Key exchange protocol for quantum network

An intermediary device comprising a processor unit, a memory unit, and a communication interface, the processor unit connected to the memory unit and the communication interface, wherein the processor unit, memory unit and communication interface are adapted to implement a computer-implemented method of key exchange between a first endpoint device and a second endpoint device communicatively coupled over communication links via the intermediary device, wherein the first endpoint device is coupled by a first communication link to the intermediary device, and the second endpoint device, the intermediary device, and one or more other intermediate devices form a group of devices, wherein the intermediary device is communicatively coupled to at least one of the one or more other intermediary devices via at least one of the communication links and the second endpoint device is coupled to a last of the one or more other intermediary devices in the group via a second communication link, the intermediary device configured to:

• exchange intermediate key information between the intermediary device and the first endpoint device based on a first key exchange protocol;
• and
• securely send data representative of the exchanged intermediate key information from the intermediary device to the second endpoint device via the one or more other intermediary devices, the secure communications over the communication links of the group of devices based on shared keys exchanged using one or more key exchange protocols over the communication links of the group of devices;
• wherein the first and second endpoint devices use a further communication channel therebetween for processing and transforming said intermediate key information into a final shared key;
• wherein each shared key is used for securing the communication of the intermediate key information from one device to next;
• wherein the intermediary device and each of the one or more other intermediary devices sends its shared key to the second endpoint device, and only encrypts any incoming communications associated with the intermediate key information with its shared key before forwarding towards the second endpoint device via its nearest neighbour device, wherein the second endpoint device uses the shared keys to decrypt the encrypted intermediate key information.