A Flexible NTT-based multiplier for Post-Quantum Cryptography

In this work an NTT-based (Number Theoretic Transform) multiplier for code-based Post-Quantum Cryptography (PQC) is presented, supporting Quasi Cyclic Low/Moderate-Density Parity-Check (QC LDPC/MDPC) codes. The cyclic matrix product, which is the fundamental operation required in this application, is treated as a polynomial product and adapted to the specific case of QC-MDPC codes proposed for Round 3 and 4 in the National Institute of Standards and Technology (NIST) competition for PQC. The multiplier is a fundamental component in both encryption and decryption, and the proposed solution leads to a flexible NTT-based multiplier, which can efficiently handle all types of required products, where the vectors have a length ≈104 and can be moderately sparse. The proposed architecture is implemented using both Field Programmable Gate Array (FPGA) and Application Specific Integrated Circuit (ASIC) technologies and, when compared with the best published results, it features a 10 times reduction of the encryption times with the area increased by 3 times. The proposed multiplier, incorporated in the encryption and decryption stages of a code-based PQC cryptosystem, leads to an improvement over the best published results between 3 to 10 times in terms of LC product (LUT times latency).