SERP-SCA: A Strengthened Side-Channel Attack Framework for FALCON Signature

NIST has selected Falcon as one of the standardized post-quantum digital signature algorithms, making the security of Falcon against side-channel attacks (SCAs) a critical area of concern. This paper introduces SERP-SCA, a strengthened SCA framework for Falcon, which exploits leakage from floating-point multiplications to recover secret floating-point values, which can subsequently be mapped to the coefficients of the secret key. The framework adopts a divide-and-conquer strategy to target the mantissa, exponent, and sign bit of floating-point values, with specialized optimizations for attacks on the mantissa and exponent. For mantissa attacks, SERP-SCA integrates bit segmentation with a sequential attack strategy to fully exploit the leakage from mantissa multiplication and incorporates an error-correction mechanism to further enhance attack efficiency. For exponent attacks, SERP-SCA leverages Fast Fourier Transform (FFT) properties to narrow the enumeration space, significantly improving time efficiency. We conduct practical attacks on Falcon-512 and Falcon-1024 implementations running on ARM Cortex-M4. Compared to state-of-the-art methods, SERP-SCA achieves an improvement of 22.11% in success rate for Falcon-512 and 18.64% for Falcon-1024, with remarkable time efficiency gains of around 195,369× and 183,175× for mantissa attacks, and 180× and 185× for exponent attacks, respectively.