An Improved Permutation-Driven Vigenère Cipher with an Extended Secret Key for Enhanced Security

Abstract The Vigenère Cipher is a classical cryptographic technique that transforms plaintext into ciphertext by repeatedly applying a single key, making the original message unreadable and ostensibly secure. However, traditional Vigenère encryption is vulnerable to cryptanalysis techniques such as brute-force attacks, the Friedman test, and frequency analysis, which can be used to determine the key length and subsequently decrypt the message. In this paper, we propose an Enhanced Permutation-Based Algorithm (EPBA) that strengthens the Vigenère Cipher by introducing key elongation and permutation techniques. The original key is transformed into a more complex and extended form through systematic permutations, increasing its length and variability. This transformation significantly obscures the original key pattern, thereby making it more resistant to conventional cryptanalytic methods. The extended key length is derived from the factorial of the original key length, specifically up to n(n!), where n represents the length of the initial key. This extension aims to