I am Constructing a Self-Destructing USB Drive
As a result of everyone knows one of the best ways to maintain your information secure is by blowing it up, proper?
Properly, for many of us, the actual reply lies with encryption. However contemplate this: there are specific international locations the place it’s harmful to be a journalist. Now faux you’re investigating political corruption in one among these international locations; in such circumstances, it is probably not secure so that you can be discovered with an encrypted drive.
My thought is to construct a USB drive that’s cosmetically and functionally equivalent to your run-of-the-mill USB. However there may be one distinction: when you plug it in usually, it doesn’t produce any information.
Now, what’s one thing a sane individual would by no means do earlier than plugging in an atypical flash drive? Lick their fingers.
That’s proper; The drive may have hidden electrodes that measure the resistance of the finger plugging it in. A finger is round 1.5MΩ, however moist fingers are round 500kΩ. When the gadget boots, the drive will seem clean if the resistance between the electrode pair is larger than a threshold. It’s not the prettiest system, however I believe it strikes a pleasant steadiness of ridiculousness and performance. The germaphobes amongst us can run their fingers beneath the faucet.
The Design
A flash drive is a comparatively easy design electrically. For the primary model, I’m going to focus on USB2.0 speeds.
The everyday flash drive consists of a USB controller (blue) linked to a NAND flash chip (purple). The flash chip holds all the info, whereas the controller comprises a USB entrance finish and logic to interface with the flash chip. To attain my desired performance, in poor health use a USB controller with a small microcontroller to learn the electrodes and inhibit the flash chip if vital.
Understanding element economics is crucial when designing {hardware}. The flash chip is generic and can be utilized in something: good TVs, pc BIOS, automobiles, you title it. Nevertheless, the USB controller is an application-specific element for flash drives.
Software-specific ICs come round when there’s an enormous market, and you must squeeze margins. There may solely be just a few dozen flash drive firms worldwide, and the engineering is stale. The lion’s share of the quantity comes from a number of large factories with razor-thin margins. There’s no sizzling new flash drive startup that’s going to disrupt the market. Digikey or Mouser isn’t the place to search for sourcing application-specific elements.
I scoured the web for flash drive teardowns, searched the textual content on the chips, and located a gold mine: a flash drive database that lists half numbers for a number of USB controller ICs. I then checked to see if I may get a datasheet and a vendor — I settled on the SM3257EN.
This chip appears prefer it ought to do the trick; the datasheet is properly written and has sufficient data. I created the half in Kicad and imported it with a NAND flash chip and USB jack.
I now need to make the gadget cover the info until the consumer licks their fingers.
A chip allow (CE) sign from the USB controller is designed to attach straight to the flash chip. When this sign is low, the flash chip will allow. I’ll use an “or gate” with my management sign to show power the reminiscence off.
When my inhibit sign is excessive, it doesn’t matter if the standing of CE. The output of the gate will likely be excessive, which disables the flash reminiscence.
As for controlling the inhibit sign itself, I’m going to make use of an ATTINY24, and a transconductance amplifier hooked as much as the electrodes. I’ll get extra into that subsequent publish.
The Mission
I’m making an attempt to construct {hardware} that solves issues and builds a group. Should you assume you may need a use for the {hardware} on this publish or want to assist out, I’d love to listen to from you. I’ve created a Discord server with like-minded individuals! All the pieces is on github!