@article{Ravi_Ezerman_Bhasin_Chattopadhyay_Sinha Roy_2021, title={Will You Cross the Threshold for Me? Generic Side-Channel Assisted Chosen-Ciphertext Attacks on NTRU-based KEMs}, volume={2022}, url={https://tches.iacr.org/index.php/TCHES/article/view/9313}, DOI={10.46586/tches.v2022.i1.722-761}, abstractNote={<p>In this work, we propose generic and novel side-channel assisted chosenciphertext attacks on NTRU-based key encapsulation mechanisms (KEMs). These KEMs are IND-CCA secure, that is, they are secure in the chosen-ciphertext model. Our attacks involve the construction of malformed ciphertexts. When decapsulated by the target device, these ciphertexts ensure that a targeted intermediate variable becomes very closely related to the secret key. An attacker, who can obtain information about the secret-dependent variable through side-channels, can subsequently recover the full secret key. We propose several novel CCAs which can be carried through by using side-channel leakage from the decapsulation procedure. The attacks instantiate three different types of oracles, namely a plaintext-checking oracle, a decryptionfailure oracle, and a full-decryption oracle, and are applicable to two NTRU-based schemes, which are NTRU and NTRU Prime. The two schemes are candidates in the ongoing NIST standardization process for post-quantum cryptography. We perform experimental validation of the attacks on optimized and unprotected implementations of NTRU-based schemes, taken from the open-source pqm4 library, using the EM-based side-channel on the 32-bit ARM Cortex-M4 microcontroller. All of our proposed attacks are capable of recovering the full secret key in only a few thousand chosen ciphertext queries on all parameter sets of NTRU and NTRU Prime. Our attacks, therefore, stress on the need for concrete side-channel protection strategies for NTRUbased KEMs.</p>}, number={1}, journal={IACR Transactions on Cryptographic Hardware and Embedded Systems}, author={Ravi, Prasanna and Ezerman, Martianus Frederic and Bhasin, Shivam and Chattopadhyay, Anupam and Sinha Roy, Sujoy}, year={2021}, month={Nov.}, pages={722–761} }