An analysis of cryptographically significant Boolean functions with high correlation immunity by reconfigurable computer

Abstract

Boolean functions with high correlation immunity can be used in cryptosystems to defend against correlation attacks. These functions are rare and difficult to find. As the variables increase, this task becomes exponentially more complex and time consuming. Three different ways to execute a program to find the correlation immunity of a function are compared in this thesis. First, a program was written in C and executed on a conventional CPU. The same program was then executed on an FPGA on the SRC-6 reconfigurable computer. A similar program was written in Verilog and executed on the FPGA. By taking advantage of the parallel processing ability of the SRC-6, a wellprogrammed Verilog macro can find functions with high correlation immunity at a much faster rate. The SRC-6 reconfigurable computer is used in this thesis to find the correlation immunity of millions of functions up to six variables. Rotation symmetric and balanced functions were examined to find subsets that contain a high percentage of functions with good correlation immunity. The nonlinearity and correlation immunity of functions of four and five variables were compared to find functions with the best balance to fend off both correlation and linear attacks on a cryptosystem.