Computers Talk Binary
Pictures are Binary
• 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
• 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.
• 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.
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
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?
How About Now?
Any Other Way to Spot Altered Photos?
Another Thing to Look At
Try it Yourself
Steganography in Other Forms