On The Design of One-Way Key Schedule Algorithms for Block Ciphers

The key schedule of a symmetr"ic key encryption algorithm derives all round sub-keys from the main encryption key and in most cases each sub-key is subsequently derived front the previous sub-key. This causes a great deal of correlation between the main key and the sub-keys and hence, many bits of the main key are revealed with the knowledge of some sub-keys. In this paper, we propose two design criteriafor the key schedule algorithm to evaluate the one-wayness of the algorithm, which ensures the security of the main key in order to avoid vulnerability to the most common generic attaclrs on symnxetric-key block ciphers. We also propose two new schemes which have improvements compared to the original algorithms.

Keywords:

Key schedule algorithm , Related key attacks , Generic Attacks , Hash Functions