In-band non-inductive authentication method and system for power system

Abstract

The invention discloses an in-band non-inductive authentication method and system for a power system. The method comprises the following steps: calculating a first equipment point product, a second equipment point product and a first authentication value; the power equipment sends the first authentication message to a monitoring unit; after receiving the first authentication message, the monitoring unit obtains a second current timestamp, generates a second random number and a first XOR value, and calculates a session key and a second authentication value; the monitoring unit sends the second authentication message to the power equipment; after receiving the second authentication message, the power equipment obtains a third current timestamp and judges whether # imgabs0 # is established, if yes, a second exclusive-or value and a session key are calculated, whether a second authentication check value is equal to a second authentication value is verified, if verification fails, the session is terminated, and if verification succeeds, it is proved that the monitoring unit is a legal monitoring unit. Authentication is carried out by utilizing the inherent characteristics of the power equipment, and a safer, more convenient and more reliable equipment authentication solution is provided.

Description

Technical Field

[0001] The present invention belongs to the technical field of power systems, and in particular relates to an in-band sensorless authentication method and system for a power system. Background Art

[0002] Traditional power systems usually rely on user identity authentication to ensure the safe operation of the system. Common methods include technologies based on passwords, fingerprints, smart cards, etc. These methods have the following problems: (1) Insufficient security: Passwords can be easily guessed or illegally obtained, resulting in the device being accessed or tampered with by unauthorized parties.

[0003] (2) Complex user operations: Users are required to perform manual operations each time they authenticate, which increases their operational burden and the risk of errors.

[0004] (3) Weak unforgeability: Traditional methods may not be able to effectively distinguish between legitimate and illegal devices and are easily counterfeited or forged.

[0005] (4) System stability issues: Traditional authentication methods may cause system instability and service interruption when facing network attacks or hardware failures. Summary of the invention

[0006] The present invention provides an in-band senseless authentication method and system for an electric power system, which are used to solve the technical problem that traditional electric power equipment authentication methods usually rely on users to input passwords or manually confirm, resulting in insufficient security.

[0007] In a first aspect, the present invention provides an in-band non-sensing authentication method for a power system, which is used for mutual authentication between a monitoring unit and a power device, comprising: The electric device generates a first random number , first current timestamp , according to the first random number and the first current timestamp , calculate the first device dot product , second device dot multiplication And the first authentication value ,in, is the concatenation symbol, is a hash function, is a base point on a finite field, is the public key, is the secret parameter key; The power device will first authenticate the message Sent to the monitoring unit, where Pseudo identity for power equipment, is the electromagnetic characteristics of the power equipment, Thermal characteristics of electrical equipment; After receiving the first authentication message, the monitoring unit obtains the second current timestamp , and generate a second random number and the first XOR value , calculate the session key and the second authentication value ; The monitoring unit sends the second authentication message Send to power equipment; The power device receives the second authentication message After that, get the third current timestamp , and judge Is it established, among which, is the maximum transmission delay. If true, calculate the second XOR value , Session Key , and verify the second authentication check value Is it the same as the second authentication value If the verification fails, the session is terminated; if the verification succeeds, it is proved to be a legitimate monitoring unit. Is the exclusive OR operator.

[0008] In a second aspect, the present invention provides an in-band sensorless authentication system for a power system, which is used for mutual authentication between a monitoring unit and a power device, comprising: A generating module configured to generate a first random number for the power device , first current timestamp , according to the first random number and the first current timestamp , calculate the first device dot product , second device dot multiplication And the first authentication value ,in, is the concatenation symbol, is a hash function, is a base point on a finite field, is the public key, is the secret parameter key; The first sending module is configured to send a first authentication message to the power device Sent to the monitoring unit, where Pseudo identity for power equipment, is the electromagnetic characteristics of the power equipment, Thermal characteristics of electrical equipment; The computing module is configured to obtain a second current timestamp after the monitoring unit receives the first authentication message. , and generate a second random number and the first exclusive OR value , calculate the session key and the second authentication value ; The second sending module is configured to monitor the unit to send the second authentication message to the power device; The verification module is configured to, after the power device receives the second authentication message , obtain the third current timestamp , and determine whether it holds, where is the maximum transmission delay. If it holds, calculate the second exclusive OR value , the session key , and verify whether the second authentication check value is equal to the second authentication value . If the verification fails, terminate the session. If the verification is successful, it proves to be a legitimate monitoring unit, where is the exclusive OR operation operator.

[0009] In a third aspect, an electronic device is provided, which includes: at least one processor, and a memory communicatively connected to the at least one processor, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the steps of the in-band non-intrusive authentication method for a power system according to any embodiment of the present invention.

[0010] In a fourth aspect, the present invention further provides a computer-readable storage medium, on which a computer program is stored, and when the program instructions are executed by a processor, the processor is enabled to execute the steps of the in-band non-intrusive authentication method for a power system according to any embodiment of the present invention.

[0011] The in-band non-intrusive authentication method and system of the present application provide a more secure, convenient and reliable device authentication solution by using the inherent characteristics of power devices, and have significant advantages compared with traditional password-based authentication methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0013] Figure 1 is a flowchart of an in-band non-intrusive authentication method for a power system provided by an embodiment of the present invention; Figure 2 Structural block diagram of an in-band passive authentication system for a power system provided by an embodiment of the present invention; Figure 3 Schematic structural diagram of an electronic device provided by an embodiment of the present invention. Detailed implementation manners

[0014] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0015] Please refer to Figure 1 , which shows a flowchart of an in-band passive authentication method for a power system according to the present application.

[0016] As Figure 1 shown, the in-band passive authentication method for a power system specifically includes the following steps: Step S101, a power device generates a first random number , a first current timestamp , and according to the first random number and the first current timestamp , calculates a first device dot product , a second device dot product , and a first authentication value .

[0017] In this step, is a concatenation symbol, is a hash function, is a base point on a finite field, is a public key, is a secret parameter key. The power device extracts a device registration tuple from the memory, inputs a first challenge value into a physically unclonable function PUF and obtains a first response value , then obtains a first verification auxiliary key and a first auxiliary value through a regenerator of the fuzzy extractor, determines whether the first verification auxiliary key is equal to the first auxiliary key . If they are equal, it indicates that the data of the power device has not been modified; subsequently, the electromagnetic characteristics and thermal characteristics ​​​​​​​​​​​​​​, and calculate the secret parameter key , where is the first key protection value.

[0018] Step S102, the power device sends the first authentication message to the monitoring unit, where is the pseudo identity of the power device, is the electromagnetic characteristic of the power device, is the thermal characteristic of the power device.

[0019] Step S103, after receiving the first authentication message, the monitoring unit obtains the second current timestamp , and generates a second random number and the first XOR value , calculates the session key and the second authentication value , where is the second key protection value.

[0020] In this step, after receiving the first authentication message , the monitoring unit obtains the second current timestamp , and judges whether holds, where is the maximum transmission delay; If it holds, then judge whether the electromagnetic characteristic of the power device and the thermal characteristic of the power device are within the set thresholds; If not, issue an alarm or trigger corresponding control measures; If so, the monitoring unit extracts the unit registration tuple , then the private key of the monitoring unit is input into the physically unclonable function PUF and the second response value is obtained, and then the second response value and the second auxiliary value are used to obtain the second auxiliary key through the regenerator of the fuzzy extractor, and calculate the secret parameter key , the second device dot product , , the first authentication check value ; Judge whether the first authentication check value is equal to the passed first authentication value ; If not equal, terminate the session; If equal, it means it is a legal power device, and the monitoring unit generates a second random number and the first XOR value , calculate the session key and the second authentication value .

[0021] Step S104, the monitoring unit sends the second authentication message to the power device; Step S105, after the power device receives the second authentication message , obtain the third current timestamp , and determine whether it holds, where is the maximum transmission delay. If it holds, calculate the second XOR value , the session key , and verify whether the second authentication check value is equal to the second authentication value . If the verification fails, terminate the session. If the verification is successful, it proves that the monitoring unit is legitimate.

[0022] In a specific embodiment, registering the power device and the monitoring unit specifically includes: The monitoring unit sends its true identity to the trusted authority to request registration; the trusted authority calculates the private key of the monitoring unit , is the private key of the trusted authority, calculates the public key of the monitoring unit , is a base point on the finite field; The power device sends a registration request to the trusted authority. When the trusted authority receives the request, the trusted authority generates the first challenge value , the secret parameter key K selects a pseudo identity of the power device , and then the trusted authority sends the first registration request message back to the power device and sends the second registration request message to the monitoring unit; After the power device receives the first registration request message , it inputs the first challenge value into the physically unclonable function PUF and obtains the first response value , and then obtains the first auxiliary value and the first auxiliary key from the first response value through the fuzzy extractor, and then calculates the first key protection value , where is the XOR operation operator. Finally, the power device stores the device registration tuple ; After the monitoring unit receives the second registration request message , it sends its private key​ Input the physical unclonable function PUF and obtain the second response value , and then use the second response value to obtain the second auxiliary value through the fuzzy extractor and the second auxiliary key , the second key protection value , and finally, the monitoring unit stores the unit registration tuple .

[0023] In summary, in this embodiment, the authentication method based on electromagnetic characteristics and thermal characteristics: uses the electromagnetic characteristics (such as electromagnetic wave intensity, spectrum characteristics, etc.) and thermal characteristics (such as temperature distribution, change law, etc.) generated by the power equipment during operation for device authentication. These characteristics are inherent in each power equipment during operation, have uniqueness and stability, and can be used to identify and distinguish different devices.

[0024] Contactless authentication method: The user does not need to directly participate in the authentication process, and the power equipment and the monitoring and control unit authenticate each other through feature data. This method avoids complex operation steps for the user and improves the usability and user experience of the system.

[0025] Application of cryptography technology: Uses elliptic curve cryptography technology to encrypt and protect data transmission and storage during the authentication process. Elliptic curve cryptography has high efficiency and security, and is suitable for encryption requirements in resource-constrained environments (such as power equipment).

[0026] Registration and verification of trusted institutions: During the registration process, a trusted third-party institution verifies and registers the power equipment and the monitoring and control unit. This ensures the identity and device legality of all parties participating in the system and prevents illegal device access and data tampering.

[0027] The method of this application can achieve the following technical effects: Contactless authentication: Traditional device authentication usually requires the user to participate and enter a password or perform manual confirmation. However, the present invention uses the inherent electromagnetic and thermal characteristics of the device for authentication, and the user does not need to directly participate, improving the convenience of the authentication process and the user experience.

[0028] High security: Uses elliptic curve cryptography technology to encrypt data transmission and storage, which is more efficient and secure than traditional encryption algorithms, effectively preventing data leakage and tampering.

[0029] Uniqueness and stability: The electromagnetic and thermal characteristics of power equipment are inherent and stable, and each device is unique, which ensures the accuracy and reliability of authentication and prevents illegal devices from accessing the system.

[0030] Compliance and legal protection: The design and implementation comply with local laws, regulations and relevant standards, especially the regulatory requirements in data privacy and security management, reducing legal risks and liabilities.

[0031] System reliability: Fault tolerance mechanisms and emergency recovery plans are introduced to ensure the availability and stability of the system in the face of hardware failures, cyber attacks or other unexpected situations.

[0032] Easy to operate: Users do not need complex operation steps. They only need to let the device pass the authentication process by itself, reducing the complexity of operation and the possibility of errors.

[0033] In summary, the present invention provides a safer, more convenient and more reliable device authentication solution by using the inherent characteristics of power equipment, which has significant advantages compared with traditional password-based authentication methods.

[0034] Please refer to Figure 2 , which shows a structural block diagram of an in-band passive authentication system for a power system of the present application.

[0035] As Figure 2 shown, the in-band passive authentication system 200 for a power system includes a generation module 210, a first sending module 220, a calculation module 230, a second sending module 240 and a verification module 250.

[0036] Among them, the generation module 210 is configured to generate a first random number , a first current timestamp for the power equipment, and calculate a first device dot product , a second device dot product and a first authentication value according to the first random number and the first current timestamp , where is a concatenation symbol, is a hash function, is a base point on a finite field, is a public key, is a secret parameter key; The first sending module 220 is configured to send a first authentication message to the monitoring unit by the power equipment, where is the pseudo identity of the power equipment, is the electromagnetic characteristic of the power equipment, is the thermal characteristic of the power equipment; The calculation module 230 is configured to obtain a second current timestamp after the monitoring unit receives the first authentication message, and generate a second random number and the first XOR value , calculate the session key and the second authentication value ; The second sending module 240 is configured to monitor the second authentication message Send to power equipment; Verification module 250, configured to receive a second authentication message from the power device After that, get the third current timestamp , and judge Is it established, among which, is the maximum transmission delay. If true, calculate the second XOR value , Session Key , and verify the second authentication check value Is it the same as the second authentication value If the verification fails, the session is terminated; if the verification succeeds, it is proved to be a legitimate monitoring unit. Is the exclusive OR operator.

[0037] It should be understood that Figure 2 Modules and references documented in Figure 1 Therefore, the operations and features described above for the method and the corresponding technical effects are also applicable to Figure 2 The modules in it will not be described in detail here.

[0038] In some other embodiments, the embodiments of the present invention further provide a computer-readable storage medium having a computer program stored thereon, wherein when the program instructions are executed by a processor, the processor executes the power system in-band sensorless authentication method in any of the above method embodiments; As an implementation mode, the computer-readable storage medium of the present invention stores computer-executable instructions, and the computer-executable instructions are configured as follows: The electric device generates a first random number , first current timestamp , according to the first random number and the first current timestamp , calculate the first device dot product , second device dot multiplication And the first authentication value ,in, is the concatenation symbol, is a hash function, is a base point on a finite field, is the public key, is the secret parameter key; The power device will first authenticate the message Sent to the monitoring unit, where Pseudo identity for power equipment, is the electromagnetic characteristics of the power equipment, Thermal characteristics of electrical equipment; After receiving the first authentication message, the monitoring unit obtains the second current timestamp , and generate a second random number and the first XOR value , calculate the session key and the second authentication value ; The monitoring unit sends the second authentication message Send to power equipment; The power device receives the second authentication message After that, get the third current timestamp , and judge Is it established, among which, is the maximum transmission delay. If true, calculate the second XOR value , Session Key , and verify the second authentication check value Is it the same as the second authentication value If the verification fails, the session is terminated; if the verification succeeds, it is proved to be a legitimate monitoring unit. Is the exclusive OR operator.

[0039] The computer-readable storage medium may include a program storage area and a data storage area, wherein the program storage area may store an operating system and application programs required for at least one function; the data storage area may store data created according to the use of the in-band senseless authentication system of the power system, etc. In addition, the computer-readable storage medium may include a high-speed random access memory, and may also include a memory, such as at least one disk storage device, a flash memory device, or other non-volatile solid-state storage device. In some embodiments, the computer-readable storage medium may optionally include a memory remotely disposed relative to the processor, and these remote memories may be connected to the in-band senseless authentication system of the power system via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0040] Figure 3 is a schematic diagram of the structure of an electronic device provided by an embodiment of the present invention, such as Figure 3 As shown, the device includes: a processor 310 and a memory 320. The electronic device may also include: an input device 330 and an output device 340. The processor 310, the memory 320, the input device 330 and the output device 340 may be connected via a bus or other means. Figure 3The example of connection via bus is taken. The memory 320 is the above-mentioned computer-readable storage medium. The processor 310 executes various functional applications and data processing of the server by running the non-volatile software programs, instructions and modules stored in the memory 320, that is, the in-band senseless authentication method of the power system of the above-mentioned method embodiment is realized. The input device 330 can receive input digital or character information, and generate key signal input related to user settings and function control of the in-band senseless authentication system of the power system. The output device 340 may include display devices such as display screens.

[0041] The electronic device can execute the method provided by the embodiment of the present invention, and has the functional modules and beneficial effects corresponding to the execution method. For technical details not described in detail in this embodiment, please refer to the method provided by the embodiment of the present invention.

[0042] As an implementation mode, the electronic device is applied to an in-band sensorless authentication system of a power system, and is used for a client, and includes: at least one processor; and a memory connected to the at least one processor in communication; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can: The electric device generates a first random number , first current timestamp , according to the first random number and the first current timestamp , calculate the first device dot product , second device dot multiplication And the first authentication value ,in, is the concatenation symbol, is a hash function, is a base point on a finite field, is the public key, is the secret parameter key; The power device will first authenticate the message Sent to the monitoring unit, where Pseudo identity for power equipment, is the electromagnetic characteristics of the power equipment, Thermal characteristics of electrical equipment; After receiving the first authentication message, the monitoring unit obtains the second current timestamp , and generate a second random number and the first XOR value , calculate the session key and the second authentication value ; The monitoring unit sends the second authentication message Send to power equipment; After the power equipment receives the second authentication message , it obtains the third current timestamp , and judges whether it holds, where is the maximum transmission delay. If it holds, the second exclusive OR value and the session key are calculated, and the second authentication check value is verified to see if it is equal to the second authentication value . If the verification fails, the session is terminated. If the verification is successful, it proves to be a legal monitoring unit, where is the exclusive OR operation operator

[0043] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on such an understanding, the essence of the above technical solution, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods of each embodiment or some parts of the embodiments

[0044] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of each embodiment of the present invention

Claims

1. A power system in-band non-sensing authentication method for mutual authentication between a monitoring unit and power equipment, characterized in that: Including: The power equipment generates a first random number and a first current timestamp . According to the first random number and the first current timestamp , calculate a first device dot product , a second device dot product and a first authentication value , where is a concatenation symbol is a hash function is a base point on a finite field is a public key is a secret parameter key; The power equipment sends the first authentication message to the monitoring unit, where is the pseudo identity of the power equipment, is the electromagnetic characteristic of the power equipment, is the thermal characteristic of the power equipment; After receiving the first authentication message, the monitoring unit obtains a second current timestamp , and generates a second random number and a first exclusive-or value , calculates a session key and a second authentication value , where The monitoring unit sends the second authentication message to the power equipment; The power equipment receives the second authentication message and then obtains the third current timestamp , and determines whether it holds, where is the maximum transmission delay. If it holds, calculate the second XOR value and the session key , and verify whether the second authentication check value is equal to the second authentication value . If the verification fails, terminate the session. If the verification is successful, it proves to be a legitimate monitoring unit, where is the XOR operation operator.

2. According to claim 1, a power system in-band non-sensing authentication method is characterized in that: Generate a first random number in the power device and a first current timestamp , and according to the first random number and the first current timestamp , calculate a first device dot product , a second device dot product and a first authentication value Before that, the method further includes: The power device extracts the device registration tuple from the memory , inputs the first challenge value into the physically unclonable function PUF and obtains the first response value , then inputs the first response value and the first auxiliary value into the regenerator of the fuzzy extractor to obtain the first verification auxiliary key , and determines whether the first verification auxiliary key is equal to the first auxiliary key . If they are equal, it indicates that the data of the power device has not been modified; subsequently, the electromagnetic characteristics and the thermal characteristics of the power device are obtained, and the secret parameter key is calculated, where is the first key protection value.

3. The method for in-band non-sensing authentication of a power system according to claim 1, characterized in that: After receiving the first authentication message, the monitoring unit obtains a second current timestamp , and generates a second random number and a first exclusive-or value , calculates a session key and a second authentication value including: After the monitoring unit receives the first authentication message it obtains the second current timestamp and determines whether it holds, where is the maximum transmission delay; If it holds, then judge the electromagnetic characteristics of the power equipment and the thermal characteristics of the power equipment whether they are within the set threshold values; If not present, issue an alarm or trigger corresponding control measures; If present, the monitoring unit extracts the unit registration tuple , and then the private key of the monitoring unit is input into the physically unclonable function PUF to obtain a second response value . Then, the second response value and the second auxiliary value are used by the regenerator of the fuzzy extractor to obtain a second auxiliary key , and the secret parameter key , the second device dot product are calculated , the first authentication verification value . Among them, is the second key protection value; Judge the first authentication verification value and the first authentication value passed are equal; If not equal, terminate the session; If they are equal, it indicates a legal power device, and the monitoring unit generates a second random number and the first exclusive OR value , calculates the session key and the second authentication value .

4. The method for in-band non-sensing authentication of a power system according to claim 1, characterized in that: Generate a first random number in the power device and a first current timestamp . According to the first random number and the first current timestamp , calculate the first device dot product , the second device dot product and the first authentication value . Before that, the method further includes: Register the power equipment and the monitoring unit, specifically including: The monitoring unit sends its true identity to the trusted institution to request registration; the trusted institution calculates the private key of the monitoring unit , which is the private key of the trusted institution, and calculates the public key of the monitoring unit , which is a base point on the finite field; The power equipment sends a registration request to the trusted institution. When the trusted institution receives the request, the trusted institution generates a first challenge value , selects a pseudo identity of the power equipment with the secret parameter key K . Subsequently, the trusted institution sends the first registration request message back to the power equipment and sends the second registration request message to the monitoring unit; The power device receives the first registration request message and then inputs the first challenge value into the physically unclonable function PUF and obtains the first response value . Then, the first response value is used to obtain the first auxiliary value and the first auxiliary key through the fuzzy extractor. Subsequently, the first key protection value is calculated, where is the exclusive OR operation operator. Finally, the power device stores the device registration tuple . After the monitoring unit receives the second registration request message it inputs its private key into the physically unclonable function PUF and obtains a second response value Then, it obtains a second auxiliary value and a second auxiliary key from the second response value through the fuzzy extractor and the second key protection value Finally, the monitoring unit stores the unit registration tuple .

5. An in-band sensorless authentication system for a power system, used for mutual authentication between a monitoring unit and power equipment, characterized in that: Including: A generation module, configured to generate a first random number for a power device and a first current timestamp . Based on the first random number and the first current timestamp , calculate a first device dot product , a second device dot product and a first authentication value , where is a concatenation symbol, is a hash function, is a base point on a finite field, is a public key, is a secret parameter key; The first sending module is configured to enable the power device to send a first authentication message to the monitoring unit, where is the pseudo identity of the power device, is the electromagnetic feature of the power device, is the thermal feature of the power device; The computing module is configured to obtain a second current timestamp after the monitoring unit receives the first authentication message , and generate a second random number and a first exclusive-or value , calculate the session key and a second authentication value ; The second sending module is configured to monitor the unit to send the second authentication message to the power device; The verification module is configured to obtain a third current timestamp after the power equipment receives the second authentication message and determine whether holds, where is the maximum transmission delay. If it holds, calculate the second XOR value , and the session key , and verify whether the second authentication check value is equal to the second authentication value . If the verification fails, terminate the session. If the verification is successful, it proves to be a legal monitoring unit. Here , is the XOR operation operator .

6. An electronic device, characterized in that, Including: At least one processor, and a memory communicatively connected to the at least one processor, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the method according to any one of claims 1 to 4.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method according to any one of claims 1 to 4.

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