A secure time transfer method and system based on bidirectional quantum key distribution

Abstract

The present invention relates to a secure time transfer system and method based on bidirectional quantum key distribution. The transfer system may include a transmission channel between a communication terminal A and a communication terminal B, wherein communication terminals A and B may send single-photon signals to each other according to a quantum key distribution protocol and respectively detect the arriving single-photon signals; communication terminal A records the emission time t of the single-photon signal based on a local clock A. SA and arrival time t RA , the communication terminal B records the emission time t of the single photon signal based on the local clock B SB and arrival time t RB ; The communication terminal A also encrypts the transmission time t SA and arrival time t RA Transmitted to communication terminal B; communication terminal B according to the transmission time t SA Arrival time t RA , launch time t SB , and arrival time t RB Calculate the clock difference T between clocks A and B AB ; and, according to the clock error T AB Clock B is adjusted to compensate for the clock difference between clocks B and A, thereby achieving time transfer.

Description

Technical Field

[0001] The present invention relates to the field of quantum technology information, and in particular to a secure time transfer method and system based on bidirectional quantum key distribution. Background Art

[0002] High-precision time and frequency are not only crucial for basic scientific research but also have widespread applications in defense, industry, and social life. For example, drones and autonomous vehicles require navigation and positioning, which is closely related to timing. Various network systems, such as computer networks, communications networks, financial markets, and power grids, require a unified time reference. If these time-synchronized systems are subject to malicious attacks, time errors can lead to navigation errors and network crashes, resulting in significant losses and potentially impacting national defense and public safety. Therefore, the security of time and frequency transmission is crucial in these areas.

[0003] Currently, existing time synchronization schemes and protocols still have many security risks. For example, the time and frequency synchronization scheme based on GPS satellites is vulnerable to spoofing attacks.

[0004] For example, existing time and frequency transmission can be divided into two forms based on the link mode: one-way and two-way. In one-way time and frequency transmission, the master clock generally broadcasts a signal with time information through a broadcast or dedicated channel. After receiving the signal, the slave clock measures the local arrival time. By comparing the time difference between the two and taking into account the propagation time of the signal, the slave clock can obtain the clock difference between itself and the master clock. Figure 1 As shown, the time when the master clock A transmits the signal is t1 A The time of arrival of the signal received from clock B is measured locally as t2 B , where the channel delay is d AB , then B can calculate the clock difference T between himself and A BA =t2 B -t1 A -d AB .

[0005] In the two-way time and frequency transmission, not only the master clock transmits synchronization signals to the slave clock, but the slave clock also transmits synchronization signals to the master clock, forming a two-way communication link. Figure 2 As shown, the time when the master clock A transmits the signal is t1 A The time of arrival of the signal received from clock B is measured locally as t2 B , In addition, B is also at t3 B The synchronization signal is transmitted at time t4, and A A After measuring the signal, A will use its own two time information t1 A and t4 ATell B that B can calculate the clock difference and distance between them based on these four times, where: BA =(t2 B +t3 B -t4 A -t1 A ) / 2, the distance between A and B R=[(t4 A -t1 A )-(t3 B -t2 B )]*C / 2.

[0006] For a time-frequency transfer system, physical signal interaction and the transmission of measurement data are required. Therefore, conventional one-way or two-way time-frequency transfer systems are vulnerable to physical and data layer attacks, posing a serious threat to the security of the system. Therefore, research is needed to find better solutions for more secure time-frequency transfer and synchronization. Summary of the Invention

[0007] In response to the shortcomings of the prior art, the present invention proposes a method and system for securely achieving time and frequency synchronization using quantum key distribution. In the present invention, single-photon signals or weak coherent state light pulse photons (hereinafter collectively referred to as single photons) in the quantum key distribution system are used to directly achieve time transfer, wherein the single-photon bidirectional time transfer is achieved in combination with the bidirectional quantum key distribution process, and the interaction of time data between the communicating parties uses the generated quantum key for data encryption and transmission. The present invention uses single photons to achieve time transfer. Based on the quantum non-cloning theorem, it can be guaranteed that eavesdropping detection of single photons will cause the error rate of the measurement end to increase; for attacks on the time delay of single-photon signals, the difference between the actual distance information and the known distance can be measured through bidirectional time transfer to determine whether it is within a reasonable range. Therefore, the physical layer security of the bidirectional time transfer of the present invention can be guaranteed. At the same time, by encrypting the time data with quantum keys, the data layer security of the bidirectional time transfer of the present invention can be guaranteed. In addition, according to the present invention, quantum key distribution and time transfer can be achieved simultaneously with the help of single photons, thereby improving the integration of the system.

[0008] Specifically, a first aspect of the present invention relates to a secure time transfer system based on bidirectional quantum key distribution, which includes a communication terminal A, a communication terminal B, and a transmission channel, wherein:

[0009] The communication end A and the communication end B are configured to send single photon signals to each other according to a quantum key distribution protocol, and respectively detect the arriving single photon signals;

[0010] The communication terminal A is further configured to record the emission time t of the single photon signal based on the local clock A.SA and the arrival time t of the detected single photon signal RA ;

[0011] The communication terminal B is further configured to record the emission time t of the single photon signal based on the local clock B. SB and the arrival time t of the detected single photon signal RB ;

[0012] The communication terminal A is further configured to transmit the transmission time t in an encrypted manner. SA and the arrival time t RA Transmit to the communication terminal B;

[0013] The communication terminal B is further configured to transmit the signal according to the transmitting time t SA , the arrival time t RA , the emission time t SB , and the arrival time t RB Calculate the clock difference T between the clock A and the clock B AB ; and, according to the clock difference T AB The clock B is adjusted to achieve clock difference compensation between the clock B and the clock A.

[0014] Furthermore, the communication end A also includes a quantum transmitting end unit, a quantum receiving end unit, and a time data encryption unit; and the communication end B also includes a quantum transmitting end unit, a quantum receiving end unit, a time data decryption unit, a clock difference calculation unit, and a feedback adjustment unit.

[0015] Furthermore, the quantum receiving end unit of the communication end B is configured to generate a quantum key in combination with the quantum transmitting end unit of the communication end A, and record the arrival time t RB The quantum receiving end unit of the communication end A is configured to generate a quantum key in combination with the quantum transmitting end unit of the communication end B, and record the arrival time t RA ; And, the quantum transmitting end unit of the communication end A is configured to record the transmitting time t SA The quantum transmitting end unit of the communication end B is configured to record the transmitting time t SB .

[0016] Furthermore, the communication terminal A and the communication terminal B are further configured to calculate the quantum bit error rate QBER(i) within the time period T(i) during the quantum key distribution process, and compare the QBER(i) with the preset security threshold Q T Compare; and, when the QBER(i) is less than the safety threshold Q TWhen the single photon signal in the time period T(i) is used to generate a quantum key and realize time transfer.

[0017] Furthermore, the communication end A and the communication end B are further configured to randomly abandon the single photon signal in the time period T(i) at a ratio of 4*QBER(i) or 4*Q T The single photon signal is retained only when the ratio is [1-4*QBER(i)] or [1-4*Q T ] is used to realize the time transfer.

[0018] Furthermore, the communication end A and the communication end B are further configured to calculate the clock error T based on the single photon signal in the time period T(i). AB , and discard the ratio of 4*QBER(i) or 4*Q T The clock difference T AB Only the data with the ratio [1-4*QBER(i)] or [1-4*Q T ] the clock difference T AB data to realize time transfer.

[0019] Preferably, the clock error data T in the time period T(i) AB In a random manner, the ratio of 4*QBER(i) or 4*Q T The clock error data T AB Or, the clock error data T within the time period T(i) AB Perform histogram distribution statistics and place the data in the center interval [1-4*QBER(i)] or [1-4*Q T ] other than the clock error data T AB give up.

[0020] The safety threshold Q T It may preferably be 1.25%; and / or, the T(i) may preferably be 1 second.

[0021] Furthermore, the time data encryption unit is configured to encrypt the transmission time t SA and the arrival time t RA The time data decryption unit is configured to decrypt the encrypted transmission time t SA and the arrival time t RA Decrypt.

[0022] Furthermore, quantum keys are used in the time data encryption unit and the time data decryption unit.

[0023] Furthermore, the clock error calculation unit is configured to calculate the clock error T based on the following formula: AB ,

[0024]

[0025] Furthermore, the communication terminal B is further configured to calculate the distance R between the communication terminal A and the communication terminal B, and calculate the distance R and the distance R of the transmission channel. p The difference between |RR p |, and the difference |RR p |With the preset safety distance threshold L T to make comparisons; and,

[0026] The communication end A and the communication end B are configured such that, in the difference |RR p | Greater than or equal to the safety distance threshold L T When , the single photon signal used to calculate the distance R is abandoned for time transfer;

[0027] in, c is the speed of light.

[0028] Optionally, the transmission channel is vacuum free space, atmospheric free space or optical fiber.

[0029] A second aspect of the present invention relates to a secure time transfer method based on bidirectional quantum key distribution, which may include the following steps:

[0030] Single photon signals are sent between communication terminals A and B according to a quantum key distribution protocol, and the arriving single photon signals are detected respectively to perform bidirectional quantum key distribution;

[0031] The communication terminal A records the emission time t of the single photon signal using the local clock A. SA and the arrival time t of the detected single photon signal RA ;

[0032] The transmitting time t of the single photon signal is recorded by the local clock B at the communication end B. SB and the arrival time t of the detected single photon signal RB ;

[0033] At the emission time t of the single photon signal used to generate the quantum key at the communication end A SA and the arrival time t RA Transmit to the communication terminal B;

[0034] At the communication end B, according to the emission time t of the single photon signal used to generate the quantum keySA , the arrival time t RA , the emission time t SB and the arrival time t RB Calculate the clock difference T between the clock A and the clock B AB ;as well as,

[0035] According to the clock difference T AB The clock B is adjusted to achieve clock difference compensation between the clock B and the clock A.

[0036] Furthermore, the emission time t SA and the arrival time t RA The data is transmitted to the communication terminal B in a quantum key encrypted manner.

[0037] The secure time transfer method of the present invention may further comprise the following steps:

[0038] Obtain the quantum bit error rate QBER(i) in the time period T(i) in quantum key distribution, and compare the QBER(i) with the preset security threshold Q T When the QBER(i) is less than the safety threshold Q T When , the single photon signal in the time period T(i) is used to generate a quantum key.

[0039] Furthermore, in the single photon signal within the time period T(i), the ratio of [1-4*QBER(i)] or [1-4*Q T ] is used to calculate the clock difference T AB .

[0040] Furthermore, the clock error T is calculated based on the single photon signal in the time period T(i). AB , and discard the ratio of 4*QBER(i) or 4*Q T The clock difference T AB Only the data with the ratio [1-4*QBER(i)] or [1-4*Q T ] the clock difference T AB data to realize time transfer.

[0041] Preferably, the clock error data T is selected and retained in a random manner or based on a histogram statistical distribution. AB .

[0042] The secure time transfer method of the present invention may further comprise the following steps:

[0043] Calculating the distance R between the communication end A and the communication end B;

[0044] Calculate the distance R and the distance R of the transmission channel between the communication end A and the communication end B p The difference between |RR p |, and the difference |RR p | is compared with the preset safety distance threshold LT, when the difference |RR p | Greater than or equal to the safety distance threshold L T When the single photon signal used to calculate the distance R is abandoned for calculating the clock error T AB .

[0045] Furthermore, the secure time transfer method of the present invention can be implemented based on the above-mentioned secure time transfer system of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0048] Figure 1 A schematic diagram of a one-way time-frequency transmission system in the prior art is shown;

[0049] Figure 2 A schematic diagram of a prior art two-way time-frequency transmission system is shown;

[0050] Figure 3 The schematic diagram shows the principle of the secure time transfer system and method based on bidirectional quantum key distribution of the present invention. DETAILED DESCRIPTION

[0051] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided by way of example so as to fully convey the spirit of the present invention to those skilled in the art to which the present invention belongs. Therefore, the present invention is not limited to the embodiments disclosed herein.

[0052] like Figure 3 As shown, the secure time transfer system based on bidirectional quantum key distribution of the present invention may include a communication terminal A, a communication terminal B and a transmission channel.

[0053] Communication end A may include clock A, a quantum transmitting end unit, a quantum receiving end unit, and a time data encryption unit.

[0054] The communication end B may include a clock B, a quantum transmitting end unit, a quantum receiving end unit, a time data decryption unit, a clock difference calculation unit, and a feedback adjustment unit.

[0055] Clock A and clock B are clock sources to be compared and synchronized, located at communication ends A and B respectively. They can provide clock signals for other local unit modules, such as quantum transmitting end units, quantum receiving end units, time data encryption or decryption units, clock difference calculation units, feedback adjustment units, etc.

[0056] The quantum transmitting end unit of communication end A (communication end B) can be the transmitting end of the quantum key distribution device, which is used to realize the random coding modulation and emission of single-photon signals to meet the requirements of the quantum key distribution protocol (such as the classic BB84 protocol).

[0057] In the present invention, the quantum transmitting end unit of the communication end A not only generates a quantum key by combining with the quantum receiving end unit of the opposite end (communication end B), but also records the emission time of the single photon signal (sequence), which is recorded as t SA , where the time data t SA The clock A in the communication terminal A is used as the time reference.

[0058] The quantum receiving end unit module of communication terminal A (communication terminal B) can be the receiving end of the quantum key distribution device, which is used to realize the photoelectric detection and signal processing of single-photon signals to meet the requirements of the quantum key distribution protocol (such as the classic BB84 protocol).

[0059] In the present invention, the quantum receiving end unit of the communication end A not only generates a quantum key by combining with the quantum transmitting end unit of the opposite end (communication end B), but also records the arrival time of the detected single photon signal (sequence), which is recorded as t RA , where the time data t RA Likewise, the clock A in the communication terminal A is used as the time reference.

[0060] Similarly, the quantum transmitting end unit of communication end B, in addition to combining with the quantum receiving end unit of the other end (communication end A) to generate the quantum key, can also record the emission time of the single photon signal (sequence), which is recorded as t SB , where the time data t SB The clock B in the communication terminal B is used as the time reference.

[0061] The quantum receiving end unit of communication end B not only generates quantum keys by combining with the quantum transmitting end unit of the other end (communication end A), but also records the arrival time of the detected single photon signal (sequence), which is recorded as t RB , where the time data t RBThe clock B in the communication terminal B is used as the time reference.

[0062] Furthermore, according to the present invention, communication terminals A and B can also obtain the quantum bit error rate (QBER) during quantum key distribution. For example, the quantum transmitting and receiving units of communication terminals A and B can calculate the corresponding QBER at regular intervals (e.g., a preset time interval T) according to a quantum key distribution protocol (e.g., the BB84 protocol). As an example, the preset time interval T can be 1 second.

[0063] After obtaining the quantum bit error rate QBER(i) in the time period T(i), the QBER(i) can be compared with the preset safety threshold Q T For comparison, since the interception and retransmission attack on a single photon signal will introduce a QBER of 25%, for the quantum bit error rate QBER(i) within the time period T(i), it means that at most 4*QBER(i) single photon signals are tampered by the attacker. Therefore, when QBER(i) is less than the security threshold Q T When , the transmission process of the single-photon signal is considered to be safe, the data of the single-photon signal in the corresponding time period T(i) can be retained, and the quantum key and time transfer can be generated based on these single-photon signals. It can be seen that in the time transfer system of the present invention, the security threshold Q of OBER can be reasonably set. T (For example, Q T It is set to a smaller value of 1.25%), which can ensure the security of the time data carrier (ie, the single photon signal) against interception and retransmission attacks.

[0064] As mentioned above, when QBER(i) in a certain time period T(i) is less than the preset safety threshold Q T When , it can be determined that among the single-photon signals detected in the time period T(i), the proportion of single-photon signals that have not been intercepted and retransmitted is [1-4*QBER(i)], that is, among the single-photon signals detected during this period, [1-4*QBER(i)] of the single-photon signals can be considered safe.

[0065] Therefore, in a preferred embodiment of the present invention, for single photon signals within time period T(i), communication end A and communication end B can randomly abandon the single photon signals with a ratio of 4*QBER(i) or 4*QBER(i). T The single photon signal is retained only when the ratio is [1-4*QBER(i)] or [1-4*Q T ] and use the time data carried on this single-photon signal to realize time transmission.

[0066] In another preferred embodiment of the present invention, the clock error data T can be calculated based on the single photon signal in the time period T(i). AB , and discard the ratio of 4*QBER(i) or 4*Q T The clock error data is only retained when the ratio is [1-4*QBER(i)] or [1-4*Q T ] and use this part of the minute difference data to realize the time transmission.

[0067] In one example, for the clock error data T in the time period T(i), AB , the ratio used for abandonment is 4*QBER(i) or 4*Q T Clock difference data T AB The selection can be random.

[0068] In another example, the clock error data T in the time period T(i) can be AB Make a histogram distribution statistic and put it in the interval [1-4*QBER(i)] or [1-4*Q T ] other clock error data T AB give up.

[0069] For example, in Q T When QBER(i) is set to 1.25%, communication terminals A and B can calculate QBER(i) in each time period T(i) and retain the clock error data T in the time period T(i) when QBER(i) is less than 1.25%. AB In addition, for the clock difference data T in the retained time period T(i) AB , 5% of the clock error data T can be discarded randomly or based on the histogram statistical distribution AB .

[0070] The time data encryption unit of communication terminal A encrypts the time data in communication terminal A. In the present invention, the time data can be encrypted using a quantum key. In one example, the key used for the time data encryption unit can be a quantum key generated by a combination of a quantum transmitting end unit and a quantum receiving end unit, for example, a quantum key accumulated in a previous quantum key distribution process, or a quantum key generated in this quantum key distribution process. The time data to be encrypted may include the time data t in the quantum transmitting end unit of communication terminal A. SA and the time data t in the quantum receiving end unit RA .

[0071] The time data encrypted by the time data encryption unit can be transmitted to the communication terminal B through the transmission channel. The transmission channel can reuse the classical channel used for the quantum key distribution process of the quantum transmitting end unit or the quantum receiving end unit, or use a separate classical channel.

[0072] As examples, the transmission channel may be vacuum free space, atmospheric space, or an optical fiber.

[0073] The time data decryption unit of communication terminal B can decrypt the encrypted time data received from communication terminal A. The decryption key used in the time data decryption unit can be the same as the encryption key used in the time data encryption unit of communication terminal A. Therefore, similarly, the key used in the time data decryption unit can be a quantum key generated by the combination of the quantum transmitting unit and the quantum receiving unit, for example, a quantum key accumulated in a previous quantum key distribution process, or a quantum key generated in this quantum key distribution process.

[0074] The time data obtained after decryption by the time data decryption unit may include the time data t in the quantum transmitting end unit of the communication end A. SA and the time data t of the quantum receiving end unit SA .

[0075] The clock difference calculation unit of communication terminal B is used to calculate the clock difference result T between clock A in communication terminal A and clock B in communication terminal B based on the time data from communication terminal A and the time data from the local communication terminal B. AB Specifically, the time data used for the clock difference calculation unit may include the time data t in the quantum transmitting end unit of the communication end A. SA , the time data t in the quantum receiving unit of communication end A RA , the time data t in the quantum receiving unit of communication end B RB , and the time data t in the quantum transmitting end unit of communication end B SB .

[0076] In the clock difference calculation unit of the present invention, the clock difference result T between clock A and clock B is AB It can be calculated by the following formula:

[0077]

[0078] The feedback control unit of the communication terminal B is used to calculate the clock difference result T output by the clock difference calculation unit. AB The clock B in the communication end B is adjusted and controlled to achieve the clock difference compensation between clock B and clock A, so as to achieve the purpose of synchronizing the clocks at both ends and thus realize the transmission of time.

[0079] A system control unit can also be provided in communication terminal A (communication terminal B), which is used to coordinate and control the work of other units in communication terminal A (communication terminal B), including but not limited to key management, command control, status monitoring, etc. generated by the quantum transmitting end unit and the quantum receiving end unit.

[0080] The following will be combined Figure 3 The time transfer system based on bidirectional quantum key distribution shown is used as an example to illustrate the time security transfer method based on bidirectional quantum key distribution of the present invention, so as to more clearly understand the principle of the present invention.

[0081] In an example of the secure time transfer method based on bidirectional quantum key distribution of the present invention, the following steps may be included.

[0082] Step 1 is used to achieve bidirectional quantum key distribution and bidirectional time signal transmission. In step 1, the quantum transmitting end unit of communication end A and the quantum transmitting end unit of communication end B respectively generate single photon signals (sequences) and send the single photon signals (sequences) to each other via the transmission channel.

[0083] In the method of the present invention, quantum key distribution can adopt the BB84 protocol or other protocols. For example, when the BB84 protocol based on polarization encoding is adopted, the quantum transmitting end unit of communication end A prepares a single photon signal with a random polarization state based on the local clock A as the time reference, and sends it to communication end B, while recording the sending time t of the single photon signal. SA The quantum receiving unit at communication end B receives the single photon signal from communication end A in a specific polarization state based on the local clock B as the time reference, and records the arrival time t of the single photon signal. RB Similarly, in the other direction, the quantum transmitting end unit of communication end B prepares a single photon signal with a random polarization state based on the local clock B as the time reference, and sends it to communication end A, while recording the sending time t SB The quantum receiving unit at communication end A uses the local clock A as the time reference, receives the single photon signal from communication end B in a specific polarization state, and records the arrival time t of the single photon signal. RA .

[0084] Step 2 is used to obtain the quantum bit error rate QBER(i) in quantum key distribution and compare QBER(i) with the preset security threshold Q T Compare; when QBER(i) is less than the safety threshold Q T When QBER(i) is used, the single-photon signal corresponding to QBER(i) is used to generate quantum keys and realize time transfer.

[0085] In one embodiment of step 2, the quantum transmitting and receiving units of communication terminals A and B can calculate the corresponding QBER(i) according to a quantum key distribution protocol (e.g., BB84 protocol) within each time period T(i). As an example, the time interval T(i) can be 1 second.

[0086] Then QBER(i) is compared with the safety threshold Q T When QBER(i) is less than the safety threshold Q T When the single photon signal and the data it carries are retained within the time period T(i), quantum keys are generated based on this and time transfer is achieved. As an example, Q T Can be set to 1.25%.

[0087] In a preferred embodiment of the present invention, for single photon signals within time period T(i), communication end A and communication end B can also randomly abandon the single photon signals with a ratio of 4*QBER(i) or 4*Q T The single photon signal is retained only when the ratio is [1-4*QBER(i)] or [1-4*Q T ] and use the time data carried on this single-photon signal to realize time transmission.

[0088] In another preferred embodiment of the present invention, the clock error data T can be calculated based on the single photon signal in the time period T(i). AB , and discard the ratio of 4*QBER(i) or 4*Q T The clock error data is only retained when the ratio is [1-4*QBER(i)] or [1-4*Q T ] and use this part of the minute difference data to realize the time transmission.

[0089] As an example, for the clock error data T in the time period T(i), AB , the ratio used for abandonment is 4*QBER(i) or 4*Q T Clock difference data T AB The selection of can be random. As another example, the clock error data T in the time period T(i) can be AB Make a histogram distribution statistic and put it in the interval [1-4*QBER(i)] or [1-4*Q T ] other clock error data T AB give up.

[0090] For example, in Q TWhen QBER(i) is set to 1.25%, communication terminals A and B can calculate the QBER(i) in each time period T(i) and retain the single photon signal and the time data it carries in the time period T(i) when QBER(i) is less than 1.25%. In addition, for the clock error data T in the retained time period T(i), AB , 5% of the clock error data T can be discarded randomly or based on the histogram statistical distribution AB .

[0091] Step three encrypts the time data from communication terminal A to communication terminal B. In step three, communication terminal A encrypts its local time data using a secure key generated by quantum key distribution (QKD), such as a quantum key accumulated from previous QKD sessions between the two terminals or a quantum key generated during the current communication. Communication terminal B uses the same secure key for decryption. This quantum key encryption and decryption process protects against tampering attacks against traditional time data.

[0092] Step 4 is used by communication terminal B to calculate the time data t SA , t RA , t SB , t RB Calculate the clock difference T between clock A and clock B AB , and / or the distance R between communication end A and communication end B.

[0093] In step 4, after receiving the time data transmitted by communication terminal A, communication terminal B has all the required time data, including t SA , t RA , t SB , t RB Thus, the communication terminal B can use formula (1) in its clock difference calculation unit to calculate the clock difference T between clock A and clock B. AB , and calculate the distance R between communication terminals A and B according to formula (2).

[0094]

[0095] where c is the speed of light.

[0096] In addition, the method of the present invention may also include the following steps: AB The clock B of the communication terminal B is adjusted and controlled to achieve the step of compensating the clock difference between the clock B and the clock A.

[0097] With the help of the time transfer system and method of the present invention, since the polarization state of a single photon is used as the time signal carrier, it can be seen from the quantum no-cloning theorem that any attempt to intercept and retransmit the single-photon signal will destroy the quantum state. This can be identified according to the size of the bit error rate during the post-processing of quantum key distribution, thereby eliminating the security issues caused by interception and retransmission attacks.

[0098] In addition, in order to defend against time delay attacks, in the present invention, the measured distance R and the pre-known transmission channel distance R can also be combined at the communication end B. p Compare. If the distance difference |RR p |Less than the preset safety distance threshold L T , the time transfer is considered secure and unaffected by time delay attacks; otherwise, the time-transferred data is discarded. The previously known transmission channel distance Rp can be obtained through other methods before communication. For example, for a fiber optic channel, this can be achieved by measuring the optical path length of the fiber; for a free-space channel, this can be achieved by measuring the distance between the two ends; if either communication end A or B is a moving satellite, this can be achieved based on the predicted satellite orbit.

[0099] Compared to traditional classical encryption-based time transfer schemes, this invention employs quantum cryptography, leveraging single-photon signals during quantum key distribution to carry time data. This approach simultaneously ensures security at both the physical and data layers of time transfer, significantly enhancing the security of time transfer. Furthermore, because this invention enables secure time transfer during quantum key distribution, it enables highly integrated quantum key distribution and secure time transfer.

[0100] Although the present invention has been described above through specific embodiments in conjunction with the accompanying drawings, it is easy for those skilled in the art to recognize that the above embodiments are merely exemplary and are used to illustrate the principles of the present invention. They do not limit the scope of the present invention. Those skilled in the art can make various combinations, modifications and equivalent substitutions to the above embodiments without departing from the spirit and scope of the present invention.

Claims

1. A secure time transfer system based on bidirectional quantum key distribution, comprising a communication terminal A, a communication terminal B, and a transmission channel, wherein: The communication end A and the communication end B are configured to send single photon signals to each other according to a quantum key distribution protocol, and respectively detect the arriving single photon signals; The communication terminal A is further configured to record the emission time t of the single photon signal based on the local clock A. SA and the arrival time t of the detected single photon signal RA ; The communication terminal B is further configured to record the emission time t of the single photon signal based on the local clock B. SB and the arrival time t of the detected single photon signal RB ; The communication terminal A is further configured to transmit the transmission time t in an encrypted manner. SA and the arrival time t RA Transmit to the communication terminal B; The communication terminal B is further configured to transmit the signal according to the transmitting time t SA , the arrival time t RA , the emission time t SB , and the arrival time t RB Calculate the clock difference T between the clock A and the clock B AB ;and , according to the clock error T AB Adjusting the clock B to achieve clock difference compensation between the clock B and the clock A; The communication terminal B is further configured to calculate the distance R between the communication terminal A and the communication terminal B, and calculate the distance R and the distance R of the transmission channel. p The difference between |RR p |, and the difference |RR p |With the preset safety distance threshold L T to make comparisons; and, The communication end A and the communication end B are configured such that, in the difference |RR p | Greater than or equal to the safety distance threshold L T When , the single photon signal used to calculate the distance R is abandoned for time transfer; in, , c is the speed of light.

2. The secure time transfer system of claim 1, wherein: The communication terminal A further includes a quantum transmitting end unit, a quantum receiving end unit, and a time data encryption unit; and, The communication terminal B also includes a quantum transmitting terminal unit, a quantum receiving terminal unit, a time data decryption unit, a clock difference calculation unit, and a feedback adjustment unit.

3. The secure time transfer system of claim 2, wherein: The quantum receiving end unit of the communication end B is configured to generate a quantum key in combination with the quantum transmitting end unit of the communication end A, and record the arrival time t RB ; The quantum receiving end unit of the communication end A is configured to generate a quantum key in combination with the quantum transmitting end unit of the communication end B, and record the arrival time t RA ;and, The quantum transmitting end unit of the communication end A is configured to record the transmitting time t SA The quantum transmitting end unit of the communication end B is configured to record the transmitting time t SB .

4. The secure time transfer system according to claim 1 or 2, wherein: The communication terminal A and the communication terminal B are further configured to calculate the quantum bit error rate QBER(i) in the time period T(i) during the quantum key distribution process, and compare the QBER(i) with the preset security threshold Q T to make comparisons; and, When the QBER(i) is less than the safety threshold Q T When the single photon signal in the time period T(i) is used to generate a quantum key and realize time transfer.

5. The secure time transfer system of claim 4, wherein: The communication end A and the communication end B are further configured to randomly abandon the single photon signal in the time period T(i) at a ratio of 4*QBER(i) or 4*Q T The single photon signal is retained only when the ratio is [1-4*QBER(i)] or [1-4*Q T ] is used to realize the time transfer.

6. The secure time transfer system of claim 4, wherein: The communication end A and the communication end B are further configured to calculate the clock difference T based on the single photon signal in the time period T(i). AB , and discard the ratio of 4*QBER(i) or 4*Q T The clock difference T AB , only keep the ratio of [1-4*QBER(i)] or [1-4*Q T ] the clock difference T AB To achieve time transfer.

7. The secure time transfer system of claim 6, wherein: The clock difference T in the time period T(i) AB , randomly abandon the ratio of 4*QBER(i) or 4*Q T The clock difference T AB ;or, The clock difference T within the time period T(i) AB Perform histogram distribution statistics and place the data in the center interval [1-4*QBER(i)] or [1-4*Q T ] other than the clock difference T AB give up.

8. The secure time transfer system of claim 4, wherein: The safety threshold Q T is 1.25%; and / or, T(i) is 1 second.

9. The secure time transfer system of claim 2, wherein: The time data encryption unit is configured to encrypt the transmission time t SA and the arrival time t RA The time data decryption unit is configured to decrypt the encrypted transmission time t SA and the arrival time t RA Decrypt.

10. The secure time transfer system of claim 9, wherein: The time data encryption unit and the time data decryption unit use a quantum key.

11. The secure time transfer system of claim 2, wherein: The clock error calculation unit is configured to calculate the clock error T based on the following formula AB , 。 12. The secure time transfer system of claim 1, wherein: The transmission channel is vacuum free space, atmospheric free space or optical fiber.

13. A secure time transfer method based on bidirectional quantum key distribution, comprising the following steps: Single photon signals are sent between communication terminals A and B according to a quantum key distribution protocol, and the arriving single photon signals are detected respectively to perform bidirectional quantum key distribution; The communication terminal A records the emission time t of the single photon signal using the local clock A. SA and the arrival time t of the detected single photon signal RA ; The transmitting time t of the single photon signal is recorded by the local clock B at the communication end B. SB and the arrival time t of the detected single photon signal RB ; At the emission time t of the single photon signal used to generate the quantum key at the communication end A SA and the arrival time t RA Transmit to the communication terminal B; At the communication end B, according to the emission time t of the single photon signal used to generate the quantum key SA , the arrival time t RA , the emission time t SB and the arrival time t RB Calculate the clock difference T between the clock A and the clock B AB ; as well as, According to the clock difference T AB Adjusting the clock B to achieve clock difference compensation between the clock B and the clock A; Calculating the distance R between the communication end A and the communication end B; Calculate the distance R and the distance R of the transmission channel between the communication end A and the communication end B p The difference between |RR p |, and the difference |RR p |With the preset safety distance threshold L T When the difference |RR p | Greater than or equal to the safety distance threshold L T When the single photon signal used to calculate the distance R is abandoned for calculating the clock error T AB .

14. The secure time transfer method according to claim 13, wherein: The emission time t SA and the arrival time t RA The data is transmitted to the communication terminal B in a quantum key encrypted manner.

15. The secure time transfer method according to claim 13, further comprising the following steps: Obtain the quantum bit error rate QBER(i) in the time period T(i) in quantum key distribution, and compare the QBER(i) with the preset security threshold Q T When the QBER(i) is less than the safety threshold Q T When , the single photon signal in the time period T(i) is used to generate a quantum key.

16. The secure time transfer method according to claim 15, wherein: In the single photon signal within the time period T(i), the ratio of [1-4*QBER(i)] or [1-4*Q T ] is used to calculate the clock difference T AB .

17. The secure time transfer method according to claim 15, wherein: The clock error T is calculated based on the single photon signal in the time period T(i) AB , and discard the ratio of 4*QBER(i) or 4*Q T The clock difference T AB , only keep the ratio of [1-4*QBER(i)] or [1-4*Q T ] the clock difference T AB To achieve time transfer.

18. The secure time transfer method according to claim 17, wherein: The clock error T is selected and retained in a random manner or based on histogram statistical distribution. AB .

19. The secure time transfer method according to any one of claims 13 to 18, which is implemented based on the secure time transfer system according to any one of claims 1 to 12.

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