Paper 2026/2177

LEANY: A Hardware-Friendly Wide-Block Block Cipher

Abstract

Wide-block block ciphers have attracted significant interest due to emerging high-throughput encryption requirements and NIST's Accordion Mode Process. The primary choice for such ciphers is Rijndael-256, also known as WAES. At the same time, independent efforts continue to explore more efficient designs and implementations. In this paper, we present LEANY, a 256-bit block cipher with a 256-bit key. LEANY is a nibble-oriented SPN whose state is an 8×8 matrix of 4-bit nibbles. Each round consists of four layers: key addition, a 4-bit S-box layer, row-wise nibble shifts, and multiplication by an 8×8 MDS matrix over $\mathrm{GF}(2^4)$. This structure follows the same shift-then-mix principle as AES, but with a wider state and a smaller cell size. LEANY consists of only 12 rounds. Since the linear diffusion layer has branch number 9, the wide-trail strategy guarantees that every four consecutive rounds activate at least $9^2=81$ S-boxes in any differential or linear characteristic. Consequently, upper bounds on the best differential and linear trail probabilities fall below $2^{-256}$ after seven rounds. We further analyze LEANY against impossible differential, invariant subspace, integral, meet-in-the-middle, boomerang, and several algebraic attacks. Finally, FPGA implementations demonstrate both compact and high-performance hardware realizations: the iterative architecture occupies only about 1.4K LUTs, whereas the fully pipelined architecture achieves a steady-state throughput exceeding 50 Gbps. Compared with existing 256-bit wide-block block ciphers, including WAES, LEANY provides substantially better area efficiency and competitive throughput (TP) and throughput-to-area ratio (TAR) results.