Method for attesting a mobile terminal for the implementation of a payment application on the mobile terminal.

Abstract

Method (100) for attesting a mobile terminal (TM) for the implementation of a payment application on the mobile terminal, the mobile terminal (TM) being configured to communicate with a server (S), the method (100) comprising the following steps implemented by the mobile terminal (TM): - sending (111) to the server (S) a request to establish a trusted communication channel (CC); - receiving (112) an attestation request (AR) from the server (S), the attestation request being randomly selected by the server (S) from a predetermined subset of a plurality of attestation requests, the attestation request defining a list of characteristics (LC) of the mobile terminal (TM), - collecting (113) a list of values ​​(LV) for the mobile terminal (TM), a value from the list of values ​​corresponding to a characteristic of the list of characteristics (LC) of the mobile terminal (TM) transmitted by the server (S);- transmission (114) to the server (S) of the list of values ​​(LV), the trusted communication channel (CC) being established (216) by the server (S) according to the list of values ​​(LV). Figure 1;

Description

Title of the invention: Method for attesting a mobile terminal for the implementation of a payment application on the mobile terminal.

[0001] The present invention relates to the field of payment applications, and in particular to software applications configured to transform a mobile commercial terminal intended for the general public into a payment terminal.

[0002] It is known to use a software application to transform a mobile retail terminal, intended for non-professional customers, into a payment terminal. This software application implements a process configured to ensure the confidentiality of payment transactions carried out by the mobile terminal.

[0003] This can only be permitted if the commercial mobile terminal meets security criteria. However, the mobile terminal cannot determine on its own that it meets the security criteria. A specific process implemented by a server is necessary to verify that the mobile terminal meets the criteria.

[0004] Payment card industry specifications do not describe how to develop and implement such an attestation process.

[0005] It is known to obtain the desired attestation from a set of information concerning the mobile terminal, the set of information being transferred "in bulk" to the server.

[0006] But this attestation process consumes a lot of processing power resources in the mobile terminal, and requires a lot of time for the collection and transfer of data to the server.

[0007] The invention therefore aims to provide a solution to all or part of these problems.

[0008] To this end, the present invention relates to a method for attesting a mobile terminal for the implementation of a payment application on the mobile terminal, the mobile terminal being configured to communicate with a server, the method comprising the following steps implemented by the mobile terminal:

[0009] - receiving an attestation request from the server, the request The attestation request is randomly selected by the server from a predetermined subset of a plurality of attestation requests, the attestation request defining a list of characteristics of the mobile terminal, - Collection of a list of values ​​for the mobile terminal, where a value from the list of values ​​corresponds to a characteristic from the terminal's list of characteristics mobile data transmitted by the server; - transmission of the list of values ​​to the server,

[0010] the trusted communication channel being established by the server according to the list of values.

[0011] According to these provisions, the server randomly choosing a limited number of attestation requests from a large number of possible attestation requests, it is very difficult for an attacker to devise a mechanism for fraudulently determining the responses expected by the server.

[0012] According to these provisions, the process allows the establishment of a trusted communication channel which is implemented for a transaction phase which uses the trusted communication channel thus established, for example said transaction, for example a payment procedure.

[0013] According to one embodiment, the invention comprises one or more of the following features, alone or in a technically acceptable combination.

[0014] According to one embodiment, the attestation request is encrypted by the server using a variable encryption key, selected from a set of encryption keys of the server, each encryption key of the set of encryption keys corresponding to a decryption key of the mobile terminal, the decryption key being recorded in a white box of the mobile terminal, and the method further includes a step of decrypting the encrypted attestation request with the decryption key of the mobile terminal recorded in the white box of the mobile terminal.

[0015] According to one embodiment, the method further includes a step of encrypting the list of values ​​with another variable encryption key of the mobile terminal stored in a white box of the mobile terminal, the encryption step producing a list of encrypted values, the list of values ​​transmitted to the server during the transmission step being the list of encrypted values.

[0016] According to one implementation method, the established trusted communication channel is secured.

[0017] According to one embodiment, the list of characteristics of the mobile terminal includes at least one of at least one of the characteristics of the mobile terminal from among a brand, a model number, and a version number of a mobile terminal operating system.

[0018] According to one embodiment, the mobile terminal is a commercially available device intended for the general public, for example of the type of smart phone, in particular a smartphone, or a tablet.

[0019] According to one embodiment, the method further comprises the following steps, implemented after the establishment of the trusted communication channel: - receipt of another attestation request from the server, the other request one attestation being randomly selected by the server from among the plurality of attestation requests, the other attestation request defining another list of characteristics of the mobile terminal; - collection of another list of values ​​for the mobile terminal, a value from the other list of values ​​corresponding to a characteristic from the other list of characteristics of the mobile terminal; - another transmission to the server of the other list of values; the communication channel being maintained or interrupted by the server depending on the other list of values.

[0020] According to these provisions, since the number of attestation requests included in the plurality of attestation requests is significant, each individual request may concern a small amount of information; the collection and transmission of this information by the mobile terminal will thus require limited computing power and load.

[0021] According to one implementation method, the step of receiving another attestation request takes place at a time that is a function of a time randomly determined by the server.

[0022] According to these provisions, the server randomly choosing a limited number of attestation requests from a large number of possible attestation requests, and the server issuing these requests at randomly determined times, it is even more difficult for an attacker to devise a fraudulent mechanism for determining the responses expected by the server.

[0023] According to one embodiment, the other attestation request is encrypted by the server using a server encryption key corresponding to a decryption key of the mobile terminal, the decryption key being recorded in a white box of the mobile terminal and the method further includes a step of decrypting the other encrypted attestation request with the decryption key of the mobile terminal recorded in the white box of the mobile terminal.

[0024] According to one embodiment, the method further includes a step of encrypting the other list of values ​​with another variable encryption key of the mobile terminal stored in a white box of the mobile terminal, the encryption step producing another list of encrypted values, the other list of values ​​transmitted to the server during the other transmission being the other list of encrypted values.

[0025] According to one embodiment, the list of characteristics of the mobile terminal includes at least one of the following characteristics: presence or absence of a specified software module among the applications installed on the mobile terminal, brand of the mobile terminal, identification number of the mobile terminal, version of the operating system installed on the mobile terminal, presence or absence of a specified file in the file system installed on the mobile terminal.

[0026] According to one aspect, the invention also relates to a method for attesting a mobile terminal for the implementation of a payment application on the mobile terminal, the mobile terminal being configured to communicate with a server, the method comprising the following steps implemented by the server: - transmission to the mobile terminal of an attestation request, the attestation request being randomly selected by the server from a predetermined subset of a plurality of attestation requests, the attestation request defining a list of characteristics of the mobile terminal; - receiving a list of values, a value from the list of values ​​corresponding to a characteristic from the list of characteristics of the mobile terminal transmitted by the server; - determination, based on the list of values, of a security level for the mobile terminal; - Establishing a trusted communication channel based on the security level of the mobile terminal.

[0027] According to these provisions, since the server randomly chooses a limited number of attestation requests from a large number of possible attestation requests, it is very difficult for an attacker to devise a mechanism for fraudulently determining the responses expected by the server.

[0028] According to one embodiment, the invention comprises one or more of the following features, alone or in a technically acceptable combination.

[0029] According to one embodiment, the process includes a transaction phase which may use the trusted communication channel established by the process, for example to implement a payment procedure.

[0030] According to one embodiment, the method further includes an encryption step by the server, using a variable encryption key, selected from a set of encryption keys of the server, each encryption key of the set of encryption keys corresponding to a decryption key of the mobile terminal, the decryption key being recorded in a white box of the mobile terminal, the encrypted attestation request being decrypted with the decryption key of the mobile terminal recorded in the white box of the mobile terminal.

[0031] According to one embodiment, the method further includes a step of decryption by the server of the list of encrypted values, with another server decryption key corresponding to a variable encryption key of the mobile terminal stored in a white box of the mobile terminal, the decryption step producing the list of values.

[0032] According to one embodiment, the trusted communication channel is established based on the security level of the mobile terminal and based on a delay between the receipt of the list of values ​​and transmission of the attestation request.

[0033] According to one implementation method, if the reception delay is greater than a determined delay, or if the security level is less than a determined threshold, the communication channel is not established by the server.

[0034] According to one embodiment, the method further comprises the following steps, implemented by the server after the communication channel has been established: - transmission of at least one other attestation request, the at least one other attestation request being randomly selected by the server from among the plurality of attestation requests; - receiving another list of values, a value from the other list of values ​​corresponding to a characteristic from the other list of characteristics of the mobile terminal, - another step of determining, on the basis of the other list of values, another level of security of the mobile terminal; - maintaining or interrupting the trusted communication channel depending on the other security level.

[0035] According to these provisions, the number of attestation requests included in the plurality of attestation requests being significant, each individual request may concern a small amount of information; the collection and transmission of this information by the mobile terminal will thus require limited computing power and load.

[0036] According to one implementation method, the step of transmitting at least one other attestation request takes place at a time determined randomly by the server.

[0037] According to these provisions, the server randomly choosing a limited number of attestation requests from a large number of possible attestation requests, and the server issuing these requests at randomly determined times, it is even more difficult for an attacker to devise a fraudulent mechanism for determining the responses expected by the server.

[0038] According to one embodiment, the other attestation request is encrypted by the server using a server encryption key corresponding to a decryption key of the mobile terminal, the decryption key being stored in a white box of the mobile terminal.

[0039] According to one embodiment, the method further includes a decryption step by the server of the other list of encrypted values, with another server decryption key corresponding to a variable encryption key of the mobile terminal stored in a white box of the mobile terminal, the decryption step producing the other list of values.

[0040] According to one embodiment, the communication channel is established according to the other security level of the mobile terminal and according to another delay between the receipt of the other list of values ​​and the transmission of the other attestation request.

[0041] According to another aspect, the invention relates to a computer program comprising a set of instructions configured to implement the method according to one of the implementation modes described above, when the instructions are executed on a processor of a mobile terminal, or the method according to one of the other implementation modes described above, when the instructions are executed on a processor of a server.

[0042] According to another aspect, the invention relates to a mobile terminal comprising a processor and a memory and a set of instructions stored in the memory, the instruction set being configured to implement the method according to implementation modes described above when the instructions are executed on the processor of the mobile terminal.

[0043] For better understanding, an embodiment and / or implementation of the invention is described with reference to the accompanying drawings, which represent, by way of non-limiting example, an embodiment or implementation of a device and / or method according to the invention. The same reference numerals in the drawings designate similar elements or elements with similar functions.

[0044] [Fig.1] is a schematic representation of the sequence of steps of the process according to one embodiment of the invention.

[0045] [Fig.2] is a schematic representation of a mobile terminal configured for an implementation of the invention.

[0046] The invention relates to a method 100, 200 for attesting a commercial mobile terminal TM, intended for non-professional customers, for example a smart phone, in particular a smartphone, the attestation of the mobile terminal TM being carried out by a server S, with a view to establishing a trusted communication channel between the mobile terminal TM and the server S, for the execution of a payment, when certain attestation conditions relating to the mobile terminal TM are satisfied.

[0047] The trusted communication channel established when the attestation conditions are met can be, for example, a trusted and secure communication channel, in other words, a communication channel between two mutually authenticated points whose communication is protected confidentially. A secure communication channel makes it possible, in particular, to guarantee the authenticity and origin of the key, and thus to protect against an attack known as a "man-in-the-middle" attack.

[0048] The steps of the attestation method 100, 200 according to the invention are described below, with reference to [Fig. 1], considering successively the steps of the method 100 implemented by the TM mobile terminal, presented from top to bottom along a vertical line TM on [Fig.1], and the steps of process 200 implemented by the server S, presented from top to bottom along a vertical line S on [Fig.1]; the steps of process 100, and of process 200 together contribute to the attestation of the mobile terminal TM for the execution of a payment.

[0049] The method includes, in particular, a phase 110, 210 of establishing a trusted communication channel between the mobile terminal TM and the server S, intended for use during a transaction phase 120, 220 TR which uses the trusted communication channel CC, CC' established and / or maintained by the server, to execute the transaction TR associated with the execution of the payment. The communication channel will be designated by the reference CC when it is the established trusted communication channel, and will be designated by the reference CC' when it is the same established and maintained trusted communication channel.

[0050] The establishment phase 110, 210 begins more specifically with a request step 111 for establishing a communication channel, emitted by the mobile terminal TM to the server; upon receipt 211 by the server S of the request 111, the server S transmits 212 to the mobile terminal TM an RA attestation request, the attestation request being randomly selected by the server S from a predetermined subset of a plurality of attestation requests, the attestation request defining a list of LC characteristics of the mobile terminal TM. Thus, a relatively small number of RA attestation requests are chosen randomly from a large number of possible attestation requests, so that it will be difficult for a fraudster to devise the required responses for the chosen RA attestation requests by listening to the responses made to previous attestation requests.

[0051] The following steps, implemented by the mobile terminal TM, are a receiving step 112 of the RA attestation request from the server S, followed by a collection step 113 of the information required by the RA attestation request; this collection leads to the creation of a list of LV values ​​for the mobile terminal TM, a value from the list of LV values ​​corresponding to a characteristic of the LC characteristic list of the mobile terminal TM transmitted by the server S; in other words, each characteristic of the LC characteristic list can take a number of particular values ​​for the mobile terminal TM in question, so that the latter collects, during the collection step, the particular value corresponding to a given characteristic of the LC characteristic list.

[0052] For example, the LC feature list will include at least one of the following features: presence or absence of a specific software module among the applications installed on the mobile terminal, brand of the mobile terminal, identification number of the mobile terminal, for example a serial number of the mobile terminal, version of the operating system installed on the mobile terminal, presence or absence of a specific file in the file system installed on the mobile terminal. For each of these characteristics, the TM mobile terminal will collect a specific value unique to it, in order to create a list of LV values.

[0053] The next step, implemented by the TM mobile terminal, is a transmission step 114 to the server S of the list of LV values.

[0054] The following steps, implemented by the server S, are respectively the steps of:

[0055] - reception 214 of the list of LV values; - determination 215, based on the list of LV values, of a security level NS of the mobile terminal TM;

[0056] - establishment 216 of the CC trusted communication channel according to the TM mobile terminal NS security level.

[0057] Thus, the security level is determined 215 based, for example, on one or more of the values ​​of the following characteristics:

[0058] -presence or absence of a specific software module among the applications installed on the mobile terminal,

[0059] - brand of mobile terminal,

[0060] - mobile terminal identification number,

[0061] - version of the operating system installed on the mobile terminal,

[0062] - presence or absence of a specific file in the file system installed on the mobile terminal.

[0063] For example, the determined security level is compared to a predetermined level: if the determined security level is higher than the predetermined level, then the CC trust communication channel is established between the server S and the mobile terminal TM. Otherwise, it is not established by the server S.

[0064] The CC trusted communication channel, as established at the end of step 216 of establishing the CC trusted communication channel, can in particular be further secured, within the meaning of the definition recalled above.

[0065] Thus, the process 100, 200 can in particular, during a phase 120, 220 of transaction TR, use the CC trust communication channel established 216 by the server S, in particular to implement a payment procedure.

[0066] According to one implementation example, the exchanges during the establishment phase 110, 210 can be encrypted to obtain enhanced security; thus, according to this implementation example, the RA attestation request is encrypted 212bis by the server S using a variable encryption key, selected from a set of encryption keys of the server S, each encryption key in the set of encryption keys corresponding to a decryption key of the mobile terminal TM, the decryption key being stored in a white box of the mobile terminal TM, and the process 100 further includes a decryption step 112bis of the encrypted RAC attestation request with the decryption key of the TM mobile terminal recorded in the white box of the TM mobile terminal.

[0067] According to a further embodiment, the method 100 further comprises an encryption step 114bis of the LV value list with another variable encryption key of the mobile terminal TM stored in a white box of the mobile terminal TM, the encryption step 114bis producing an LVC encrypted value list, the value list transmitted to the server S during the transmission step 114 being the LVC encrypted value list. Conversely, according to this embodiment, the method 200 further comprises a decryption step 214bis by the server S of the LVC encrypted value list, with another server S decryption key corresponding to a variable encryption key of the mobile terminal TM stored in a white box of the mobile terminal TM, the decryption step 214bis producing the LV value list

[0068] Optionally, the process 100 may further include, after the establishment 216 by the server S of the trusted communication channel CC, and in particular during the phase 120, 220 of transaction TR which uses the trusted communication channel, the following steps: - reception 112' of one or more other ARA attestation requests from the server S, each other ARA attestation request being randomly selected by the server S from the plurality of attestation requests, each other attestation request defining another list of ALC characteristics of the TM mobile terminal; - collection 113' from another list of ALV values ​​for the TM mobile terminal, a value from the other list of ALV values ​​corresponding to a characteristic from the other list of ALC characteristics of the TM mobile terminal; - transmission 114' to server S of the other list of ALV values; the communication channel CC' being maintained or interrupted 216' by the server S depending on the other list of ALV values.

[0069] Similarly, from the point of view of server S, the corresponding steps of process 200 are implemented by the server:

[0070] - transmission 212' of one or more other ARA attestation requests; - receipt 214' of one or more other ALV value lists, each other value list corresponding to one of the other ARA attestation requests; - determination 215', on the basis of each other list of ALV values, of another ANS security level of the TM mobile terminal; - maintenance or interruption 216' of the CC' communication channel depending on the other ANS security level.

[0071] Thus, since the number of attestation requests included in the plurality of attestation requests is significant, each individual request may concern a small amount of information; the collection and transmission of this information by the mobile terminal will therefore require limited computing power and load.

[0072] In particular, the transmission step 212' by the server of the other ARA attestation request takes place at a time determined randomly by the server S, during an exchange of messages between the mobile terminal TM and the server S which uses the CC trust communication channel, so that the reception step 112' by the mobile terminal TM of the other ARA attestation request takes place at a time depending on the time determined randomly by the server S (the time of the reception 112' of the other attestation request by the mobile terminal TM is in fact a function of the time of the transmission 212' of said other request by the server S, the time of the transmission 212' by the server S being determined randomly by the server S).The mechanism for issuing one (or more) other ARA attestation request(s) is thus "intertwined" with the functional dialogue between the TM mobile terminal and the S server which uses the CC trusted communication channel, in particular for a phase 120, 220 of implementation of a TR transaction.

[0073] According to these provisions, the server randomly choosing a limited number of attestation requests from a large number of possible attestation requests, and the server issuing these requests at randomly determined times, it is even more difficult for an attacker to devise a fraudulent mechanism for determining the responses expected by the server.

[0074] According to a further example of implementation of the method 100, 200, the CC trust communication channel is established based on the NS security level of the mobile terminal TM and based on a delay between the reception 214 of the list of values ​​LV and the transmission 212 of the attestation request; Thus, for example, if the reception delay is greater than a specified delay, or if the NS security level is less than a specified threshold, the CC trust communication channel is not established by the server S;Similarly, the trusted communication channel is maintained or interrupted 216' by the server S depending on the other ANS security level of the mobile terminal TM and depending on another delay between the reception 214' of the other list of ALV values ​​and the transmission 212' of the other ARA attestation request, among the plurality of other attestation requests that the server S is likely to issue after the establishment of the CC trusted channel, in particular during phase 120, 220 of implementation of a TR transaction..;

[0075] In the same way that information exchanges can be encrypted during the establishment phase 110, 220, before the establishment 216 of the trusted communication channel CC by the server S, information exchanges after the establishment 216 of the CC trusted communication channel by the server S, for the purpose of maintaining or interrupting 216' of the CC' communication channel by the server S, can also be encrypted. Thus, according to an implementation example, the other ARA attestation request is encrypted 212'bis by the server S using an encryption key of the server S corresponding to a decryption key of the mobile terminal TM, the decryption key being stored in a white box of the mobile terminal TM, and the other encrypted ARAC attestation request is decrypted 112'bis with the decryption key of the mobile terminal TM stored in the white box of the mobile terminal TM.

[0076] Similarly, the method 100 may further include an encryption step 114'bis of the other ALV value list with another variable encryption key of the mobile terminal TM stored in a white box of the mobile terminal TM, the encryption step 114'bis producing another ALVC encrypted value list, transmitted to the server S during the other transmission 114'; conversely, the method 200 further includes a decryption step 214'bis by the server S of the other ALVC encrypted value list, with another server S decryption key corresponding to the variable encryption key of the mobile terminal TM, the decryption step 214bis producing the other ALV value list.

[0077] According to one aspect, the invention relates to a computer program comprising a set of instructions configured to implement method 100, according to one of the embodiments described above, when the instructions are executed on a processor of a mobile terminal TM, or method 200 according to one of the embodiments described above, when the instructions are executed on a processor of a server S.

[0078] According to another aspect, the invention relates to a mobile terminal TM comprising a PC processor and a memory M and an instruction set stored in the memory M, the instruction set being configured to implement the method 100 according to one of the implementation modes described above when the instructions are executed on the processor of the mobile terminal TM.

Claims

Claims

1. Method (100) for attesting a mobile terminal (TM) for implementing a payment application on the mobile terminal, the mobile terminal (TM) being configured to communicate with a server (S), the method (100) comprising the following steps implemented by the mobile terminal (TM): - receiving (112) an attestation request (RA) from the server (S), the attestation request being randomly selected by the server (S) from a predetermined subset of a plurality of attestation requests, the attestation request defining a list of characteristics (LC) of the mobile terminal (TM), - collecting (113) a list of values ​​(LV) for the mobile terminal (TM), a value of the list of values ​​corresponding to a characteristic of the list of characteristics (LC) of the mobile terminal (TM) transmitted by the server (S);- transmission (114) to the server (S) of the list of values ​​(LV), a trusted communication channel (CC) being established (216) by the server (S) as a function of the list of values ​​(LV) and a security level of the mobile terminal (TM) determined on the basis of the list of values ​​(LV).;

2. Method (100) according to one of claims 1, in which the established trusted communication channel (CC) is secure.

3. A method (100) of attestation according to one of claims 1 or 2, further comprising the following steps, implemented after the establishment of the trusted communication channel (CC): - receiving (112') another attestation request (ARA) from the server (S), the other attestation request (ARA) being randomly selected by the server (S) from among the plurality of attestation requests, the other attestation request defining another list of characteristics (ALC) of the mobile terminal (TM); - collecting (113') another list of values ​​(ALV) for the mobile terminal (TM), a value of the other list of values ​​(ALV) corresponding to a characteristic of the other list of characteristics (ALC) of the mobile terminal (TM); - another transmission (114') to the server (S) of the other list of values ​​(ALV); the communication channel (CC) being maintained or interrupted (CC') by the server (S) based on the other list of values ​​(ALV).

4. Method (100) according to the preceding claim, in which the step of receiving (112') another attestation request (ARA) takes place at a time depending on a time determined randomly by the server (S).

5. Method (200) for attesting a mobile terminal (TM) for implementing a payment application on the mobile terminal, the mobile terminal (TM) being configured to communicate with a server (S), the method (200) comprising the following steps implemented by the server (S): - transmission (212) to the mobile terminal (TM) of an attestation request (RA), the attestation request being randomly selected by the server (S) from a predetermined subset of a plurality of attestation requests, the attestation request defining a list of characteristics (LC) of the mobile terminal (TM); - reception (214) of a list of values ​​(LV), a value of the list of values ​​corresponding to a characteristic of the list of characteristics (LC) of the mobile terminal (TM) transmitted by the server (S); - determination (215), on the basis of the list of values ​​(LV), of a security level (NS) of the mobile terminal (TM);- establishment (216) of a trusted communication channel (CC) according to the security level (NS) of the mobile terminal (TM).;

6. Method (200) according to claim 5, wherein the trusted communication channel is established as a function of the security level (NS) of the mobile terminal (TM) and as a function of a delay between the reception (214) of the list of values ​​(LV) and the transmission (212) of the attestation request.

7. A method (200) of attestation according to claim 6, further comprising the following steps, implemented by the server (S) after the establishment of the communication channel: - transmission (212') of at least one other attestation request (ARA), T at least one other attestation request being randomly selected by the server (S) from the plurality of attestation requests; - reception (214') of another list of values ​​(ALV), a value of the other list of values ​​(ALV) corresponding to a characteristic of the other list of characteristics (ALC) of the mobile terminal (TM), - another step of determining (215'), on the basis of the other list of values ​​(ALV), another security level (ANS) of the mobile terminal (TM); - maintaining or interrupting (216') the trusted communication channel (CC') depending on the other security level (ANS).

8. Method (200) according to claim 7, in which the step of transmitting (212') at least one other attestation request (ARA) takes place at a time randomly determined by the server (S).

9. Method (200) according to claim 7 or 8, wherein the communication channel is established according to the other security level (ANS) of the mobile terminal (TM) and according to another delay between the reception (214') of the other list of values ​​(ALV) and the transmission (212') of the other attestation request (ARA).

10. Computer program comprising a set of instructions configured to implement the method (100) according to one of claims 1 to 4 when the instructions are executed on a processor of a mobile terminal (TM), or the method (200) according to one of claims 5 to 9 when the instructions are executed on a processor of a server (S).

11. Mobile terminal (TM) comprising a processor (PC) and a memory (M) and a set of instructions stored in the memory (M), the set of instructions being configured to implement the method (100) according to one of claims 1 to 4 when the instructions are executed on the processor of the mobile terminal (TM).

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