Pentimento: Data Remanence in Cloud FPGAs

Remote attackers can recover "FPGA pentimento" -longremoved data belonging to a prior user or proprietary design image on a cloud FPGA. Just as a pentimento of a painting can be exposed by infrared imaging, FPGA pentimentos can be exposed by signal timing sensors. The data constituting an FPGA pentimento is imprinted on the device through bias temperature instability effects on the underlying transistors. Measuring this degradation using a time-to-digital converter allows an attacker to (1) extract proprietary details or keys from an encrypted FPGA design image available on the AWS marketplace and (2) recover information from a previous user of a cloud-FPGA. These threat models are validated on AWS F1, with successful AES key recovery under one model.

• Security and privacy → Side-channel analysis and countermeasures.