Relay QKD Networks & Bit Transport

We show how it is possible to operate end-to-end relays on a QKD network by treating each relay as a trusted eavesdropper operating an intercept/resend strategy. It is shown that, by introducing the concept of bit transport, the key rate compared to that of single-link channels is unaffected. The technique of bit transport extends the capability of QKD networks. We also discuss techniques for reducing the level of trust required in the relays. In particular we demonstrate that it is possible to create a simple quantum key exchange scheme using secret sharing such that by the addition of a single extra relay on a multi-relay channel requires the eavesdropper to compromise all the relays on the channel. By coupling this with multi-path capability and asynchronous quantum key establishment we show that, in effect, an eavesdropper has to compromise all relays on an entire network and collect data on the entire network from its inception.