WO2007090857A1

WO2007090857A1 - Method of secure updating of a nonvolatile memory

Info

Publication number: WO2007090857A1
Application number: PCT/EP2007/051190
Authority: WO
Inventors: Thierry Garnier; Jean-Marie Valade; Patrick Van-Haver
Original assignee: Gemplus
Priority date: 2006-02-08
Filing date: 2007-02-07
Publication date: 2007-08-16
Also published as: FR2897192A1

Abstract

The invention relates to a method of updating a data item (D0) in a block-erasable main non-volatile memory (MNV), consisting in: saving in a save area (S) the old value of the data item (D0) and at least one active save indicator (I0) indicating that a data item has just been saved and that a modification is underway; copying the block (P) relevant to the data item to be updated into a non-volatile memory buffer area (B); erasing said block (P) from the main memory (MNV); reconstructing the block (P) on the basis of the data copied into the buffer area and of the new value of the data item to be updated and writing said reconstructed block (P) into the main memory (MNV); deactivating the indicator of the save area if the update operation has run correctly.

Description

METHOD FOR SECURE UPDATING OF NO MEMORY

VOLATILE

The present invention relates to nonvolatile memories, such as EEPROM memories or flash memories and associated management circuits for updating in a secure manner the data stored in these memories. The present invention applies in particular to nonvolatile memories of this type in microprocessor chip cards.

The updating of a data item consists in replacing, at a given address of the memory, an old data item with a new data item. This updating operation can be critical with respect to the integrity of the data concerned. Indeed, nonvolatile memory technologies such as EEPROM or flash memory imply that the data to be updated is first erased before the new data can be programmed to the specified address. It may happen that the supply voltage of the memory is accidentally cut during this phase, causing both the old data and the new data to be lost. Such a situation is obviously not acceptable, especially when it comes to data whose conservation is critical in the application in question. Mechanisms to respect the integrity of the data during a memory update phase were then developed. These secure update mechanisms mainly consist, before performing the updating operation of a data, to save the old data in a dedicated backup area of the non-volatile memory (called "backup area" in English language) before updating the new data to the desired address.

In this way, in case of accidental loss of memory supply during the updating operation, at least the old value of the data considered is preserved.

In addition to saving the data, all the information necessary to retrieve the corresponding value of the data must also be saved. This system information typically relates to the address of the data in the memory, its length, as well as indicators to indicate whether the backup area is still active or not. When the data has been correctly updated, the old value of the data is no longer useful and the dedicated backup area for this data and its associated system information can be released. In case of detection of loss of memory power during an update operation, specific mechanisms ("rollback" according to the English terminology ") are then provided to trigger the reset of the memory , allowing to restore the data of the memory in their initial state before updating. To do this, these mechanisms detect active backup areas in memory and copy the old values stored therein to the appropriate memory locations indicated by the information. corresponding system also saved together with the data.

In the context of nonvolatile memories, the difficulty of realizing these secure updating mechanisms lies in the management of the memory spaces that must be used to save the old data and its associated system information.

Indeed, these existing mechanisms, making it possible to ensure the secure updating of the data, have hitherto been developed to address nonvolatile memories comprising a fine memory granularity, that is to say of the order of 1. 'byte. An effective and efficient implementation of these mechanisms is therefore correlated to the use of a non-volatile memory previously cut into a number of blocks of a predefined size, typically one byte, defining a fine granularity of the memory.

Now, the trend is towards the development of non-volatile memories of large capacity, NOR flash type, which then has a much less granularity, of the order a few tens / hundreds of bytes to several kilo / ten kilo octets (KB ). Such memories can be programmed byte by byte, but can only be erased by an entire block of memory defined by the granularity of the memory of the order of a few tens / hundreds of bytes to several kilo / tens of kilobytes. (Ko) These memories can also be programmed per page, corresponding to a predefined fixed size memory block, defining the maximum number of bytes that can be written to during a single operation when memory programming is not done byte-by-byte.

Thus, because of the management constraints of flash memories with large granularity, the secure updating of a data of the coded memory for example on a single byte with application of the mechanisms of "backup" previously exposed ensuring a potential restoration of the state of the memory in case of accidental power failure during the updating operation, would require to copy beforehand in the predefined storage area of the memory a large part of memory constituted by the entire block of memory containing the byte to be updated, ie a data block of a few tens / hundreds of bytes to several kilo / tens of kilobytes (KB), depending on the nominal granularity of the memory.

Indeed, the update of a data item in a nonvolatile memory with a large flash granularity implies not only to previously erase the data concerned, but also to erase the entire block containing the data concerned, since erasure of these memory can be performed only by integer block, defining the granularity of the memory. It is therefore an entire block of memory, that is to say 8 KB, 16 KB, 32 KB or more, which must be saved via the mechanism of "backup" in the zone backup, while the update concerns only one byte for example of the memory block in question. Also, the existing mechanisms described above to respect the integrity of data during an update process are unsuited to non-volatile memories that have a low degree of fragmentation. Thus, the size of the backup area required to store the backup information corresponding to the entire block of memory concerned by the update would be unreasonable. The invention aims to solve this drawback, by proposing a non-volatile memory management system of high capacity and high granularity, in which the existing mechanisms ensuring the integrity of the data when they are updated in the event of accidental breakage The power supply can continue to be used, keeping a size of the backup area provided for this purpose and memory usage performance within acceptable limits. With this object in view, the subject of the invention is a method for updating at least one data item in a predefined fixed block memory nonvolatile primary non-volatile memory, consisting of: a- saving in an area of backup memory the old value of the data; b- save in the backup area at the same time as the old value of the data the system information related to the data item to be updated, comprising at least one active backup indicator indicating that data has just been saved and that a data modification is in progress; said method being characterized in that it further comprises the steps of: c- copying the entire block concerned by the data item to be updated into a nonvolatile memory buffer area corresponding in size to at least the fixed block size predefined main memory, said buffer zone being distinct from the backup area; d- erase from the main non-volatile memory the block concerned by the data item to be updated; e- reconstructing the block from the data of the block copied in the buffer zone and the new value of the data item to be updated and write said block with the data item updated in the main non-volatile memory; f- disable the indicator of the backup area if the update operation was successful.

According to a particular embodiment in which the updating involves a plurality of data of the main non-volatile memory involved in the realization of a transaction, said transaction data not having to be updated separately, the method consists of repeating steps a- to e- of the process consecutively for each data item concerned by the transaction.

Preferably, according to the particular embodiment, the old data values and the associated system information corresponding to each data of the transaction, are saved in the same memory sector of the backup area. According to the particular embodiment, the step f- is implemented if the update operation of the plurality of data has proceeded correctly, and consists in deactivating the backup indicators previously saved in the backup zone. respectively for each updated data.

According to a variant of the invention, the step f- implemented is replaced by a step of erasing the contents of the backup area. Advantageously, the size of the buffer zone is a multiple N, N greater than or equal to 1, of the predefined block size for the main non-volatile memory.

Advantageously, after a memory power interruption occurring during a memory update operation, the following steps are implemented consisting of:

- check the presence of at least one backup indicator in the active state in the backup area; if at least one backup indicator is in the active state, restoring the old value of each of the data saved in the backup zone whose associated backup flag is in the active state to the non-volatile main memory, then disable the corresponding backup flag.

Advantageously, the step of restoring a piece of data in memory consists of:

- recover the starting address in the main memory of the data block concerned by the data to be restored, from the system information saved with the old value of the data in the backup area, said information including the original address in the main memory of the data; reconstructing the block concerned as it was in its initial state, from the data of the block concerned copied in the buffer zone and from the old value of the data to be restored saved in the backup zone; - program the restored block into the memory at the retrieved address.

According to one embodiment, if the buffer zone is empty, the step of rebuilding the block concerned by the data item to be restored comprises previously copying in the buffer zone the data of the block concerned, starting from the previously recovered starting address. block in the main non-volatile memory.

According to one characteristic, the programming step in the memory of the restored block first comprises the erasure of the corresponding block of the memory and then the writing of the restored block into memory.

According to a particular embodiment, the main non-volatile memory comprises characteristics of high capacity and large granularity and the buffer zone comprises characteristics of low capacity and fine granularity.

The invention also relates to a portable digital apparatus comprising a microprocessor, a main memory non-volatile memory erasable by memory block of predefined fixed size and a data backup area of the main non-volatile memory during a data updating process, characterized in that it comprises a buffer zone of non-volatile memory, of size corresponding to at least the fixed size of predefined block of the main memory, and memory management means adapted to control the progress of data update operations in memory according to the method according to any one of the preceding claims.

Preferably, the main non-volatile memory is a flash memory.

Preferably, it is a smart card. Other features and advantages of the present invention will emerge more clearly on reading the following description given by way of illustrative and nonlimiting example and with reference to the appended figures in which: FIGS. 1 and 2 illustrate the steps of FIG. method of the invention ensuring the update of a single data memory, with respect for its integrity; FIGS. 3 to 5 illustrate the steps of the method of the invention guaranteeing the updating of two data of the memory intervening in the completion of a transaction, with respect for the principle of atomicity of transactions.

The invention will preferably be implemented in a smart card, comprising a non-volatile memory for storing data, and a microprocessor for managing data exchanges between the inside and the outside of the card.

Among the memories of the card, there is therefore a main non-volatile memory MNV, programmable and electrically erasable, for the recording of data useful for or applications of the smart card. These data are subject to change during successive uses of the card and these modifications must be made while ensuring the integrity of the data. In particular, the data updated in the memory must not be lost during an untimely interruption during the update operation of this data, due for example to the tearing of the card of the reader with which it communicates for updating the data, or has a power failure.

In the context of the present invention, the memory MNV is a non-volatile memory of large capacity, for example of the order of several megabytes, very high integration density. This is for example a NOR flash memory type. The size of a memory block, defining the minimum amount of bytes that is effectively erased during a single memory erase operation, can range from 128 bytes to a few tens / hundreds of KB (coarse grain granularity). eg 8KB, 16KB, 32KB or more. The card also includes a non-volatile backup memory area S, programmable and electrically erasable, provided to save the old value of a data while updating this data in the main memory MNV. This save area is represented as a separate memory from the main non-volatile memory MNV. However, it can be physically constituted by a portion dedicated for this purpose of the main memory MNV. The backup area is preferably divided into sectors of size equal to the predefined size of a data block of the main non-volatile memory MNV and each sector makes it possible to save data of the card to be updated in the main memory. MRV. The corresponding field of data saved in the save area is sized according to the maximum size of the data that can be saved.

System information related to the data is saved at the same time in the backup area.

This system information related to the saved data includes a backup indicator, encoded for example on a bit, indicating that a data has just been saved and a modification is in progress. The active state of this indicator then makes it possible to indicate that the old value of the data can be recovered if the update does not proceed correctly until its end.

This information further includes information about the data length, the original address in the main memory of the data saved in the backup area, and in general, any information needed to interpret the data stored in the backup area and to check the integrity of that data. Thus, the original address of a data item saved is necessary to be able to possibly restore the data in the case where the update would not proceed correctly.

According to the invention, the card further comprises a portion B of nonvolatile memory, intended to act as a persistent buffer vis-à-vis the entire blocks of data of the main nonvolatile memory, as will be explained in more detail hereinafter. According to one embodiment, the buffer zone B is a non-volatile memory of small capacity, whose size is a multiple N (N> = 1) of the size of a data block of the main non-volatile memory. This is for example a memory type EEPROM, FeRam, MRAM ... According to a particular embodiment given by way of example, this buffer may have intrinsic characteristics different from the main memory MNV and the backup area S

(fine granularity of the order of the byte, advantageous in terms of simplicity of update - no block integrity to manage - and / or better access speed).

The buffer zone B alongside the main non-volatile memory MNV serves to replace the existing backup zone S, conventionally used by the mechanisms already described for backup and recovery, in order to save the entire blocks of data. data concerned with the data or data to be updated in the main non-volatile memory.

The buffer zone can then advantageously make it possible not to compromise the overall performance of the system, because of the intrinsic characteristics of the buffer zone and in any case avoids the need to provide an oversized size for the data saving zone S, this which would be problematic given the specific constraints related to embedded systems. Indeed, thanks to the buffer zone B, the backup area S remains, as in the state of the art, dedicated solely to the backup of the data to be updated with their associated system information. The data blocks of the main memory concerned by the update are in turn stored in the buffer zone B provided for this purpose.

In addition, unlike a conventional data buffer, the buffer zone is a persistent type of memory, which is particularly advantageous concerning the processing of the integrity of the data.

The steps of the updating method according to the invention, taking into account the memory architecture previously described, will now be described with reference to FIGS. 1 and 2, in the case where the data backup is purely individual, that is, that is to say when it is not necessary to ensure the coherence of several data at the same time. According to the example, this is to update a datum D ₀ located in the block P of the main memory. As already explained before, because of granularity characteristics of the main memory MNV, the block P comprising this data D ₀ to update will then have to be erased in full to allow the update of the data D ₀ . In step 1, the old value of the data item D ₀ to be updated in the main nonvolatile memory MNV is written in the backup area S for the purpose of saving it, as well as the associated system information I ₀ , including including its original address and the backup indicator. The backup flag is then activated, representing the presence of saved and reusable data in the event of a problem. This is the same mechanism that is currently implemented during the secure update in an EEPROM.

The actual update of the data D ₀ then comprises the following steps:

In step 2, the entire block P of data comprising the data item D ₀ to be updated is copied to the buffer zone B dedicated for this purpose;

In step 3, the block P in the main memory is erased;

In step 4, a new block P is reconstructed from the data of the block P stored in the buffer zone B and of the new value of the updated data item Di, then the block P thus reconstructed with the updated data item. O ₁ is written in the main non-volatile memory MNV to the corresponding address, obtained from the system information I ₀ saved in the backup area S; In step 5, the buffer zone is erased and, in step 6, the backup indicator corresponding to the saved datum D ₀ is deactivated if the progress of the operation has been normal from one end to the other. other. A variant of step 6 is to erase the backup area.

In the case where the flow has been normal, the card can be removed from the associated reader and reused normally. The progress of the last stages of the updating process is given here as an example. Thus, the erasure of the buffer zone B can be executed at another time of the process, the important thing being that the erasure of the buffer zone is effective before the step 2 implemented during a process of updating. next day. A process could therefore be envisaged where the erasure of the buffer zone would be executed just before the next step 2. This remark also applies to the following example. FIGS. 3 to 5 now illustrate the steps of the method of the invention concerning the updating of a plurality of data of the memory of the card, in this case two data D ₀ and D ₂ , said data having to remain coherent between them and therefore, can not be updated separately. This is typically data involved in performing a transaction via the card, for example a certain value is removed from the current value of a first data memory and the same value is added to the current value of a second data of the memory. The method according to the invention advantageously makes it possible to respect the principle of atomicity of transactions, that is to say that it makes it possible to ensure that the transaction is considered as an indivisible operation, which can only execute entirely or, failing that, be canceled entirely.

Thus, in step 1, the old value of the data item D ₀ involved in the transaction and to be updated in the main nonvolatile memory MNV is written in the backup area S in order to save it, as well as that the associated system information I ₀ , including including its original address and the backup indicator in the active state.

In step 2, the entire block P1 of data comprising the data D ₀ to be updated is copied to the buffer zone B dedicated thereto;

In step 3, the block P1 is erased in the main memory and, in step 4, a new block P1 is reconstructed from the data of the block P1 previously stored in the buffer zone B and the new value of the updated data Di. The block P1 thus reconstructed with the updated datum D1 is then written in the main nonvolatile memory MNV at the corresponding address of the block P1, obtained from the system information _I0 stored in the backup area S;

In step 5, buffer zone B is erased. The previously described steps of the method are then repeated consecutively for the other data item D ₂ concerned by the transaction and to be updated at the same time as the data item D ₀ . Thus, in step 6, the old value of the data item D ₂ involved in the transaction and to be updated in the main nonvolatile memory MNV is written in the backup area S in order to save it, likewise the associated system information I ₂ , including in particular its original address and the backup indicator in the active state.

In step 7, the entire block P2 of data comprising the data D ₂ to be updated is copied to the buffer zone B dedicated for this purpose;

In step 8, the block P2 is erased in the main memory then, in step 9, a new block P2 is reconstructed from the data of the block P2 previously stored in the buffer zone B and the new value of the updated data D ₃ . The P2 block thus reconstructed with the updated data D ₃ is then written in the main nonvolatile memory MNV at the corresponding address of the block P2, obtained from the system information I ₂ saved in the backup area S;

In step 10, the buffer area B is erased. Finally, in a step 11, the backup indicators corresponding to the data saved D ₀ and D ₂ are deactivated if the progress of the update operation involved in the transaction has been normal from one end to the other. The data is updated one by one, however the individual data backup flags are not disabled immediately after each data update. On the contrary, it is expected that all data have been updated to do so, since all data form a whole, whose coherence must be preserved. Thus, if an interruption occurs during the process of updating the second data, while the first data has already been updated, it is possible to restore the initial state of both the first and the second data. given, since their backup flag is kept in the active state until the end of the process. These flags are disabled only if the update operation has been complete for all relevant data.

The following paragraphs discuss cases of abnormal termination of the update process and the restoration of old data to its original state before the update process began. The interruption is in practice a power failure, including inadvertent withdrawal of the card.

If the abnormal interrupt occurs while at least one backup flag is in the active state, it means that an update operation of data in the main memory has started. We do not know if the main memory contains the old data, or the new data, or an empty area resulting from the erasure of the entire block including the data before rewriting, hence the need to restore the memory in its state. initial state before the start of the update operation.

At each power-up of the card following an abnormal supply interruption, memory management means verify systematically the presence of backup indicators in the active state in the backup zone S of the card. If at least one backup flag is in the active state, the contents of the associated data field containing the old value of the data being updated is restored to the main non-volatile memory MNV. Then, the corresponding backup flag is disabled. The main memory is then in the state it had before the failed attempt to update.

The restoration of the data requires in fact the restoration in main memory of the complete block comprising the data. To do this, the step of restoring data in main memory consists first of recovering the starting address in the memory of the data block concerned by the data to be restored, from the system information saved with the old value of the data in the backup area S. In fact, this information includes the original address in the memory of the data, from which, knowing the predefined size of a block of the main memory, we can find the starting address of the concerned block.

Then, the process of restoring the data in main memory consists in reconstructing the block concerned as it was in its initial state, from the data of the block concerned which are copied in the buffer zone B and the old value of the data item to be restored which is saved in the backup area S. The restored block is then programmed into the main memory MNV at the retrieved address. The programming step in the memory of the restored block first comprises erasing the corresponding block of the memory and then writing the restored block into memory. However, one can end up in a situation where the buffer zone B is empty. This is for example the case if the interruption occurs between the previously described steps 5 and 6 where the buffer zone has already been erased. In this case, the restoration of the main memory in its initial state as before the update, can not be based on the buffer zone to reconstruct the concerned block of the main memory in its initial state.

However, it may be noted that during a data updating process, there is always a valid data block, corresponding to the data block concerned by the update, that is at its normal location in the database. main memory, either in the buffer zone. Also, if the buffer zone B is empty, it means that the block concerned is still at its normal location in the main memory. It is then expected that the step of rebuilding the block concerned by the data to be restored comprises beforehand the copying in the buffer zone B of the data of the block concerned, taken from the starting address of the block in question in the main memory. .

The main advantage of copying this block from the main memory to the persistent buffer zone, in order to restore the block to its initial state in the main memory, is to guard against a Abnormal power interruption occurring during the restoration process itself. Indeed, the restoration process involves, when the restored block is programmed in main memory, to delete the concerned block in main memory before writing the restored block. However, an abnormal interruption during the programming step of the restored block will not compromise the integrity of the data, the latter being saved in the non-volatile memory buffer zone.

Claims

A method for updating at least one datum (D ₀ ) in a predefined fixed size fixed memory block erasable non-volatile main memory (MNV), comprising: a- saving (1) in a memory area saving (S) the old value of the data (D ₀ ); b- save in the backup area (S) together with the old value of the data the system information related to the data item to be updated, comprising at least one active backup indicator (I ₀ ) indicating that a data has just been saved and a data modification is in progress; said method being characterized in that it further comprises the steps of: c- copying (2) the entire block (P) concerned by the data item to be updated in a buffer zone (B) of non-volatile memory of size corresponding to at least the predefined fixed block size of the main memory, said buffer zone being distinct from the backup area (S); d- erasing (3) the main nonvolatile memory (MNV) the block (P) concerned by the data item to be updated; e- reconstruct (4) the block (P) from the data of the block copied in the buffer zone (B) and the new value of the data item to be updated and write said block (P) with the updated data item (D1) in the main nonvolatile memory (MNV); f- disable (6) the indicator of the backup area if the update operation was successful.

2. The method of claim 1, wherein the update involves a plurality of data (D ₀ , D ₂ ) of the main nonvolatile memory (MNV) involved in carrying out a transaction, said transaction data does not not to be updated separately, characterized in that it consists in repeating consecutively stages a- to e- of the process for each data item concerned by the transaction.

3. Method according to claims 2, characterized in that the old data values (D ₀ , D ₂ ) and the associated system information (I ₀ , I ₂ ) corresponding to each data item of the transaction, are saved in the same memory sector of the backup area (S).

4. Method according to claims 2 or 3, characterized in that step f- is implemented if the updating operation of the plurality of data has been carried out correctly, and consists in deactivating the backup indicators. previously saved in the save zone respectively for each data update.

5. Method according to any one of the preceding claims, characterized in that the step f- implemented is replaced by a step of erasing the contents of the backup area (S).

6. Method according to any one of the preceding claims, characterized in that the size of the buffer zone (B) is a multiple N, N being greater than or equal to 1, the predefined block size for the main non-volatile memory. .

7. Method according to any one of the preceding claims, characterized in that after an interruption of supply of the memory involved during a memory update operation, the following steps are implemented consisting of: :

- checking the presence of at least one backup indicator in the active state in the backup area (S);

- if at least one backup flag is in the active state, restore in the main non-volatile memory (MNV) the old value of each of the data saved in the backup area whose associated backup flag is at the same time. state, and then disable the corresponding backup flag.

8. Method according to claim 7, characterized in that the step of restoring a datum in memory (MNV) consists of: recovering the starting address in the main memory (MNV) of the data block concerned by the data to be restored, from the system information saved with the old value of the data in the backup zone (S), said information including the original address in the main memory of the data; reconstructing the block concerned as it was in its initial state, from the data of the concerned block copied in the buffer zone (B) and from the old value of the data to be restored saved in the backup zone (S); program the restored block into the memory (MNV) at the retrieved address.

9. Method according to claim 8, characterized in that if the buffer zone (B) is empty, the step of rebuilding the block concerned by the data item to be restored comprises, beforehand, copying in the buffer zone data of the block concerned, to from the previously recovered starting address of the block in the main nonvolatile memory (MNV).

10. The method of claim 8 or 9, characterized in that the programming step in the memory of the restored block comprises first erasing the corresponding block of the memory and then writing the restored block in memory.

11. Method according to any one of the preceding claims, characterized in that the Main nonvolatile memory (MNV) includes high capacity and large granularity characteristics and the buffer zone (B) includes characteristics of low capacity and fine granularity.

12. Portable digital apparatus comprising a microprocessor, a main non-volatile memory

Fixed value memory block (MNV) and a backup area (S) of the data of the main non-volatile memory during a data updating process, characterized in that it comprises a buffer zone (B) nonvolatile memory, of size corresponding to at least the predefined fixed block size of the main memory, and memory management means adapted to control the progress of the data update operations in memory according to the method according to any one of the preceding claims.

Portable digital apparatus according to claim 12, characterized in that the main nonvolatile memory (MNV) comprises characteristics of high capacity and large granularity and the buffer zone (B) comprises characteristics of low capacity and fine granularity.

14. Apparatus according to claim 12 or 13, characterized in that the main nonvolatile memory (MNV) is a flash memory.

15. Apparatus according to any one of claims 12 to 14, characterized in that it is a smart card.