UCloD: Small Clock Delays to Mitigate Remote Power Analysis Attacks

This paper presents UCloD, a novel random clock delay-based robust and scalable countermeasure against recently discovered remote power analysis (RPA) attacks. UCloD deploys very small clock delays (in the picosecond range) generated using the tapped delays lines (TDLs) to mitigate RPA attacks. UCloD provides the most robust countermeasures demonstrated thus far against RPA attacks. RPA attacks use delay sensors, such as Time to Digital Converters (TDC) or Ring Oscillators (ROs) to measure voltage fluctuations occurring in power delivery networks (PDNs) of Field Programmable Gate Arrays (FPGAs). These voltage fluctuations reveal secret information, such as secret keys of cryptographic circuits. The only countermeasure proposed thus far activates ROs to consume significant power and has managed to secure Advanced Encryption Standard (AES) circuits for up to 300,000 encryptions. Using TDLs available in FPGAs, UCloD randomly varies the clock to the cryptographic circuits under attack to induce noise in the adversary's delay sensor(s). We demonstrate correlation power analysis (referred to as CPA) attack resistance of UCloD AES implementations for up to one million encryptions. Compared to an unprotected AES circuit, UCloD implementations have minimal overheads (0.2% Slice LUT overhead and 4.8% Slice register overhead for Xilinx implementations and 0.5% LogicCells overhead for Lattice Semiconductor implementations).