OVERVIEWINTRODUCTIONDIGITAL APPROCHESREASON FOR USING DIGITAL IMAGESEXAMPLES OF STEGNOGRAPHYIMAGE BASED TECHNIQUESLSB INSERTIONMASKING AND FILTERINGUSESWATERMARKING VS STREGNOGRAPHYSUMMARY
INTRODUCTIONGreek for “covered writing”.STEGANOS – “Covered”GRAPHIE – “Writing”“The art and science of writing hidden messages insuch a way that no one apart from the intendedrecipient even knows that a message has been sent.”
Clandestine CommunicationCryptographyScrambles the message into cipherSteganographyHides the message in unexpected places
Uncompressed ImagesGrayscale Bitmap images (bmp)256 shades of intensity from black to whiteCan be obtained from color imagesArranged into a 2-D matrixMessages are hidden in the least significantbits (lsb)Matrix values change slightlyInterested in patterns that form messages
Compressed ImagesGrayscale jpeg images (jpg)Joint Photographic Experts Group (jpeg)Converts image to YCbCr colorspaceDivides into 8x8 blocksUses Discrete Cosine Transform (DCT)Obtain frequency coefficientsScaled by quantization to remove somefrequenciesHigh quality setting will not be noticedHuffman CodingAffects the images statistical properties
DIGITAL APPROACHESToday, it often exists within digital formatsIt makes use of seemingly innocent cover files such astext, audio, and image filesThe embedded message may be anything that can beencoded in binary
REASONS FOR USING DIGITALIMAGESIt is the most widely used medium being used todayTakes advantage of our limited visual perception ofcolorsThis field is expected to continually grow as computergraphics power also growsMany programs are available to apply steganography
EXAMPLESTattoos on shaved headsWax-covered tabletsMicrodots – shrunken picturesInvisible Inks - milk, fruit juice,urine
IMAGE-BASED TECHNIQUESLeast Significant Bit InsertionMasking and Filtering
LSB INSERTIONReplaces least significant bits with the message to beencoded.Most popular technique when dealing with images.Simple, but susceptible to lossy compression.
LSB –Continued…Best to use a grayscale palette or one with gradualchanges in shades.Otherwise, it is best to use images with “noisy areas”– areas with sample color variation and without largeareas of solid color.
MASKING & FILTERINGMasks secret data over the original data by changingthe luminance of particular areas.During masking, it embed the message withinsignificant bits of the cover image.Not susceptible to lossy techniques because imagemanipulation does not affect the secret message.
MASKING & FILTERING - UsesDigital Watermarking – provides identificationpertaining to the owner; i.e. license or copyrightinformation.- Invisible vs VisibleFingerprinting – provides identification of the user;used to identify and track illegal use of content.
Watermarking vs SteganographyGoal of steganographyIntruder cannot detect a messagePrimarily 1:1 communicationGoal of watermarkingIntruder cannot remove or replace the messagePrimarily 1:many communication
Digital Applications ofSteganographyCan be hidden in digital data MS Word (doc) Web pages (htm) Executables (exe) Sound files (mp3, wav, cda) Video files (mpeg, avi) Digital images (bmp, gif, jpg)
SUMMARYSteganography as a whole has existed in many formsthroughout much of history.Lossless compression of images with a great deal ofcolor variation work best as a cover image to embed amessage.Steganography can be used as benefitial tool forprivacy.
REFERENCESWikipediaExploring Steganography: Seeing the Unseen – N.Johnson & S. Jajodiawww.jjtc.com/stegdoc/steg1995.htmlInformation Hiding: Techniques for Steganographyand Digital Watermarking” – S. Katzenbeisser, F.PetitcolasDigital Watermarking – H. Bergel, L. O’Gorman