A hacker can reproduce a circuit on a chip by discovering what key transistors are doing in a circuit – but not if the transistor “type” is undetectable.

Purdue University photo/John Underwood

Purdue University engineers have demonstrated a way to disguise which transistor is which by building them out of a sheet-like material called black phosphorus. This built-in security measure would prevent hackers from getting enough information about the circuit to reverse engineer it.

Reverse engineering chips is a common practice – both for hackers and companies investigating intellectual property infringement. Researchers also are developing x-ray imaging techniques that wouldn’t require actually touching a chip to reverse engineer it.

The approach that Purdue researchers have demonstrated would increase security on a more fundamental level. How chip manufacturers choose to make this transistor design compatible with their processes would determine the availability of this level of security.

How to fool a hacker?

A chip computes using millions of transistors in a circuit. When a voltage is applied, two distinct types of transistors – an N type and a P type – perform a computation. Replicating the chip would begin with identifying these transistors.

“These two transistor types are key since they do different things in a circuit. They are at the heart of everything that happens on all our chips,” said Joerg Appenzeller, Purdue’s Barry M. and Patricia L. Epstein Professor of Electrical and Computer Engineering.

“But because they are distinctly different, the right tools could clearly identify them – allowing you to go backwards, find out what each individual circuit component is doing and then reproduce the chip.”

If these two transistor types appeared identical upon inspection, a hacker wouldn’t be able to reproduce a chip by reverse engineering the circuit.

Appenzeller’s team showed in their study that camouflaging the transistors by fabricating them from a material such as black phosphorus makes it impossible to know which transistor is which. When a voltage toggles the transistors’ type, they appear exactly the same to a hacker.

Building a…