Patent ID: 8650401

Claim:
A method of quantum key distribution between a first node and a second node over an optical network via a network path, the network path between the first node and the second node comprising at least one intermediate node, the method comprising: agreeing a quantum key between the first node and each subsequent node in the network path in sequence until a quantum key is agreed between the first node and the second node, wherein agreeing a quantum key between the first node and each subsequent node in the network path includes: exchanging a quantum signal between a targeted node in the network path and the previous node in the network path, and agreeing a quantum key between the first node and the targeted node based on the quantum signal, wherein, when the first node is not itself involved in said quantum exchange, the first node communicates with the node previous to the targeted node in the network path such that the first node has the information necessary for agreeing a quantum key, the communication between the first node and the node previous to the targeted node being encrypted using the quantum key established with the previous node.