Construction of highly nonlinear injective S-boxes with application to CAST-like encryption algorithms
Amr Youssef, Z.G. Chen, Stafford E. Tavares · 2002
We present two methods for constructing highly nonlinear injective S-boxes. Both of these methods, which are based on exponential sums, outperform previously proposed methods. In particular, we are able to obtain injective 8/spl times/32 S-boxes with nonlinearity equal to 80 and maximum XOR table entry of 2. We also reevaluate the resistance of the CAST like encryption algorithms constructed using randomly selected S-boxes to the basic linear cryptanalysis.