Practical approach in evaluating the resistance of stream ciphers against algebraic attacks

Abstract

Stream ciphers are the oldest technique in cryptography subject and still applicable in the modern era as it provides better speed and accuracy during encryption decryption process. It is also easy to be abuse and breakable if the algorithm is not designed properly because its key generator was constructed based on Boolean function which normally using Line Feedback Shift Register technique. Together with secret key, it will generate key stream bit that will be used to encrypt the plaintext into cipher text. Far from that, Algebraic Attacks and Fast Algebraic Attack has become popular among cryptographers as the nature of the attack was to recover the secret key by solving or decomposing the Boolean function that constructed the cryptosystems. This study mainly is to provide a practical way or approach on how to evaluate the resistance of stream ciphers against these two types of attack. As all of us know that cryptography always involve complex discrete arithmetic by nature. As a result, we as non-mathematician computer scientist or information systems practitioner practically leave any cryptographic problems to the mathematician to evaluate and observe the cryptosystems they want to implement. Hence, this case study has also presented some practical method on how to construct an evaluation capability from mathematical formulas designed by mathematician cryptographers. The prototype solution was built using Microsoft Visual Studio VB.Net 2008 and the simulation testing was successfully done and shows similar result when we compare with cryptanalysis report produced by cryptographers.