While Encryption is detectable and a target for questions by the government
as well as hackers, Steganography takes it one step further and hides the
message within an encrypted message or other mediums; such as images, making it
virtually impossible to detect. It is a method related to the art of hiding a
secret message within a larger one in such a way that the unwanted person cannot
make out the presence or contents of the hidden message being sent. It can be
hidden in a picture or a sound file.

Most communication channels like telephone lines and radio broadcasts
transmit signals, which are always followed by some kind of, noise. This noise
can be replaced by a secret signal that has been changed into a form that is not
detectable from noise without knowledge of a secret key and this way, the secret
signal can be transmitted undetectable. [1]

A. Purpose of this paper

The purpose of this paper is to introduce steganography by explaining what it
is and how it works in conjunction with cryptography; provide a brief history;
note on the types of software programs available and how effective they are.

B. Body

First, I will define stenography, along with cryptography and digital
watermarking. I will also discuss the differences between the two. Second, I
will discuss briefly the history of steganography. Finally, I will review
several different software applications available that provide steganography,
how they are implemented and discuss any failures that may occur.

C. Conclusion

I will review the topics, which were discussed and give my personal opinion
on a particular software programs that I tried out.


A. Definition

Steganography comes from the Greek word Steganos meaning covered or secret,
basically hidden writing. Steganography is a non-cryptographic technique for
hiding data in the natural noise component of some other signal. Steganography
simply takes one piece of information and hides it within another. It uses
computer files (images, sounds recordings, even disks) which contain unused or
insignificant areas of data. Invisible inks, microdots, character arrangement,
digital signatures, covert channels, and spread spectrum communications also use
Steganography. Steganography takes advantage of these areas, replacing them with
information (encrypted mail, for instance). The least significant bits (LSBs) of
most digitized signals; music or images for instance; are randomly distributed.
You can change these bits to anything you like without noticeably changing the
music or images.

Cryptography disguises the text of the message but doesnít hide the fact
that it is doing so. PGP (Pretty Good Privacy), a very strong cryptographic
tool. Its popularity doesn\'t stem from the fact that nobody knows how to break
the system other than by a brute-force attack (which is a prerequisite for any
good cryptosystem). PGP became popular because it is extremely well designed,
fast, and has an excellent key management. There are many cryptographic
algorithms as strong as the one used in PGP, but PGP\'s popularity and free
availability made it a de facto standard for secure electronic communications
all over the world. [2]

Digital watermarking which is a special technique of creating invisible
digital marks in images and audio files that carry copyright information. These
marks can be detected by special programs that can derive a lot of useful
information from the watermark: when the file was created, who holds the
copyright, how to contact the author etc. As you know tons of copyrighted
materials are reproduced, i.e. stolen on the Net every day so this technology
might be useful if you are a designer.

B. History

Steganography dates back to ancient Greece. During ancient Greek wars, if a
solder needed to notify his leader that he had information on enemies planning
to attack at a certain place and time, he would take a blank tablet write the
message then cover the tablet with wax. This was a way to conceal the
information as he passed through inspections. [3]

Another way they used to send hidden messages was to shave the messengerís
head then tattoo the information. Once his hair had grown enough to cover the
message, he was then sent on his way to deliver the message. Of course, he had
to have his hair shaved again for the message to be revealed then let his hair
grow back.

During World War II, the Germans developed the microdot. A secret message was
photographically reduced to the size of a period, and affixed as the dot for the
letter \'i\' or other punctuation on a paper containing a written message.
Microdots permitted the transmission of large amounts of printed data, including
technical drawings, and the fact of the transmission was effectively hidden.