A Modification of the Hill Cipher Based on Doubly Periodic Encryption and Length Variation

Abstract

In this research, we propose a modification of the Hill cipher using doubly periodic encryption, which requires two types of keys with different periodicity when encrypting each block of plaintext. Length variation is also used for extending the ciphertext so that there are several extended ciphertexts available, which prevent any third-party to determine the true length of secret keys successfully. Our study shows that our modified Hill cipher is more resistant to known-plaintext attack, ciphertext-only attack and frequency analysis, than the modified Hill cipher proposed by Adinarayana Reddy et al. (2012). Moreover, our modified Hill cipher requires less space for the secret keys than the classical Hill cipher.