S-boxes are often the only nonlinear components in modern block ciphers. They are commonly selected to comply with very specific criteria in order to make a cipher secure against, for example, linear and differential attacks. An M x N S-box can be thought of as a lookup table that relates an M-bit input value to an N-bit output value, or as a set of N boolean functions of M variables (Schneier, 1996).
Although cipher specifications generally describe S-boxes using their lookup tables, they can also be described as boolean functions or logic gate circuits. sboxgates, which is presented here, finds equivalent logic gate circuits for S-boxes, given their lookup table specification. Generated circuits are output in a human-readable XML format. The software can convert the output files into C or CUDA (a parallel computing platform for Nvidia GPUs) source code. The generated circuits can also be converted to the DOT graph description language for visualization with Graphviz (Ellson et al., 2002).
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