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Active wire fences for multitenant FPGAs

Ognjen Glamocanin, Andela Kostic, Stasa Kostic, Mirjana Stojilovic

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.

2023

RDS: FPGA Routing Delay Sensors for Effective Remote Power Analysis Attacks

Ognjen Glamocanin, David Spielmann, Mirjana Stojilovic

State-of-the-art sensors for measuring FPGA voltage fluctuations are time-to-digital converters (TDCs). They allow detecting voltage fluctuations in the order of a few nanoseconds. The key building component of a TDC is a delay line, typically implemented as a chain of fast carry propagation multiplexers. In FPGAs, the fast carry chains are constrained to dedicated logic and routing, and need to be routed strictly vertically. In this work, we present an alternative approach to designing on-chip voltage sensors, in which the FPGA routing resources replace the carry logic. We present three variants of what we name a routing delay sensor (RDS): one vertically constrained, one horizontally constrained, and one free of any constraints. We perform a thorough experimental evaluation on both the Sakura-X side-channel evaluation board and the Alveo U200 datacenter card, to evaluate the performance of RDS sensors in the context of a remote power side-channel analysis attack. The results show that our best RDS implementation in most cases outperforms the TDC. On average, for breaking the full 128-bit key of an AES-128 cryptographic core, an adversary requires 35% fewer side-channel traces when using the RDS than when using the TDC. Besides making the attack more effective, given the absence of the placement and routing constraint, the RDS sensor is also easier to deploy.

2023

Temperature Impact on Remote Power Side-Channel Attacks on Shared FPGAs

Ognjen Glamocanin, Mathias Josef Payer, Mirjana Stojilovic

To answer the growing demand for hardware acceleration, Amazon, Microsoft, and many other major cloud service providers have included field-programmable gate arrays (FPGAs) in their datacenters. However, researchers have shown that cloud FPGAs, when shared between multiple tenants, face the threat of remote power side-channel analysis (SCA) attacks. FPGA time-to-digital converter (TDC) sensors enable adversaries to sense voltage fluctuations and, in turn, break cryptographic implementations or extract confidential information with the help of machine learning (ML). The operating temperature of the TDC sensor affects the traces it acquires, but its impact on the success of remote power SCA attacks has largely been ignored in literature. This paper attempts to fill in this gap. We focus on two attack scenarios: correlation power analysis (CPA) and ML-based profiling attacks. We show that the temperature impacts the success of the remote power SCA attacks: with the ambient temperature increasing, the success rate of the CPA attack decreases. In-depth analysis reveals that TDC sensor measurements suffer from temperature dependent effects, which, if ignored, can lead to misleading and overly optimistic results of ML-based profiling attacks. We evaluate and stress the importance of following power side-channel trace acquisition guidelines for minimizing the temperature effects and, consequently, obtaining a more realistic measure of success for remote ML-based profiling attacks.

2023