Read_Me. . Conference - Grapevine - H2K2-HOPE Hackers on Planet Earth

Afterimage, Sept-Oct, 2002 by Are Flagan

For those interested in subversive uses of media and still remain somewhat puzzled by the contention last year that Osama bin Laden was inserting hidden messages in his video broadcasts (rather than straightforward arguments), would have appreciated the talk Peter Wayner (www.wayner.org) gave on steganography, which translates as the art and science of hiding information in digital data.

Although he was hard pressed to define "hidden," and was shrewdly hiding his lack of a definition behind Goedel's theorem that prevents us from being logical about detection, the methods outlined were elucidating enough to bypass such premises. Generally, to hide data in data means that it must be inserted in places where it will not be detectable unless you know where and how to look for it. In some respects (and just to confuse matters further), you essentially need to know what has taken place to describe what has happened. The Catch-22 can look like this: in a standard image file data can be replaced up to a threshold wit hout affecting how the image appears to the viewer. Examining the distribution of tones, however, may indicate certain levels of suspicious patterns, but this is not a guarantee that something secret or evil has been embedded; it may be the work of a benign compression algorithm, for example. Of the methods covered, the least technical was the replacement of digital noise, or redundant information, with a message. Wayner showed Illustrations of how he, through algorithms, had performed such tasks in image files. It basically involves replacing the least significant bit in the bit plane with one that belongs to the "hidden" message; i.e if a value of 255 is changed to 254 in a binary notation the result goes from 11111111 to 11111110, where the last digit signifies the alteration of data. Without any residual evidence, or a comparative analysis that points to this manipulation, the conundrums of detection discussed above are obviously haunting any claims about secret transmissions. Interestingly, researchers l ooking to embed digital watermarks in copyrighted content have embraced steganography to turn the copying of digital files into an ally in their protection schemes. One not-so-secret message here is that any unauthorized use of images, for example, can be successfully contested in a court of law, as the steganographic content, once unveiled, can be submitted as evidence that the offending file is indeed controlled and owned by the prosecuting party. Uses of the same science have essentially gone from being banned to becoming highly desirable once the rights to and benefits of secrecy are reversed.