International Association
for Cryptologic Research

In 2009 and 2011, Toorani and Falahati introduced two variants of the classical Hill Cipher, together with protocols for the exchange of encrypted messages. The designers claim that the new systems overcome the weaknesses of the original Hill Cipher, and are resistant to any ciphertext-only, known-plaintext, chosen-plaintext, or chosen-ciphertext attack. However, we describe a chosen-plaintext attack that easily breaks both Toorani-Falahati Hill Ciphers, and we present computational results that confirm the effectiveness of our attack.