Anticipating Decoder Side-channel Attacks in Fault-tolerant Quantum Computers

As quantum computing emerges as an applied technology, there is a growing need to protect quantum computers against information security attacks. This work identifies a new class of side-channel attacks against fault-tolerant quantum computers, in which the syndrome data that is sent to the decoder system is used to infer which computation (logical circuit) is taking place on the quantum computer. Our work introduces the concept of gate fingerprints, which describes those patterns present in syndrome data that indicate which logical operation took place on the quantum computer. We show different effects by which logical operations produce gate fingerprints by focusing on Clifford+T computation in the surface code. We then explore how gate fingerprint information can be used to make inferences about the circuits or algorithms run on a quantum computer. Our findings indicate that decoder systems can be a vector for side-channel attacks and thus to prevent this, decoder systems should either be secured or built by a trusted party.