STEGANOGRAPHY
INTRODUCTION
Steganography is the art and science of writing hidden messages in
such a way that no one apart from the sender and intended recipient even
realizes there is a hidden message. By contrast, cryptography obscures
the meaning of a message, but it does not conceal the fact that there is
a message. Today, the term steganography includes the concealment of digital
information within computer files. For example, the sender might start with an
ordinary-looking image file, then adjust the color of every 100th pixel to
correspond to a letter in the alphabet-a change so subtle that someone who
isn't actively looking for it is unlikely to notice it.
The word steganography
is of Greek origin and means "covered, or hidden writing". Its
ancient origins can be traced back to 440 BC. Herodotus mentions two examples
of steganography in The Histories of Herodotus . Demaratus sent a
warning about a forthcoming attack to Greece by writing it on a wooden
panel and covering it in wax. Wax tablets were in common use then as re-usable
writing surfaces, sometimes used for shorthand. Another ancient example is that
of Histiaeus, who shaved the head of his most trusted slave and tattooed a
message on it. After his hair had grown the message was hidden. The purpose was
to instigate a revolt against the Persians. Later, Johannes Trithemius
published the book Steganographia, a treatise on cryptography and
steganography disguised as a grimoire.
Generally, a steganographic message will appear to be something else: a
picture, an article, a shopping list, or some other message. This apparent
message is the covertext. For instance, a message may be hidden by using
invisible ink between the visible lines of innocuous documents.
Steganography has revolutionized the
world of internet security . It has found several applications also other than
covert communication which was predominantly used during those days. As a gift
from past modern day computer algorithms and techniques have made it more
powerfull than any one could possibly imagine.
ISSUES RELATED TO
STEGANOGRAPHY
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During and after World War II, espionage agents
used photographically produced microdots to send information back and forth.
Since the dots were typically extremely small-the size of a period produced by
a typewriter or even smaller-the stegotext was whatever the dot was hidden
within. If a letter or an address, it was some alphabetic characters. If under
a postage stamp, it was the presence of the stamp. The problem with the WWII
microdots was that they needed to be embedded in the paper, and covered with an
adhesive (such as collodion), which could be detected by holding a suspected
paper up to a light and viewing it almost edge on. The embedded microdot would
reflect light differently than the paper.
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More obscurely, during World War II, a spy for
the Japanese in New York City, Velvalee Dickinson,
sent information to accommodation addresses in neutral South
America. She was a dealer in dolls, and her letters discussed how
many of this or that doll to ship. The stegotext in this case was the doll
orders; the 'plaintext' being concealed was itself a codetext giving
information about ship movements, etc. Her case became somewhat famous and she
became known as the Doll Woman.
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Counter-propaganda: During the Pueblo Incident, US crew members of the USS Pueblo (AGER-2)
research ship held as prisoners by North Korea
communicated in sign language during staged photo ops to inform the United States that they had not defected, but
had instead been captured by North Korea
and were still loyal to the U.S.
In other photos presented to the US, the crew members gave "the
finger" to the unsuspecting North Koreans, in an attempt to discredit the
pictures that showed them smiling and comfortable.
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A citation from the USA Today article:
"Lately, al-Qaeda operatives
have been sending hundreds of encrypted messages that have been hidden in files
on digital photographs on the auction site eBay.com". These rumors
were cited many times-without ever showing any actual proof-by other media
worldwide, especially after the terrorist attack of 9/11.
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In October 2001, the New York Times published an
article claiming that al-Qaeda had used steganographic techniques to encode
messages into images, and then transported these via e-mail and possibly via USENET
to prepare and execute the September 11, 2001 Terrorist Attack.
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