SHIFT SNARE: Uncovering Secret Keys in FALCON via Single-Trace Analysis

This paper presents a novel singletrace sidechannel attack on FALCON a latticebased postquantum digital signature protocol recently approved for standardization by NIST We target the discrete Gaussian sampling operation within FALCONs key generation scheme and demonstrate that a single power trace is sufficient to mount a successful attack Notably negating the results of a 63bit rightshift operation on 64bit secret values leaks critical information about the assignment of 1 versus 0 to intermediate coefficients during sampling These leaks enable full recovery of the secret key We demonstrate a groundup approach to the attack on an ARM CortexM4 microcontroller executing both the reference and optimized implementations from FALCONs NIST round 3 software package We successfully recovered all of the secret polynomials in FALCON We further quantify the attackers success rate using a univariate Gaussian template model providing generalizable guarantees Statistical analysis with over 500000 tests reveals a percoefficient success rate of 999999999478 and a fullkey recovery rate of 9999994654 for FALCON512 We verify that this vulnerability is present in all implementations included in FALCONs NIST submission package This highlights the vulnerability of current software implementations to singletrace attacks and underscores the urgent need for singletrace resilient software in embedded systems