EP1495472A1

EP1495472A1 - Method for modification of data on a memory card on a transaction

Info

Publication number: EP1495472A1
Application number: EP03740616A
Authority: EP
Inventors: Eric Gerbault
Original assignee: ASK SA
Current assignee: ASK SA
Priority date: 2002-04-16
Filing date: 2003-04-15
Publication date: 2005-01-12
Also published as: KR20040096762A; WO2003088262A1; FR2838536A1; TW200307201A; FR2838536B1; HK1069668A1; KR100977640B1; MXPA03011636A; AU2003262197A1; CA2452672A1; BR0304525A; US20050071539A1; CN1533575B; CN1533575A; JP2005524133A; US7146472B2; JP4211890B2; TWI291617B; IL159335A0

Abstract

The invention relates to a method for modification of data in a card transaction system, comprising a memory card and a reader for reading the card. The card comprises a first memory (RAM) and a second memory (EEPROM) with locations occupied by data recordings. Each transaction involves the modification of at least one of the data locations or the addition of a new recording. The method comprises the following steps a) read (17) the address of a free location from a previous control register located in a first fixed location in the EEPROM memory, b) write (18) the new modified recording or addition in the free location, repeat steps a) and b) for each new recording to be modified or added and write (22) in a second fixed location in the EEPROM memory a new control register containing the addresses of free locations within the EEPROM memory to use in the next transaction.

Description

Method for modifying data on a memory card during a transaction

Technical Field The present invention relates to systems in which part of the data records stored in the card is modified during a transaction carried out with a card reader and more particularly relates to a method for modifying the data of a memory card. during a transaction with a reader.

State of the art

Memory cards, also called smart cards, are increasingly used as a data carrier associated with card holders. Among these cards, contactless cards for which information is exchanged by remote electromagnetic coupling between an antenna housed in the card and an associated reader have been developed as means of access to controlled access areas, means of identifying people or electronic purses.

The memory containing the data in a smart card is generally a non-volatile, erasable and rewritable memory and preferably of the EEPROM type. This type of memory is divided into a plurality of locations containing data records of a determined length, for example 32 bytes.

During a transaction, several records contained in the card memory must generally be modified to adapt to the new conditions resulting from the transaction. Unfortunately, the memory, and in particular when it is an EEPROM memory, requires a relatively long erase / write time (for example 5 ms), during which a possible power cut runs the risk of losing the data contained in the record.

In addition, the various operations of the transaction during which several data records are modified operate in all or nothing mode. For reasons of transaction security, it is indeed essential to start the entire transaction again if a power outage occurs during the course of the transaction, on pain of irreparably losing sensitive data (for example the credit balance an electronic wallet) if it is not possible to start from the beginning of the transaction.

In order to provide an answer to the problem stated above, thought has been given to storing the recording of data in a buffer memory before proceeding with its modification. When all the changes have been made to the records to be changed, the old records are deleted from the buffer.

Unfortunately, this method requires for each recording a backup operation in the buffer zone, an operation to erase the recording to be modified, a rewriting operation and an operation to erase the old recording in the buffer zone. , or 4 operations per record. When the transaction includes many operations, for example 8 operations as may be the case, the transaction may take a long time incompatible with the time taken by the gesture of the card holder presenting it to the reader. In addition, this method has the major drawback that the records of the data zone are always in the same locations and that the buffer zone occupies a fixed place in the memory, this increases the "stress" of the memory and limits the number transactions that can be performed as long as the number of transactions for each location is limited to a given value guaranteed by the silicon manufacturer.

Another problem which is added to those mentioned above, concerns the designation of the free sectors where to place the modified records. The classic method is to scan the memory to find a free sector. This operation takes time which is added to the time necessary for the recording and erasing operations already mentioned. But this time becomes very important and incompatible with the transaction time when there are several records to modify and therefore several searches for free sectors.

Disclosure of the invention This is why the object of the invention is to carry out a method of modifying data of a memory card during a transaction which allows synchronization in all or nothing mode of the modifications to be carried out during of the transaction, this for a short period of time compatible with the access time limited to the card during the transaction, while avoiding the use of a part of the memory as a buffer memory for saving the data and therefore in avoiding memory “stress” due to writing data always in the same memory areas. The invention therefore relates to a method for modifying data in a card transaction system comprising a memory card and a reader capable of reading the card when the latter is in a determined position relative to the reader. The card comprises a first memory (RAM) and a second non-volatile, erasable and rewritable memory (EEPROM), the latter comprising locations occupied by data records in relation to the transactions carried out by the card, each transaction resulting in the modification of at least one of the data locations or the addition of a new record.

The method according to the invention comprises the following steps: a) for a data record to be modified or a record to be added, read from a previous control register located at a first determined location in the second memory the address of a free place in the second memory, b) write the new modified or added record in the free place, c) repeat steps a) and b) for each of the new records to be modified or added, d) write in a second place determined from the second memory a new control register containing the addresses of the free locations of the second memory to be used in the next transaction.

Brief description of the drawings The objects, objects and characteristics of the invention will appear more clearly on reading the following description made with reference to the single figure representing a flow diagram of the method according to the invention.

Detailed description of the invention

In the description which follows, it has been assumed that the smart card used for the transaction comprises an EEPROM memory divided into identical sectors, for example of 32 bytes. An essential characteristic of the invention is the use of a control register occupying one of the sectors of the memory. This control register contains data intended to be used to carry out the transaction, including the identification of the free sectors of the memory that can be used to record there new data. The control register contains in particular the following fields:

FlagOpen: indicates whether a transaction is open or not,

- OldSect: indicates the sector numbers before their modification,

PrevReg: indicates the sector number where the previous control register was located. NextReg: indicates the sector number where the following control register will be written, - FlagClose: indicates whether the transaction is closed or not,

NewSect: indicates the numbers of the free sectors for further modifications,

Assuming that a transaction is carried out, the method according to the invention takes place according to the flowchart illustrated in FIG. 1. There is first of all an initialization step (step 10) consisting in initializing 4 variables in the Card RAM memory:

- Control register address: sector number in which the control register is located, - NbUpdates: variable incremented after each modification of a record or addition of a new record. TransactionLevel: bit indicating that the transaction is in progress,

OldSector: indicates the sector numbers where data is recorded during the transaction.

The second step is the opening step of the transaction (step 12) during which the bit

TransactionLevel of the RAM memory went from 0 to 1 and the FlagOpen field of the control register which was 0 is set to the hexadecimal value A5.

In the next step, it is determined whether there is a record to modify or to add to a memory location (step 14). If this is the case, the old sector number is written in RAM memory (step 16), the address of the sector in which the new record must be written is read in the control register (step 17), the new record is written in a sector identified by a number read in the control register (step 18), and the modifications of the control data in RAM memory (step 20). The process then loops back to determine if there is still a record to modify or add (step 14). Note that the advantage of the invention lies mainly in the fact that a transaction almost always requires modifying several records, which allows the use of the control register without loss of time since the free sectors are indicated in the register without the need to search for them.

It should be noted that, when it is a question of adding a record and not a modification, there is no memorization of a sector number in RAM memory since this sector does not exist , but storing a virtual number 0.

When there is no more record to write in memory, a new control register containing new data is written in a free sector whose number is provided by the old control register (step 18), the old control register is erased (step 20), the old sectors containing records which have given rise to modification are erased (step 22) and the control variables of the RAM memory are reset to zero (step 24).

In order to illustrate the method of the invention, the following example can be considered in which the EEPROM memory is presented as follows before the transaction: Content Sector

1 record # 1

2 record # 2

3 record # 3

4 record # 4

5 control register

6 free, new control register

7 free, candidate modification # 1

8 free, candidate modification # 2

9 free, candidate modification # 3

10 free, candidate modification # 4

11 free, candidate modification # 5

12 free, candidate modification # 6

13 free, candidate modification # 7

14 free, candidate modification # 8

The control register in sector 5 contains the following data:

FlagOpen 00

OldSect 0, 0, 0, 0, 0, 0, 0, 0, 0

PrevReg 0

NextReg 6

FlagClose A5

NewSect: 7, 8, 9, 10, 11, 12, 13, 14 Assuming that the transaction is made up of four consecutive changes:

- modification of record 2

- modification of the recording 3 addition of the recording 5 second modification of the recording 2

After the initialization step, the process steps are as follows: - Opening of the transaction: writing of the FlagOpen field to A5 in hexadecimal in the current register and initialization of the variables: NbUpdates = 0> TransactionLevel = 1

> 01dSect [8] = {0,0,0,0,0,0,0,0,0}

- Modification of record # 2: memorize the old sector # 2 in RAM, write the new record in sector # 7, the RAM variables are:> NbUpdates = 1 TransactionLevel = 1

> 01dSect [8] = {2,0,0,0,0,0,0,0,0}

- Modification of record # 3: memorize the old sector # 3 in RAM, write the new record to sector # 8. The RAM variables are:

> NbUpdates = 2 TransactionLevel = 1

> 01dSect [8] = {2,3,0,0,0,0,0,0,0}

- Addition of the record # 5: memorize the old sector # 0 in RAM (0 means the old absent sector), write the new record to sector # 9. RAM variables are,

> NbUpdates = 3

> ^• TransactionLevel = 1

> 01dSect [8] = {2,3,0,0,0,0,0,0,0} - Modification of record # 2: memorize the old sector # 7 in RAM, write the new record to the sector # 10. RAM variables are,

> NbUpdates = 4

> TransactionLevel = 1> 01dSect [8] = {2,3,0,7,0,0,0,0,0}

- Closing of the transaction:

> decrement TransactionLevel

> write the new register to sector # 6 with FlagClose = 0 > delete the old control register

> delete old sectors # 2, # 3, # 7

> write FlagClose to $ A5

> initialize:

"NbUpdates = 0 'TransactionLevel = 0 ¹ OldSect [8] = {x, x, x, x, x, x, x, x, x} The EEPROM memory is presented as follows after the transaction:

The new control register contains the following data:

- FlagOpen: 00

- OldSect: 2, 3, 0, 7, 0, 0, 0, 0 - PrevReg: 5

- NextReg: 11

- FlagClose: A5

- Ne Sect: 12, 13, 14, 15, 16, 17

It can therefore be seen that the new control register contains the identification of the old sectors whose values were supplied by the RAM memory, the identification of the sector where the old control register was located, the identification of the sector in which the put the next control register, the numbers of the free sectors where the next modifications should be written, and the indication (FlagClose) that the transaction has been closed.

If a power failure occurs during the modifications made to the EEPROM memory, the contents of the RAM memory are lost, but the state of the data makes it possible to start from scratch by carrying out the whole transaction again without fear of having lost sensitive data. Indeed, it suffices to erase all the sectors which have been likely to be written using new data, either by erasing all the sectors marked “free” in the control register, or by erasing only those which have have been written after scanning their content to check if they have been written (otherwise they contain zeros).

Note that if the power cut occurs during the closing of the transaction, having set the value 0 in the FlagClose field of the new control register lets you know that the transaction is not closed and that we must consider the content of the old sectors which are not erased until the penultimate operation, the last operation being the writing of FlagClose indicating the closing of the transaction.

The method according to the invention saves cycles if it is compared to the method calling for saving in a buffer memory. In fact, in the conventional method, 4 EEPROM operations are required for each modification of data: writing to the buffer memory area, erasing the future location, writing new data to this location and erasing the location of the area. buffer. To this must be added the management of the buffer memory and the management of information relating to the data to be stored.

On the other hand, the method according to the invention requires only 2 EEPROM operations for each modification, namely writing new data in a new sector and erasing the old sector, as well as 4 general operations, namely, writing FlagOpen to the control register at the start, erasing the old control register, writing the new control register and writing FlagClose to the control register.

Thus, for N modifications, the following comparison table can be established giving the number of EEPROM operations in the conventional method and in the method according to the invention, as well as the gain achieved.

If a write or erase operation in the EEPROM memory lasts 5 ms, the gain achieved with a minimum number of 4 operations is 30 ms.

In addition, to this time saving, it is necessary to add the time saving resulting from the fact that it is not necessary to scan the EEPROM memory to find 4 free sectors since the numbers of the free sectors are indicated in the control register. .

Claims

1. Method for modifying data in a card transaction system comprising a memory card and a reader capable of reading said card when the latter is in a determined position relative to the reader, said card comprising a first random access memory and a second non-volatile, erasable and rewritable memory, the latter comprising locations occupied by data records in relation to the transactions carried out by said card, each transaction involving the modification of at least one of said data locations or the adding a new record, said process being characterized by the following steps: a. for a data record to be modified or a record to be added, read (17) in a previous control register located at a first determined location in said second memory the address of a free location in said second memory, b. write (18) the new modified or added record in said free space, c. repeat steps a) and b) for each of the new records to be changed or added, and d. write (22) in a second determined location of said second memory a new control register containing the addresses of the free locations of said second memory to be used in the next transaction.

2. Method according to claim 1, further comprising the following step carried out prior to step a), i) write (16) the number of the location in which the record to be modified or added is located in said first random access memory.

3. The method of claim 2, wherein said location number written in said first random access memory is a virtual number when the operation to be performed concerns a record to be added.

4. Method according to claim 1, 2 or 3, in which two variables are recorded in memory at the initialization of the transaction, a first variable (NbUpdates) being set to zero so as to be incremented with each operation of modification or d 'addition of a record and a second variable (TransactionLevel) being set to zero so as to be modified from 0 to 1 when the transaction is in progress.

5. Method according to one of claims 1 to 4, wherein the locations containing the records which have been modified or added are deleted (26) at the close of the transaction.

6. The method of claim 5, wherein said first determined location containing the previous control register is erased at the end of the transaction (24).

7. The method of claim 6, wherein the numbers of said locations containing the records which have been modified or added are written in said new control register from said first random access memory at the close of the transaction.

8. The method of claim 7, wherein said variables of said first random access memory are reset to zero at the end of the transaction (28).

9. The method as claimed in claim 8, in which a field (FlagClose) of said new control register is set to zero before said previous control register and said records which have been modified or added are erased and set to another value (A5 ) after these operations have been carried out.

10. System comprising means suitable for implementing the steps of the method according to one of claims 1 to 9.