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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.

Comments

  1. Requiem says:

    And that’s why you just burn the document if it is that important to hide.

  2. Elias says:

    Using a proper cross-cut shredder will make it way too time consuming to reassemble, so no fire needed :)

  3. tyco says:

    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

  4. Tamas says:

    Does anyone know any commercial unshredder?

  5. Hacksaw says:

    Cool new software for identity thieves…

  6. M4CGYV3R says:

    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.

  7. Mario says:

    I don’t remember an X-Files Episode where they reconstructed a shredded paper using a computer program. But I do remember a Lone Gunmen episode (An X-Files spinoff): http://www.youtube.com/watch?v=zwhuVw_HhQc

  8. jefb says:

    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.

  9. gnarf says:

    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

  10. trialex says:

    Seems like the engines used for panorama stitching software (like hugin) might be able to be used.

    Maybe they already are and I should RTFA.

  11. 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.

    • Black Soap says:

      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?”

  12. Ltb0b says:

    use flashpaper and burn it what could go wrong :P

  13. cmholm says:

    This (and the manual method the Iranis used back in ’79) is why today’s anal-retentive high-end shredders turn paper into dust.

  14. 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.

    • Mr K says:

      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.

    • Malikaii says:

      I’m not sure what kind of secure facility you’re referencing, but I can list a LOT of places where that isn’t happening,and should be.

  15. Greatevil says:

    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.

    • kernelcode says:

      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.

  16. Haku says:

    DARPA really should have called it the Oswald Cobblepot challenge.

  17. razor says:

    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)

    • Daid says:

      I have 1 more:
      -A cat.

      Leaving any paper near a cat would grantee it to be shredded to tiny irregular parts.

      • Quin says:

        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.

      • anonymouse says:

        not entirely effective as my cat will just sit on a piece of paper…stupid cat

    • grelfod says:

      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.

  18. reyya says:

    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.

  19. stephen says:

    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

    • kernelcode says:

      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?

  20. Mike says:

    Funny timing, I saw some shredded documents in the trash the other day, and got really curious :D

  21. Kiss says:

    A lot more technical description of puzzle solving:D
    http://people.csail.mit.edu/taegsang/Documents/JigsawSolver.pdf

  22. Jehu says:

    Kinda takes the fun outta doing it by hand. I used to reassemble them for the fun of it when I was younger

  23. Dutch says:

    “I hope this will become the easy test… although.. ROEL” ;)

  24. Drone says:

    Study “The Calculus of Variations”.

  25. Whatnot says:

    So this only works for handwritten things? uhm.. who does that anymore?

  26. tjb says:

    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.

    • littledaz says:

      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

  27. Will says:

    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.

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