Enhancing Key-Recovery Chosen-Ciphertext Side-Channel Attacks on NTRU Using LDPC

In this work, we introduce novel techniques for adapting the SCA-LDPC framework to NTRU-style Key Encapsulation Mechanisms (KEMs). Our approach significantly reduces the required measurements compared to prior analyses under similar oracle noise, validated through extensive simulations, and shows robustness against decision errors in the constructed oracle. Furthermore, we present the first documented power analysis attack targeting a first-order masked NTRU implementation. We constructed a plaintext-checking (PC) oracle achieving a low 0.5% decision error rate, importantly, within a practical cross-device setting where training and attack devices differ. Our results show that approximately 1250 side-channel measurements are sufficient to recover the secret key in this challenging scenario.