Layout Dependent Phenomena A New Side-channel Power Model

Abstract

The energy dissipation associated with switching in CMOS logic gates can be used to classify the microprocessor’s activity. In VLSI design, layout dependent phenomena, such as capacitive crosstalk, become a major contributor to the power consumption and delays of on-chip busses as transistor technology get smaller. These effects may be known to the security community but have received little attention. In a recent paper we presented a new power model, taking into consideration capacitive crosstalk. We have shown that capacitive crosstalk has a significant effect on gate energy dissipation. Our results confirm that the dissipated energy from CMOS switching gates depends not only on the hamming distance (HD), but also on the direction of switching activity on nearby data lines. We show that for an 8 bit data bus, crosstalk may improve detection performance from 2.5 bits (HD based detector) to a theoretical 5.7 bits and simulated 5.0 bits (crosstalk based detector) of information per sample. In this paper we elaborate on the theory and simulations of layout dependent phenomena and how they must be considered when analyzing security implications of power and electromagnetic side-channels. We have also added a small case study, i.e. the electromagnetic side-channel of a smart card, that supports our simulations/theoretical results.