Covert hard drive fragmentation embeds a spy's secrets

GOOD news for spies. There is now a way to hide data on a hard drive without using encryption. Instead of using a cipher to scramble text, the method involves manipulating the location of data fragments.

The inventors say their method makes it possible to encode a 20-megabyte message on a 160-gigabyte portable hard drive. It hides data so well that its existence would be "unreasonably complex" to detect, they say.

Encryption should sometimes be avoided, says Hassan Khan at the University of Southern California in Los Angeles, because the gobbledegook it creates is a dead giveaway: it shows someone might have something to hide. That could spell disaster for someone trying to smuggle information out of a repressive country.

So "steganography", hiding data in plain sight, is coming to the fore. Normally, data intended to be secret is added to the pixels in digital images, or used to change the transmission timing of internet packets. But these techniques are well known and easily detected, says Khan. So, with colleagues at the National University of Science and Technology in Islamabad, Pakistan, he has developed an alternative.

Their technique exploits the way hard drives store file data in numerous small chunks, called clusters. The operating system stores these clusters all over the disc, wherever there is free space between fragments of other files.

Khan and his colleagues have written software that ensures clusters of a file, rather than being positioned at the whim of the disc drive controller chip, as is usually the case, are positioned according to a code. All the person at the other end needs to know is which file's cluster positions have been encoded.

The code depends on whether sequential clusters in a file are situated adjacent to each other on the hard disc or not. If they are adjacent, this corresponds to a binary 1 in the secret message. If sequential clusters are stored in different places on the disc, this encodes a binary 0 (Computers and Security, DOI: 10.1016/j.cose.2010.10.005). The recipient then uses the same software to tell them the file's cluster positions, and hence the message. The researchers intend to make their software open source.

reference:http://www.newscientist.com/article/mg21028095.200-covert-hard-drive-fragmentation-embeds-a-spys-secrets.html