Building a self destructing USB drive

• Today's world demands high security devices, like an aggressively self-destructing USB drive. I would like advice on the possibility of creating such a thing if one wouldn't mind offering wisdom. Hello! I have a security/electrical engineering project idea I am still fleshing out, and I would like some input on its possibilities, implementations, and execution. For high-security PC builds, it is common to have full-disk encryption on a hard disk with the whole shebang bolted down by a TPM chip. It is also reasonable practice to use a Live OS booted off of USB and use no disk at all. My idea will focus on the latter. I read some papers recently about the relationship between data retention on RAM chips and their temperature. RAM which is designed to not retain memory without a power source has an interval of time after losing power such that the data can still be retained, as it takes time for the electricity to "leak" out of the chips and leave them blanked. As I understand it the colder the chips are on a device, the slower the information "leaks" out of them. This knowledge can be used in a compromising manner towards the end user. For example, some clever researchers have discovered how to bypass Android's fulldisk encryption/bypass PINs/etc. by using a special recovery image and storing the phone in a very cold area. (https://www1.informatik.uni-erlangen.de/frost) The idea: To create a USB thumbdrive with a capacitor, small battery and charging function, hereafter lovingly referred to as NUKE. NUKE's purpose is to provide immediate current to the RAM chip in an attempt to clear any data that may be remaining, or at the least mangle it enough to make it unrecoverable. I recently realized a setup i toyed with as a child was a rapid high-discharge setup, and may be able to work in the manner i described. In my childhood years I had toyed with the flash on disposable cameras. If the two leading wires from the flash bulb were cut and stripped, the two leading wires could be applied to some [relatively] high resistance items and still discharge successfully when the button was pressed. Ask any of our friends, we tasered each other quite a bit with homemade NUKE gloves. An unsuspecting pat on the back could produce a visible wound (don't do that at home! I was a reckless child) Following this idea along, I believe NUKE could be applied to a USB drive to inflict damage throughout the RAM chip on demand by making a complete circuit through it and pumping massive current. By extension I would hope this could be applied to SSD drives for laptops/PCs as well, so long as power requirements were adjusted accordingly. I do not know much of the circuitry of USB devices. My largest fear is that the overload of electricity would not traverse the entirety of the RAM chip by causing too much damage in an early phase of discharge which would make the exercise pointless. Another fear is that the current surge may not do damage at all and could possibly just keep the data on the chip alive, not scramble it, etc. Anyway, that is the idea sitting in front of me. The finished device would behave as a normal USB drive yet at the press of a button, NUKE fires and all is lost. Can anyone experienced in this field offer some input? Implementation ideas, potential problems, or other suggestions? Thank you!

• Answer:

  You don't erase data by overvolting the flash chip or setting it on fire (jesus christ). The correct approach is to minimize the amount of secret data, make it volatile, and make it hard to get to. So your drive encrypts all data with a symmetric cipher (like AES) on the device, before it is stored on the flash chips. The cipher key is stored in SRAM on the encryption chip, backed by a small lithium watch battery. There are tamper-sensitive sensors inside the drive housing as well as the on the encryption chip die that clear the SRAM when tampering is detected. You could design your own encryption chip on some cheap commodity 90nm process and get it fabbed.The design is pretty simple. I bet you could do it for under a million bucks, including hiring someone to design it, fabbing, etc. Alternatively, use an FPGA which already has all these tamperproof features already designed in. Companies like Xilinx have been doing this exact thing for decades to protect their customer's designs that are loaded into the FPGA. After all, you their FPGA customers don't want a shady competitor to read out the FPGA program and loading it into black market counterfeit products. The downside with using an FPGA is that there is most likely a backdoor accessible by Xilinx. It's strong enough to resist pretty serious industrial espionage type adversaries, but probably not the NSA (which would have Xilinx's cooperation of course). Googling fpga bitstream security will probably turn up some interesting papers for you to read. This is a well known, established field with plenty of neat research over the years.