Exploring Side-Channel Protections in Hardware Implementations of PQC ML-KEM Verification
For hardware designers of post-quantum cryptography, this paper highlights that current side-channel protections are insufficient on FPGAs, posing a security risk.
This work evaluates side-channel vulnerabilities of ML-KEM decapsulation verification on FPGA and microcontroller implementations, finding that even higher-order masked designs on FPGAs leak enough first-order information for full secret-key recovery.
As ML-KEM is adopted as a post-quantum cryptographic standard, resilience against physical side-channel attacks has become essential. Among the constituent steps, the decapsulation Fujisaki-Okamoto (FO) verification is particularly vulnerable to side-channel power and electromagnetic (EM) analysis. In this work, we focus on common FPGA-based implementations and examine their side-channel vulnerabilities, and compare them with those of microcontroller implementations. Three verification implementations, unprotected, hash-based (first-order), and higher-order masked, are evaluated for side-channel security on both a microcontroller and an FPGA. While FPGAs offer higher speed and parallelism, they often exhibit stronger side-channel leakage, especially in high bandwidth configurations. The higher-order masked designs still leak information about the underlying data due to hardware-level effects and data-dependent processing. Our experiments show that their parallelized processing on FPGAs introduces sufficient first-order leakage for full secret-key recovery. These results underscore the persistent challenge of securing PQC algorithms in performance-constrained and parallelized hardware environments.