Block Cipher Design after AES and the New Cipher Nahrainfish

In this work, we present some deeper insights into the state-of-the-art in block cipher design. This is mainly achieved by assessment of the evaluation process of the AES (Advanced Encryption Standard). We conclude (with maybe a little bit surprising result) that the required security level, for a block cipher to be used for the present and foreseeable future, maybe underestimated during AES evaluation. In accordance, we propose a new block cipher that we call Nahrainfish, which we believe that it offers the required security level without a big sacrifice in efficiency and other related criteria. Instead of building Nahrainfish totally from scratch, we have made a benefit mainly from some AES finalists to develop the new cipher by an over-engineering approach leading to the required higher security level. Nahrainfish is a classical Feistel network based on a novel combination of both key-dependent S-boxes and data-dependent rotations. It operates on 128-bit blocks and accepts a variable key length up to 1024 bits. The paper also includes some important notes on the security and performance of the cipher.