MEMS gyroscopes, it turns out, are useful as a Physical Unclonable Function (PUF), a device used to create a cryptographic key. When interrogated, a PUF produces a unique response (‘physical function’) that cannot be predicted by inspecting the physical device, nor can it be duplicated (‘unclonable’). Simply put, a PUF is a tamper proof, copy proof, black box that generates a unique code.
MEMS devices with electrostatic comb fingers (see image) – such as accelerometers and gyroscopes – have large surface areas, which make them vulnerable to silicon etch process variation.
Subtle variations in the etch process make each gyro uniquely imperfect in a random, unpredictable way. And even if one could thoroughly measure and inspect it, a gyro could not be perfectly duplicated because silicon etch processes cannot be controlled that finely. All of which are excellent characteristics for a PUF.
A research group at Bosch recently demonstrated how to use a commercially available gyro as a PUF to generate a 128bit cryptographic key. Further optimisation of a MEMS PUF design could produce a longer, and therefore more secure, key.
Should you think this cryptography application for a gyro is merely an academic curiosity, think again: All data generating devices in the IoT will need encryption – even seemingly innocent wearables – to protect them from hacking. Only recently, researchers determined that sensor data intercepted from smart watches and fitness trackers can reveal an ATM PIN.
A dual-purpose MEMS device which not only offers sensing functionality, but which can also produce its own encryption key is a very exciting emerging technology with huge potential in future IoT markets.
Author profile:
Alissa Fitzgerald is founder of MEMS engineering consultancy AM Fitzgerald and Associates