Abstract
Laser fault injections induce transient faults into ICs by locally generating transient currents that temporarily flip the outputs of the illuminated gates. Laser fault injection can be anticipated or studied by using simulation tools at different abstraction levels: physical, electrical or logical. At the electrical level, the classical laser-fault injection model is based on the addition of current sources to the various sensitive nodes of MOS transistors. However, this model does not take into account the large transient current components also induced between the VDD and GND of ICs designed with advanced CMOS technologies. These short-circuit currents provoke a significant IR drop that contribute to the fault injection process. This thesis describes our research on the assessment of this contribution. It shows by simulation and experiments that during laser fault injection campaigns, laser-induced IR drop is always present when considering circuits designed in deep submicron technologies. It introduces an enhanced electrical fault model taking the laser-induced IR-drop into account. It also proposes a methodology that uses standard CAD tools to allow the use of the enhanced electrical model to simulate laser-induced faults at the electrical level in large-scale circuits. On the basis of further simulations and experimental results, we found that, depending on the laser pulse characteristics, the number of injected faults may be underestimated by a factor as large as 3 if the laser-induced IR-drop is ignored. This could lead to incorrect estimations of the fault injection threshold, which is especially relevant to the design of countermeasure techniques for secure integrated systems. Furthermore, experimental and simulation results show that even though laser fault injection is a very local and accurate fault injection technique, the induced IR drops have a global effect spreading through the supply network. This gives experimental evidence that the effect of laser illumination is not as local as usually considered.