  Significant research efforts have been dedicated to designing cryptographic
algorithms that are quantum-resistant. The motivation is clear: robust quantum
computers, once available, will render current cryptographic standards
vulnerable. Thus, we need new Post-Quantum Cryptography (PQC) algorithms, and,
due to the inherent complexity of such algorithms, there is also a demand to
accelerate them in hardware. In this paper, we show that PQC hardware
accelerators can be backdoored by two different adversaries located in the chip
supply chain. We propose REPQC, a sophisticated reverse engineering algorithm
that can be employed to confidently identify hashing operations (i.e., Keccak)
within the PQC accelerator - the location of which serves as an anchor for
finding secret information to be leaked. Armed with REPQC, an adversary
proceeds to insert malicious logic in the form of a stealthy Hardware Trojan
Horse (HTH). Using Dilithium as a study case, our results demonstrate that HTHs
that increase the accelerator's layout density by as little as 0.1\% can be
inserted without any impact on the performance of the circuit and with a
marginal increase in power consumption. An essential aspect is that the entire
reverse engineering in REPQC is automated, and so is the HTH insertion that
follows it, empowering adversaries to explore multiple HTH designs and identify
the most suitable one.
