Unshredding Paper

[Roel] had read that people won the DARPA shredder challenge, but that their technology was kept a secret, interested in this concept he also remembered an episode of the X-Files where they had reconstructed shredded paper using a computer system. Unlike most computer based TV show BS this did not seem to be too far fetched so he went about trying it himself.

First a note is written, and then cut up into strips, the strips are then scanned into a computer where the magic happens. Next each strip outlined in polygons and then the software is to follow the polygon outline looking for a change in color at the pixel level. The software then goes into a pattern matching mode and reassembles the paper based on a scoring system.

While not many people use old fashioned strip shredders anymore, the basic idea works and if you really wanted to expand it could be applied to cross cut or particle shredders.

50 thoughts on “Unshredding Paper

        1. You have to be sure you got it from the right parallel universe, however. Last time I tried this, I was looking for one of the documents Oliver North shredded in the Iran-Contra scandal and found that in that parallel universe I grabbed them from we had been selling weapons to the Contras to bankroll the Iranians instead of the other way around. The documents were completely useless.

  1. Sometimes, I have a sensitive document (receipts usually) and I’m not near a shredder. If the document has only one or two sensitive items in it, I’ll tear out half of each of the sensitive items, and throw away those portions in a place completely different from the rest of the page. This is actually more secure than a cross-cut shredder.

    But if it was really important, I’d probably just burn it. :D

  2. This is one of those “How did I not think of that already” moments.

    Oh well – it seems the fact that someone else has already done it quite successfully(and probably better than I could) doesn’t seem to hamper my ability to patent the idea these days.

  3. This is why I use it for kitty litter fill…

    And for the shredder folks out there. Iran reconstructed documents from the US Embassy that were shredded. Given enough time most anything can be reconstructed.

  4. the darpa win was made with the use of the yellow dots that printers embet in documents they print
    that can lead investigators to the printer

    its a repetitive pattern over the whole page

  5. the cut papers are too thick… use an exacto and a ruler to cut finer papers and try with that… also, you can make a program where you swap the order of the papers and have a neural network or ocr program get letters from it… if you can get letters you know the papers order is right.

    1. Build a smart shredder that cuts out individual letters so there is no ink overlap between adjacent bits of confetti.

      Then have it alphabetize them.

      Won’t work for images, only text.

      Anyone know the singular form of “confetti?”

  6. This is why secure shredders deposit even and odd strips into separate compartments. In a secure environment, different colored trash bags are used to receive the even and odd strips. These color-coded bags are placed into different guarded dumpsters stored at different locations at the facility, and the are retrieved and processed by different secure trash processing services. If one of the services gets compromised, it is unlikely that the strips can be aligned to retrieve significant information.

    1. Umm… what? I’ve worked in government, with a clearance above TS, for 10 years and we’ve never used what you describe. Different levels of classification require different characteristics for shredders, but all classified documents (shredded and unshredded) get placed into clearly marked “burn bags”, and all classified paperwork gets shredded before the “burn bags” are disposed of.

  7. I was just thinking about this kind of problem. Since edge detection is kind of a “done” thing now. I want a cell phone app that you can point at a puzzle with a missing piece and then point at the pile of pieces and have it highlight likely candidates. Generally puzzle pieces only have 4 “edges” and it is either an in or an out…. I might have to start whacking away at this…. adds to the to-do pile.

    1. My sister was doing a puzzle over Christmas and struggling to fit pieces towards the end – I had this exact same idea.
      I didn’t think the camera resolution would be sufficient for picking out the exact piece, so I too though finding the candidates would be as good as it got.

  8. 3 solutions
    water-soluble paper (surprisingly not too expensive)
    shred pen with paper (messy, but effective, esp. mixed with iso alcohol)
    use water under shredder with coffee grounds and tea bags (also messy, stinky long-term, and well… dangerous around electrical shredders)

      1. And then those tiny, irregular shapes get mixed in with cat litter and disposed of after they have been used.

        Also works for disposing old medication or anything else. Disolve in bowl of water, mix in cat liter, put in same bag as other, real used, cat liter. No on will go near it.

    1. We have used something akin to a garbage disposer when we had to ‘dispose’ of a quantity of documents. It ground the paper in water and made buckets of paper mache…
      we had no doubt that no one was piecing anything back together. It was cheap and quick (albeit a bit messy)
      If we had a garden would have used a chipper/shredder with a hose and then roto-tilled it in as mulch but alias we live in the city.

  9. that’s why my favorite personal shredders will always be gerbils… they leave miniscule bits of paper with fuzzy and torn edges, then they pee all over it. the urine starts the breakdown process, causes clumping and makes it pretty much impossible to reassemble.

  10. what about double-sided prints? sounds like a lot of work to try every combination..
    let’s say youhave a DIN A4 sheet of 21.6mm, which makes 11 stripes of 2mm. so you would have to scan 2^11 = 2048 different combinations (worst case). not to mention particle-cut shredders

    1. Surely you would do 2 scans – both sides of all of the strips – then let the computer do the work?
      What’s the point in writing software to do the job if you’re just going to go and do 2^11 scans by hand?

  11. I have found that strait cut burns better than cross cut. It is almost like soaking the paper in gas! We also have a real fireplace. So EVERY bit of discarded paper gets run threw the shredder and then used to start the fireplace. In summer said paper goes in the out door fire pit. By shredding both important and unimportant data it adds to the total amount of shred. We do this because it makes starting fires easy and generates less paper wast to deal with. The security is a side benny.

    1. I store my shreddings up then a few times a year I soak them for a week and put them through a press to make briquettes to go on my fire, each one will burn for an hour or two and it’s basically free fuel. like you I find the security an added bonus

  12. You just need to assess the value of what you’re shredding to a potential attacker.

    For dealing with basic dumpster-diving opportunistic identity thieves, a plain strip shred is probably sufficient. Chances are, your neighbor isn’t shredding his garbage, and the thieves will just move on to him.

    A cross-cut shredder makes it even less appealing.

    For valuable info, and an attacker that has time and resources to really focus on your paperwork, cross-cut shredding and then burning will do the trick. The papier mache, litter box, and composting methods are all good ideas, too.

    And if it’s more valuable than that, don’t put it on paper, or a computer.

  13. Curious that with so much interest in the ability to reconstruct shredded documents that there is no business out there doing it? All the search links to possible sources come up dry. A lot of academic papers but no practical services…

  14. The one comment that stip shred isn’t used as much is true but the most common type of shred, especially in mobile applications is pierce-and-tear that has large pieces that don’t need to be put back together. The most popular manufacurer of this type of equipment admits that large pieces of paper and whole checks can pass through unshredded. Even under the best conditons (new equipment) the pieces are large enough to read. These truck don’t have eye level viewing windows as the more secure trucks do, and they won’t allow you to look in the back. Due Diligence is necessary if you’re really concerned about security.

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