A directional coupler attack against the Kish key distribution system
This work exposes a critical flaw in a proposed secure communication system, potentially impacting its practical deployment for users relying on classical key distribution methods.
The authors tackled the security of the Kish key distribution system, a classical alternative to quantum key distribution, by demonstrating its vulnerability to nonidealities like finite resistance in transmission lines, and introduced a novel directional coupler attack that experimentally showed efficacy by exploiting causality and propagation delays.
The Kish key distribution system has been proposed as a class ical alternative to quantum key distribution. The idealized Kish scheme elegantly promise s secure key distribution by exploiting thermal noise in a transmission line. However, we demonstrate that it is vulnerable to nonidealities in its components, such as the finite resistance of the transmission line connecting its endpoints. We introduce a novel attack against this nonideality using directional wave measurements, and experimentally demonstrate its efficacy. Our attack is based on causality: in a spatially distributed system, propagation is needed for thermodynamic equilibration, and that leaks information.