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Steganography: Hidden Messages

Steganography: Hidden Messages. (Parts by Dr. Kenny Hunt, The University of Wisconsin – La Crosse). Definitions. Steganography “the art of concealing the existence of information within seemingly innocuous carriers ” “ an encrypted message may draw suspicion while a hidden message will not”

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Steganography: Hidden Messages

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  1. Steganography: Hidden Messages (Parts by Dr. Kenny Hunt, The University of Wisconsin – La Crosse)

  2. Definitions • Steganography • “the art of concealing the existence of information within seemingly innocuous carriers” • “an encrypted message may draw suspicion while a hidden message will not” • Neil Johnson • Image Processing and Steganography • “the art of concealing the existence of information within seemingly innocuous digital images”

  3. Hiding text within text • Message sent by a German spy in WWII: “Apparently neutral’s protest is thoroughly discounted and ignored. Isman hard hit. Blockade issue affects pretext for embargo on by-products, ejecting suets and vegetable oils.”

  4. Hiding text within text • Message sent by a German spy in WWII: “Apparently neutral’s protest is thoroughly discounted and ignored. Isman hard hit. Blockade issue affects pretext for embargo on by-products, ejecting suets and vegetable oils.” Pershing sails from NY June I.

  5. Looking for hidden messages... • “Beautiful Mind”: Prof Nash looks for hidden messages in magazines. • Al-Qaeda images on the internet, supposedly concealed messages

  6. Background(Bit Planes) An Image is a 2D array of pixels Each pixel (in gray-scale) is 8 bits Each bit carries information Not all bits carry the same amount

  7. A0 A7 Bit Planes One pixel split into it’s 8-bits

  8. (a) (b) (c) (d) Background(Bit Planes) • White indicates an ON bit and black an OFF bit • 8-bit grayscale source image • Most significant bit plane (a7) of the source • Least significant bit plane (a0) of the source • Bit plane a4 of the source image

  9. Cover Image A7 A6 A5 A4 A3 A2 A1 A0 Secret Message A7 A6 A5 A4 A3 M2 M1 M0 Stego Image (Cover image with message) The Big Idea(LSB embedding) • An image contains more information than can be perceived. • Replace the “imperceptible bits” of a cover image with the bits of a “secret message”. The Challenge: Write code to LSB embed a secret message in an image. The secret message can be “any object”.

  10. Result • Messages hidden in images, and you can’t see the difference.

  11. Images within images • Take last 2 bits of each RGB value, result is nearly black. But, make the result 85 times brighter, and you get:

  12. More Hidden Messages • You can hide any media within any other media • Words • Pictures • Music • Movies The amount of information you can hide is bigger as the media is bigger.

  13. Discussion • What advantages does steganography have over cryptography? Vice versa? • How could a hidden message in an image get corrupted? • If you suspected a message of having a hidden meaning, what algorithm could you use to see if you are right?

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