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Comment by ampdepolymerase | Hacker News Reader

Current office shredders are almost all capable of double shredding but considering how easy it is to reverse by OP's project, it may be necessary to implement further measures for document destruction.

A laser or enzymic based method could work but neither are particularly office-friendly.

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I used to work for a defense contractor, in the mid-1980s.

Once a week, this big-ass tandem truck would park outside the entrance, and the janitors would carry out boxes of papers, under armed guard.

The truck had a huge shredder (crosscut), and also a big kiln.

Once the paper was shredded, it was burned, and the ashes were shredded, just to be sure.

Then, the truck would take the ashes away; never to be seen again.

How has that truck not appeared in an organised crime film yet?

Not sure.

I’ll bet Iron Mountain still does it (this was before Iron Mountain, but it could have been the same folks).

Once upon a time in Germany, I was put on several special duty assignments to guard documents overnight (with a machine gun!) prior to their destruction by companies like this.

OP's method relies on the permutation of elements in (columns or rows) to be in the same order for each (column or row).

If you're just handed a pile of confetti you don't have that same correspondence.

Also, you generally have written correspondence, not images. I doubt that the similarity metric of OPs method produces reasonable results on text, and a good similarity metric for text would be much more complicated.

On the other hand physical shredders typically have other weaknesses, for example if you don't stir the shredded result you have a high correlation between original the current and original relative position of the individual pieces.

With written text, you would expect that at least some the letters from one shred would continue on its neighbors. I don't see why the similarity metric would not work. Also normally you have a pretty high contrast between the letter and the background, unlike the image that was used in the example.

If you have a language model, then sequences of characters appearing in your text will add further information to your edge matches.

https://a.pomf.cat/uayjgu.jpg

Roy Mustang does it with way more style ;)

Just dump the shredded remains into a water-based mixing device, and then dry out the remains and launch them into the sun.

We used to cross-cut shred, and then turn the shredded remains into recycled paper, at one of my old workplaces.

Could someone invent a shredder that pre-analyses an image of what it's shredding and then shreds in a manner that makes reconstruction infeasible due to the increased likelihood of false positives? (e.g. the flipped and mirrored images in OP)

I think that would be a lot more complicated mechanically than adding a chemical process like bleaching the paper after it's been shredded. Or replacing the shredder with an off the shelf wood stove if you're in a city that doesn't have a ton of restrictions on what you can burn for heat

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