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The Rise of Anti-Forensics

New, easy to use antiforensic tools make all data suspect, threatening to render computer investigations cost-prohibitive and legally irrelevant

Liu agrees but takes it further. He believes developing antiforensics is nothing less than whistle-blowing. “Is it responsible to make these tools available? That’s a valid question,” he says. “But forensic people don’t know how good or bad their tools are, and they’re going to court based on evidence gathered with those tools. You should test the validity of the tools you’re using before you go to court. That’s what we’ve done, and guess what? These tools can be fooled. We’ve proven that.”

For any case that relies on digital forensic evidence, Liu says, “It would be a cakewalk to come in and blow the case up. I can take any machine and make it look guilty, or not guilty. Whatever I want.”

Liu’s goal is no less than to upend a legal precedent called the presumption of reliability. In a paper that appeared in the Journal of Digital Forensic Practice, Liu and coauthor Eric Van Buskirk flout the U.S. courts’ faith in digital forensic evidence. Liu and Van Buskirk cite a litany of cases that established, as one judge put it, computer records’ “prima facie aura of reliability.” One decision even said computer records were “uniquely reliable in that they were computer-generated rather than the result of human entries.” Liu and Van Buskirk take exception. The “unfortunate truth” they conclude, is that the presumption of reliability is “unjustified” and the justice system is “not sufficiently skeptical of that which is offered up as proof.”

It’s nearly a declaration that, when it comes to digital information, there’s no such thing as truth. Legally anyway. As Henry likes to put it, “Antiforensic tools have rendered file systems as no longer being an accurate log of malicious system activity.”

Computer forensics in some ways is storytelling. After cordoning off the crime scene by imaging the hard drive, the investigator strings together circumstantial evidence left at the scene, and shapes it into a convincing story about who likely accessed and modified files and where and when they probably did it. Antiforensics, Liu argues, unravels that narrative. Evidence becomes so circumstantial, so difficult to have confidence in, that it’s useless. “The classic problem already with electronic crimes has been, How do you put the person you think committed a crime behind the guilty machine they used to commit the crime?” says Brian Carrier, another forensic researcher, who has worked for the Cerias infosecurity research program at Purdue University. Upending the presumption of reliability, he says, presents a more basic problem: How do you prove that machine is really guilty in the first place? “I’m surprised it hasn’t happened yet,” says Liu. “But it will.”