We have previously covered the Tillitis Tkey, an open-source security key in a USB-C case but the Ovrdrive USB stick is not a security key. It is a simple, plain USB flash drive with a special security feature. It will appear completely blank unless you plug this drive in three times in quick succession.
The Ovrdrive flash drive is aimed at journalists in repressive areas and security researchers but may be useful to other security and open-source hardware enthusiasts.
As for how it works, the Ovrdrive has two identical circuits connected to the ATtiny24A microcontroller that controls the rapid plug-in functionality. When the flash is plugged in, the microcontroller powers on, and the CHG1 node goes high, charging C3 through D2. The pin will remain high for a while and then slowly discharge via R1 and body resistance. C3 and the identical C14 will remain high through power cycling/a quick on/off event. There is a one-second delay in the flowchart to ensure that plug and unplug events are rapid.
The best part of the Ovrdrive is that it looks like a basic, run-of-the-mill flash drive, unlike many of the alternatives on the market. It leverages security through obscurity, but it is not intended to serve as a replacement for cryptographic encryption. Also, it has circuitry to reverse the voltage supplied to the flash chip and heat it to over 100°C, which is not hot enough to destroy the chip most times but can serve as a catalyst for a “DIY self-destruct implant.”
The first revision required the user to use wet fingers to activate the flash drive and included an actual self-destruct mechanism. However, that proved too unreliable for mass production and changes had to be made.
- Microcontroller – Microchip ATtiny24A
- Encryption – Software (user-defined)
- Type-A, v2.0
- SM3257ENT controller
- Capacity – 8GB
- NAND flash – MT29F64G08CBABAWP
- Destruction – Yes
- Dimensions – 60 x 18 x 8.5 mm
The project is currently being funded on Crowd Supply and has reached more than half of its $3,500 goal. The USB flash drive can be purchased for $69 on Crowd Supply, with free shipping within the US and a $12 shipping fee for the rest of the world. Orders should ship by August 05, 2024.
Tomisin is a writer specializing in hardware product reviews, comparisons, and explainers. He is very passionate about small form factor and single-board computers.