Active Wire Fences for Multitenant FPGAs

When spatially shared among multiple tenants, field-programmable gate arrays (FPGAs) are vulnerable to remote power side-channel analysis attacks. Using carefully crafted on-chip voltage sensors, adversaries can extract secrets (e.g., encryption keys or the architectural parameters of neural network accelerators) from collocated tenants. A common countermeasure against power side-channel attacks is hiding; in hiding, the goal is to introduce noise and worsen the signal-to-noise ratio visible to the attacker. In a multitenant FPGA setting, hiding countermeasures can be implemented with an active fence placed between tenants. Previous work demonstrated the effectiveness of active fences built using NAND-based ROs. We enhance the state-of-the-art active fence implementation with novel wire-based power wasters, at no increase in resource overhead. Compared to an RO-based fence, our active wire fence makes the side-channel attack considerably more difficult. When using the RO fence to protect an AES-128 cryptographic module, we recovered all the bytes of the secret key with one million sensor traces, on average. In comparison, when using our novel wire fence, more than six million traces (an improvement of at least 6×) were required to recover all the bits of the secret key.