyusedcantheinformationberecoveredandthendecrypted.

Steganographyandelectronicwatermarking

Firstofall,intheoverviewofsteganography,wemustmentionitscloserelative,watermarking.Watermarkingisusedtoidentifytheauthenticityofitems(suchas:ThefaintlyvisibleportraitofMaoZedongontheplumblossomandtherenminbicanbeseenontheflipoftheNewTaiwandollar),eitherasamarkofcopyrightdeclaration,oraddingworkattributeinformation.Thesimilaritybetweenelectronicwatermarkingandsteganographyisthatbothofthemsteganographicallywriteonefileintoanother,andthedifferencebetweenthetwoliesinthepurposeofuseandtheprocessingalgorithm.Electronicsteganographyfocusesonhidingsecretfiles,whileelectronicwatermarkingpaysmoreattentiontothedeclarationandmaintenanceofcopyright,preventingmultimediaworksfrombeingillegallycopied,andsoon.Oncetheelectronicsteganographyisdiscovered,thesecretfileisveryeasytoberead.Onthecontrary,theelectronicwatermarkdoesnothidetheconcealmentofthesteganographicfile,butcaresaboutstrengthening(Robustness)toremovetheattackofthealgorithm.

ModernSteganography

Thelargerthecoverfilesize(referringtothedatacontent,measuredinbits)ofthecoverfile,theeasieritistohidethelatter.

Forthisreason,digitalimages(containinglargeamountsofdata)arewidelyusedtohidemessagesontheInternetandothermedia.Theextenttowhichthismethodisusedisunclear.Forexample:thethreecolorcomponents(red,greenandblue)ofeachpixelina24-bitbitmaparerepresentedby8bitseach.Ifweonlyconsiderblue,itmeansthattherearetwodifferentvalues​​torepresentdifferentshadesofblue.Thebluerepresentedbythetwovalues​​like11111111and11111110isalmostindistinguishablebythehumaneye.Therefore,thisleastsignificantbitcanbeusedtostoreinformationotherthancolor,andtosomeextentitisalmostundetectable.Ifthesameoperationisperformedonredandgreen,onebyteofinformationcanbestoredinalmostthreepixels.

Toputitmoreformally,whatmakessteganographicinformationdifficulttodetectistoensurethatthe"payload"(thesignalthatneedstobeconcealed)modulatesthe"carrier"(theoriginalsignal)tothecarrier.Theimpactofsigmaseemstobenegligible(ideallyandevenstatistically).Thismeansthatthischangeshouldbeindistinguishablefromthenoiseinthecarrier.

(Fromthepointofviewofinformationtheory,thismeansthatthecapacityofthechannelmustbegreaterthantheneedtotransmitthe"superficial"signal.Thisiscalledchannelredundancy.Foradigitalimage,thisredundancyTherestmaybethenoiseoftheimagingunit;fordigitalaudio,itmaybethenoisegeneratedbytherecordingoramplificationequipment.Anysystemwithananalogamplificationstagewillhavetheso-calledthermalnoise(or"1/f"noise),whichcanbeusedInaddition,lossycompressiontechnology(suchasJPEG)willintroducesomeerrorsinthedecompresseddata,anditispossibletousetheseerrorsforsteganographypurposes.)

SteganographycanalsobeusedAsadigitalwatermark,amessage(oftenjustanidentifier)​​ishiddeninanimage,sothatitssourcecanbetrackedorverified.Steganographyusingcomputerfontdesign.

Usage

Inrecentyears,thefieldofsteganographyhasbecomethefocusofinformationsecurity.BecauseeveryWebsitereliesonmultimedia,suchasaudio,video,andimages.Steganographyisatechnologythatcanembedsecretinformationintodigitalmediawithoutdamagingthequalityofitscarrier.Thethirdpartyisneitherawareoftheexistenceofsecretinformation,norawareoftheexistenceofsecretinformation.Therefore,keys,digitalsignatures,andprivateinformationcanallbesafelytransmittedinanopenenvironment(suchastheInternetorIntranet).Mainlyintroducethebasicprinciplesofsteganographyandvariousapplications.

Tools

Manysteganographyalgorithmshavebeendevelopedintosteganographytools.Johnsonsortedandcollectedthesesoftwareandlistedmorethan100software.Thetablelistssomecommonsteganographysoftwarethatusesimagesascarriers.