CMOS gates consume different amounts of power whether their output has a falling or a rising edge. Therefore the overall power consumption of a CMOS circuit leaks information about the activity of every single gate. This explains why, using differential power analysis (DP A), one can infer the value of specific nodes within a chip by monitoring its global power consumption only. We model the information leakage in the framework used by conventional cryptanalysis. The information an attacker can gain is derived as the autocorrelation of the Hamming weight of the guessed value for the key. This model is validated by an exhaustive electrical simulation. Our model proves that the DPA signal-to-noise ratio increases when the re- sistance of the substitution box against linear cryptanalysis increases. This result shows that the better shielded against linear cryptanalysis a block cipher is, the more vulnerable it is to side-channel attacks such as DPA.