On the Effects of Clock and Power Supply Tampering on Two Microcontroller Platforms

Forcing faulty outputs of devices implementing cryptographic primitives in order to reveal some secret information is a well-known attack strategy. Tampering with the clock signal or the supply voltage are two popular techniques for generating erroneous behaviour. In this work we perform an in-depth analysis of the vulnerability of two different microcontroller platforms on clock and supply voltage tampering. The influence on three different groups of instructions is discussed in detail: arithmetical/logical instructions, branch instructions and memory instructions. A novel approach, combining short-time under powering with clock glitches, is applied in order to increase the reproducibility of the fault and the probability for the fault to occur. Results show that the fetch stage and the execution stage of the instruction pipeline are mainly affected by clock glitches, leading to skipped or duplicated execution or faulty calculation results. One sample per platform is used for the experiments, but for each fault type an interval for the parameters leading to the fault with a probability of 100% is given. The values in the middle of this interval are less sensitive to sample distribution as well as environmental influences. This knowledge allows to efficiently attack software implementations of cryptographic primitives implemented on one of the evaluated platforms.