A calibratable detector for invasive attacks

Microprobing is commonly used by adversaries to extract firmware or cryptographic keys from microcontrollers. We introduce the calibratable lightweight invasive attack detector (CaLIAD) to detect microprobing attacks. The CaLIAD measures timing imbalances between lines that are caused by the capacitive load of a probe. Compared to protection mechanisms from industry, it does not require an additional protection layer such as meshes do; in contrast to bus encryption, it does not introduce delay cycles. Compared to state-of-the-art low area probing detectors, it can be calibrated and, thus, allows compensating manufacturing variations as well as small layout imbalances. This capability allows us to significantly reduce the detection margin compared to the prior art while maintaining the low rate of false positives. We can finally show that capacitive loads of 23 fF or less can be detected, depending on how the CaLIAD is used. This includes all state-of-the-art commercial microprobes we are aware of.