FR3124287A1 - Method and device for controlling access to a storage medium. - Google Patents

Abstract

A method for controlling access to a storage medium via a communication bus comprises the reception (E11), via the communication bus, of a set of electric signals comprising an electric signal representative of an operation command intended performing an operation on at least one area of the storage medium. The control method further comprises: - the verification (E2) of the value of at least one parameter relating to at least one electrical signal of the set of electrical signals received; and - the authorization (E31) or the refusal (E32) of the implementation of the operation command on said at least one zone of the storage medium, depending on the result of said verification (E2). Figure for abstract: Fig. 2

Description

Method and device for controlling access to a storage medium.

The present invention relates to a method for controlling access to a storage medium as well as a device for controlling access to the storage medium implementing this method.

It also relates to a storage medium comprising such a control device as well as an object comprising such a storage medium.

The invention applies in particular to the control of access to storage media used by connected objects, a connected object being any object configured to transmit or receive data via a communication network.

Connected objects are more and more widespread and have various uses, whether in the private sphere of users, in industries, in buildings or smart cities or other.

In general, a connected object comprises at least one device or storage medium (or memory) intended to store computer programs and data necessary for the proper functioning of the object, such as Wi-Fi keys or private keys allowing the object to connect with other devices. This storage medium or memory is external to the modules controlling the operation of the connected object (processors and/or microcontrollers) and is generally embedded in the printed circuit comprising these modules.

The processors and/or microcontrollers controlling the operation of the connected object and the storage medium exchange information via a communication bus.

Often these external memories are non-volatile and rewritable memories, for example of the Flash type. Of course, the invention can be applied to the control of access to data in any type of memory.

The data stored in a memory can be usurped or modified by a malicious person in possession of the connected object. For example, the person can open the connected object and retrieve or modify the contents of the memory via the communication bus connecting the memory to the processor and/or microcontroller managing the operation of the connected object.

During this type of attack, personal data such as Wi-Fi keys or data relating to the design of the connected object can be collected. In addition, private connection keys of the connected object can be obtained to attack service platforms or to connect to service platforms using the identity of the object. Also, analyzes can be carried out on the software installed in the object aimed at identifying vulnerabilities that can be exploited remotely, or spyware can be installed.

To date, solutions exist to mitigate some of these risks. For example, the use of memories containing sectors that can only be programmed once or memories whose writing or reading of data must be unlocked by the provision of a password or a key. Nevertheless, concerning the former, although the modification of their content is avoided, reading is still possible. Regarding the seconds, a command containing a password or a key can be intercepted on the communication bus.

Sometimes these solutions are coupled with the implementation of verification software executed by the programs managing the operation of the connected object (or firmware of the connected object) in order to detect and prevent attempted attacks. However, since access to the memory installed in the connected object can be performed via a physical connection from an external device to the object on the communication bus, without using the modules for managing the operation of the connected object, attacks may go undetected.

The present invention aims to improve this situation and proposes a method for controlling access to a storage medium making it possible to control access to the storage medium.

To this end, the invention relates, according to a first aspect, to a method for controlling access to a storage medium via a communication bus, the control method comprising the reception, via said communication bus, of a set electrical signals comprising an electrical signal representative of an operation to be implemented on the storage medium.

According to the invention, the access control method further comprises:
- verification of the value of at least one parameter relating to at least one electrical signal of said set of electrical signals received; and
- the authorization or refusal of the implementation of the operation on the storage medium, depending on the result of the verification.

Thus, access to the storage medium is controlled, that is to say authorized or refused, by checking the value of at least one parameter relating to at least one of the signals of the set of electrical signals.

The set of electrical signals comprises several electrical signals necessary for the implementation of an operation on the storage medium. In particular, the set of electrical signals includes at least one electrical signal representative of an operation command, an operation command being a command intended for the implementation of an operation on the storage medium. In other words, the electrical signal is representative of an operation to be implemented on at least one storage medium area. Thus, an electrical signal representative of an operation command is an electrical signal configured to contain a sequence of data representative of the operation.

It will be noted that the set of electrical signals defines an operation to be implemented as well as operating parameters of the storage medium for the implementation of the operation. If, for example, an operating parameter of the storage medium is the supply voltage of the storage medium, at least one of the electrical signals of the set of signals defines the value of the supply voltage of the storage medium for the implementation of the operation defined by the electrical signal representative of the operation command.

In other words, said at least one parameter relating to at least one electrical signal corresponds to an operating parameter of the storage medium. Thus, the implementation of an operation, such as a write or a read, on a zone of the storage medium is authorized or refused according to the value of at least one operating parameter of the storage medium established for implementing the received operation command.

The access control according to a value of at least one parameter makes it possible to predict the conditions of access to the storage medium during the design of a connected object comprising the storage medium, these access conditions being unknown to users of the connected object. Consequently, the access control method makes it possible to prevent the access of a malicious person to the storage medium of the connected object, thus securing the data stored in the storage medium of this object, these data ensuring a correct and safe operation of the object.

Since the operating parameters of the storage medium are physical characteristics, their values cannot be accessed by a malicious person, and the use of a storage medium is secure. Indeed, an attacker seeks to access the content of the storage medium to obtain, for example, a password or a key. Thus, the parameters used to authorize or deny access to the storage medium corresponding to physical parameters relating to the electrical signals received by the storage medium, would not be obtained by collecting the content of the storage medium.

Said at least one verified parameter may belong to a set of parameters relating to the set of electrical signals. The parameter set contains parameters relating to at least one electrical signal of the signal set.

According to one characteristic, the verification is implemented for several parameters of the set of parameters relating to the set of electrical signals. Thus, the value of one or more parameters relating to at least one electrical signal of said set of electrical signals is verified.

Therefore, storage medium access control can be implemented based on the result of checking one or more parameters. In other words, one or more parameters can be taken into account to deny or authorize access to the storage medium.

According to one characteristic, the set of parameters comprises at least one parameter from among a voltage represented by at least one electrical signal from the set of signals, a frequency of at least one electrical signal from the set of signals, or a sequence of data contained by said at least one electrical signal of the set of signals.

According to one characteristic, said at least one parameter is a voltage represented by at least one electrical signal from the set of electrical signals or a frequency of at least one electrical signal from the set of received electrical signals, or a sequence of data contained by said at least one electrical signal of the set of electrical signals.

As indicated above, the electrical signals of the assembly define an operation to be implemented and the value of the operating parameters of the storage medium to be used for the implementation of the operation. Thus, for example, the set of parameters relating to the set of electrical signals received define at least one parameter from among a supply voltage of the storage medium, a frequency of a clock signal applied to the storage medium or a communication mode supported by the storage medium.

It will be noted that the value of these parameters is defined during the design of equipment embedding the storage medium, the value being selected from among the values provided by the designers and manufacturers of the storage medium.

The set of parameters relating to the set of electrical signals may include other parameters relating to at least one electrical signal of the set of electrical signals received by the storage medium. The verification of the value of at least one parameter can be implemented for one or more parameters of the set.

According to one embodiment, during the verification, the value of all the parameters of the set of parameters is verified.

Thus, the verification is implemented for a set of parameters. The received operation command is allowed or denied depending on the result of checking the parameter values of the parameter set.

The data stored in the storage medium is further protected. Indeed, access to the storage medium is authorized or denied according to a predefined combination of parameter values.

Security is further increased in embodiments in which the predefined combination of values changes over time.

For example, storage medium access control, i.e. allowing or denying the implementation of the operation command, is implemented by comparing the values of the set of values with values of a set of reference values comprising reference values associated respectively with the parameters of the set of parameters.

Note that the set of parameters can comprise a single parameter.

According to one characteristic, the implementation of said operation is authorized if, according to the result of said verification, the value of said at least one parameter is equal to a predefined reference value associated with said at least one parameter or is within a range of determined values including said reference value.

Thus, access to the storage medium is authorized when said at least one parameter has the reference value or a value close to the reference value, or in other words when said at least one parameter has a value equal or substantially equal to the reference value. This reference value is predefined prior to receipt of the operation command.

On the contrary, the implementation of the operation command is refused if, according to the result of the verification, the value of said at least one parameter is different from the predefined reference value associated with said at least one parameter or is not included in a determined range of values including said reference value.

When the value of several parameters of the set of parameters is checked, the implementation of the operation command is authorized if, according to the result of the check, the value of each parameter is equal to a reference value associated with the parameter or is included in a determined range of values including the reference value.

According to one characteristic, the control method comprises the comparison of the value of said at least one parameter with the reference value predefined beforehand and or the verification of the presence of the value of said at least one parameter in the range of values comprising the value of reference.

For example, the reference value is predefined when designing the connected object comprising the storage medium.

According to one characteristic, the predefined reference value associated with said at least one parameter and the range of values are stored in the storage medium.

According to one characteristic, the method further comprises the transmission of a configuration command intended to modify said reference value associated with said at least one parameter.

For example, the issuance of a configuration command is implemented when powering up said storage medium.

According to another embodiment, the emission of a configuration command is implemented periodically.

Thanks to the modification of the reference value over time, illegitimate access to the storage medium is further avoided and the use of a connected object comprising the storage medium is more secure.

According to one characteristic, if according to the result of the check, said value of said at least one parameter is different from the predefined reference value or is not included in a range of predefined values comprising said reference value, the checking method comprises further issuing a deletion command intended to erase the contents of said storage medium.

The issuance of this command allowing the deletion of the data stored in the storage medium constitutes a defense mechanism in the event of an attempt to read or write fraudulently, i.e. malicious access to the storage medium.

According to another characteristic, if according to the result of the verification, the value of said at least one parameter is different from the predefined reference value or is not included in a determined range of values comprising said reference value, the control method further comprises the emission of a signal intended to damage the equipment emitting the operation to be implemented.

For example, this signal can be a very large electrical current that can damage equipment attempting to fraudulently access the storage medium.

According to one embodiment, the storage medium comprises a first controlled-access data zone and a second free-access data zone.

In this embodiment, the access method comprises:
- if the implementation of the operation is authorized, implementation of the operation on the first zone,
- if the implementation of the operation is refused, implementation of the operation on the second zone.

Thus, when the implementation of the operation is refused following verification of the value of at least one parameter relating to at least one electrical signal, the commanded operation is nevertheless executed on the second storage zone which thus acts as a decoy for malicious third parties. Indeed, the operations commanded by a malicious third party are executed on the second storage zone and the device controlled by the malicious third party receives the results of this execution. The malicious third party cannot perform an analysis of the firmware of the connected object for example. Also by way of example, the malicious third party cannot collect sensitive data, such as cryptography keys. Moreover, the malicious third party does not detect, or at least is slowed down in the detection, that its actions have no effect on the storage medium and thus on the operation of the connected object.

Consequently, any operation carried out on the second storage area then has no impact on the operation of a connected object which stores useful data, such as its firmware, data that is sensitive or not, in the storage medium. This data ensures correct and safe operation of the object. The operations commanded by a malicious third party are executed on the second storage zone and the device controlled by the malicious third party receives the results of this execution.

Access to the first storage area that stores real data is only possible for authorized third parties.

According to a variant, still in the embodiment in which the storage medium comprises a first controlled-access data zone and a second free-access data zone, the method comprises:
- when the implementation of the operation on the storage medium is authorized, that the set of signals received carries information representative of a request to unlock access to the medium, and that access is authorized, the first area of the storage medium is accessed as an operation execution area on the storage medium,
- otherwise, a second storage area of the storage medium is accessed as an operation execution area on the storage medium.

In this embodiment, once the implementation of an operation is authorized by checking the value of at least one parameter, an additional check is implemented. This additional access control makes it possible to verify, by another means, that the device trying to access the storage medium is authorized or not. When he is not authorized, either because he is not informed that access control has been set up, or because he does not have unlocking information, the operations ordered, which have been authorized by the first access control, are executed on the second storage zone which thus acts as a decoy for malicious third parties.

This second storage area stores decoy data.

Access to the first storage area that stores real data is possible only for third parties authorized by the two access controls.

Any operation performed on the second storage area then has no impact on the operation of a connected object which stores useful data, such as its firmware, sensitive data or not, in the storage medium. This data ensures correct and safe operation of the object. The operations commanded by a malicious third party are executed on the second storage zone and the device controlled by the malicious third party receives the results of this execution. For example, the malicious third party cannot perform a firmware analysis of the connected object. Also by way of example, the malicious third party cannot collect sensitive data, such as cryptography keys. Moreover, the malicious third party does not detect, or at least is slowed down in the detection, that its actions have no effect on the storage medium and thus on the functioning of the connected object.

In a particular embodiment, the second data zone is selected as an operation execution zone on the storage medium during an activation of the storage medium.

Thus, the second storage area that stores decoy data is selected by default when activating the storage medium.

In a particular embodiment, the request to unlock access to the medium includes an access code.

In this embodiment, the set of electrical signals received carries the unlocking command as well as an access code. The operation(s) that will be executed on the first storage zone are thus received subsequently as long as the storage medium remains activated.

In a particular embodiment, the second zone of the storage medium comprises at least one marking datum belonging to the group comprising at least one identifier of the storage medium and a uniform resource locator.

These marking data present in the second storage area make it possible to subsequently detect that a malicious third party has attempted to access the storage medium. When the marking data is an identifier of the storage medium, the publication by the malicious third party of the data of the second storage zone makes it possible to identify the storage medium concerned. When the marking data is a uniform resource locator, a subsequent connection of the malicious third party makes it possible to collect information, such as an IP address (for “Internet Protocol”) of a device used by the malicious third party.

In a particular embodiment, a counter is incremented for an operation executed on the second storage zone.

This counter thus enables the connected object to detect that a malicious third party has attempted to access the storage medium. This makes it easier to detect attacks.

The characteristics of the access control method presented above can be taken in isolation or in combination with each other.

The present invention relates, according to a second aspect, to a device for controlling access to a storage medium via a communication bus, said control device comprising a reception module configured to receive, via said communication bus, a set of electrical signals comprising an electrical signal representative of an operation to be implemented on the storage medium.

The access control device further comprises:
- a verification module configured to verify the value of at least one parameter relating to at least one electrical signal of the set of electrical signals received; and
- a control module configured to authorize or refuse the implementation of the operation on the storage medium, depending on the result of said verification.

The present invention relates, according to a third aspect, to a storage medium comprising an access control device according to the invention implementing an access control method according to the invention.

The present invention relates, according to a fourth aspect, to a connected object comprising a storage medium and a management module configured to manage the operation of the connected object, the management module and the storage medium communicating with each other via a communication bus. communication. The connected object further comprises a device for controlling access to the storage medium in accordance with the invention and implementing the access method in accordance with the invention.

According to one embodiment, the storage medium access control device is integrated into the storage medium.

The present invention relates, according to a fifth aspect, to a computer program comprising code instructions for implementing the steps of the control method according to the invention, when it is executed by a processor.

The access control device, the storage medium, the connected object and the computer program have characteristics and advantages similar to those described previously in relation to the method of controlling access to a storage medium.

Other features and advantages of the invention will appear further in the description below.

In the accompanying drawings, given by way of non-limiting examples:
- the schematically represents a connected object, a storage medium and an access control device in accordance with a first embodiment of the invention;
- the schematically represents a connected object, a storage medium and an access control device in accordance with a second embodiment of the invention;
- the illustrates steps of an access control method in accordance with a first embodiment of the invention;
- the illustrates steps of an access control method in accordance with a second embodiment of the invention;
- the illustrates a hardware architecture that can implement the access control method according to the invention; and
- the is a functional representation of an access control device according to one embodiment of the invention.

The invention applies to any connected object, such as a mobile telephone terminal, a laptop computer, a tablet, a gateway, a printer, an audio speaker, a television decoder, a television set, a game console, a household appliance, a sensor, a camera, etc.

The invention applies particularly to any connected object comprising a storage medium such as a rewritable non-volatile memory. It can nevertheless be applied to connected objects comprising memories of another type.

More generally, the invention applies to any communicating object, that is to say objects configured to communicate (send or receive data) with other equipment.

In the remainder of this document, the term object or connected object will be used interchangeably, and also applies to communicating objects.

In addition, the storage medium can be embedded in the connected object or external to the connected object (for example a memory card or a storage medium that can be connected to the connected object for example via a USB type bus ( for "Universal Serial Bus")).

FIGS . 1a and 1b schematically represent a connected object 1 comprising a module 10 for managing the operation of the connected object and a device or storage medium 20. The management module 10 notably comprises a processor or a microcontroller.

The storage device or medium 20 may be a rewritable non-volatile memory, such as a Flash type memory. This memory may include computer programs and other data necessary for the operation of the connected object 1.

For example, the storage medium 20 and the management module 10 are placed in the same electronic management card containing the electronic circuits necessary for the operation of the connected object 1.

Of course, the storage medium 20 and the management module 10 can be placed in different electronic cards.

The management module 10 and the storage medium 20 communicate with each other via a communication bus 100. The management module 10 communicates with the storage medium 20 for example to exchange information necessary for the operation of the object, private keys necessary to establish a connection with a server, Wi-Fi keys or others. Furthermore, the management module 10 sends operation commands to the storage medium 20, these operation commands being typically write commands, read commands and erase commands.

The communication bus 100 used is for example a serial data bus allowing the implementation of an SPI link (for “Serial Peripheral Interface”) between the management module 10 and the storage medium 20.

This type of link allows simultaneous communications between the management module 10 and the storage medium 20.

Of course, other types of communication bus can be used, for example communication buses of the I2C type (for "Inter-Integrated Circuit"), or of the USB type (for "Universal Serial Bus") used in cases external memories.

An embodiment will be described in which the storage medium 20 is a Flash type memory and the communication bus 100 used for the exchanges between the management module 10 and the storage medium 20 is an SPI type bus. However, the invention applies to the management of access to storage media of other types via communication buses of other types.

The SPI type communication bus is a synchronous serial interface. It is configured to transmit a set of electrical signals. For this purpose, the communication bus comprises a set of lines, four at most for an SPI type bus.

In one embodiment, the set of electrical signals comprises a clock signal CLK, a memory selection or activation signal CS and two data signals used to exchange data between the management module 10 and the storage medium. storage 20. Each electrical signal uses a line of the communication bus.

The storage medium 20 shown in comprises a control pin or control input (“pin” in English terminology), “Chip Select” intended for the activation of the storage medium and being connected to a line intended for transporting the selection or activation signal CS.

The storage medium or memory 20 comprises a pin or input CLK connected to a line intended for transporting the clock signal CLK as well as a data input pin DATA_IN and a data output pin DATA_OUT respectively connected to the lines carrying data signals. A data signal can be an operation command sent by the management module 10 and intended for the memory 20, data to be written in an address of the memory or data read in an address of the memory 20. It will be noted that the operation command or the data to be written are addressed to the memory 20 via the line of the communication bus connected to the input pin DATA_IN or in other words constitute input data to the memory 20. As for the data read at a memory address, they constitute memory output data and are addressed to the management module 10 via the communication bus line connected to the DATA_OUT output pin.

It is thus considered that the set of electrical signals transmitted by the communication bus includes an operation command to be implemented in the storage medium. In other words, the set of electrical signals comprises an electrical signal representative of an operation command.

Thus, the storage medium 20 is configured to receive a set of electrical signals comprising an operation command. The electrical signals of the assembly are generated by the management module 10 taking into account a set of operating parameters of the storage medium. The value of these parameters is selected by the designer of the connected object from among the values given by the manufacturer of the storage medium.

The values of the operating parameters of the storage medium, for the implementation of the operation, are defined by the set of electrical signals received. The set of electrical signals thus defines the operation to be implemented and values of the operating parameters of the storage medium for the implementation of the operation.

By way of non-limiting example, for the implementation of a read operation, the management module 10 generates a set of signals comprising a read command. In other words, an electrical signal from the set of electrical signals is representative of a read command. For example, the electrical signal represents a series of data defining the operation. The signal set further includes the memory enable signal and the clock signal. Thus, for the implementation of a read operation, the management module 10 sends the memory activation signal, the clock signal and a read command.

Activation of the “Chip Select” control input is implemented by applying to the CS activation pin the activation signal representing a predefined voltage. For this, the activation signal is a logic signal, presenting a voltage level equivalent to the predefined voltage. The predefined voltage can be the minimum value, for example 0V, the activation signal then being at the low voltage level. Of course, in other configurations, the memory can be activated by an activation signal presenting a high voltage level.

The memory receiving this activation signal is informed that an operation command is going to be addressed to it and starts listening for the reception of operation commands, being in the given example a read command.

Such a read command can take, for example, the form of the following data sequence: "0x03 0x00 0x01 0x00 0x00", where 0x03 indicates, in hexadecimal values, that the operation to be implemented is a read operation and the rest of the command represents the address of the memory to be read. Once the operation has been implemented, the data read is present in the data line connected to the DATA_OUT output pin and addressed to the management module 10.

In the embodiment described, the electrical signal representing the operation command is a logic signal whose voltage level varies so as to represent the sequence of data (information bits) forming the operation command. It is considered that the operation command takes the form of a logic signal representing the series of data (or bits of information) constituting the operation command. This type of electrical signal, used by SPI type communication buses is known to those skilled in the art and does not need to be described in detail here.

In the embodiment described, the management module 10 generates a clock signal making it possible to exchange an information bit at each edge (for example rising) of the clock signal. For example, if the management module 10 implements the reading of data stored in the storage medium 20, one bit is obtained at each edge (for example rising) of the clock signal, i.e. one byte after eight rising edges.

The speed at which the data are transferred via the communication bus 100 is fixed according to the characteristics of the electronic components forming the management module 10 and the storage medium 20. By way of non-limiting example, the storage medium is a flash memory which can be powered by voltages between 2.8V and 3.6V and the data can be received and/or transmitted via the communication bus 100 at speeds between 0 and 120 MHz.

In addition, different exchange (or communication) modes can be used between the management module 10 and the memory 20, the exchange or communication modes being defined by the polarity (CPOL) and the phase (CPHA) of the clock signal when the memory receives the enable signal on the CS pin. The modes correspond to combinations of the values of the polarity and the phase of the clock signal (CPOL, CPHA). The polarity (CPOL) and phase (CPHA) of the clock signal control the active clock edge where the memory receives or sends data. If the CPOL polarity has the value 0, the clock signal is on standby at the low voltage level, i.e. the data will be exchanged when the clock signal is at the high voltage level. If the CPOL polarity has the value 1, the clock signal is on standby at the high voltage level, i.e. the data will be exchanged when the clock signal is at the low voltage level. If the CPHA phase has the value 0, the data is obtained on a rising edge of the clock signal and if the CPHA phase has the value 1, the data is obtained on a falling edge of the clock signal.

For example, four communication modes are possible, named modes 0, 1, 2 and 3. For example, modes 0 and 3 can be used to exchange data with the memory 20. Mode 0 corresponds to the pair (CPOL, CPHA ) of value (0,0), mode 1 to (0, 1), mode 2 to (1, 0) and mode 3 to (1,1).

Of course, the frequency and voltage values as well as the data exchange mode used may be different depending on the type and model of the memory used. The designer of the connected object takes into account the values to be used for parameters relating to the electronic components. For example, the designer takes into account the values given by the manufacturer of the memory used, for parameters such as the supply voltage, the frequency and the exchange mode supported. Thus, in particular the management module 10 is configured to take account of these values for the generation of the set of signals comprising the operation command.

Note that memory manufacturers give different acceptable ranges of supply voltage, frequency and supported communication modes in the memory datasheets. The designer of the connected object selects values for the operating parameters within these ranges. The connected object 1 further comprises an access control device 200 to the storage medium 20. The access control device 200 will be described below with reference to Figures 4a and 4b. The access control device 200 is configured to implement the method for controlling access to the storage medium in accordance with the invention which will be described with reference to FIGS. 2 and 3. The implementation of this method makes it possible to controlling access to the storage medium 20, i.e. the implementation of operations on the storage medium, in particular on a data storage area 210 of the storage medium 20 (zone or sector of the memory). As indicated above, the operations may be the reading or writing of data in an area of the storage medium 20. Another operation may be the erasing of an area of the storage medium.

The access control device 200 can be embedded in the storage medium 20 ( ) or can be located outside the storage medium, between the management module 10 and the storage medium 20 ( ).

The connected object 1 also includes a random access memory or RAM (not shown).

In one embodiment, the storage medium 20, in particular the data storage area 210 comprises, in the data storage areas 210, a first storage area 2101 comprising useful data, that is to say the data that is used by the application running on the connected object. In this first storage area 2101 are thus stored the data to which an ill-intentioned third party must not access. Access to this data is controlled by the access control device 200.

A second storage area 2102, distinct from the first storage area 2101, includes decoy data, that is to say data which is not used by the application which is executed on the connected object. More precisely, these data are intended to make the malicious third party believe that he is indeed accessing the first storage area 2101. The sizes of these first 2101 and second 2102 storage areas are for example identical. This reinforces the effect of normal access to the storage medium. This second storage area 2102 corresponds to a decoy area (also called a “ honeypot ” in English). It limits malicious interactions with the storage medium. Thanks to the proposed technique, the malicious third party will attempt to exploit data or even steal data, without this corresponding to the data useful to the connected object. The malicious third party reads a data zone that does not include any sensitive or confidential information or even alters data without this having any impact on the operation of the connected object. In a particular embodiment, this second storage area 2102 includes marking data. This is, for example, marking data comprising an identifier of the storage medium 210, such as the serial number. Thus, if the malicious third party publishes the data from the second storage zone 2102, it is possible to identify the storage medium 20 which has been attacked. These marking data can be added using a digital watermarking mechanism. For example, the identifier of the storage medium is partitioned into N pieces, which are stored at fixed addresses of the second storage zone, these fixed addresses not being public. Still by way of illustration, these are marking data comprising a uniform resource locator or URL (for “Uniform Resource Locator”), or address of a resource on the Internet network. If the malicious third party tries to access this location address, it is then possible to detect that an attack has taken place and to obtain its IP address from the malicious third party.

Of course, the partition of the aforementioned data storage area 210 is optional, the data storage area possibly being a single area.

The method for controlling access to the storage medium 20 according to a first embodiment is illustrated in .

In the embodiment described, the data storage area 210 is a single area, that is to say it does not include first 2101 and second 2102 execution areas.

When the management module 10 wishes to implement an operation on the memory 20, it sends to the memory a set of electrical signals comprising a memory activation signal, a clock signal and an electrical signal representing a command operation, the operation command defining the operation to be implemented. These electrical signals are generated by the management module 10 taking into account the values at which the operating parameters of the storage medium 20 must be established for the implementation of the operation, such as the supply voltage, the frequency of the clock signal or others.

Indeed, when an operation is going to be implemented on a memory 20, the memory 20 must be activated E0. For example, a memory is activated by applying a supply voltage to the input or power pin (“pin” in Anglo-Saxon terminology) and by activating the input or control pin intended for the activation of the “Chip Select” memory. If the memory is already powered, it is enabled by turning on the CS enable pin. As indicated above with reference to Figures 1a and 1b, the activation of the "Chip Select" control input is implemented by the application of a predefined voltage. The predefined voltage can be the minimum value, for example 0V, or a supply voltage value.

Once the memory is activated, it is checked E11 if a clock signal is applied to the CLK control input of memory 20. If a clock signal is applied, it is checked E12 if an operation command to implement is received E11 by the memory 20 on the DATA_IN data input.

In this embodiment, the supply voltage, the frequency of the clock signal and the read mode used by the storage medium are operating parameters defined by the electrical signals received. Thus, the value of the parameters of the set of parameters is defined by the signals of the set of signals received by the memory 20.

If the above set of electrical signals is received, the value of at least one parameter relating to at least one electrical signal is checked E2. In other words, the value of at least one memory operating parameter is checked E2. In one embodiment, multiple parameters of the parameter set are checked. The implementation of the operation is authorized or denied depending on the checked value.

In the embodiment described, the value of all the parameters of the set of parameters is checked E2 to decide whether to authorize or deny access to the memory 20. Thus, the implementation of the operation is allowed or denied based on a combination of parameter values.

Of course, the verification can be implemented for one or more parameters of the set, in number less than the totality of the parameters of the set.

It will be noted that in an embodiment, such as the one shown, the verification of the value of the set of parameters is implemented if, in addition to having received an operation command, a clock signal is applied to memory 20.

In one embodiment, the set of verified operating parameters includes the supply voltage V of the memory, the frequency f of the clock signal CLK applied and the communication mode used by the memory to dialogue via the communication bus. communications 100.

According to different embodiments, the set of parameters may comprise one or more parameters from among the aforementioned parameters, or other memory operating parameters.

In one embodiment, during the verification E2 of the value of the set of parameters or verification of the set of values, each parameter value is verified with respect to a reference value associated with the parameter.

For example, it is checked whether the value of the parameter is equal to the reference value associated with the parameter.

The reference values for the parameters of the assembly have been recorded beforehand in the memory 20. Typically, these values are defined and recorded by the designer of the connected object 1 comprising the memory 20. The reference values for the parameters of operation of the assembly are selected from ranges of values given by the memory manufacturer.

By way of non-limiting example, the memory 20 used can be powered by voltages from 2.8V to 3.6V, exchange data at speeds from 0 to 120 MHz and use modes 0 and 3 for data exchange via the communication bus 100.

In the embodiment described, during the design of the connected object 1 using this memory 20, reference values are selected for these three operating parameters, that is to say the supply voltage, the speed or frequency of the clock signal and the communication mode supported by the memory.

For example, the V_ref reference value selected for the supply voltage is 2.75 V, the f_ref reference frequency is 87654321 Hz, and the mode_ref reference mode is mode 3.

Of course, these values are given to illustrate the description and other reference values can be selected. Furthermore, it will be noted that the values of the operating parameters may be different depending on the type and model of the memory used.

In the embodiment shown in , during verification E2, it is verified whether each value of a parameter of the set is included in a range of values comprising the reference value V_ref, f_ref, mode_ref associated with the parameter. These ranges of values are defined to take into account slight variations of the values of the parameters compared to the reference values. Thus, it is checked whether the values of the parameters are substantially equal to the reference values respectively.

Of course, in other embodiments, it can be checked whether the value of a parameter of the set is equal to the reference value.

According to one embodiment, the range of values defined for the supply voltage can comprise values between V_ref – ((V_max-V_min)/100) and V_ref + ((V_max-V_min)/100), where V_max corresponds to the maximum power value supported by the memory and V_min corresponds to the minimum power value supported by the memory. As shown below, these values are provided by the memory manufacturer.

Similarly, the range of values defined for the frequency of the clock signal can include values between (f_ref – (f_max/100) and f_ref + (f_max/100), where f_max corresponds to the maximum frequency allowed by the memory As with the supply voltage, the maximum frequency value is set by the memory manufacturer.

For example, verification E2 includes for each parameter, a comparison of a value of the parameter obtained and the reference value associated with the parameter. The value of the parameter is obtained from at least one electrical signal of the set of electrical signals received.

Thus, according to one embodiment, the verification of the value of a parameter relating to an electrical signal includes obtaining the value of the parameter followed by a comparison of this value obtained with the reference value. The value of a parameter is typically obtained using a measurement, these operations being known to those skilled in the art

In this embodiment, the frequency, polarity and phase of the clock signal are measured, by conventional methods. The supply voltage is measured, also by conventional methods, using one of the signals from the set of signals (for example the clock signal).

In the embodiment described, it is checked E21 if the value of the supply voltage obtained from the set of signals received (for example by measuring the level of one of the signals) is included in the range of values defined for the supply voltage. It is also checked E22 if the value of the frequency of the clock signal is included in the range of values defined for the frequency.

In addition, in this embodiment, it is checked E23 if the communication mode defined in the operation command corresponds to the reference mode mode_ref.

If it results from the aforementioned checks E21, E22, E23 (E2) that the supply value V is included in the range of data associated with the supply voltage, that the frequency of the clock signal f is included in the data range associated with the frequency, and the communication mode set for the operation is the reference mode, the implementation of the operation command is allowed E31.

On the contrary, if at least one of these three conditions is not verified, the implementation of the operation command is refused E32.

In other words, if for the implementation of the operation command, the value of the supply voltage V and the value of the frequency f are substantially equal respectively to the predefined reference values V_ref, f_ref, and if the communication mode corresponds to the reference mode mode_ref, the implementation of the operation command is authorized E31. If at least one of these conditions is not verified, the implementation of the operation command is refused E32. illustrates steps of the method for controlling access to the storage medium 20 according to a second embodiment.

According to one embodiment, several reference values can be associated with at least one parameter of the set of parameters.

According to different embodiments, several reference values can be associated with several parameters of the set of parameters. In one embodiment, multiple reference values are associated with all of the parameters in the parameter set.

For example, multiple reference values for the frequency of the clock signal can be stored, with the frequency value to be used to communicate with the memory cyclically alternating between the stored reference values. For example, if two reference frequency values are stored f_ref, f_ref_2, a first reference value f_ref is used for a predetermined number N of clock cycles and a second reference value f_ref_2 is used for the N clock cycles following. Then the first reference value f_ref is used for the next N clock cycles and so on.

Thus, in this embodiment in which several reference values are used for the frequency of the clock signal CLK, the control method includes a step E10 of establishing the reference frequency value. This step is implemented after the activation E0 of the memory and is repeated cyclically after the expiry of the predetermined number N of cycles.

Of course, in other embodiments, several values can be associated with the supply voltage and/or the exchange mode, what has just been described for the frequency values applies in a similar way for the values of the other operating parameters, that is to say for the supply voltage value and/or for the exchange mode.

Common steps with are not described again with reference to the .

According to one embodiment, the reference value of one or more parameters of the set of parameters is modified regularly. For example, the reference value of the parameters can be modified by a configuration command sent by the control device 200 and intended for the memory 20. According to one embodiment, this configuration command can be sent each time the the memory 20. According to another embodiment, the configuration command can be transmitted periodically.

The access control method shown in includes the emission E01 of a configuration command during the activation of the memory. Of course, the transmission of the configuration command is optional and can be implemented at other times of the method. In addition, this step can be implemented in other embodiments such as the one shown in .

Changing reference values further enhances memory security.

It should be noted that the devices used to recover and/or modify the contents of a memory by a malicious third party only support a limited number of supply voltages (often values of 3.3V and 5V) and frequencies making it possible to exchange data with the memory, these values corresponding to the values commonly used by the memories. Also, dynamic change of supply voltage or clock signal frequency is not utilized by these devices.

An example configuration command is described below. The configuration command described is intended for a flash type memory and is generated by an access control device according to the invention.

It will be noted that the instructions or operations addressed to a flash type memory are represented by hexadecimal values on one byte. This value identifies the operation to be implemented. For example, the value 0x03 is a standard value used for a read operation. This value is followed by a memory address where the reading is desired.

The configuration command thus contains a first byte containing an identifier of the configuration command (called in English terminology “ Access control parameters update ”).

By way of non-limiting example, the identifier of the configuration command is 0xEE.

The second byte of the configuration command contains the number of frequency reference values f_ref defined in the command. For example, this byte can take a value between 0x01 to 0x08 (1 to 8).

A third byte defines the reference mode to be used for implementing an operation. For example, this third byte can take a value from 0x00 to 0x03 (mode 0, 1, 2 or 3).

The fourth and fifth bytes define the reference value for the supply voltage. For example, the reference value is rounded to two decimal places and multiplied by 100. If the V_ref reference value is 2.71V, the value represented by the fourth and fifth bytes is 271, that is, 0x10F. The fourth byte contains the value V_ref[0]=0x01 and the fifth byte the value V_ref[1]=0x0F. Note that the fourth byte contains the most significant bit. Of course, in other embodiments, it could contain the least significant bit.

The sixth through ninth bytes define the reference value for the f_ref frequency, expressed in Hz. For example, if the f_ref reference value is 87654321 Hz, i.e. 0x5397FB1, the sixth byte contains the f_ref value [0]=0x05, the seventh byte the value f_ref[1]=0x39, the eighth byte the value f_ref[2]=0x7F and the ninth byte the value f_ref[3]=0xB1.

According to other embodiments, additional bytes can be used to define additional reference values for the frequency f_ref_2, f_ref_3 etc. expressed in Hz, if the number of frequencies defined in the second byte is greater than or equal to 2.

For example, a command to set the reference communication mode mode_ref to mode 3, the reference value for supply voltage V_ref to 2.71V and reference value for frequency f_ref to 87.654321MHz is therefore: 0xEE 0x01 0x03 0x01 0x0F 0x05 0x39 0x7F 0xB1.

According to one embodiment, when the value of a parameter of the set is not equal to the reference value associated with the parameter or is not included in the range of values determined for this parameter, the control method further comprises the emission E40 of a deletion command intended to erase the contents of the memory (when the memory zone comprises two memory zones, the command may be intended to erase the contents of the first storage zone or else of the first and second storage zones).

According to another embodiment, when the value of a parameter of the set is not equal to the reference value associated with the parameter or is not included in the range of values determined for this parameter, the method of control further comprises the transmission E41 of a signal intended to damage the equipment attempting access to the storage medium. This signal is for example an electric current of high intensity. This electric current can be generated by a large discharge of a capacitor integrated in the access control device (not shown in the figures).

These transmission steps E40, E41 can also be implemented by the access control method described with reference to the .

In another embodiment, the method includes the transmission of a message intended for the management module 10 of the object informing of the attempt to implement a fraudulent operation. The management module could provide for example to send an informative message to a terminal or server connected with the object connected via a communication network, or that it is connected again if it had been disconnected. For example, the memory access control device can be configured to store information in memory indicating that an attack has been detected. Additionally, the management module can be configured to periodically poll the access control device to ask if an attack has been detected. Thus, the management module can be informed of the attacks detected by the access control device.

In an embodiment not shown, in which the data storage area 210 comprises a first area 2101 and a second area 2102, when the operation is refused E32, the second area is selected as the execution area of operation on the storage medium. The operation is then implemented on this second execution zone 2102. In other words, when the operation is refused E32, the operation is implemented on the second zone. When the operation is authorized E31, the first zone 2101 is selected as an operation execution zone on the storage medium, the operation being implemented on this first zone 2101. In other words, when the operation is authorized E31, the operation is implemented on the first zone.

In another embodiment not shown, in which the data storage zone 210 comprises a first zone 2101 and a second zone 2102, once the memory has been activated (such as in step E0 of and 3), second storage area 2102 is selected as the operation execution area on storage medium 20.

If a clock signal is applied, it is checked whether an operation command to be implemented is received by the memory 20 on the data input DATA_IN via the communication bus. If this is not the case, the process returns to awaiting receipt of an operation command.

When an operation is received and authorized (step E31 of FIGS. 2 and 3) after the verification of at least one parameter (such as in step E2 of FIGS. 2 and 3), it is verified whether the set of signals received carries information representative of a request to unlock access to the medium.

When the set of signals received carries information representative of a request for unlocking access to the medium, such as an unlocking command, it is checked whether this unlocking command carries a valid access code. If this is the case, access to the storage medium is authorized and the first storage area 2101 is selected as the operation execution area on the storage medium 20. The method returns to waiting for reception of data on the DATA_IN data input via the communication bus. Thus, when an operation command is received on the data input, the first data storage area 2101 is accessed and the operation is performed on the first data storage area 2101 as long as the storage medium remains activated.

When the set of signals received does not carry information representative of a request for unlocking access to the medium, the operation received is executed on the second storage zone 2102. Thus if the access control has been carried out if successful, the access is authorized and the operation is performed on the first storage area 2101. Otherwise, the second storage area 2102 is accessed and the operation is performed on the second storage area 2102. The process returns to waiting for data reception on the DATA_IN data input via the communication bus.

When the access code is not valid, the process returns to waiting for data reception on the DATA_IN data input via the communication bus.

These steps are thus implemented as long as the enable signal is present on the CS enable pin. When the storage medium is deactivated, i.e. when the supply voltage applied to the activation pin CS has varied from 0V to a value greater than the minimum voltage Vmin, the method returns to waiting for detection of the activation signal.

In a particular embodiment, the storage medium 20 stores a counter in a persistent register. This counter represents the number of times that a read, write, erase operation has been executed on the second storage area 2102. It is incremented each time an operation is executed on the second storage area. counter is transmitted to the management module 10 upon receipt of a get_command_value command. This command is sent by the management module 10 at start-up and then periodically, for example every twelve hours. When the counter increases, the management module 10 identifies that attacks have been attempted. In this case, the management module 10 sends a storage zone change command change_zone to select the second storage zone 2102. It dumps the data from the second storage zone. Subsequent analysis of this data is then performed locally or on a remote server to which the connected object is connected. The data that has been unloaded corresponds, for example, to malicious firmware (“ firmware ”) downloaded by a malicious third party.

It is emphasized here that the data stored in the second storage zone 2102 can be updated remotely by the manufacturer of the connected object or else by a legitimate user. This makes it possible to update marking data depending for example on the version of the firmware and complicates the detection of these marking data by a malicious third party.

The method has been described in a particular embodiment in which the management module 10 sends an unlocking request comprising an access code. There are no limitations attached to this unlocking mechanism.

In another embodiment, the first data area is selected as the operation execution area on the storage medium upon activation. When the set of signals received does not carry information representative of a request for unlocking access to the medium or when access is authorized, the second zone of the storage medium is accessed as an execution zone. operation on the storage medium. This second storage zone remains the only one accessed as an operation execution zone, as long as the storage medium is activated. It is understood that an authorized access control makes it possible to switch to the first storage zone as an operation execution zone.

Thus, when the set of signals received carries information representative of a request to unlock access to the medium and access is authorized, the first zone of the storage medium is accessed as an execution zone. operation on the storage medium, and if not, the second storage area of the storage medium is accessed as the operation execution area on the storage medium.

The schematically illustrates a hardware architecture of an access control device 200 that can implement the control method according to the invention. As illustrated in Figures 1a and 1b, the control device 200 can be embedded in the storage medium 20 ( ) or be external to the storage medium 20 ( ). The illustrates a control device 200 external to the storage medium 200.

The control device 200 comprises a communication bus 2000 to which can be connected:
- A processing unit 2001, named in the figure CPU (for "Central Processing Unit") and may include one or more processors;
a non-volatile memory 2002, for example ROM (for “Read Only Memory”), EEPROM (for “Electrically Erasable Read Only Memory”) or a Flash memory;
- a 2003 random access memory or RAM (for "Random Access Memory").

It will be noted that the aforementioned elements may be present or absent depending on the configurations according to which the control device is embedded in the storage medium or is external to the storage medium. For example, in certain embodiments, the non-volatile memory 2002 and/or the random access memory may be absent from the access control device, the control device using the memory or memories of the storage medium 20 for which the access is controlled.

In an embodiment in which the control device is external to the storage medium 20 (like the one shown in ), it comprises a communication interface 2004, named COM in the figure, suitable for exchanging data with the storage medium 20. In addition, it is connected to the communication bus 100 to which the storage medium 20 is connected.

Random access memory 2003 includes registers suitable for recording variables and parameters created and modified during the execution of a computer program comprising instructions for implementing the control method according to the invention. The program instruction codes stored in non-volatile memory 2002 are loaded into RAM memory 2003 with a view to being executed by the processing unit CPU 2001.

The non-volatile memory 2002 is for example a rewritable memory of the EEPROM or Flash memory type which can constitute the support within the meaning of the invention, and which can comprise a computer program comprising instructions for the implementation of the control method according to the invention.

This program defines, by means of its instructions, functional modules of the control device 200 which are implemented and/or control the hardware elements described above. The is a functional representation of a control device 200 according to one embodiment.

These modules include:
- A reception module 201 configured to receive, via said communication bus, a set of electrical signals comprising an electrical signal representative of an operation command to be implemented on at least one zone of the storage medium;
- a verification module 202 configured to verify the value of at least one parameter relating to at least one electrical signal from the set of electrical signals received; and
- A control module 203 configured to authorize or refuse the implementation of said operation command on said at least one area of the storage medium, depending on the result of the verification.

The aforementioned modules and means are controlled by the processor of the processing unit 2001. They can take the form of a program executable by a processor, or a material form (or “hardware”), such as a specialized integrated circuit (known in Anglo-Saxon terminology known as ASIC for “Application-Specific Integrated Circuit”), a system on chip (known in Anglo-Saxon terminology as SoC for “System On Chip”), or an electronic component of the programmable logic circuit type, such than an FPGA type component (for “Field-Programmable Gate Array”).

Claims (12)

Method for controlling access to a storage medium (20) via a communication bus (100), said control method comprising the reception (E11), via said communication bus, of a set of electrical signals comprising a signal representative of an operation to be implemented on the storage medium (20), and being characterized in that it further comprises:
- the verification (E2) of the value of at least one parameter relating to at least one electrical signal of said set of electrical signals received; and
- the authorization (E31) or the refusal (E32) of the implementation of said operation on the storage medium, depending on the result of said verification (E2). Control method according to claim 1, in which the implementation of said operation is authorized (E31) if according to the result of said verification (E2), the value of said at least one parameter (V, f, mode) is equal to a predefined reference value (V_ref, f_ref, mode_ref) associated with said at least one parameter or is included in a range of values including said reference value. Control method according to claim 2, further comprising the transmission (E01) of a configuration command intended to modify the said reference value associated with the said at least one parameter. Control method according to one of Claims 2 or 3, in which if, according to the result of said verification (E2), the value of said at least one parameter is different from said predefined reference value or is not included in a determined range of values comprising said reference value, the control method further comprises the transmission of a deletion command (E41) intended to erase the content of said storage medium. Control method according to one of Claims 2 or 3, in which if, according to the result of said verification (E2), the value of said at least one parameter is different from said predefined reference value or is not included in a determined range of values comprising said reference value, the control method further comprises the emission (E42) of a signal intended to damage the equipment emitting said electrical signal representative of an operation to be implemented. Control method according to one of the preceding claims, in which the said at least one parameter is a voltage represented by at least one electric signal of the set of electric signals or a frequency of at least one of the electric signals of the set of electrical signals received, or a series of data contained in at least one of the electrical signals of the set of electrical signals. Control method according to one of the preceding claims, said storage medium comprising a first controlled-access data zone (2101) and a second free-access data zone (2102), said method comprising:
- if the implementation of the operation is authorized, implementation of the operation on the first zone,
- if the implementation of the operation is refused, implementation of the operation on the second zone. Method according to one of Claims 1 to 6, the said storage medium comprising a first data zone with controlled access, the said method comprising
- when the implementation of the operation on the storage medium is authorized, that the set of signals received carries information representative of a request to unlock access to the medium, and that access is authorized, the first area of the storage medium is accessed as an operation execution area on the storage medium,
- otherwise, a second storage area of the storage medium is accessed as an operation execution area on the storage medium. Device for controlling access to a storage medium via a communication bus, said control device comprising a reception module (201) configured to receive, via said communication bus, a set of electrical signals comprising an electrical signal representative of an operation to be implemented on at least one area of the storage medium, and being characterized in that it further comprises:
- a verification module (202) configured to verify the value of at least one parameter relating to at least one electrical signal from the set of electrical signals received; and
- a control module (203) configured to authorize or refuse the implementation of said operation on said at least one zone of the storage medium, depending on the result of the verification. Storage medium comprising an access control device (200) in accordance with claim 9 and implementing an access control method in accordance with one of claims 1 to 8. Connected object comprising a storage medium (20) and a management module (10) configured to manage the operation of said connected object (1), the management module (10) and the storage medium (20) communicating with each other via a communication bus (100), said connected object (1) being characterized in that it comprises an access control device (200) to said storage medium (20) in accordance with claim 9 and implementing a method of access according to one of claims 1 to 8. Computer program comprising code instructions for implementing the steps of the control method in accordance with one of Claims 1 to 8, when it is executed by a processor.