Betrayed by Light: How Photon Emission Microscopy Empowers Register Bit-Level Laser Attacks on Microcontrollers

Photons are emitted through various physical phenomena when current goes through the transistors of Integrated Circuits (IC). Etching the packaging of an IC to reveal the silicon die lets an observer measure that light for the purpose of retroengineering or data extraction. This Photon Emission Microscopy (PEM) technique has applications in the fields of failure analysis and hardware security. The purpose of this paper is to present how time-integrated PEM can be added to a Laser Fault Injection (LFI) attack workflow for the quick retro-engineering of the position of a microcontroller's digital building blocks, such as its core registers, on a relatively low-cost laser bench. Firstly, the extraction of the position of multiple core registers is presented for three different ARM Cortex microprocessor implementations. Subsequently, the extraction of the position of their individual bits is confronted with the results of a traditional LFI on the same registers.