On the Differential Transparency Order of Boolean Functions

Lower differential transparency order ( \(\mathcal {DTO}\) ) has good resistance to energy leakage in side channel attack for vectorial Boolean functions. In this paper, we characterize the differential transparency order for Boolean functions, and give the tight upper bound and the tight lower bound on \(\mathcal {DTO}\) for Boolean functions. Then, the upper bound on \(\mathcal {DTO}\) is determined by the sum-of-squares indicator of Boolean functions. Finally, some relationships between \(\mathcal {DTO}\) and other cryptographic indicators are obtained.