Exploring Effect of Residual Electric Charges on Cryptographic Circuits: Extended Version

摘要

We study a new transistor-level side-channel leakagecaused by charges trapped in between stacked transistors namely residualelectric charges (RECs). Building leakage models is important in designingcountermeasures against side-channel attacks (SCAs). The conventionalwork showed that even a transistor-level leakage is measurable witha local electromagnetic measurement. One example is the current-pathleak [1], [2]: an attacker can distinguish the number of transistors in thecurrent path activated during a signal transition. Addressing this issue,Sugawara et al. proposed to use a mirror circuit that has the same numberof transistors on its possible current paths. We show that this countermeasureis insufficient by showing a new transistor-level leakage, caused byRECs, not covered in the previous work. RECs can carry the history ofthe gate’s state over multiple clock cycles and changes the gate’s electricalbehavior. We experimentally verify that RECs cause exploitable sidechannelleakage. We also propose a countermeasure against REC leaks anddesigned advanced encryption standard-128 (AES-128) circuits using IOmaskeddual-rail read-only memory with a 180-nm complementary metaloxide-semiconductor (CMOS) process. We compared the resilience of ourAES-128 circuits against EMA attacks with and without our countermeasureand investigated an RECs’ effect on physically unclonable functions(PUFs). We further extend RECs to physically unclonable function. Wedemonstrate that RECs affect the performance of arbiter and ring-oscillatorPUFs through experiments using our custom chips fabricated with 180- and40-nm CMOS processes.