Physical secret extraction via rapid undervolting

Hardware fault injection in AMD Artix 7 and Kintex 7 FPGAs allows physically proximate attackers to extract retained secrets. A rapid supply-voltage drop falls below the logic threshold but remains above the retention threshold, freezing switching while preserving register and memory contents and outrunning the XADC tamper response. Physical access to the power rail and side-channel measurement equipment is required; successful exploitation discloses sensitive programmable-logic state such as cryptographic keys.