Large Laser Spots and Fault Sensitivity Analysis

Falk Schellenberg, Markus Finkeldey, Nils C. Gerhardt, Martin R. Hofmann , Amir Moradi, Chris­tof Paar

IEEE International Symposium on Hardware Oriented Security and Trust, HOST 2016, McLean, VA, USA, May 3-5, 2016 (best student-pa­per award).


Laser Fault Injection (LFI) is a powerful method of introducing faults into a specific area of an integrated circuit. Because the minimum spot size of the laser spot is physically bounded, many recent publications investigate down to which technology node individual transistors can be targeted. In contrast, we develop a novel attack that is applicable even when a large number of gates is affected at the smallest feature sizes. To achieve this, we adapt Fault Sensitivity Analysis to the laser setting. Such attacks require reasoning about the critical path of a combinatorial circuit and were previously only considered for clock glitches. Indeed, we show that this prerequisite is available for LFI as well. This leads to a very relaxed fault model, especially in terms of the required laser spot size. We conclude that there is no intrinsic protection for the latest technology nodes and LFI remains a serious threat for embedded devices. Experimental results are provided by targeting the combinatorial AES Sbox of an Atmel ATxmega microcontroller with an artificially large laser spot. Finally, we discuss why this attack is still applicable to the smallest structure sizes.

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