Side channel

A side channel is an unintended path through which information leaks from a system via observable effects of its operation, such as timing, power consumption, and electromagnetic or acoustic emissions ¹.

A covert channel is related but deliberate: two cooperating parties use an unintended channel to transfer information in a way that violates a system's security policy ¹. Side channels can leak secrets that verification designs aim to protect: BarraCUDA used electromagnetic analysis to recover the parameters of neural networks running on an edge GPU ², and a 2026 MIRI Technical Governance Team post describes microarchitectural side channels as a limitation of trusted execution environments ³. Covert channels threaten the checks themselves: another post from the same team describes electromagnetic, acoustic, power-line and fibre-optic channels that could carry data around a data centre's monitored network links, and proposes shielded enclosures, jamming combined with sensing, inspection and filtering, the approach of side-channel suppression ⁴. One low-trust system design sets its suppression target at covert bandwidths of kilobits per second rather than zero ⁵. Physical signals can also serve the verifier: training and inference often differ in accelerator utilization and power draw, which workload classification uses ⁶.