Lawrence Snyder University of Washington, Seattle © Lawrence Snyder 2004 Computing Is Pretty Strange

 The process of hiding information  Two Greek roots meaning: “stego” == “roof” “stega” == “cover” 2/6/2016© Larry Snyder2

 Most common reason to hide information is to avoid being caught with it  Military and spy documents  Repressive governments restricting news/info  Avoid others “snooping” – privacy  Hiding is different than encryption … uses the fact that the searcher doesn’t know it’s there 2/6/2016© Larry Snyder3

 The Plan …  hide “subversive” protest photo in “calendar art” 2/6/2016© Larry Snyder4 Guest Image Host Image

 We don’t need all of the bits in RGB to get a decent picture 2/6/2016© Larry Snyder All bitsLeft 2 bits of each color only

 Put guest bits into right 2 bits of host 2/6/2016© Larry Snyder

 2/6/2016© Larry Snyder7 foglg.jpg stegFog.png Really? Just Do It! Really? Just Do It!

Each of the colors is shifted left 1 bit at a time … and then we’ll see the details 2/6/2016© Larry Snyder Original Hidden Picture

 2/6/2016© Larry Snyder9 Encoding Code Code To Save Result on Click

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 After the pictures are loaded Clear right 2 bits of host Extract left 2 bits of guest New combined color 2/6/2016© Larry Snyder xx xx xx

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 Read in the file, and then on key press, shift the bits left one position 2/6/2016© Larry Snyder14 Just Do It! Again Just Do It! Again

 Run A Test … 2/6/2016© Larry Snyder15 The Original

2/6/2016© Larry Snyder16 Steganized

 Steganography can be used extensively – there are many places to hide information  Tomorrow, you’ll hide a picture, too. 2/6/2016© Larry Snyder17