A secure cryptographic algorithm improving security over known plain text attack based on Hill Cipher

Abstract

The secrecy of sensitive information against unauthorized access or deceitful changes has been of prime concern throughout the centuries. With the introduction of computer, the security of data or information (stored on a computer for a shared system or during their transmission in a distributed system) to maintain its confidentiality, proper access control, integrity and availability has been a major issue. The only way to address all these issues is cryptology. Hill Cipher is one of the most famous symmetric cryptosystem that can be used to protect information from unauthorized access. Hill cipher is a multi-letter and polygraph substitution cipher. Although the Hill Cipher is resistant to frequency letter analysis and strong against ciphertext only attack, it succumbs to known-plaintext attack. The other disadvantage of the Hill Cipher is non invertible key matrix because all the matrices don’t posses their inverses and this reduces the number of possible keys from actual number of possible keys and leads to the chances of brute-force attack. In the scheme that is going to be proposed, a variant of the Hill cipher is introduced that makes the Hill Cipher more secure and retains the efficiency. The scheme uses the Cipher Block Chaining (CBC) mode of operation and bitwise XOR operation that leads to diffusion and confusion and make the scheme strong against the known-plaintext attack.