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. 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 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.

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. But because they are distinctly different, the right tools could clearly identify them, allowing a hacker 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. 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. While camouflaging is already a security measure that chip manufacturers use, it is typically done at the circuit level and doesn't attempt to obscure the functionality of individual transistors — leaving the chip potentially vulnerable to reverse-engineering hacking techniques with the right tools. The new camouflaging method would be building a security key into the transistors.

Current camouflaging techniques always require more transistors in order to hide what's going on in the circuit. But hiding the transistor type using a material like black phosphorus — a material as thin as an atom — requires fewer transistors, taking up less space and power in addition to creating a better disguise.

For more information, contact Kayla Wiles at This email address is being protected from spambots. You need JavaScript enabled to view it.; 765-494-2432.

Tech Briefs Magazine

This article first appeared in the March, 2021 issue of Tech Briefs Magazine.

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