If I were to frequently work on sensitive data on a LUKS partition and wanted to be able to quickly destroy the keys to it, I figure it would make sense to—

  1. encrypt that partition with a key file,

  2. place the only copy of that key file on some sort of removable medium,

  3. come up with a plan for destroying that removable medium quickly,

  4. carry the removable medium (and equipment to destroy it) everywhere.

That way, if The Final Reckoning arrives, I can immediately destroy the removable medium, making the partition's data inaccessible.

The difficulty lies in choosing a medium which is both easy to use and easy to destroy.

  • USB sticks are convenient to use: just configure the boot partition to read the keyfile from there. However, they are difficult to destroy quickly and reliably, necessitating destructive tools that are difficult to carry safely, and illegal to take on planes.

  • QR-codes printed on paper are inconvenient to use: I don't know of any LUKS implementation that allows key input by QR-scan. However, they can be destroyed without equipment, by just eating the paper.

  • Memorising the key is both inconvenient to use (takes a while to rehearse, then have to type it in every time) and difficult to destroy (voluntary forgetting is difficult, though it is plausibly deniable).

How could I get both?

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    I'm probably missing something, but do you really need to destroy a USB stick during a flight? I ask this because you wrote that those tools are "illegal to take on planes". – A. Darwin May 30 '16 at 5:52
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    i want to invent a ram-based thumb drive for this very reason; remove the power, data go bye bye. it might be possible to use a low-power device like a pi (raspberrypi.stackexchange.com/a/1090) to emulate a kb that types the key, or a beagleboard that can mount a ramdisk as a linux usb volume. a mini CD-R and sandpaper could be viable too, if messy. a barcode KB wedge would allow paper keys you could chew up, or an etch-a-sketch barcode you can shake. – dandavis May 30 '16 at 6:53
  • @A.Darwin That was intended as an example. I'd like to be able to destroy the medium as quickly as possible, in as many situations as possible. (Being feasible on a commercial flight is not a hard requirement.) – Anko May 30 '16 at 13:51
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    @dandavis Storing the key in RAM is not 100% safe. See for example how android encryption can be tackled (extremetech.com/computing/…). – Potaito May 30 '16 at 15:00
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    @potAito: ok, sub a "marching-bit" RAM burn-in test on button press for yanking the power. – dandavis May 30 '16 at 19:01

Your best bet would be a CD or DVD, as they are easy to use and easy to destroy (see below), with CDs being even easier to destroy because of the different data density. The main disadvantage is that they're bigger than a flash drive, and thus also harder to conceal, but I'm not sure if that's your problem. Anyway, if you don't fear X-rays, body scanners or a proper patdown, you could try to conceal one under your clothes.

There are shredders which can be specifically used to destroy CDs and DVDs, and if you don't have access to them, you can always improvise using a garden scissor (or any kind of scissors/blade capable of cutting through plastic and such) and a blender. I think you could mechanically destroy a CD in this way in under 5 minutes. You can also shred them using a microwave - which is probably quicker -, or even combine different techniques.

For more information, read this question on Superuser and its answers.

The other possibility would be a USB drive or a SD card. They are smaller and easier to conceal, and easy to use, but they're also harder to destroy via improvised, mechanical means.

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  • CD would be better than dvd since a fragment the same size would have many fewer intact bits. to wit; the us standard for destruction is tighter for dvd than cd, and bluray is very difficult. – dandavis May 30 '16 at 18:57
  • @dandavis I honestly didn't think about it. I'm going to edit my answer. – A. Darwin May 30 '16 at 19:12
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    you can buy credit-card shaped CD-Rs or cheaper round 80mm once, which hold about 50mb... – dandavis May 30 '16 at 23:03
  • @dandavis But a CD also has larger, more easily readable bits. I'd prefer to hide sensitive audio on a microSD than I would on a vinyl record, despite the fact that a smashed record has far fewer bits per fragment than a smashed microSD! – forest Dec 11 '17 at 6:05

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