# US 12,010,223 B2 · Joint twin-field quantum key distribution cryptosystem

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- Number: US 12,010,223 B2
- Document ID: US12010223B2
- Status: Granted
- Kind: B2
- Application number: 17/373,445
- Filed: 2021-07-12
- Published: 2022-01-13
- Granted: 2024-06-11
- Earliest claimed: 2020-07-13
- Assignees: Arizona Board of Regents on Behalf of the University of Arizona
- Applicants: Arizona Board of Regents on Behalf of the University of Arizona
- Inventors: Ivan Djordjevic
- Web page: https://patentgrep.com/patent/US12010223B2

## CPC

- H04L 9/0852: {Quantum cryptography (transmission systems employing electromagnetic waves other than radio waves, e.g. light, infrared H04B10/00; wavelength-division multiplex systems H04J14/02; WDM arrangements H04J14/03)}
- H03M 13/116: {Quasi-cyclic LDPC [QC-LDPC] codes, i.e. the parity-check matrix being composed of permutation or circulant sub-matrices}
- H03M 13/63: {Joint error correction and other techniques (H03M13/31 and H03M13/33 take precedence)}
- H04B 10/40: Transceivers
- H04B 10/70: Photonic quantum communication
- H04L 1/0061: {Error detection codes}
- H04L 1/004: {by using forward error control (H04L1/0618 takes precedence; coding, decoding or code conversion, for error detection or correction H03M13/00)}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- H03M: CODING; DECODING; CODE CONVERSION IN GENERAL (using fluidic means F15C4/00; optical analogue/digital converters G02F7/00; coding, decoding or code conversion, specially adapted for particular applications, see the relevant subclasses, e.g. G01D, G01R, G06F, G06T, G09G, G10L, G11B, G11C, H04B, H04L, H04M, H04N; ciphering or deciphering for cryptography or other purposes involving the need for secrecy G09C)
- H04B: TRANSMISSION

## Abstract

The present disclosure is directed to systems and methods of providing a secure quantum key distribution cryptosystem in which the quantum key data is exchanged between Alice and Bob using a quantum channel and the parity bits associated with the quantum key data are encrypted using a post-quantum computing (PQC) encryption method and communicated between Alice and Bob using a public channel.

## Claims

### Claim 1

A quantum communications system, comprising:
a quantum domain comprising a first quantum transmitter circuitry and a second quantum transmitter circuitry to communicate over a quantum channel link; the first quantum transmitter circuitry and the second quantum transmitter circuitry to generate a raw encryption key using quantum communications via the quantum channel link;
a public domain comprising first public channel circuitry and second public channel circuitry to communicate over a public channel link; the second public channel circuitry to generate a sifted key based on the raw key, and to generate a parity bits syndrome vector with respect to the sifted key; the second public channel circuitry further to encrypt the syndrome vector and transmit the encrypted syndrome vector, over the public channel link to the first public channel circuitry, to enable the first public channel circuitry to determine a corrected key that is based on the sifted key; wherein the first public channel circuitry further to decrypt the encrypted syndrome vector and wherein the first public channel circuitry includes low-density parity check (LDPC) code to decode the decrypted syndrome vector and generate the corrected key.

### Claim 2 (depends on 1)

The system of claim 1, wherein the first public channel circuitry to encrypt the syndrome vector using a post-quantum cryptography (PQC) protocol.

### Claim 3 (depends on 2)

The system of claim 2, wherein the PQC protocol comprises a McEliece PQC protocol.

### Claim 4 (depends on 1)

The system of claim 1, wherein the second public channel circuitry includes syndrome generation circuitry to generate the syndrome vector my multiplying the sifted key by a parity-check matrix H representing low-density parity check (LDPC) code.

### Claim 5 (depends on 1)

The system of claim 1, wherein the second public channel circuitry also to reduce a size the syndrome vector by removing all-zero submatrices within the syndrome vector.

### Claim 6 (depends on 1)

The system of claim 1, further comprising Bell state measurement circuitry disposed between the first quantum channel circuitry and a second quantum channel circuitry along the quantum channel link, the Bell state measurement circuitry to determine Bell state measurements regarding quantum communications between the first quantum channel circuitry and a second quantum channel circuitry.

### Claim 7

A method to reduce information leakage between two link partners, using a joint quantum key distribution (QKD) and post-quantum cryptography (PQC) system, the method comprising:
generating a raw key between a first transceiver system and a second transceiver system communicating over a quantum channel link, the raw key being generated using a quantum key distribution (QKD) technique;
sifting, by the first and second transceiver systems, the raw key to obtain a sifted key (x);
generating, by the second transceiver system, a parity bits syndrome vector (p) by multiplying the sifted key x by a parity-check matrix H representing low-density parity check (LDPC) code;
encrypting, by the second transceiver system, the syndrome (p) using a post-quantum cryptography (PQC) protocol;
transmitting, by the second transceiver system, the encrypted syndrome (p) to the first transceiver system over a public channel link;
decrypting, by first transceiver system, the encrypted syndrome vector using the PQC protocol; and
decoding, by first transceiver system, using low density parity check (LDPC) circuitry, performed on the decrypted syndrome vector and sifted key to generate a corrected key.

### Claim 8 (depends on 7)

The method of claim 7, wherein the PQC protocol comprises a McEliece PQC protocol.

### Claim 9 (depends on 7)

The method of claim 7, further comprising reducing a size of the parity-check matrix of corresponding spatially coupled LDPC code by introducing the layer index so that all-zero submatrices are removed.

### Claim 10 (depends on 7)

The method of claim 7, further comprising determining, by Bell state measurement circuitry disposed between the first transceiver system and the second transceiver system along the quantum channel link, Bell state measurements regarding quantum communications between first transceiver system and the second transceiver system.

### Claim 11

At least one non-transitory storage device that includes machine-readable instructions that, when executed by one or more processors, cause the one or more processors to perform operations, comprising:
generate a raw key between Alice and Bob communicating over a quantum channel link, the raw key being generated using a quantum key distribution (QKD) technique;
generate a raw key between a first transceiver system and a second transceiver system communicating over a quantum channel link, the raw key being generated using a quantum key distribution (QKD) technique;
sift, by the first and second transceiver systems, the raw key to obtain a sifted key (x);
generate, by the second transceiver system, a parity bits syndrome vector (p) by multiplying the sifted key x by a parity-check matrix H representing low-density parity check (LDPC) code;
encrypt, by the second transceiver system, the syndrome (p) using a post-quantum cryptography (PQC) protocol;
transmit, by the second transceiver system, the encrypted syndrome (p) to the first transceiver system over a public channel link;
decrypt, by first transceiver system, the encrypted syndrome vector using the PQC protocol; and
decode, by the first transceiver system Alice decoder using low-density parity check (LDPC) decoding circuitry, the decrypted syndrome vector and the sifted key to generate a corrected key.

### Claim 12 (depends on 11)

The at least one non-transitory storage device of claim 11, wherein the PQC protocol comprises a McEliece PQC protocol.

### Claim 13 (depends on 11)

The at least one non-transitory storage device of claim 11, wherein the machine-readable instructions that, when executed by one or more processors, cause the one or more processors to perform operations, comprising:
reduce a size the syndrome vector by removing all-zero submatrices within the syndrome vector.

### Claim 14 (depends on 11)

The at least one non-transitory storage device of claim 11, wherein the machine-readable instructions that, when executed by one or more processors, cause the one or more processors to perform operations, comprising:
determining Bell state measurements regarding quantum communications between the first and second transceiver systems.

### Claim 15 (depends on 1)

The system of claim 1, wherein the second public channel circuitry further to encrypt the syndrome vector using a private cryptosystem protocol.