International Association
for Cryptologic Research

On-chip sensors, built using reconfigurable logic resources in field programmable gate arrays (FPGAs), have been shown to sense variations in signalpropagation delay, supply voltage and power consumption. These sensors have been successfully used to deploy security attacks called Remote Power Analysis (RPA) Attacks on FPGAs. The sensors proposed thus far consume significant logic resources and some of them could be used to deploy power viruses. In this paper, a sensor (named VITI) occupying a far smaller footprint than existing sensors is presented. VITI is a self-calibrating on-chip sensor design, constructed using adjustable delay elements, flip-flops and LUT elements instead of combinational loops, bulky carry chains or latches. Self-calibration enables VITI the autonomous adaptation to differing situations (such as increased power consumption, temperature changes or placement of the sensor in faraway locations from the circuit under attack). The efficacy of VITI for power consumption measurement was evaluated using Remote Power Analysis (RPA) attacks and results demonstrate recovery of a full 128-bit Advanced Encryption Standard (AES) key with only 20,000 power traces. Experiments demonstrate that VITI consumes 1/4th and 1/16th of the area compared to state-of-the-art sensors such as time to digital converters and ring oscillators for similar effectiveness.

Field-programmable gate arrays (FPGAs) deployed on commercial cloud services are increasingly gaining popularity due to the cost and compute benefits offered by them. Recent studies have discovered security threats than can be launched remotely on FPGAs that share the logic fabric between trusted and untrusted parties, posing a danger to designs deployed on cloud FPGAs. With remote power analysis (RPA) attacks, an attacker aims to deduce secret information present on a remote FPGA by deploying an on-chip sensor on the FPGA logic fabric. Information captured with the on-chip sensor is transferred off the chip for analysis and existing on-chip sensors demand a significant amount of bandwidth for this task as a result of their wider output bit width. However, attackers are often left with the only option of using a covert communication channel and the bandwidth of such channels is generally limited. This paper proposes a novel area-efficient on-chip power sensor named PPWM that integrates a logic design outputting a pulse whose width is modulated by the power consumption of the FPGA. This pulse is used to clear a flip-flop selectively and asynchronously, and the single-bit output of the flip-flop is used to perform an RPA attack. This paper demonstrates the possibility of successfully recovering a 128-bit Advanced Encryption Standard (AES) key within 16,000 power traces while consuming just 25% of the bandwidth when compared to the state of the art. Moreover, this paper assesses the threat posed by the proposed PPWM to remote FPGAs including those that are deployed on cloud services.