Steganography Essay, Research Paper
I. INTRODUCTION
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.
II. STEGANOGRAPHY
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 doesn?t 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 messenger?s
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.
Another form of hiding
messages). The real message is "camouflaged" in an innocent sounding
message. Due to the "sound" of many open coded messages, mail filters
detected the suspect communications. However "innocent" messages were
allowed to flow through. An example of a message containing such a null cipher
is:
News Eight Weather: Tonight increasing snow.
Unexpected precipitation smothers eastern towns. Be
extremely cautious and use snowtires especially heading
east. The highways are knowingly slippery. Highway
evacuation is suspected. Police report emergency
situations in downtown ending near Tuesday.
By taking the first letter in each word, the following message can be
derived:
Newt is upset because he thinks he is President.
The following message was actually sent by a German Spy in WWII [Kahn67]:
Apparently neutral’s protest is thoroughly discounted
and ignored. Isman hard hit. Blockade issue affects
pretext for embargo on by products, ejecting suets and
vegetable oils.
Taking the second letter in each word the following message emerges:
Pershing sails from NY June 1.
Recently, Margaret Thatcher was so irritated with numerous press leaks of
cabinet documents, she had the word processors programmed to encode their
identity in the word spacing, so that disloyal ministers could be traced. [4]
C. Software
Three types of stegonagraphic software packages were evaluated by Neil
Johnson and Sushil Jajodia (authors of Exploring Steganography: Seeing the
Unseen) on their limitations and flexibility. [5] They are StegoDos, White Noise
Storm and S-Tools for Windows.
StegoDos is a share-ware program, which can be downloaded for free off the
internet (http://www.demcom.com). Its limitation is that it only works with 320
x 200-pixel images with 256 colors. Using a Renoir painting, they tried to
insert a photo of the Russian strategic bomber base (http://edcwww.cr.usgs.gov/dclass).
It could not be used because of size restrictions. They were able to use the
software in the Shakespeare image once it was cropped and fitted into the 320 x
200 pixel image. There was some distortion to the image but not very noticeable.
StegoDos uses LSBs (Least Significant Bits) to hide it?s messages. It is the
less successful tool of the three tested.
White Noise Storm is a DOS application and is very effective. It uses the LSB
approach and applies this to IBM Paintbrush (PCX) files. They were able to embed
the Russian strategic bomber base into the Renoir painting with no degradation
to the image. But, there were problems due to noise interference in the
integrity of the image, which altered the color palette considerably in the
Renoir painting. The main disadvantage of this encryption method is the loss of
many bits that can be used to hold information. [5]
The last software evaluated was S-Tools for Window. This freeware program
lets you hide files of any type in .gif and .bmp images as well as in .wav
sounds. Furthermore, S-Tools is actually a steganographic and cryptographic
product in one, because the file to be hidden is encrypted using one of the
symmetric key algorithms: Triple DES and IDEA are very secure as of today.
Another good steganography product is Steganos for Windows 95. It has almost
the same functions as S-Tools, but applies a different algorithm (HWY1) and is
able to hide data in .bmp and .wav files as well as in plain text and HTML files
in a very clever way. Steganos just adds a certain number of additional spaces
at the end of each text line. Steganos also adds an option of sending files from
your hard drive to the shredder, which makes it impossible to recover them.
III. CONCLUSION
In conclusion, I gave a brief definition of steganography as well as
cryptography and digital watermarking. Next, I went into a little history about
Steganography and where it originated. Finally, I discussed some of the software
that is available, what implementations were used and noted any limitations with
those software programs.
Steganography is much powerful tool when used in conjunction with
cryptography because it adds another layer of protection to an encrypted file.
Commercial applications of steganography, digital watermarking and digital
fingerprinting is now in use to track the copyright and ownership of electronic
media. [5]
[1] Markus Kuhn, 1995
http://www.iks-jena.de/mitarb/lutz/security/stegano.html
[2] Introduction to PGP
http://sun1.bham.ac.uk/N.M.Queen/pgp/pgp.html
[3] Mr. Byte, Steganography, 1997-1999
http://www.tamos.com/privacy/steganoen.htm
[4] Anderson, Ross J., Petitcolas, Fabien A.P., On The Limits of
Steganography
16[4] 474-481, May 1998
[5] Johnson, Neil F., Steganography, 26-34
http://www.jjtc.com/stegdoc/