International Association
for Cryptologic Research

Template Attacks consist of two stages, the profiling stage and the extraction stage. In order to improve the key-recovery efficiency of Template Attacks, a feasible way is to characterize signals and noises accurately. Under the assumption that a reference device is available, in the profiling stage, one can operate the reference device as many times as possible and samples a large number of power traces to help accurately characterize signals and noises at different interesting points. However, in some practical scenarios, it is not always the case and one can only record a limited number of power traces. In this paper, we show that one can still make Template Attacks practical and more powerful in the above scenario if he could obtain some kind of priori knowledge about the reference device. For example, the priori knowledge is some kind of priori distribution of the signal component in the instantaneous power consumption for fixed operation on fixed data. Evaluation results show that the priori knowledge poses potential threat to the physical security of cryptographic devices and this kind of threat can not be neglected.