Somewhere on the Internet, tucked away among thousands of Web sites is information that was used to execute the Sept. 11 attack on America. Federal agents said they are certain that the terrorists employed message boards and Web sites to talk among themselves. After the attacks, investigators searched the hard drives of computers at public libraries where it is believed some of the suspects had logged on, but as of last November were reluctant to reveal what they had found.
If the FBI is correct, then the terrorists used a digital version of steganography, from the Greek word meaning “covered writing,” to avoid arousing any suspicions. They hid their messages by embedding them in the computer codes of e-mails and pictures. The secret directives were then sent to a Web site where they were available 24 hours a day and hidden to all but the intended recipients. Officials believe that innocuous sites such as sport chat rooms and the content of pornographic Web sites served as an extra layer of protection to hide secret messages.
“The bad guys always figure out a way to use technology against the good guys,” said Bob Breeden, special agent with the Florida Department of Law Enforcement. “Henry Ford didn't expect his Model T to be used in bank robberies either.”
There are legitimate and practical reasons for hiding information in an image, music and document. One is to provide copyright information and protect intellectual property.
In a windowless-basement office on the FSU campus, Yvo Desmedt, director of the Security and Assurance in Information Technology Laboratory, develops algorithms to make things disappear. Desmedt, a computer science professor and doctoral student Tri Le-van experiment with hiding digital watermarks that can be used to show ownership of computer generated images and audio.
His contribution to this nascent field may make it easier for consumers to enjoy music, films and literature on computers and television sets. The fear that intellectual property will be pirated because of the ease with which digital files can be copied and shared has prevented the entertainment industry from embracing the Internet as a way to distribute its products.
“One of the things that has been lacking is tying distribution back to revenue collection,” said Sean Wargo, senior analyst with the Consumer Electronics Association, a group supported by electronic manufacturers. “The search is on for a way that everyone is compensated without the consumer losing fair usage rights.”
“It's a most challenging task,” said Paul Jessop of the Secure Digital Music Initiative, a consortium of 200 companies formed to discourage the unauthorized recording and distribution of music.
Digital watermark-ing gives whoever has the exclusive right to reproduce a creative work the ability to insert in their property information unnoticeable to the human eye and ear. Then, theoretically, they could search the Internet and track down illegal copies of their music and images.
“Research shows if it (the watermark) is not hidden it will not work, and will be removed,” said Desmedt.
Steganography, the act of hiding information within something that is in plain sight, dates to ancient Greece. The Trojan horse may be the most familiar example. Inside a wooden horse— a digital file for this discussion—were soldiers, information that the citizens of Troy could not see. And Chinese rebels distributed written plans inside cakes for an uprising against the Mongols. In a digital environment the hidden content could be a copyrighted logo or other information.
One method Desmedt and Le have experimented with requires two images to reveal the hidden text. For example, the pictures on page 40 appear to be identical. But there are subtle alterations hidden deep within the digital files of both. One can decipher no message with just one of the images. But when the two files are combined, one laid over the other, the message appears. These photos concealed a simple text but it could have been a much more elaborate message. And one would need both images to decode it.
Desmedt has had remarkable success with concealing information within an audio file, as well.
“This sounds like ordinary music. Does it not?” He asked while playing a piano concerto on a personal computer.
“Now here's a different version of the same selection. It sounds the same, right?” he asked a visitor.
But when he played them together, simultaneously, there was no music. What was heard was former President Bill Clinton delivering a speech. Desmedt inserted it by manipulating the phases of the two signals so that when played together the unwanted sounds cancelled out each other leaving only the speech to be heard (For a demonstration of the technique, visit www.cs.fsu.edu. The technique could, after further research, be used to add a watermark that included a code that would prevent the selection from being re-recorded and played with an unauthorized player. And the undetectable watermark could also serve as notice that the selection is a legal copy. Watermarking means the pop group Uncle Cracker gets paid each time a copy of the band's latest CD is sold.
A further refinement of the technique could determine whether music and videos are played on a computer hard drive, come on a disc or transmitted via cable, satellite or broadcast. According to analysts, the industry wants copyright protection before agreeing to a system that enables digital TV sets, DVD players, digital cable and satellite receivers to connect to each other digitally.
“A watermark code permitting just a single use and preventing copying can be done,” said Scott Brown, a senior vice president with Nielsen Media Research. “Watermarking to protect content is paramount to many in the industry.”
In a digital world, without any safeguards, producers could lose control of how their product is distributed. By striking a single keystroke, a counterfeiter could create high-quality duplicates of video and music files and offer them to the public.
“The people who own the original materials have concerns about that,” noted Walt Ciciora, a Connecticut-based consultant on cable and consumer electronics issues. “The movie industry is very fearful of perfect digital copies made freely available either on the Internet or by other means and reducing the value of their intellectual property.”
Desmedt conceals information within the millions of digits that create the images and sounds viewed and listened to on a digital player.
The digital world is based on the binary system. When something is digitized it is reduced to a series of number that are a multiple of two. In this system a numerical version of the 26 letters of the alphabet require five columns representing 16, 8, 4, 2 and 1. The letter Z, the 26th letter is written as 11010 (one multiple of 16, one of 8, no multiples of 4, one of 2 and none of 1). The number 00001 would represent the letter A. The more columns used to represent information the more opportunities there are to hide something.
Say someone wanted to place a watermark in a photo of a landmark taken on a bright cloudless day. Copyright information could be hidden in the sky at the corner of the image. This would require manipulating the number containing the information of the color blue in one of several thousand pixels that make up the picture.
If a seven-digit number represents the pixel, a steganography program would change one digit. The human eye is unable to notice when a blue pixel represented by 1,000,000 is altered to 1,000,001. This can be done to thousands of pixels without causing any noticeable change in the image. The sky remains blue, the watermark is inserted and no one is any wiser. That is until someone is hauled into court on charges of counterfeiting copyrighted material.
“If you know where to use extra software then you can reveal the watermark and show ownership,” said Desmedt.
“It is a two-edged sword,” he added. “It can be used for good purposes and for some not so good purposes.”