  We show how QKD on a multi-user, multi-path, network can be used to establish
a key between any two end users in an asynchronous fashion using the technique
of bit-transport. By a suitable adaptation of our previous secret-sharing
scheme we show that an attacker has to compromise all of the intermediate
relays on the network in order to obtain the key. Thus, two end users can
establish a secret key provided they trust at least one of the network relays.
