A Matrix-Based Polyalphabetic Algorithm for Information Encoding and Decoding Using Number Sequences

In this paper, we propose a matrix-based polyalphabetic data encoding and decoding scheme using Fibonacci, Leonardo, Jacobsthal, and Lucas sequences. The method employs three sequence-based alphabets for character substitution and a Lucas-based auxiliary alphabet for word separators. A position-dependent selector, $$\sigma =(v^2+(i-1)+(j-1))(\mathrm{m}\mathrm{o}\mathrm{d}3),$$ distributes repeated plaintext symbols among different numerical alphabets, thereby reducing frequency concentration. The resulting numerical matrix is divided into $3\times 3$ blocks and transformed using powers of the Leonardo $Q$-matrix with block-dependent keys generated from pre-shared parameters $(s,p)$. A collision-free public prime $P$ is used to keep ciphertext entries bounded while preserving unique decoding. A worked example and preliminary statistical, entropy, avalanche, and timing results indicate that the proposed modular construction is computationally efficient and provides improved distributional behavior compared with standard monoalphabetic substitution.