  Physical side-channel attacks can compromise the security of integrated
circuits. Most physical side-channel attacks (e.g., power or electromagnetic)
exploit the dynamic behavior of a chip, typically manifesting as changes in
current consumption or voltage fluctuations where algorithmic countermeasures,
such as masking, can effectively mitigate them. However, as demonstrated
recently, these mitigation techniques are not entirely effective against
backscattered side-channel attacks such as impedance analysis. In the case of
an impedance attack, an adversary exploits the data-dependent impedance
variations of the chip power delivery network (PDN) to extract secret
information. In this work, we introduce RandOhm, which exploits a moving target
defense (MTD) strategy based on the partial reconfiguration (PR) feature of
mainstream FPGAs and programmable SoCs to defend against impedance side-channel
attacks. We demonstrate that the information leakage through the PDN impedance
could be significantly reduced via runtime reconfiguration of the
secret-sensitive parts of the circuitry. Hence, by constantly randomizing the
placement and routing of the circuit, one can decorrelate the data-dependent
computation from the impedance value. Moreover, in contrast to existing
PR-based countermeasures, RandOhm deploys open-source bitstream manipulation
tools on programmable SoCs to speed up the randomization and provide real-time
protection. To validate our claims, we apply RandOhm to AES ciphers realized on
28-nm FPGAs. We analyze the resiliency of our approach by performing
non-profiled and profiled impedance analysis attacks and investigate the
overhead of our mitigation in terms of delay and performance.
