Methods and devices for biometric authentication and validation of a user

Abstract

The invention relates to a method for biometric authentication of a user, said method being implemented by a biometric authentication device and characterized in that it comprises: a first step of transmitting, to a first smart contract recorded on a blockchain, at least a first cryptographic representation of a biometric attribute of said user, referred to as the reference biocode; a step of obtaining at least a second cryptographic representation, referred to as the current biocode, of said biometric attribute of said user; a second step of transmitting, to a second smart contract recorded on said blockchain, said current biocode; a step of receiving a validity status of said authentication determined according to the result of a comparison of said current biocode with said reference biocode. Figure 4 (for the abstract)

Description

Title of the invention: Methods and devices for biometric authentication and validation of a user

[0001] 1. Scope of the invention

[0002] The invention relates to the general field of telecommunications networks and more particularly to technologies enabling the authentication of a user with a service.

[0003] 2. Prior Art

[0004] Today, many applications rely on biometrics. Indeed, biometrics has quickly distinguished itself as the most suitable technology for reliably and rapidly identifying and / or authenticating a person. It offers a wide range of techniques and can be used in very diverse fields (national security, consumer applications, etc.).

[0005] In a known manner, user authentication is carried out by comparing the user's biometric data presented during a transaction with pre-recorded biometric data of the person the user claims to be.

[0006] However, it is not possible to compare two biometric data points unless they are, at some point, stored in plain text in the memory of a verification device. The verification must therefore be performed within a so-called trusted device. This trusted device could, for example, be a centralized and controlled server, a trusted terminal, or a personal security component (also known as a "secure element").

[0007] From a data protection perspective, an authentication process most often involves a decentralized medium such as a smart card or a secure enclave. Thus, during authentication, the user's biometric data is stored on a decentralized medium belonging to them, thereby limiting the risk of fraud. However, a decentralized medium has a cost and may also be tied to a particular ecosystem (for example, a manufacturer).

[0008] There is therefore a need for a solution enabling biometric authentication in a decentralized manner, regardless of the user's ecosystem / technical environment.

[0009] 3. Description of the invention

[0010] The invention improves upon the prior art and, to this end, proposes a method for the biometric authentication of a user, said method being implemented by a biometric authentication device and characterized in that it comprises: - a first step of issuing, to a first smart contract registered on a blockchain, at least a first cryptographic representation of a biometric attribute of said user, called reference biocode; - a step of obtaining at least a second cryptographic representation, called current biocode, of said biometric attribute of said user; - a second issuance stage, destined for a second smart contract registered on said blockchain, of said current biocode; - a step of receiving a validity status of said authentication determined according to the result of a comparison of said current biocode with said reference biocode.

[0011] Advantageously, the invention allows a user to authenticate to a service via a biometric solution that uses a blockchain. Specifically, the user enrolls in a first smart contract by providing a reference biocode whose content is derived from a biometric attribute belonging to them (a signature, a fingerprint, a behavior, etc.).

[0012] The process then obtains a new biocode of the same attribute, called the current biocode, for example, following an authentication request received from the service. Alternatively, the current biocode is obtained and stored in memory by the process while awaiting an authentication request from the service.

[0013] The process then sends the current biocode to a second smart contract on the blockchain so that user authentication can be performed. To do this, the current biocode is compared to the reference biocode. If the comparison results in a similarity percentage below a predetermined threshold, then the reference biocode is considered different from the current biocode and authentication fails. Otherwise, authentication is successful. This comparison can, for example, be performed using a Hamming function.

[0014] The physical and behavioral traits that are recorded in a biometric system (e.g., a person's face, fingerprints or voice) are called "biometric characteristics / attributes".

[0015] As indicated in the document (https: / / fr.wikipedia.org / wiki / Blockchain), blockchain technology is a technology for storing and transmitting information without a central authority. Technically, it is a distributed database in which information sent by users and internal links to the database are verified and grouped at regular time intervals into blocks, the whole being secured by cryptography, thus forming a chain. By extension, a blockchain is a distributed database that manages a list of records protected against falsification or modification by storage nodes; it is therefore a distributed and secure ledger of all transactions carried out since the system's startup. Blockchains are characterized in particular by the fact that their contents cannot be modified or deleted: information published (that is, recorded or saved) in a blockchain remains there forever.

[0016] A smart contract (in English, "smart contract") in a blockchain is a computer program that allows transactions to be carried out under certain conditions. The objective of these smart contracts is to replace paper contracts with computer code in order to digitize processes (they emulate the logic of contractual clauses).

[0017] According to a particular embodiment of the invention, a process as described above is characterized in that said reference biocode and said current biocode are obtained as a function of a first private encryption key of said user.

[0018] This implementation method allows the user to avoid disclosing the biometric attribute used for biocode generation and to retain control over it (the user's biometric attribute remains confidential). Note that biocode generation is, for example, performed using a so-called "BioHashing" algorithm.

[0019] According to a particular embodiment of the invention, a method as described above is characterized in that said first private encryption key of said user corresponds to an encryption key of the user enabling him to carry out a transaction within said blockchain.

[0020] This implementation method makes it possible to link the individual user, and more specifically their biocode, to a user account that provides access to the blockchain. Thus, this implementation strengthens the link between the key / account and the generated biocodes.

[0021] Note that the user's encryption key, which allows them to carry out a transaction within the blockchain, can be a private key and / or a public key, for example, hosted within a blockchain wallet. As a reminder, a blockchain wallet uses asymmetric cryptography. The user possesses a private key and a public key in order to exchange / carry out transactions securely on the blockchain. The public key (or one of its derivatives) is known to everyone and serves as the address for exchanges carried out within the blockchain. The private key, for its part, authorizes the transactions.

[0022] According to a particular embodiment of the invention, a method as described above is characterized in that said reference biocode is encrypted via a second encryption key and in that said second issuance stage further includes a decryption key for said reference biocode.

[0023] Advantageously, this implementation method increases the security level of the solution by providing a decryption key for the encrypted reference biocode only when necessary, i.e., when a user authentication request is made. Indeed, the encrypted reference biocode is not usable in its current state. To perform authentication, the encrypted reference biocode must first be decrypted and then compared to the current biocode. It should be noted that the encryption of the reference biocode can implement a symmetric encryption algorithm (the encryption and decryption keys are then identical) or an asymmetric encryption algorithm.

[0024] According to a particular embodiment of the invention, a method as described above is characterized in that at least a third cryptographic representation is obtained, called replacement current biocode, of said biometric attribute of said user, said replacement current biocode being generated according to a third private encryption key of said user and in that said replacement current biocode is issued to said first smart contract or said second smart contract.

[0025] Advantageously, this embodiment allows the use of a single-use current biocode. Indeed, in addition to the current biocode sent by the process, the latter emits an encrypted replacement current biocode that can serve as a new reference biocode if the required conditions are met.

[0026] The various modes or embodiments mentioned above can be added independently or in combination with each other to the authentication process defined above.

[0027] The invention also relates to a method for validating biometric authentication, said method being implemented by a second smart contract recorded on a blockchain and characterized in that it comprises: - a step of receiving a first cryptographic representation of a user's biometric attribute, called current biocode; - a step of obtaining a result of a comparison of said current biocode with at least a second cryptographic representation of said biometric attribute of said user, said reference biocode, said reference biocode being obtained from a first smart contract recorded on said blockchain; - a step of issuing a validity status of said authentication determined according to said result.

[0028] Advantageously, the invention enables the validation of a biometric authentication request issued by a service via a blockchain-based solution. Specifically, the method, executed within a smart contract on a blockchain (for example, a smart contract deployed in connection with the service or by the user themselves), compares a current biocode received in a biometric authentication request with a reference biocode. The reference biocode is, for example, contained within the smart contract or obtained from another smart contract recorded on the blockchain. When the comparison result indicates a similarity percentage below a predetermined threshold, the reference biocode is considered different from the current biocode, and the authentication fails. Otherwise, the authentication is successful. This comparison can, for example, be performed using a Hamming function.The authentication result is then sent to the user terminal that initiated the biometric authentication request. Alternatively, or cumulatively, the authentication result is sent to a smart contract on the blockchain, for example, deployed by the service. Note that the first and second smart contracts, as defined by the invention, can be one and the same smart contract.

[0029] According to a particular embodiment of the invention, a process as described above is characterized in that said reference biocode obtained is encrypted and in that said reference biocode is decrypted via a decryption key received during the reception step.

[0030] Advantageously, this implementation method increases the security level of the solution by receiving a decryption key for the encrypted reference biocode only when necessary, i.e., when a user authentication request is received. Indeed, the encrypted reference biocode is not usable in its current state. To perform authentication, the encrypted reference biocode must first be decrypted and then compared to the current biocode. It should be noted that the encryption of the reference biocode can implement a symmetric encryption algorithm (the encryption and decryption keys are then identical) or an asymmetric encryption algorithm.

[0031] According to a particular embodiment of the invention, a method as described above is characterized in that the reception step further comprises at least a third encrypted cryptographic representation, called replacement current biocode, of said biometric attribute of said user and in that said reference biocode is replaced within said second smart contract by said received encrypted replacement current biocode.

[0032] Advantageously, this implementation allows the use of a single-use current biocode. Indeed, in addition to the current biocode received by the process, an encrypted replacement current biocode is also received so that it replaces the reference biocode during the next authentication request issued by the user.

[0033] The various modes or embodiments mentioned above can be added independently or in combination with each other to the validation process defined above.

[0034] The invention also relates to a biometric user authentication device characterized in that it comprises: - a first transmission module, intended for a first smart contract registered on a blockchain, of at least a first cryptographic representation of a biometric attribute of said user, called reference biocode; - a module for obtaining at least one second cryptographic representation, called current biocode, of said biometric attribute of said user; - a second transmission module, intended for a second smart contract registered on said blockchain, of said current biocode; - a receiving module for a validity status of said authentication determined according to the result of a comparison of said current biocode with said reference biocode.

[0035] The invention also relates to a device for validating a biometric authentication request, said method being implemented by a first smart contract recorded on a blockchain and characterized in that it comprises: - a module for receiving a first cryptographic representation of a user's biometric attribute, called the current biocode; - a module for obtaining a result of a comparison of said current biocode with at least a second cryptographic representation of said biometric attribute of said user, said reference biocode, said reference biocode being obtained from a first smart contract registered to said blockchain; - a module for issuing a validity status of said authentication determined according to said result.

[0036] The term module can refer to a software component, a hardware component, or a set of hardware and software components; a software component itself corresponding to one or more computer programs or subprograms, or more generally to any element of a program capable of implementing a function or set of functions as described for the modules concerned. Similarly, a hardware component corresponds to any element of a hardware assembly capable of implementing a function or set of functions for the module concerned (integrated circuit, smart card, memory card, etc.).

[0037] According to a particular embodiment of the invention, a biometric authentication device as described above is characterized in that it is included in a mobile terminal.

[0038] The invention also relates to one or more computer programs comprising instructions for implementing the above methods according to any one of the particular embodiments described above, when said programs are executed by a processor. The methods can be implemented in various ways, including in hardwired or software form. These programs can use any programming language and be in the form of source code, object code, or code intermediate between source and object code, such as in a partially compiled form, or in any other desirable form.

[0039] The invention also relates to a computer-readable recording or information medium containing instructions for a computer program as described above. The aforementioned recording media can be any entity or device capable of storing the program. For example, the medium may include a storage means, such as a ROM, for example a CD-ROM or a microelectronic circuit ROM, or a magnetic recording means, for example a hard drive. Furthermore, the recording media may be a transmissible medium such as an electrical or optical signal, which can be transmitted via an electrical or optical cable, by radio, or by other means. The programs according to the invention can, in particular, be downloaded from a network such as the Internet.

[0040] Alternatively, the recording media may correspond to an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the process in question.

[0041] These biometric authentication devices, validation of a biometric authentication request and these computer programs have characteristics and advantages similar to those described above in relation to the authentication and validation processes.

[0042] 4. List of figures

[0043] Other features and advantages of the invention will become more apparent upon reading the following description of particular embodiments, given by way of simple illustrative and non-limiting examples, and the accompanying drawings, among which:

[0044] [Fig-1] [Fig. 1] illustrates an example of an implementation environment for the invention according to a particular embodiment of the invention,

[0045] [Fig.2] Fig.2 represents the hardware architecture of a device biometric authentication according to a particular implementation method;

[0046] [Fig.3] Fig.3 represents the hardware architecture of a validation device according to a particular method of implementation;

[0047] [Fig.4] Figure [Fig.4] represents in flowchart form the main stages of the authentication and validation methods according to a particular embodiment of the invention.

[0048] 5. Description of an embodiment of the invention

[0049] Figure 1 illustrates an example of an implementation environment for the invention according to a particular embodiment. The environment shown in Figure 1 comprises a blockchain BC and a terminal T belonging to a user (UT) of the blockchain. The terminal T incorporates an authentication device capable of implementing the authentication process.

[0050] The BC blockchain includes one or more smart contracts capable of implementing the validation process in whole or in a distributed manner.

[0051] Terminal T is for example a smartphone (smartphone in English), tablet, server, connected television, connected object, car on-board computer, personal computer or any other terminal capable of communicating (sending and / or receiving requests) according to state-of-the-art technologies via a communication network R, the network being able to be private or public.

[0052] The environment represented in [Fig. 1] further includes a server S capable of providing a service to the user UT via his terminal T.

[0053] According to a particular embodiment of the invention, the BC blockchain can be hosted by one or more computer servers.

[0054] Figure 2 illustrates a biometric authentication device DISP1 configured to implement the authentication process according to a particular embodiment of the invention. The DISP1 device has the classic architecture of a computer and includes, in particular, a memory MEM1, a processing unit UT1, equipped, for example, with a processor PROC1, and driven by the computer program PG1 stored in memory MEM1. The computer program PG1 includes instructions for implementing the steps of the authentication process as described later in support of Figure 4, when the program is executed by the processor PROC1.

[0055] At initialization, the code instructions of the computer program PG1 are, for example, loaded into memory before being executed by the processor PROC1. The processor PROC1 of the processing unit UT1 implements, in particular, the steps of the authentication process according to any one of the specific embodiments described in relation to [Fig. 4] and according to the instructions of the computer program PG1.

[0056] The DISP1 device includes an SND11 module capable of sending, to a first smart contract registered in a blockchain (BC), at least a first cryptographic representation of a biometric attribute of a user (reference biocode within the meaning of the invention).

[0057] The DISP1 device further includes an OBT1 acquisition module capable of obtaining at least a second cryptographic representation of the user's biometric attribute (current biocode within the meaning of the invention).

[0058] Generally, a biometric attribute can be obtained via a biometric sensor (not shown) included in or associated with the biometric authentication device, the biometric sensor being capable of collecting a biometric characteristic of a user (fingerprints, voiceprints, behavioral characteristics, etc.).

[0059] According to a particular embodiment of the invention, a biometric attribute within the meaning of the invention may correspond to data which includes one or more biometric characteristics of the user.

[0060] The DISP1 device also includes an SND12 module capable of transmitting to a second smart contract recorded on the blockchain (BC) the current biocode obtained via the OBT1 module.

[0061] The DISP1 device further includes a RECV1 receiving module capable of receiving a validity status of an authentication determined according to the result of a comparison of the current biocode with the reference biocode.

[0062] According to a particular embodiment of the invention, the DISP1 device also includes a feedback module (screen, speaker, vibrator motor, etc.) capable of providing the user with the validity status of the authentication received by the RECV1 module.

[0063] According to a particular embodiment of the invention, the modules SND11, SND12, RECV1 are a single module or distributed in a plurality of modules.

[0064] Figure 3 illustrates a biometric authentication validation device DISP2 configured to implement the validation process according to a particular embodiment of the invention. The DISP2 device has the classic architecture of a computer, and includes in particular a memory MEM2, a processing unit UT2, equipped for example with a PROC2 processor, and controlled by the computer program PG2 stored in memory MEM2. The computer program PG2 includes instructions for implementing the steps of the validation process as described later in support of [Fig.4], when the program is executed by the PROC2 processor.

[0065] At initialization, the code instructions of the computer program PG2 are, for example, loaded into memory before being executed by the PROC2 processor. The PROC2 processor of the processing unit UT2 implements, in particular, the steps of the validation process according to any one of the specific embodiments described in relation to [Fig. 4] and according to the instructions of the computer program PG2.

[0066] The DISP2 device includes a RECV2 module capable of receiving a first cryptographic representation of a user's biometric attribute also called current biocode.

[0067] The DISP2 device further includes an OBT2 acquisition module capable of obtaining the result of a comparison of the current biocode received via the RECV2 module with at least a second cryptographic representation of the biometric attribute of said user also called reference biocode obtained from a smart contract recorded on a blockchain.

[0068] The DISP2 device also includes an SND2 emission module capable of issuing a validity status of a biometric authentication determined according to the result obtained via the OBT2 module.

[0069] [Fig.4] illustrates steps of the authentication and validation processes according to a particular embodiment of the invention in relation to the implementation environment described in support of [Fig.1].

[0070] During step E10, the terminal T, and more specifically the authentication process, obtains one or more ATB biometric characteristics / attributes of the user UT (fingerprint, voiceprint, behavioral characteristic, etc.) from one or more biometric sensors included in or associated with the terminal T. Once obtained, the ATB biometric attribute(s) are encrypted using an encryption key belonging to the user UT in order to generate a cryptographic representation of the user UT's ATB biometric attribute(s) (reference biocode within the meaning of the invention). It should be noted that the encryption can implement a symmetric encryption algorithm (the encryption and decryption keys are then identical) or an asymmetric encryption algorithm.

[0071] According to a particular embodiment of the invention, in the case of asymmetric encryption of the user's biometric attribute(s), the encryption key may correspond to a private encryption key of the user that allows them to carry out a transaction within the blockchain. This key is, for example, hosted within a blockchain wallet.

[0072] According to a particular embodiment of the invention, the reference biocode is encrypted via an encryption key Kc according to a symmetric or asymmetric encryption algorithm.

[0073] The process then transmits the reference biocode to the SCu smart contract registered on the BC blockchain.

[0074] According to a particular embodiment of the invention, the SCu smart contract was deployed by the user UT. Advantageously, this embodiment allows the user UT to retain control of their personal data, as the smart contract and the associated execution conditions are known to the user UT.

[0075] During step E30, the reference biocode is received by the SCu smart contract. This step marks the end of the UT user enrollment process.

[0076] During step E1, the process sends a biometric authentication of the user UT to service S, for example, in response to a request from service S. This request includes a second cryptographic representation (current biocode within the meaning of the invention) of the biometric attribute(s) (ATB) of the user UT used during the enrollment phase. Naturally, the encryption key and the encryption algorithm used to generate the current biocode are identical to those used to generate the reference biocode. The biometric authentication of the user UT, and more specifically the current biocode, is then re-sent (E22) by service S to the smart contract (SCs) registered on the blockchain (BC).

[0077] According to a particular embodiment of the invention, the smart contract SCs was deployed by the service S.

[0078] When the current biocode is received by the smart contract SCs (E42), the latter implements the validation process. Specifically, the smart contract SCs obtains the reference biocode (E43, E34, E34, E44) from the smart contract SCu and then compares it with the current biocode received during step E42.

[0079] When the comparison result indicates a similarity percentage below a predetermined threshold, the reference biocode is considered different from the current biocode, and biometric authentication fails. Otherwise, biometric authentication is successful.

[0080] During step E45, the status of the biometric authentication (valid / invalid) is broadcast within the blockchain. Service S receives the status during step E25 and sends it back (E26) to terminal T. Terminal T receives (E16) the status of the biometric authentication and notifies user UT.

[0081] Alternatively (not shown) the status of the biometric authentication (valid / invalid) is received by the SCu smart contract and then re-transmitted to terminal T.

[0082] Alternatively (not shown) the status of the biometric authentication (valid / invalid) is issued by the smart contract SCs directly to the terminal T.

[0083] According to a particular embodiment of the invention, the terminal T transmits, to the SCu smart contract, a third cryptographic representation of the ATB biometric attributes of the user UT (replacement reference biocode within the meaning of the invention). The encryption key used to generate the replacement reference biocode is then different from the one used to generate the reference biocode. When the status of the biometric authentication of the user UT broadcast during step E45 indicates that the authentication is valid, the SCu smart contract replaces the reference biocode with the replacement reference biocode (the reference biocode is deleted and the replacement reference biocode becomes the reference biocode). Otherwise, the reference biocode is retained as a reference for validating the next biometric authentication of the user UT.The replacement reference biocode is stored in memory but not used until a successful biometric authentication of the UT user replaces the reference biocode.

[0084] According to a particular embodiment of the invention, when the replacement of the reference biocode by the replacement reference biocode is effective, the SCu smart contract can notify the terminal T so that it generates and emits a new replacement reference biocode via a new encryption key.

[0085] According to a particular embodiment of the invention, the smart contract SCu obtains the replacement reference biocode from the smart contract SCs.

[0086] According to a particular embodiment of the invention, the replacement reference biocode is encrypted via an encryption key K'c according to a symmetric or asymmetric encryption algorithm.

[0087] According to a particular embodiment of the invention, when the reference biocode issued during step E10 has been encrypted, the biometric authentication issued (Eli) by terminal T to the smart contract SCs via service S further includes the decryption key Kd enabling the decryption of the encrypted reference biocode obtained by the smart contract SCs from the smart contract SCu (E43, E34, E34, E44). This embodiment increases the security level of the solution by providing a decryption key for the encrypted reference biocode only when necessary, i.e., when a user authentication request is made.

[0088] According to a particular embodiment of the invention, the smart contracts SCs and SCu are one and the same smart contract.

Claims

Demands

1. A biometric authentication method for a user, said method being implemented by a biometric authentication device and characterized in that it comprises: - a first transmission step (E30), to a first smart contract registered in a blockchain, of at least a first cryptographic representation of a biometric attribute of said user, called the reference biocode; - a step of obtaining (Eli) at least a second cryptographic representation, called the current biocode, of said biometric attribute of said user; - a second transmission step (Eli), to a second smart contract registered in said blockchain, of said current biocode; - a reception step (El6) of a validity status of said authentication determined according to the result of a comparison of said current biocode with said reference biocode.

2. A method according to claim 1 wherein said reference biocode and said current biocode are obtained as a function of a first private encryption key of said user.

3. A method according to claim 2 wherein said first private encryption key of said user corresponds to an encryption key of the user enabling him to carry out a transaction within said blockchain.

4. Method according to claim 1 wherein said reference biocode is encrypted via a second encryption key and wherein said second emission step further comprises a decryption key for said reference biocode.

5. A method according to claim 1 wherein at least a third cryptographic representation is obtained, referred to as replacement current biocode, of said biometric attribute of said user, said replacement current biocode being generated based on a third private encryption key of said user and wherein said replacement current biocode is issued to said first smart contract or said second smart contract.

6. A method for validating biometric authentication, said method being implemented by a second smart contract registered on a blockchain and characterized in that it comprises: - a step of receiving (E42) a first cryptographic representation of a biometric attribute of a user, called the current biocode; - a step of obtaining (E44) a result of a comparison of said current biocode with at least a second cryptographic representation of said biometric attribute of said user, called the reference biocode, said reference biocode being obtained from a first smart contract registered on said blockchain; - a step of issuing (E45) a validity status of said authentication determined according to said result.

7. A method according to claim 6 wherein said reference biocode obtained is encrypted and wherein said reference biocode is decrypted via a decryption key received during the reception step.

8. Method according to claim 6 wherein the receiving step further comprises at least a third encrypted cryptographic representation, referred to as replacement current biocode, of said biometric attribute of said user and wherein said reference biocode is replaced within said second smart contract by said received encrypted replacement current biocode.

9. A biometric authentication device for a user characterized in that it comprises: - a first emitting module (SND11), intended for a first smart contract registered on a blockchain, of at least a first cryptographic representation of a biometric attribute of said user, referred to as the reference biocode; - a retrieval module (OBT1) of at least a second cryptographic representation, referred to as the current biocode, of said biometric attribute of said user; - a second emitting module (SND12), intended for a second smart contract registered on said blockchain, of said current biocode; - a receiving module (RECV1) of a validity status of said authentication determined according to the result of a comparison of said current biocode with said reference biocode.

10. Terminal characterized in that it comprises a biometric authentication device according to claim 9.

11. Device for validating a biometric authentication request, said process being implemented by a first smart contract registered on a blockchain and characterized in that it comprises: - a receiving module (RECV2) of a first cryptographic representation of a biometric attribute of a user, called current biocode; - a obtaining module (OBT2) of a result of a comparison of said current biocode with at least a second cryptographic representation of said biometric attribute of said user, called reference biocode, said reference biocode being obtained from a first smart contract registered on said blockchain; - an emitting module (SND2) of a validity status of said authentication determined according to said result.

12. Computer program comprising instructions for implementing the authentication method according to any one of claims 1 to 5 and / or the validation method according to any one of claims 6 to 8, when the program is executed by a processor.

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