How Safe Are Your Shredded Documents?
One of the shredded documents used in the DARPA Shredder Challenge.
Credit: www.shredderchallenge.com

What do the Watergate and Enron scandals have in common? There's the criminal aspect of course, but in both cases the bad guys went straight for the shredders the moment they got caught, turning mountains of incriminating paperwork into hamster bedding.

Shredders are a supposedly secure way of destroying evidence, not only in criminal endeavors but also as a way for businesses to protect their clients from garbage-rummaging identity thieves, and for governments to get rid of classified documents.

But just how secure are those shredded bits of paper that get tossed in the dumpster?

That's exactly what the Department of Defense's Defense Advanced Research Project Agency, commonly known as DARPA, is trying to find out.

On October 27, DARPA issued a challenge to the world: build a computer program that could analyze bits of shredded documents and piece them back together. The goal, as stated on the shredder challenge website, was "to identify and assess potential capabilities that could be used by our warfighters operating in war zones, but might also create vulnerabilities to sensitive information that is protected through our own shredding practices throughout the U.S. national security community"

While the challenge went unnoticed in many spheres of society, the computer programming world sat up and took notice. More than 9,000 teams registered to compete for the $50,000 prize. To reach the finish line, the teams had to reconstruct documents for five separate problems, and correctly answer questions about the information contained in the documents.

A team named 'All Your Shreds are Belong To Us' won the top prize on December 2. Led by computer programmer Otavio Good, the team was made up of a group of acquaintances from the San Francisco Bay area.

Good entered the contest on a whim, thinking that it would be a fun project to tinker with on weekends. But over the course of a month, he and his two teammates spent more than 600 hours programming and putting together the equivalent of a really difficult jigsaw puzzle.

A really hard virtual jigsaw puzzle, that is. The official puzzle consisted of five documents shredded into 10,120 small strips. These were then scanned into a digital document, so that everyone participating would have the same material to work with.

Good and his team designed a computer program that would examine the scanned pieces and suggest connecting shreds to a human operator. He said that the program came together over time, and they eventually trained it to recognize connecting letters, patterns on the paper, and other distinguishing features.

So, if Good and his friends can write a computer program that can piece together shredded documents, just how safe are your shredded bank statements? Right now, they're probably ok. A group of people can eventually reconstruct shredded documents by hand if they work long enough, especially if the document in question is only torn into a few hundred pieces instead of a few thousand.

And even with a program like Good's helping out, it takes hours upon hours to piece thousands of shreds of paper together, and when they're mixed in with the remains of other pieces of paper, the task gets exponentially harder. While it's certainly possible to rebuild your shredded tax returns, the time required to do so is usually enough of a deterrent. Especially if you're a relatively low-profile target, as most of us are.