Ultra-compact and Side-channel Resistant Design of FIFO-based NTT Core for PQCs

Cryptographic algorithms like CRYSTALS-Kyber and Dilithium might be insecure with their naive implementation facing side-channel attacks (SCA). This work presents a compact implementation of Number Theoretic Transform (NTT) with shuffling countermeasure against power analysis attacks (PA). At first, a compact FIFO-only Shuffler module is presented to perform group-wise first-index randomization (FIR). A modified butterfly (BF) unit using optimized modulus reduction is then promoted to restore the misaligned data flow, which is critical for forming efficient shuffle pattern. The shuffler module and BF unit are then used in a pipelined BRAM-free NTT baseline. Through efficient shuffling, the proposed design maintains compactness akin to its baseline while enhancing robust SCA resistance with a permutation space of up to 2<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">494</sup>. Compared to its prior state-of-the-art designs, the proposed NTT core presents an improvement of 53.2% in area-time trade-off while offering ×1.7 times more bits of randomness to improve hardware security.