EP1344137A1

EP1344137A1 - Method and device for making secure data processing

Info

Publication number: EP1344137A1
Application number: EP01996790A
Authority: EP
Inventors: Olivier Benoit
Original assignee: Gemplus Card International SA; Gemplus SA
Current assignee: Thales DIS France SA
Priority date: 2000-11-16
Filing date: 2001-11-15
Publication date: 2003-09-17
Also published as: AU2002220786A1; US8006058B2; CA2326036A1; WO2002041151A1; US20110307650A1; US20040093306A1; CN1484791A

Abstract

The invention concerns a device for making secure electronic devices against attacks (for example lateral path attacks) during the processing of sensitive and/or confidential data by a central processing unit (CPU) to a volatile storage (for example the RAM) of an electronic device such as, for example, a smart card, a PDA or a cellular telephone. The method consists in storing confidential data to a storage site dynamically and randomly allocated, thereby making analysis more difficult and, consequently, attacks (for example lateral path attacks).

Description

METHOD AND DEVICE FOR SECURING A DATA PROCESSING

Field of the Invention The present invention relates to electronic devices. More particularly, the present invention relates to a method for securing an internal processing of electronic devices.

The present invention relates to electronic devices. More particularly, the present invention relates to a method for securing an internal processing of electronic devices. Technological background of the invention

Chip cards, as a particular embodiment of electronic devices, were originally designed to improve the security of distributed systems. Smart card applications include, for example, phone cards, identification cards, medical cards, transaction cards (debit / credit bank cards, department store or restaurant loyalty cards, etc.) and security cards. All of these applications require that certain sensitive and confidential data be processed inside the smart card.

As can be seen in Figure 1, which is entitled "Prior Art", an electronic device 10 traditionally includes a Central Processing Unit (CPU) 12, which is the main processor / controller of the electronic device 10. The CPU 12 can optionally include a large number of internal registers 13, such as, for example, in reduced instruction set computers (RISC).

The electronic device 10 also includes a volatile memory in the form of a RAM

(RAM) 14, Read only memory (ROM) 16, Read only memory

Electrically Erasable (EEPROM) 18, and optionally, a Cache 15, which are all coupled to the CPU 12. To better understand the following description, the term "volatile memory" used below can include RAM, Internal Registers and / or the Cache. An input / output (I / O) device, such as a terminal 20, allows a smart card 10 to share data with a distributed system (not shown), by controlling the inputs / outputs to and from the electronic device 10 , via the CPU 12. The smart card 10 includes an I / O port (not shown) making it possible to transfer the data to and from the I / O device 20.

The CPU 12 processes instructions for managing the data stored in the electronic device and includes a program which provides protection against access to sensitive and / or confidential data contained and processed in the smart card 10 by unauthorized entities, such as , for example, hackers. In fact, in many examples, sensitive information and / or confidential contained or treated in the device have an important value (financial or other) for their holder.

It was discovered that certain breaches remained gaping, in terms of data protection, against different attacks such as "lateral attacks" which include, for example "Analysis of

Power "and" Radiofrequency Analysis ".

The power analysis is based on the measurement of the power consumption during the processing of confidential information encoded in binary in a smart card. RF analysis consists of intercepting and analyzing the radio frequency emitted during the transfer of confidential data. These two types of attack use either the variation in energy consumption or the variation in RF radiation emitted during the processing of confidential data. Knowing one of these variations allows mathematically to recover confidential data.

In fact, conventional secure programs used in electronic devices include means for temporarily storing confidential data in volatile memory, in a given, predetermined location in memory, since it has been found to be preferable to for execution, to work with fixed memory locations. Therefore, only confidential data can change in the storage and reading process since the memory location do not change. In these cases, when the CPU processes confidential data, for example, when confidential data is transferred from the CPU to volatile memory, hackers may attempt to retrieve confidential data, using "side scan" attacks Or similar attack.

The conventional algorithms used to allocate memory in the device 10, such as Dynamic Memory Management (DMM), are not sufficient to effectively protect against confidential data processed therein. In fact the classic DMM algorithms are predictable, since they follow classic rules. Therefore, if a given method is executed twice and under the same conditions, the same memory allocation should be expected. FIG. 2 which is entitled "prior art" illustrates a dedicated area 19 in which the confidential data 21, of size k, are stored.

Summary of the invention

According to the present invention, there is provided a method for securing the storage of data in a volatile memory of an electronic device, this method comprising the following steps: definition of a dedicated area in the volatile memory; the length of the dedicated area being at least equal to the length of the data which must be stored; definition, at random, of an offset from the start of the dedicated area; and transferring the data to the area dedicated to the data at a location in the memory determined by the offset; which allows the data to be transferred to a random location in the memory in the dedicated area.

According to another aspect of the present invention, there is provided a device for securing the storage of data in a volatile memory of an electronic device, comprising: means making it possible to define a dedicated area in the volatile memory; the length of the dedicated area being at least equal to the length of the data which must be stored; means making it possible to define, at random, an offset from the start of the dedicated area; and means for transferring the data to the dedicated area for the data, in a memory location determined by the offset; which allows the data to be transferred to a randomly determined memory location in the dedicated area.

According to yet another aspect of the present invention, there is also proposed a secure electronic device making it possible to process data received from an input / output device, this device comprising: an Electrically Erasable Read Only Memory (EEPROM) making it possible to receive the data from the input / output device; an input / output port for transferring data between the input / output device and the EEPROM; a volatile memory making it possible to transfer the data during the processing; volatile memory including a dedicated area; the length of the dedicated area being at least equal to the length of the data to be transferred; and a data processing CPU comprising means for determining a random offset and data transfer means responsive to the random offset and interposed between the data and a memory location of the dedicated area determined by the offset.

Other objects, advantages and features of the present invention will become more apparent from the reading of the following, non-restrictive description of its preferred embodiments, given by way of examples only, with reference to the accompanying drawings. Brief description of the drawings

In the accompanying drawings: FIG. 1, which is entitled "prior art", is a block diagram illustrating the main elements of an electronic device; Figure 2, which is entitled "prior art", is a schematic illustration of a dedicated area, in volatile memory, as managed by conventional electronic devices of the prior art; Figure 3 is a schematic illustration of a dedicated area in which confidential data has been stored, according to a first embodiment of the present invention; Figure 4 is a flow chart of a method for randomly allocating a volatile memory area according to a first embodiment of the present invention; Figure 5 is a schematic illustration of a RAM buffer, in which confidential data has been stored, according to a second embodiment of the present invention; and Figure 6 is a flowchart of a method for randomly allocating memory according to a second embodiment of the present invention. Description of the preferred embodiment

Briefly, the present innovation consists of a method for securing the processing of data from an electronic device using a random memory location for the storage of confidential data.

In this way, the method according to the present invention prevents the recovery of confidential data by means, for example, of a side channel signal analysis during the processing of confidential data therein.

The method of the invention also makes the lateral analysis during the secret processing more complex by adding an unknown parameter, that is to say, a random memory location, in a data area provided in the memory. volatile electronic device. This process can be carried out inside an electronic device 10, using, for example, digital software. A first embodiment of the method of the present invention will now be described with reference to FIGS. 3 and 4.

As can be seen in FIG. 3, the first embodiment of the method of the present invention involves a dedicated area in a volatile memory 22 having a length (2k) which is greater than the length (k) of the confidential data 24 which should be stored in it. Note that since the confidential data 24 is usually of a known predetermined length, the length of the dedicated zone 22 can also be predetermined. In the example, given by way of illustration, in FIG. 3, the length of the dedicated area 22 has been selected as being twice the length of the confidential data 24.

As can be seen in FIG. 3, the confidential data 24 are not necessarily stored at the start of the dedicated area 22, but start at a random memory location inside the dedicated area 22 which is determined by a offset value 26.

Thus, during the processing of confidential data, the address to which confidential data is stored or transferred will be different at each execution, which makes the so-called lateral analysis more complex.

If we now briefly consider Figure 4 of the accompanying drawings, the memory allocation method according to the first embodiment of the present invention will be described.

The first step 28 consists in defining a dedicated area 22 in a volatile memory 14 of the electronic device 10. One can refer to such a dedicated area 22 in a volatile memory 14 as being a RAM buffer. The dedicated area 22 has a predetermined length (in the present example, 2k).

In the second step 30, a random offset value 26 is defined for the address for storing the confidential data 24 inside the dedicated area 22. As described above, the data confidential 24 are stored in volatile memory 14 at the storage address defined by the starting address 23 of the dedicated area 22 plus the offset 26. It should be noted that, since all of the confidential data 24 must be stored in the dedicated area 22, the random offset 26 must be chosen randomly so as to prevent confidential data 24 from going beyond the dedicated area 22. This can be obtained by selecting a random number between zero and the difference between the length of the dedicated area 22 and the length of confidential data 24 minus 1.

In the example of Figures 3 and 4, since the length of confidential data 24 is k, and the length of dedicated area 22 is 2k, the offset 26 must not be greater than the value k-1 (2k-kl) to prevent memory overflow.

In step 32, the confidential data 24 are transferred from the non-volatile memory 18 to the address defined by the starting address 23 of the dedicated area 22 in the volatile memory 14 plus the offset 26. The expression transferred aims, in this case, to include storage, access or any other operation carried out on confidential data 24.

As will be readily understood by those skilled in the art, since the location of the confidential data 24 is known to the CPU, the confidential data 24 can then be processed or can access it directly from their location in the dedicated zone 22 in the volatile memory 14.

Consequently, each execution of the method transfers the confidential data 24 to a random memory location in the dedicated area 22, even if the method is repeated several times under the same conditions. Thus, a lateral analysis must take into account two unknown parameters: the value of confidential data 24 and their address. This kind of analysis becomes much more difficult to perform since it requires that we find two equations or relations which link the side channel signal and the parameters.

In other words, the data 24 is transferred to a randomly determined memory location, in the dedicated data area 22, which makes analysis, and consequently attacks, more difficult (for example, lateral attacks). As will be readily understood by those skilled in the art, depending on the length of the volatile memory 14 of the electronic device 10, the dedicated area 22 defining step 28 can be omitted, for example, in the case of the management of the static memory when 'A dedicated area is defined during the compilation / linking of the program.

A second embodiment of the method of the present invention will now be described with reference to FIGS. 5 and 6. The main distinction between the first and second embodiments lies in the approach used to store confidential data in the dedicated area. In this case, the dedicated area 100 has the same length as the confidential data 102 which must be stored there.

In fact, it has been discovered that, instead of providing a dedicated area larger than the data to be stored there, it is possible to provide a dedicated area of the same length and to loop confidential data 102, when the end of dedicated area 100 is reached. In this way, it is possible to provide the improved security of the present invention while optimizing the use of the limited amount of volatile memory provided, generally, in electronic devices (e.g., smart cards).

More specifically, as shown in FIG. 5, and for purposes of illustration, each confidential data bit 102 has been illustrated separately, with its position in a memory location 104, 105, 106 and 110 in the dedicated area 100 represented in square brackets for example CD [0] for the first bit of confidential data 102 and CD [k-1] for the last. Confidential data 102 is stored in dedicated area 100 starting at a memory location 105 determined by the start of dedicated area 22 and by random shift 108. However, confidential data 102 is looped until the start 106 of the dedicated area 100 once the end 110 of the dedicated zone 100 has been reached. Consequently, depending on the value of the offset 108, each bit of the confidential data 102 can take any memory location in the dedicated area 100. FIG. 6 summarizes the method according to this second embodiment.

In step 112, a dedicated area 100 (RAM buffer) is defined in the volatile memory 14. The length of the dedicated area is advantageously the same as the length of the confidential data.

In step 114, a random offset 108 is defined for the address for storing the confidential data 102. Again, the value of the offset is between zero (0) and k-1. In step 116, the first part of the confidential data 102 is transferred to the dedicated zone 100 at the address defined by the offset 108. The length of the first part of the confidential data 102 corresponds to the difference between the length of the zone dedicated and the offset 108.

In step 118, the last part of the confidential data 102 is transferred to the start of the dedicated area 100.

Consequently, the obvious advantage of this second embodiment is the optimization of the volatile memory 14.

Again, since the location of the confidential data is known by the CPU 12, the confidential data 102 can be processed or can be accessed directly from their location in the dedicated area 100.

It should be noted that, although the two embodiments of the method of the present invention described above have been presented as safe and independent methods against attacks (for example, sideways attacks) for card technology. chip, they can be advantageously combined with other conventional security features of smart cards.

It is also part of the present invention to combine the two embodiments into a method in which the dedicated area is longer than the confidential data which must be stored therein and in which the confidential data is looped at the start of the dedicated area if the end of the dedicated area was reached. This allows you to choose the offset randomly throughout the dedicated area. As will be readily understood by those skilled in the art, although the present invention has been described above as being advantageous when confidential data is transferred from the CPU to the volatile memory of a smart card, the term "transfer" should be interpreted as including the direct generation of confidential data in volatile memory by the CPU and not simply as being the transfer from it. Likewise, the present invention is also advantageous when confidential data is transferred from the non-volatile memory to the volatile memory of the electronic device.

Optionally, the offset value can be chosen, at random, at the start of a session instead of being chosen at the start of each storage operation.

As will be apparent to those skilled in the art, the nature of the electronic device is not limited to smart cards as described above. In fact, the method of the present invention could be advantageously implemented in other types of electronic devices such as, for example, Personal Digital Assistants (PDAs and cell phones. Although the present invention has been described below) above by means of its preferred embodiments, it can be modified without departing from the spirit and nature of the invention in question, as defined in the appended claims.

Claims

1. Method for securing the storage of data in a volatile memory of an electronic device, this method comprising the following steps: definition of a dedicated area in the volatile memory; the length of the dedicated area being at least equal to the length of the data which must be stored; definition, at random, of an offset from the start of the dedicated area; and transferring the data to the area dedicated to the data at a location in the memory determined by the offset; which allows the data to be transferred to a random location in the memory in the dedicated area.

2. Method according to claim 1, in which the definition of a dedicated area comprises the selection of the length of the dedicated area greater than the length of the data which must be transferred there.

3. Method according to claim 2, in which the definition, at random, of an offset comprises the prevention, for the transferred data, of going beyond the dedicated area.

4. The method as claimed in claim 3, in which the prevention, for the transferred data, of going beyond the dedicated area comprises the selection, as offset, of a number between zero and the difference between the length of the dedicated area and the length of confidential data minus one.

5. Method according to claim 1, in which the definition of a dedicated area comprises the selection of the length of the dedicated area equal to the length of the data which must be transferred there.

6. The method as claimed in claim 5, in which the transfer of the data comprises the transfer of a first part of the data into a memory location in the dedicated area defined by the offset and the transfer of a second part of the data into a location. memory corresponding to the start of the dedicated area; the length of said first part corresponding to the difference between the end of the dedicated area and the offset.

7. A device for securing the storage of data in a volatile memory of an electronic device, comprising: means making it possible to define a dedicated area in the volatile memory; the length of the dedicated area being at least equal to the length of the data which must be stored; means making it possible to define, at random, an offset from the start of the dedicated area; and means for transferring the data to the dedicated area for the data, in a memory location determined by the offset; which allows the data to be transferred to a randomly determined memory location in the dedicated area.

8. Device according to claim 7, in which the length of the dedicated area is greater than the length of the data which must be stored there.

9. Device according to claim 7, in which the means making it possible to define, in a random manner, an offset comprises means making it possible to prevent the transferred data from going beyond the dedicated area.

10. Device according to claim 9, in which the means making it possible to prevent the transferred data from going beyond the dedicated area comprises means making it possible to choose, as an offset, a number between zero and the difference between the length of the dedicated area and the length of confidential data minus one.

11. Device according to claim 7, in which the means making it possible to define a dedicated area comprises means making it possible to choose the length of the dedicated area equal to the length of the data which must be stored there.

12. Device according to claim 11, in which the means making it possible to transfer the data comprises means making it possible to store a first part of the data in a memory location in the dedicated area defined by the offset and means making it possible to store a second part data in a memory location corresponding to the start of the dedicated area; the length of said first part corresponding to the difference between the end of the dedicated area and the offset.

13. Secure electronic device for processing data received from an input / output device, this device comprising: an electrically erasable read only memory

(EEPROM) for receiving data from the input / output device; an input / output port for transferring data between the input / output device and

1 EEPROM; a volatile memory making it possible to transfer the data during the processing; volatile memory including a dedicated area; the length of the dedicated area being at least equal to the length of the data to be transferred; and a data processing CPU comprising means for determining a random offset and data transfer means responsive to the random offset and interposed between the data and a memory location of the dedicated area determined by the offset.

14. Device according to claim 13, in which said volatile memory is chosen from the group consisting of random access memory (RAM), internal register and cache memory.

15. Device according to claim 13, in which the electronic device is chosen from group consisting of a smart card, a Personal Digital Assistant (PDA), and a cell phone.

16. Method for securing the storage of data in a volatile memory of an electronic device, this method comprising the following steps: definition, at random, of an offset from the start of the dedicated area; transferring data in volatile memory to a memory location determined by the offset; which allows the data to be transferred to a random location in the volatile memory.