Photonic Emission Microscopy (PEM) stands out among other side channel techniques as it can provide an attacker with a full view of the (otherwise hidden) internal operations of an integrated circuit. It has proven to be a useful failure analysis tool. However, it is a dual-use tool that can also be used for attack purposes.
PEM can be carried out through the backside of an integrated circuit, the photons emitted by the target’s switching transistors travel well through the silicon substrate. The photons are then captured by an InGaAs (or CCD) camera to produce a photon emission map that reveals the location of the target’s active logic blocks. This makes PEM a powerful backside contactless observation tool with access to the entire target area. It can be used to locate points of interest to facilitate further hardware attacks (e.g., a laser fault injection attack), or even to extract confidential data (e.g., cryptographic keys).
This talk will focus on describing how PEM can be used to extract data from a microcontroller’s embedded SRAM or Flash memories as they are written or read. The strong constraints and limitations of PEM are discussed and the mechanisms behind light emission in ICs are explained. The used optical setup and the operational characteristics of embedded MCU memories are described. It also aims to raise awareness of this threat by presenting realistic attack scenarios that overcome the limitations of PEM.