RandOhm: Mitigating Impedance Side-channel Attacks using Randomized Circuit Configurations

TL;DR

Impedance-based side-channel attacks threaten cryptographic hardware by exploiting data-dependent PDN impedance. RandOhm tackles this with a modular moving-target defense that uses partial reconfiguration to randomly relocate and route secret-sensitive circuitry in real time, decoupling data-dependent computation from PDN impedance. The approach combines coarse-grained slice multiplexing and fine-grained register-sequence scrambling, enabled by open-source bitstream manipulation tools, and is validated on AES implementations on 28 nm FPGAs/SoCs against profiled and non-profiled attacks, with measured overheads. This work offers a practical defense that complements masking and enables resilient, real-time impedance mitigation for FPGA-based cryptography.

Abstract

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.

Figures (13)

• Figure 1: (a) Equivalent RLC circuit model of the power distribution network (PDN) of the PCB and chip monfared2023leakyohm. (b) Contribution of different parts of the PDN to the impedance over frequency. (c) Contribution of a CMOS inverter to PDN's impedance mosavirik2023silicon.
• Figure 2: Impact of different FPGA routing configurations on PDN's impedance
• Figure 3: Real-time Target Slice Multiplexer
• Figure 4: Real-time Register Sequence Multiplexer
• Figure 5: High-level block-diagram description of RandOhm