Steganography

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Steganography

  1. 1. ByP.PRABAKARA PANDIANN.SUMATH
  2. 2. OVERVIEWINTRODUCTIONDIGITAL APPROCHESREASON FOR USING DIGITAL IMAGESEXAMPLES OF STEGNOGRAPHYIMAGE BASED TECHNIQUESLSB INSERTIONMASKING AND FILTERINGUSESWATERMARKING VS STREGNOGRAPHYSUMMARY
  3. 3. INTRODUCTIONGreek 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.”
  4. 4. Clandestine CommunicationCryptographyScrambles the message into cipherSteganographyHides the message in unexpected places
  5. 5. Uncompressed ImagesGrayscale Bitmap images (bmp)256 shades of intensity from black to whiteCan be obtained from color imagesArranged into a 2-D matrixMessages are hidden in the least significantbits (lsb)Matrix values change slightlyInterested in patterns that form messages
  6. 6. Compressed ImagesGrayscale jpeg images (jpg)Joint Photographic Experts Group (jpeg)Converts image to YCbCr colorspaceDivides into 8x8 blocksUses Discrete Cosine Transform (DCT)Obtain frequency coefficientsScaled by quantization to remove somefrequenciesHigh quality setting will not be noticedHuffman CodingAffects the images statistical properties
  7. 7. ENCODING FLOWCHART
  8. 8. DECODING FLOWCHART
  9. 9. DIGITAL APPROACHESToday, it often exists within digital formatsIt makes use of seemingly innocent cover files such astext, audio, and image filesThe embedded message may be anything that can beencoded in binary
  10. 10. REASONS FOR USING DIGITALIMAGESIt is the most widely used medium being used todayTakes advantage of our limited visual perception ofcolorsThis field is expected to continually grow as computergraphics power also growsMany programs are available to apply steganography
  11. 11. EXAMPLESTattoos on shaved headsWax-covered tabletsMicrodots – shrunken picturesInvisible Inks - milk, fruit juice,urine
  12. 12. IMAGE-BASED TECHNIQUESLeast Significant Bit InsertionMasking and Filtering
  13. 13. LSB INSERTIONReplaces least significant bits with the message to beencoded.Most popular technique when dealing with images.Simple, but susceptible to lossy compression.
  14. 14. ExampleA sample raster data for 3 pixels (9 bytes)may be:Insertingthe binaryvalue forA(10000001)changes4 bits00100111 11101000 1100100000100110 11001000 1110100011001001 00100111 1110101100100111 11101001 1100100000100111 11001000 1110100111001000 00100111 11101011
  15. 15. 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.
  16. 16. GRAYSCALE PALETTE
  17. 17. NEBULA PALETTE
  18. 18. “NOISY AREAS” - ExampleRenoirpainting
  19. 19. Contaminated Image
  20. 20. MASKING & FILTERINGMasks 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.
  21. 21. MASKING & FILTERING - UsesDigital Watermarking – provides identificationpertaining to the owner; i.e. license or copyrightinformation.- Invisible vs VisibleFingerprinting – provides identification of the user;used to identify and track illegal use of content.
  22. 22. Visible Watermark - Example
  23. 23. UV Watermarking
  24. 24. Watermarking vs SteganographyGoal of steganographyIntruder cannot detect a messagePrimarily 1:1 communicationGoal of watermarkingIntruder cannot remove or replace the messagePrimarily 1:many communication
  25. 25. Digital Applications ofSteganographyCan 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)
  26. 26. SUMMARYSteganography 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.
  27. 27. REFERENCESWikipediaExploring Steganography: Seeing the Unseen – N.Johnson & S. Jajodiawww.jjtc.com/stegdoc/steg1995.htmlInformation Hiding: Techniques for Steganographyand Digital Watermarking” – S. Katzenbeisser, F.PetitcolasDigital Watermarking – H. Bergel, L. O’Gorman

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