US 12,335,378 B2
To quantum key distribution
Marco Menchetti, London (GB)
Assigned to British Telecommunications Public Limited Company, London (GB)
Appl. No. 17/754,170
Filed by British Telecommunications Public Limited Company, London (GB)
PCT Filed Aug. 18, 2020, PCT No. PCT/EP2020/073086
§ 371(c)(1), (2) Date Mar. 25, 2022,
PCT Pub. No. WO2021/063590, PCT Pub. Date Apr. 8, 2021.
Claims priority of application No. 19200429 (EP), filed on Sep. 30, 2019.
Prior Publication US 2022/0294619 A1, Sep. 15, 2022
Int. Cl. H04L 9/08 (2006.01)
CPC H04L 9/0858 (2013.01) [H04L 9/0825 (2013.01); H04L 9/0866 (2013.01)] 10 Claims
OG exemplary drawing
 
1. A method of establishing at least a portion of an encryption key, comprising:
transmitting a first photon along a channel;
making a modification to the channel so as to change a length of time it takes a photon to propagate along the channel;
transmitting a second photon along the modified channel;
determining a length of time the first photon takes to propagate along the channel;
determining a length of time the second photon takes to propagate along the modified channel;
using the determined lengths of time to determine the at least a portion of the encryption key; and, separately,
using the fact that the modification has been made to the channel to determine the at least the portion of the encryption key.