Steganography

 
Steganography
Steganography is the practice of hiding information within other information. The term literally
means “covered writing.” Like cryptography, steganography has been used since ancient
times. Steganography allows you to take a piece of information, such as a message or
image, and hide it within another image, message or even an audio clip. Steganography
takes advantage of insignificant space in digital files, in images or on removable disks
[***S. Katzenbeisser and F. Petitcolas, Ed., Information Hiding: Techniques for Steganography
and Digital Watermarking (Norwood, MA: Artech House, Inc., 2000) 1-
2.***] Consider a simple example: If you have a message that you want to send secretly,
you can hide the information within another message, so that no one but the intended receiver
can read it. For example, if you want to tell your stockbroker to buy a stock and your
message must be transmitted over an unsecure channel, you could send the message “BURIED
UNDER YARD.” If you have agreed in advance that your message is hidden in the
first letters of each word, the stock broker picks these letters off and sees “BUY.”
An increasingly popular application of steganography is digital watermarks for intellectual
property protection. An example of a conventional watermark is shown in Fig. 7.7.
A digital watermark can be either visible or invisible. It is usually a company logo, copyright
notification or other mark or message that indicates the owner of the document. The
owner of a document could show the hidden watermark in a court of law, for example, to
prove that the watermarked item was stolen.
Digital watermarking could have a substantial impact on e-commerce. Consider the
music industry. Music publishers are concerned that MP3 technology is allowing people to
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distribute illegal copies of songs and albums. As a result, many publishers are hesitant to
put content online, as digital content is easy to copy. Also, since CD-ROMs are digital,
people are able to upload their music and share it over the Web. Using digital watermarks,
music publishers can make indistinguishable changes to a part of a song at a frequency that
is not audible to humans, to show that the song was, in fact, copied. Microsoft Research is
developing a watermarking system for digital audio, which would be included with default
Windows media players. In this digital watermarking system, data such as licensing information
is embedded into a song; the media player will not play files with invalid information.
e-Fact 6.11
Record Companies are losing approximately $5 billion per year due to piracy. [***D.Mc-
Cullagh, “MS May Have File-Trading Answer”, 1 May 2001 <http://
www.wired.com/news/print/0,1294,43389,00.html>***] 6.11
Blue Spike’s Giovanni™ digital watermarking software uses cryptographic keys to
generate and embed steganographic digital watermarks into digital music and images (Fig.
7.8). The watermarks can be used as proof of ownership to help digital publishers protect
their copyrighted material. The watermarks are undetectable by anyone who is not privy to
the embedding scheme, and thus the watermarks cannot be identified and removed. The
watermarks are placed randomly.
Fig. 6.7 Example of a conventional watermark. (Courtesy of Blue Spike, Inc.)
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Giovanni incorporates cryptography and steganography. It generates a symmetric
secret key based on an encryption algorithm and the contents of the audio or image file that
will carry the watermark. The key is then used to place (and eventually decode) the watermark.
The software identifies the perceptually insignificant areas of the image or audio file,
enabling a digital watermark to be embedded inaudibly, invisibly and in such a way that if
the watermark is removed, the content is likely to be damaged.
Digital watermarking capabilities are built into some image-editing software applications,
such as Adobe PhotoShop 5.5 (www.adobe.com). Companies that offer digital
watermarking solutions include Digimarc (www.digimark.com) and Cognicity
(www.cognicity.com).
In the last few chapters, we discussed the technologies involved in building and running
an m-business, and how to secure online and wireless transactions and communications.
In Chapter 7, Legal, Ethical and Social Issues; Web Accessibility, we discuss a
number of major legal and ethical concerns that have developed from the introduction of
the Internet and the World Wide Web.
Fig. 6.8 An example of steganography: Blue Spike’s Giovanni digital
watermarking process. (Courtesy of Blue Spike, Inc.)
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