Paper 2026/856

MERIDIAN: A Toroid-Inspired Permutation Block Cipher for Constrained Environments

Abstract

We introduce MERIDIAN, a 128-bit block cipher designed for resource-constrained environments as a lightweight alternative to AES-128. MERIDIAN retains the AES-128 interface, including a 128-bit block, 128-bit key, and 4×4 byte state, while reusing the standard AES S-box. This enables compatibility with existing AES-128 modes such as ECB, CBC, CFB, OFB, CTR, XTS, CMAC, CCM, and GCM, and allows implementations to reuse established S-box ROMs and GF(28) inverse circuits. The cipher is based on three round operations: Directional Substitution (DS), Meridian Diffusion (MD), and Admittance Mixing (AM), followed by a round constant. Its state is represented over the discrete torus Z4 × Z4. The MD layer combines two orthogonal byte permutations, meridian and parallel, with column mixing to obtain full byte diffusion within three rounds without requiring MDS multiplication. MERIDIAN uses twelve rounds and avoids an expanded key schedule. We present MILP-verified differential and linear bounds, including exact active-S-box counts up to eleven rounds and a sub-additive bound for twelve rounds. We also provide AES-aligned cryptanalysis covering differential, linear, integral, biclique, slide, related-key, invariant-subspace, fault, meet-in-the-middle, and algebraic attacks. A reproducible fifteen-experiment benchmark suite compares MERIDIAN directly with AES-128, including key agility, cold-start latency, energy, masking cost, memory, throughput, and hardware complexity. Empirical results show that MERIDIAN reaches strict avalanche behavior in three rounds, matches AES-128 in entropy and NIST SP 800-22 fitness, reduces unrolled gate count, lowers RAM usage, and improves constrained-device efficiency. MERIDIAN is proposed as a research prototype for further public cryptanalysis.

Note: Dear Editor, This version has removed one author at his request.