Efficient vernam's one time pad encryption method for optical space communication

Abstract

[Problem] To provide an optical space communication system where data can be efficiently transmitted even when packet loss has occurred in a concealed packet. [Solution] Provided is a system for implementing optical space communication between a transmission device and a reception device. The transmission device comprises: an encryption unit that encrypts data by using an encryption key, thereby obtaining encrypted data; a packet generation unit that adds, to the encrypted data, information related to the data size of the encrypted data, identification information of the data, and information related to the encryption key, and generates a packet for optical space communication; and a packet transmission unit that transmits the packet for optical space communication to the reception device. The reception device comprises: a packet reception unit that receives the packet for optical space communication; and a decryption unit that decrypts the encrypted data by using the information that is related to the encryption key and is included in the packet for optical space communication.

Description

Efficient Vernam's one time pad encryption scheme for optical space communications

[0001] The present invention relates to a system and method for performing free-space optical communications, and more particularly to a system and method for performing encrypted free-space optical communications that are packet loss tolerant and concealed.

[0002] Japanese Patent No. 7120607 describes a secret key sharing system. This system enables free-space optical communication using packets that are encrypted using an encryption key. However, there has been a demand for a free-space optical communication system that allows efficient data transmission even when packet loss occurs in encrypted packets.

[0003] Patent No. 7120607

[0004] An object of the present invention is to provide an optical space communications system that enables efficient data transmission even when packet loss occurs in a concealed packet.

[0005] This invention is based on the finding that, as a countermeasure against packet loss, adding the data size, data ID, and initial address of key ID to each packet ensures encryption key synchronization, and since this information is repeatedly transmitted, packet loss can be efficiently detected. If there is a gap in the data ID number, a retransmission request is transmitted via RF, thereby making it possible to provide resistance to packet loss.

[0006] The first invention relates to a system 1 for performing free-space optical communications between a transmitting device and a receiving device. This system includes a transmitting device 3 and a receiving device 5. The transmitting device 3 has an encryption unit 11, a packet generation unit 13, and a packet transmitting unit 15. The encryption unit 11 is a component for encrypting data using an encryption key to obtain encrypted data. The packet generation unit 13 is a component for adding information about the data size of the encrypted data, data identification information, and information about the encryption key to the encrypted data to generate a free-space optical communications packet. The packet transmitting unit 15 is a component for transmitting the free-space optical communications packet to the receiving device 5. The receiving device 5 also has a packet receiving unit 21 and a decryption unit 23. The packet receiving unit 21 is a component for receiving the free-space optical communications packet. The decryption unit 23 is a component for decrypting the encrypted data using information about the encryption key included in the free-space optical communications packet.

[0007] Examples of data identification information include the file number of the data and the number in the file identified by the file number of the data. An example of information related to the encryption key is the key start number. Thus, in this example, the same file number is assigned to multiple packets and sent multiple times. The key start number also means the starting address of the encryption key.

[0008] A preferred example of the above system 1 further includes a packet count acquisition unit 17. The packet count acquisition unit 17 is an element that uses optical space climate information, which is information about the climate of the optical space where optical space communication is performed, and the required number of transmissions of optical space communication packets in the optical space climate information as training data to construct a learning model that determines the number of times to transmit optical space communication packets, and that determines the number of times to transmit optical space communication packets using the optical space climate information and the learning model.

[0009] In a preferred example of the above system 1, the receiving device 5 further includes a non-received data information acquisition unit 25 and an RF transmission unit 27. The non-received data information acquisition unit 25 is an element for analyzing optical space communication packets and acquiring identification information related to non-received data, which is data that has not been correctly received. The RF transmission unit 27 is an element for transmitting identification information related to non-received data due to packet loss to the transmitting device 3 using RF band communication. In this example, the transmitting device 3 further includes an RF receiving unit 19 that receives the identification information related to the non-received data. The packet transmission unit 15 then transmits a retransmission packet, which is an optical space communication packet containing encrypted data identified by the identification information related to the non-received data, to the receiving device 5. In this example, if there is a gap in the data number of the received data, packet loss is likely to have occurred, and therefore a transmission request can be made via RF.

[0010] The second invention relates to a method for performing free-space optical communications between a transmitting device and a receiving device. This invention is basically a method for performing free-space optical communications using the above-described system. The transmitting device 3 performs an encryption step, a packet generation step, and a packet transmission step. That is, the transmitting device 3 encrypts data using an encryption key to obtain encrypted data (encryption step). The transmitting device 3 adds information about the data size of the encrypted data, data identification information, and information about the encryption key to the encrypted data to generate a free-space optical communications packet (packet generation step). The transmitting device 3 transmits the free-space optical communications packet to the receiving device 5 (packet transmission step). The receiving device 5 then performs a packet reception step and a decryption step. That is, the receiving device 5 receives the free-space optical communications packet (packet reception step). The receiving device 5 decrypts the encrypted data using information about the encryption key included in the free-space optical communications packet (decryption step).

[0011] The present invention can provide an optical space communications system that enables efficient data transmission even when packet loss occurs in encrypted packets.

[0012] Fig. 1 is a block diagram of a system for performing free-space optical communication, and Fig. 2 is a conceptual diagram showing an image of the data format configuration.

[0013] The following describes embodiments of the present invention with reference to the drawings. The present invention is not limited to the embodiments described below, but also includes appropriate modifications of the embodiments that are obvious to those skilled in the art.

[0014] FIG. 1 is a block diagram of a system for performing free-space optical communications. As shown in FIG. 1, this system 1 includes a transmitting device 3 and a receiving device 5. This system 1 is a system for performing free-space optical communications between the transmitting device and the receiving device. This system 1 is mainly used for optical communications between satellites and the ground. Packet loss occurs very frequently in optical communications between satellites and the ground. This system is tolerant to packet loss and is therefore preferably used for optical communications between satellites and the ground. In this system, an encryption key can be shared between the transmitting device 3 and the receiving device 5. The transmitting device 3 and the receiving device 5 are implemented as a computer or a server.

[0015] The computer has an input unit, an output unit, a control unit, a calculation unit, and a memory unit, and each element is connected by a bus or the like to enable information exchange. For example, a control program or various information may be stored in the memory unit. When predetermined information is input from the input unit, the control unit reads the control program stored in the memory unit. Then, the control unit reads the information stored in the memory unit as appropriate and transmits it to the calculation unit. The control unit also transmits the input information to the calculation unit as appropriate. The calculation unit performs calculation processing using the received various information and stores it in the memory unit. The control unit reads the calculation results stored in the memory unit and outputs them from the output unit. In this manner, various processes and steps are performed. The various units and means execute these various processes. The computer may have a processor, and the processor may realize various functions and steps. The computer may be standalone. Some of the functions of the computer may be distributed between a server and a terminal. In this case, it is preferable that the server and the terminal can exchange information via a network such as the Internet or an intranet. The computer may include a processor and a memory coupled to the processor. The memory may store instructions that, when executed by the processor, cause the computer to perform various processes or function as various elements. The computer may be provided with various training data to construct a learning model and perform various calculations through machine learning. In this case, the computer may perform various analyses using the learning model created through machine learning and deep learning of AI (artificial intelligence).

[0016] The transmitting device 3 includes an encryption unit 11, a packet generation unit 13, and a packet transmission unit 15. The transmitting device 3 may further include either or both of a packet count acquisition unit 17 and an RF reception unit 19. An example of the transmitting device 3 is a data communication device mounted on a satellite (e.g., a low-earth orbit satellite).

[0017] The encryption unit 11 is a component that encrypts data using an encryption key to obtain encrypted data. That is, the encryption unit 11 encrypts data using an encryption key to obtain encrypted data (encryption process). Methods for encrypting data are well known, and well-known encryption methods and systems can be appropriately adopted. It is preferable to achieve highly confidential optical communication (preferably completely confidential communication) in optical communication between a satellite and the ground. From this perspective, an encryption method using a Vernam encryption key (e.g., a Vernam one-time pad (OTP) encryption) is preferred. For example, Japanese Patent No. 3876324 describes a system in which a Vernam encryption key is shared between a transmitting device and a receiving device. In this example, the transmitting device has an encryption device, which selects a number sequence from a random number sequence output from a random number sequence sharing device according to a sampling rule, and uses this as a Vernam encryption key. Then, the received information (data) is Vernam-encrypted using the generated Vernam encryption key. The receiving device has a decryption device. The receiving device selects a number sequence from a random number sequence output from the random number sequence sharing device according to a sampling rule, and uses this as a Vernam encryption key. The receiving device then Vernam-decrypts the received information using the generated Vernam-cipher key. One-time pad (OTP) encryption is a cryptographic method that uses a random number sequence only once.

[0018] FIG. 2 is a conceptual diagram showing an image of the data format configuration. The transmitting device 3 receives data. This data may be transmitted from another communication means or may be read from a storage unit of the transmitting device 3. An example of the encryption unit 11 is an OTP encryption unit. The OTP encryption unit selects a number sequence from a random number sequence using a sampling rule and generates a one-time pad (OTP) encryption key. The encryption unit 11 may receive not only data but also data identification information. The OTP encryption unit encrypts the data using the OTP encryption key to obtain OTP encrypted data. The OTP encryption unit obtains information about the encryption key, such as a key start number, and stores it in a storage unit as appropriate. The OTP encryption unit may also store either or both information about the data size of the encrypted data and data identification information in the storage unit.

[0019] The packet generation unit 13 is a component that adds information about the data size of the encrypted data, data identification information, and information about the encryption key to the encrypted data, thereby generating a packet for optical space communication. That is, the packet generation unit 13 adds information about the data size of the encrypted data, data identification information, and information about the encryption key to the encrypted data, thereby generating a packet for optical space communication (packet generation process). Examples of data identification information include the file number of the data and the number in the file identified by the file number of the data. Another example of data identification information is the data number. An example of information about the encryption key is the key start number. For example, the packet generation unit 13 not only obtains OTP-encrypted data from the encryption unit 11, but also receives other data from the encryption unit 11 or reads other data from the storage unit. In this way, the packet generation unit 13 obtains encrypted data, information about the data size of the encrypted data, data identification information, and information about the encryption key, and adds information about the data size of the encrypted data, data identification information, and information about the encryption key to the encrypted data. In this way, the packet generation unit 13 generates a packet for optical space communication. The packet generator 13 may perform interleaving processing as necessary, or may further add an error correction code such as a Reed-Solomon code to generate a packet for free-space optical communication. Alternatively, as shown in FIG. 2 , the encrypted data that has undergone various processes may be stored in the payload for optical communication to generate a packet for free-space optical communication. An example of an optical communication protocol is a connectionless communication protocol, a specific example of which is UDP. UDP is an abbreviation for User Data Protocol, and is a communication protocol that emphasizes high-speed communication. As such, the packet for free-space optical communication may be one that has undergone appropriate known processing as long as it contains data based on the encrypted data. Since the data is encrypted and a packet for free-space optical communication is generated based on the above protocol, key synchronization can be ensured.

[0020] The packet transmitter 15 is an element for transmitting free space optical communication packets to the receiving device 5. That is, the packet transmitter 15 transmits the free space optical communication packets to the receiving device 5 (packet transmitting process). An example of the packet transmitter 15 is a QKD unit. QKD stands for quantum key distribution. The QKD unit converts the free space optical communication packets into signal light, combines this with synchronization light, and outputs the combined signal light to the transmitting device 5. An example of the packet transmitter 15 is a telescope that can output a beacon, and the packet for free space optical communication may be transmitted to the receiving device 5 using a light beam system.

[0021] The packet count acquisition unit 17 is an element for calculating the number of times to transmit packets for optical space communication using optical space climate information and a learning model (trained model). The packet count acquisition unit 17 obtains the number of times to transmit packets for optical space communication (packet transmission count acquisition process). The packet count acquisition unit 17 outputs the number of times to transmit packets for optical space communication to the packet generation unit 13 or the packet transmission unit 15. The packet transmission unit 15 receives the number of times to transmit packets for optical space communication and transmits a certain packet that number of times. By transmitting the same packet multiple times, it is possible to provide resistance to packet loss. Furthermore, by setting the number of transmissions appropriately, it is possible to improve processing efficiency.

[0022] The packet count acquisition unit 17 preferably uses machine learning to construct a trained model and obtain an appropriate packet transmission count. The trained model may be a model that calculates the number of times to transmit packets for optical space communication using optical space climate information, which is information about the climate in the optical space where optical space communication is performed, and the required number of transmissions of optical space communication packets in the optical space climate information, as training data. Examples of the information about the climate in the optical space may be one or more of weather, cloud cover, temperature, humidity, satellite altitude, and aerosol concentration. Including correct answer data in the training data can improve the accuracy of the trained model. Furthermore, repeating optical communication and feeding back the results of the optical communication can improve the accuracy of the trained model. Furthermore, information about attenuation of light intensity due to atmospheric conditions and information about empirical values ​​of optical packet fading may be used as training data.

[0023] The receiving device 5 includes a packet receiving unit 21 and a decoding unit 23. The receiving device 5 may further include a non-received data information acquiring unit 25 and an RF transmitting unit 27. An example of the receiving device 5 is receiving equipment provided in a ground station.

[0024] The packet receiving unit 21 is an element for receiving a packet for free-space optical communication. That is, the packet receiving unit 21 receives a packet for free-space optical communication (packet receiving step). The packet receiving unit 21 receives, for example, the packet for free-space optical communication and separates it into synchronization light and signal light using, for example, an optical demultiplexer.

[0025] The decryption unit 23 is an element for decrypting encrypted data using information about the encryption key included in the optical space communication packet. The decryption unit 23 decrypts the encrypted data using information about the encryption key included in the optical space communication packet (decryption process). For example, the decryption unit 23 has a QKD (quantum key distribution) module, and a key management unit having the QKD module creates an encryption key for decrypting the optical space communication packet using information about the encryption key. The decryption unit 23 then decrypts the encrypted data using the created encryption key. The decrypted data may be stored in a storage unit as appropriate, or may be output to a user's terminal.

[0026] In a preferred example of the system 1, the receiving device 5 further includes a non-received data information acquisition unit 25 and an RF transmitting unit 27. The transmitting device 3 further includes an RF receiving unit 19 that receives identification information related to the non-received data.

[0027] The non-received data information acquisition unit 25 is an element that analyzes optical space communication packets and acquires identification information regarding non-received data, which is data that has not been correctly received. The non-received data information acquisition unit 25 analyzes optical space communication packets, acquires data identification information, and stores it in a storage unit. If there is missing data, the non-received data information acquisition unit 25 designates that data as non-received data. If the data identification information is the file number of the data and a number in the file identified by the file number of the data, the non-received data information acquisition unit 25 reads the numbers in the file for the file number from the storage unit and confirms whether all numbers have been received. If there is a number that has not been received for a certain file number, the non-received data information acquisition unit 25 acquires the file number and the data number for that file number as identification information regarding the non-received data. The non-received data information acquisition unit 25 may store the acquired identification information regarding the non-received data in a storage unit. If the data identification information is a data number, the non-received data information acquisition unit 25 reads the data number from the storage unit and causes the calculation unit to perform a calculation to determine the data number that has not been received. If the result is a data number that has not been received, the non-received data information acquisition unit 25 acquires the data number as identification information related to the non-received data. The non-received data information acquisition unit 25 may store the acquired identification information related to the non-received data in the storage unit.

[0028] The RF transmitter 27 is an element for transmitting identification information related to the non-received data to the transmitter 3 using RF band communication. The RF transmitter 27 transmits the identification information related to the non-received data to the transmitter 3 by radio signal using RF band communication (non-received data information transmitting step). RF band communication is wireless communication that typically uses a frequency band lower than 750 MHz. An example of the RF transmitter 27 is an output device including an antenna.

[0029] The transmitting device 3 has an RF receiving unit 19 that receives identification information related to the non-received data. The RF receiving unit 19 receives the identification information related to the non-received data (non-received data information receiving process). An example of the RF receiving unit 19 is an antenna. The RF receiving unit 19 converts the received radio signal into, for example, an electrical signal related to the identification information related to the non-received data. The identification information related to the non-received data is output to the packet generating unit 13 or the packet transmitting unit 15. The packet transmitting unit 15 transmits a retransmission packet to the receiving device 5. The retransmission packet is an optical space communication packet containing encrypted data identified by the identification information related to the non-received data. This retransmission packet may be regenerated by the packet generating unit 13 and output from the packet transmitting unit 15. It is extremely difficult to establish bidirectional communication between a satellite and the ground. In this example, if there is a gap in the data number of the received data, packet loss is likely, so a transmission request can be made via RF, providing resistance to packet loss.

[0030] The present invention can be used in the field of free space optical communications, etc. In particular, since the present invention has tolerance to packet loss, it can be preferably used in the fields of satellite quantum key distribution and completely secure communications.

[0031] REFERENCE SIGNS LIST 1 System 3 Transmitter 5 Receiver 11 Encryptor 13 Packet generator 15 Packet transmitter 17 Packet count acquirer 19 RF receiver 21 Packet receiver 23 Decoder 25 Non-received data information acquirer 27 RF transmitter

Claims

1. A system for performing free space optical communications between a transmitting device and a receiving device, wherein the transmitting device has an encryption unit that encrypts data using an encryption key to obtain encrypted data, a packet generation unit that adds information regarding the data size of the encrypted data, identification information of the data, and information regarding the encryption key to the encrypted data to generate a packet for free space optical communications, and a packet transmitting unit that transmits the packet for free space optical communications to the receiving device, and the receiving device has a packet receiving unit that receives the packet for free space optical communications, and a decoding unit that decrypts the encrypted data using information regarding the encryption key included in the packet for free space optical communications.

2. A system as described in claim 1, wherein the identification information of the data includes a file number of the data and a number in a file identified by the file number of the data, and the information regarding the encryption key is a key start number.

3. A system as described in claim 1, which uses optical space climate information, which is information regarding the climate of the optical space in which the optical space communication is performed, and the required number of transmissions of the optical space communication packet in the optical space climate information as training data to construct a learning model that determines the number of times to transmit the optical space communication packet, and further includes a packet count acquisition unit that uses the optical space climate information and the learning model to determine the number of times to transmit the optical space communication packet.

4. A system as described in claim 1, wherein the receiving device has a non-received data information acquisition unit that analyzes the optical space communication packet and acquires identification information regarding non-received data, which is data that has not been correctly received among the data, and an RF transmitting unit that transmits the identification information regarding the non-received data to the transmitting device using RF band communication, the transmitting device further has an RF receiving unit that receives the identification information regarding the non-received data, and the packet transmitting unit transmits a retransmission packet, which is an optical space communication packet including encrypted data identified by the identification information regarding the non-received data, to the receiving device.

5. A method for performing free space optical communication between a transmitting device and a receiving device, comprising: an encryption step in which the transmitting device encrypts data using an encryption key to obtain encrypted data; a packet generation step in which the transmitting device adds information on the data size of the encrypted data, identification information of the data, and information on the encryption key to the encrypted data to generate a packet for free space optical communication; a packet transmission step in which the transmitting device transmits the packet for free space optical communication; a packet reception step in which the receiving device receives the packet for free space optical communication; and a decryption step in which the encrypted data is decrypted using information on the encryption key included in the packet for free space optical communication.

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