Cryptology ePrint Archive: Report 2021/718

Will You Cross the Threshold for Me? - Generic Side-Channel Assisted Chosen-Ciphertext Attacks on NTRU-based KEMs

Prasanna Ravi and Martianus Frederic Ezerman and Shivam Bhasin and Anupam Chattopadhyay and Sujoy Sinha Roy

Abstract: In this work, we propose generic and novel side-channel assisted chosen-ciphertext 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 decryption-failure 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 NTRU-based KEMs.

Category / Keywords: public-key cryptography / Lattice Based Cryptography, Streamlined NTRU Prime, Chosen-Ciphertext Attacks, Side-Channel Attacks, Plaintext Checking Oracle, Decryption Failure Oracle, NIST PQC Standardization process

Date: received 29 May 2021, last revised 14 Oct 2021

Contact author: PRASANNA RAVI at ntu edu sg

Available format(s): PDF | BibTeX Citation

Note: Accepted at IACR TCHES-2022

Version: 20211014:093643 (All versions of this report)

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