# US 2022/0045855 A1 · Secure communication network > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2022/0045855 A1 - Document ID: US20220045855A1 - Status: Published application - Kind: A1 - Application number: 17/505,720 - Filed: 2021-10-20 - Published: 2022-02-10 - Earliest claimed: 2019-02-22 - Assignees: Kabushiki Kaisha Toshiba - Applicants: Kabushiki Kaisha Toshiba - Inventors: Zhiliang YUAN; Andrew James SHIELDS - Web page: https://patentgrep.com/patent/US20220045855A1 ## CPC - H04L 9/0855: {involving additional nodes, e.g. quantum relays, repeaters, intermediate nodes or remote nodes} - H04B 10/70: Photonic quantum communication - H04L 9/0643: {Hash functions, e.g. MD5, SHA, HMAC or f9 MAC} - H04L 9/0662: {with particular pseudorandom sequence generator} - H04L 9/0841: {involving Diffie-Hellman or related key agreement protocols} - H04L 9/3066: {involving algebraic varieties, e.g. elliptic or hyper-elliptic curves} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - H04B: TRANSMISSION ## Abstract A method of exchanging a combined cryptographic key between a first node and a second node, the first node and the second node being connected through a first communication and a second communication network, wherein the first communication network is a quantum communication network wherein information is encoded on weak light pulses; and the first node and the second node being configured to: exchange one or more first cryptographic keys on the first communication network; exchange one or more second cryptographic keys using the second communication network; and form the combined cryptographic key by combining the one or more first cryptographic keys and the one or more second cryptographic keys, such that the first node and the second node share knowledge of the combined cryptographic key. ## Claims ### Claim 1 A method of exchanging a combined cryptographic key between a first node and a second node, the first node and the second node being connected through a first communication and a second communication network, wherein the first communication network comprises a quantum communication network wherein information is encoded on weak light pulses, and wherein the first communication network comprises at least one intermediate node, other than the first node and the second node, said intermediate node configured to receive and transmit a signal encoded on weak light pulses; and the first node and the second node being configured to: exchange one or more first cryptographic keys on the first communication network; exchange one or more second cryptographic keys on the second communication network; and form the combined cryptographic key by combining the one or more first cryptographic keys and the one or more second cryptographic keys, such that the first node and the second node share knowledge of the combined cryptographic key, wherein the first node is configured to send information through the first communication network to: exchange a quantum cryptographic key with the at least one intermediate node; generate a local secret key, the local secret key being used to form the one or more first cryptographic keys; form a further key using the local secret key and the quantum cryptographic key; and transmit the further key to the at least one intermediate node. ### Claim 2 (depends on 1) A method according to claim 1, wherein the at least one intermediate node is configured to: receive the further key; extract the local secret key using the further key and the exchanged quantum cryptographic key; form a second further key using the local secret key and the second quantum cryptographic key; and transmit the second further key to another of the at least one intermediate node or to the second node. ### Claim 3 (depends on 2) A method according to claim 2, wherein the second node is configured to: receive the second further key; and extract the local secret key using the second further key and the second quantum cryptographic key, such that the second node has knowledge of the local secret key generated by the first node. ### Claim 4 (depends on 1) A method according to claim 1 wherein the second communication network is a classical network directly connecting the first node and the second node, the second communication network comprising a communication channel between the first node and the second node. ### Claim 5 (depends on 4) A method according to claim 4 wherein the second cryptographic key is exchanged between the first node and the second node using a classical key exchange protocol. ### Claim 6 (depends on 5) A method according to claim 5 wherein the classical key exchange protocol uses a quantum-resistant algorithm. ### Claim 7 (depends on 6) A method according to claim 6 wherein the quantum-resistant algorithm comprises lattice, multivariate, hash, code, and supersingular elliptic curve cryptography. ### Claim 8 (depends on 1) A method according to claim 1 wherein the one or more first cryptographic keys and the one or more second cryptographic keys are combined using operations comprising exclusive-or, and/or universal hashing, and/or pseudorandom functions. ### Claim 9 (depends on 8) A method according to claim 8 wherein the one or more first cryptographic keys have equal lengths with the one or more second cryptographic keys. ### Claim 10 (depends on 8) A method according to claim 8 wherein the one or more first cryptographic keys have different lengths from the one or more second cryptographic keys. ### Claim 11 (depends on 1) A method according to claim 1 wherein the first node and the second node are configured to store the one or more first cryptographic keys in an indexed key store, wherein each entry in the indexed key store corresponds to a particular pair of the first node and the second node. ### Claim 12 (depends on 11) A method according to claim 11 wherein the first node and/or the second node comprises a counter, the value of the counter being used to select the one or more first cryptographic key corresponding to the particular pair of the first node and the second node. ### Claim 13 (depends on 12) A method according to claim 12 wherein the counter is incremented after the one or more first cryptographic key is provided. ### Claim 14 A communication network for exchanging a combined cryptographic key between a first node and a second node, wherein the first node and the second node are connected through a first communication and a second communication network, the first communication network comprising a quantum communication network wherein information is encoded on weak light pulses, and comprising at least one intermediate node, other than the first node and the second node, said intermediate node configured to receive and transmit a signal encoded on weak light pulses; and the first node and the second node are configured to: exchange one or more first cryptographic keys on the first communication network; exchange one or more second cryptographic keys on the second communication network; and form the combined cryptographic key by combining the one or more first cryptographic keys and the one or more second cryptographic keys, such that the first node and the second node share knowledge of the combined cryptographic key, wherein the first node is configured to send information through the first communication network to: exchange a quantum cryptographic key with the at least one intermediate node; generate a local secret key, the local secret key being used to form the one or more first cryptographic keys; form a further key using the local secret key and the quantum cryptographic key; and transmit the further key to the at least one intermediate node. ### Claim 15 A first node configured to exchange a combined cryptographic key with a second node on a communication network, the first node being connected to at least one intermediate node through a first communication network, the first communication network comprising a quantum communication network wherein information is encoded on weak light pulses, wherein the first communication network comprises at least one intermediate node, other than the first node and the second node, said intermediate node configured to receive and transmit a signal encoded on weak light pulses, wherein the first node is configured to exchange a quantum cryptographic key with the at least one intermediate node; the first node being directly connected to the second node using a second communication network; the first node and the second node being further configured to: exchange one or more first cryptographic keys on the first communication network; exchange one or more second cryptographic keys on the second communication network; and form the combined cryptographic key using the one or more first cryptographic keys and the one or more second cryptographic keys, such that the first node and the second node share knowledge of the combined cryptographic key wherein the first node is configured to send information through the first communication network to: exchange a quantum cryptographic key with the at least one intermediate node; generate a local secret key, the local secret key being used to form the one or more first cryptographic keys; form a further key using the local secret key and the quantum cryptographic key; and transmit the further key to the at least one intermediate node.