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the art and science of writing hidden messages
Steganography
Dr. Frank Li
Steganography
στεγανός
γραφία
covered
writing
the art and science of writing hidden messages in such
a way that no one, apart from the sender and intended
recipient, suspects the existence of the message
Steganography in Ancient Greece
-- Tattoo message on head
An ancient Greek historian Herodotus reports that messages
were tattooed onto the shaved heads of slaves. Once the hair
grew back, the slaves were sent to the recipient, with the
message hidden “in plain sight”.
Steganography in World War I
-- Null Cipher
The message below was sent by the German
embassy in World War I.
PRESIDENT'S EMBARGO RULING SHOULD HAVE IMMEDIATE
NOTICE. GRAVE SITUATION AFFECTING INTERNATIONAL
LAW. STATEMENT FORESHADOWS RUIN OF MANY
NEUTRALS. YELLOW JOURNALS UNIFYING NATIONAL
EXCITEMENT IMMENSELY.
Taking the first letter in each word of message reveals the
hidden text: PERSHING SAILS FROM NY JUNE 1.
Steganography in Espionage
-- Invisible ink
Spies use milk, fruit juice or urine as invisible inks,
which darken when heated.
An FBI agent is shown using
ultraviolet light to read secret
writing on a paper from a
suspected spy case
Steganography in Modern Days
• Digital media lend themselves to steganography
because of the large amount of information in
certain file types
• Steganography Carrier Files:
–
–
–
–
–
–
bmp
jpeg
gif
wav
mp3
Amongst others…
Steganography Terminology
Carrier File
Carrier File with
Hidden Message
Some Steganography Tools
•
•
•
•
•
•
•
•
Steganos
S-Tools (GIF, JPEG)
StegHide (WAV, BMP)
Invisible Secrets (JPEG)
JPHide
Camouflage
Hiderman
And many others…
(We will try it today …)
RGB Color Model in Image Files
• red, green, and blue light are added
together in various ways to reproduce a
broad array of colors.
(0, 0, 0) is black
(255, 255, 255) is white
(255, 0, 0) is red
(0, 255, 0) is green
(0, 0, 255) is blue
(255, 255, 0) is yellow
(0, 255, 255) is cyan
(255, 0, 255) is magenta
A Common Technique of Steganography
-- LSB
• The simplest and most common type of steganography is
LSB (least significant bit). The one’s bit of a byte is
used to encode the hidden information.
• Suppose we want to encode the letter A (ASCII 65 or
binary 01000001) in the following 8 bytes of a carrier file.
01011101 11010000 00011100 10101100
11100111 10000111 01101011 11100011
becomes
01011100 11010001 00011100 10101100
11100110 10000110 01101010 11100011
Left image is original JPEG file
Right image is with hidden message
Steganography Application
-- UV Watermarking
Steganography Tools
A list of over 100 steganography tools:
http://www.jjtc.com/Steganography/toolmatrix.htm
Some of them run in Linux platform
• JPHS (JPHide JPSeek, JP hide and seek)
http://linux01.gwdg.de/~alatham/stego.html
• Steghide
• Outguess
• Blindside
• Gifshuffle
• GzSteg
• Etc.
Steganalysis
• Steganalysis is the counter-measure
against steganography.
– Attempts to analyze a data stream to
determine whether or not it contains hidden
messages.
In Conclusion …
Steganography is really cool
– It’s fun to play with
– Easy to implement but fairly effective.
– Obviously has a lot of good and bad applications, as
with an technology.
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