Steganography - University Of Illinoispublish.illinois.edu/digital-forensics/files/2016/10/Steganography.pdfSTEGANOGRAPHY Computers Talk Binary 011010000110010101101100011011000110111100

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STEGANOGRAPHY  

Computers Talk Binary

011010000110010101101100011011000110111100100000011101110110111101110010011011000110

0100  !!!  

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Binary  Conversions  

• http://www.roubaixinteractive.com/PlayGround/Binary_Conversion/Binary_to_Text.asp  

• http://www.roubaixinteractive.com/PlayGround/Binary_Conversion/The_Characters.asp  

Pictures  are  Binary  

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Steganography  

• Means  covered  writing  

• Dates  back  to  ancient  Greece  • common  practices    • etching  messages  in  wooden  tablets  and  covering  them  with  wax  •  tattooing  a  shaved  messenger's  head,  letting  his  hair  grow  back,  then  shaving  it  again  when  he  arrived  at  his  contact  point    

“Invisible  Writing”  

• Another  common  form  of  Steganography  is  through  the  use  of  Invisible  inks.    

• Such  inks  were  used  with  much  success  as  recently  as  WWII.    

• An  innocent  letter  may  contain  a  very  different  message  written  between  the  lines    

• Can  you  see  me    • Early  in  WWII  steganographic  technology  consisted  almost  exclusively  of  invisible  inks  [Kahn67].  Common  sources  for  invisible  inks  are  milk,  vinegar,  fruit  juices  and  urine.  All  of  these  darken  when  heated.    

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Steganography  

• Art  and  science  of  disguising  or  hiding  information  in  the  form  of  something  else  • embedding  messages  within  other  text  •  images  or  information  may  be  encoded  into  pictures  or  texts  files  

• The  “invisible”  files  can  be  (compiled  and)  retrieved  by  those  with  code  

Embedding  Messages  Within  Other  Text    

Fishing   freshwater   bends  and   saltwater   coasts  rewards   anyone   feeling  stressed.   Resourceful  ang le rs   usua l l y   find  masterful   leapers   fun  and  admit   swordfish   rank  overwhelming  anyday.    

• By  taking  the  third  letter  in  each  word,  the  following  message  emerges  

• “Send  Lawyers,  Guns,  and  Money“  

Null ciphers (unencrypted messages). The real message is "camouflaged" in an innocent sounding message.

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Famous  German  Spy  Message  from  WWII    

Apparently   neutral's  protest   is   thoroughly  d i s c o u n t e d   a n d  ignored.   Isman   hard  hit.   Blockade   issue  affects   pretext   for  e m b a r g o   o n   b y  products,   e ject ing  suets   and   vegetable  oils.    

• Taking  the  second  letter  in  each  word  the  following  message  emerges:    

• “Pershing  sails  from  NY  June  1”  

Embedding  Text  in  Pictures  

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Embedding  Messages  within  photos  

• Message  Size  <<<  File  Size  or  File  Size  >>>  Message  Size  to  hide  effectively  

• Picture  files  are  PERFECT  for  this!  • a  24-­‐bit  bitmap  will  have  8  bits  representing  each  of  the  three  color  values  (red,  green,  and  blue)  at  each  pixel.    

• The  difference  between  11111111  and  11111110  in  the  value  for  blue  intensity  is  likely  to  be  undetectable  by  the  human  eye.    

• Therefore,  the  least  significant  bit  can  be  used  (more  or  less  undetectably)  for  something  else  other  than  color  information.  If  we  do  it  with  the  green  and  the  red  as  well  we  can  get  one  letter  of  ASCII  text  for  every  three  pixels.    

Can  you  tell  the  difference?  

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How  About  Now?  

Any  Other  Way  to  Spot  Altered  Photos?  

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Another  Thing  to  Look  At  

Try  it  Yourself  

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Steganography  in  Other  Forms