NFBC: an efficient FPGA based NFSR-oriented lightweight block cipher suitable for embedded system.

Efficiency is essential in lightweight cryptography to ensure robust protection within constrained environments. This paper introduces a lightweight block cipher built on a Non-Linear Feedback Shift Register (NFSR), referred to as the NFSR-Based Block Cipher (NFBC). The cipher is designed for constrained environments where both efficiency and strong security are critical. NFBC operates as a Nonce-based Authenticated Encryption with Associated Data (NAEAD) scheme, providing confidentiality and authenticity within a single framework. The design achieves robust protection while maintaining minimal hardware overhead. NFBC operates on 128-bit data, key, and nonce sizes, fully aligning with National Institute of Standards and Technology (NIST) lightweight cryptography requirements. The design integrates a Non-Linear Feedback Shift Register (NFSR) for generating high-entropy round subkeys, dynamic chaotic substitution box (S-boxes) for strong confusion, and a Group Permutation (GRP) mechanism that ensures rapid diffusion with hardware-friendly efficiency. Security is rigorously evaluated across multiple dimensions. NFBC passes all 15 NIST Statistical Test Suite (STS) tests, achieves near-ideal avalanche and Bit Independence Criterion (BIC), and demonstrates consistently high nonlinearity across 200 independent chaotic S-box instances. The S-box achieves a maximum differential probability of 10/256 and maximum linear probability of [Formula: see text], confirming strong resistance to classical attacks. To strengthen theoretical guarantees, a provable branch-number analysis is introduced, establishing conservative lower bounds on active S-boxes ([Formula: see text] across 20 rounds), with corresponding differential and linear probabilities that are vanishingly small. Formal AEAD security is ensured through an Encrypt-then-MAC (EtM) construction. Implementation on a Xilinx Artix-7 FPGA confirms practicality: NFBC achieves superior throughput-per-area compared to several NIST Round-2 lightweight candidates (SPOC, SPOOK, GIFT-COFB, ESTATE, SAEAES, Oribatida) and CAESAR finalists (Ascon-128, Ascon-small, CLOC-AES, SILC-AES). Estimated countermeasure overheads for masking and fault detection demonstrate feasibility against side-channel and fault attacks. These results confirm NFBC as a secure, efficient, and practically deployable lightweight cryptographic solution.