JP5724387B2 - Portable device and dynamic data storage position changing method - Google Patents

Description

  The present invention relates to a technique for improving tamper resistance against a laser attack, which is one of attack methods for a portable device such as an IC card.

  In recent years, many researches have been conducted on attack methods for portable devices that store confidential data (for example, encryption keys) such as IC cards used for financial purposes.

  The DPA attack (Differential Power Analysis) in which the secret key of the DES stored in the portable device is decrypted by observing the power consumption is famous as an attack method for the portable device. In addition to attacks, attacks other than DPA attacks include laser attacks in which an IC chip mounted on a portable device is irradiated with a laser to cause a malfunction in the IC chip, and secret data is decrypted based on this malfunction.

  In a laser attack, it is necessary to identify a memory cell that causes a malfunction that becomes the basis for decryption of confidential data by irradiating the laser, and it is necessary to irradiate the specified memory cell with a laser. However, laser attack is theoretically possible but less effective, and it was thought that countermeasures against laser attack were unnecessary. With the development of small lasers and improved laser irradiation accuracy, in particular, in the field of IC cards, countermeasures against laser attacks have become necessary.

  An invention for improving tamper resistance against laser attack has already been disclosed. As a technique for improving tamper resistance against laser attack, a method of detecting a change in data using an error code (for example, Patent Document 1), light irradiation A technique for detecting laser irradiation using a detectable sensor circuit (for example, Patent Document 2) is disclosed.

  However, these inventions are designed to detect that the laser has been irradiated, and are designed to prevent the identification of a memory cell in which a malfunction that becomes a starting point for decrypting confidential data occurs. Absent.

Japanese Patent Laid-Open No. 2005-45760 JP 2010-279003 A

  Therefore, an object of the present invention is to provide a portable device in which it is difficult to specify a memory cell in which a malfunction that becomes a foothold for decryption of confidential data occurs in order to improve tamper resistance against a laser attack.

According to a first aspect of the present invention for solving the above-described problem, a relative position based on an offset value is described in an operand of a program code that uses dynamic data generated after a computer program operates, and the dynamic data As the physical address for storing the dynamic data, the offset value and the relative position within a predetermined range generated using a random number at the time of activation are set to the start address of the work area set in the memory for storing the dynamic data. The portable device is configured such that a physical address for storing the dynamic data is changed by a random number using the added value.

  In the first invention, the portable device means a device mounted with a semiconductor integrated circuit (IC chip) and used in a system that requires high security. Specifically, an IC card, USIM or USB is used. Means a key.

Furthermore, a second invention for solving the above-described problem is a method for changing a storage position of dynamic data, and when a mobile terminal is activated, a step of generating an offset value within a predetermined range using a random number; As the physical address for storing dynamic data generated after the computer program operates, the mobile terminal sets the dynamic data to the start address of the work area set in the memory for storing the dynamic data. It looks including the step of using a value obtained by adding the relative position and the offset value described in the program code of the operands to be used, wherein the physical address for storing the dynamic data is to be changed by a random number, This is a method for changing the storage position of dynamic data.

  According to the present invention described above, the value obtained by adding the offset value and the relative position to the start address of the work area set in the memory for storing the dynamic data is used as the physical address for storing the dynamic data. With this configuration, each time the portable device is restarted, the physical address where dynamic data is stored will change, and a memory cell in which a malfunction that becomes a starting point for decryption of confidential data will be identified. Becomes difficult.

The figure explaining the IC card concerning this embodiment. The figure explaining the addressing of dynamic data. The figure explaining the effect of this invention.

  From here, it explains to the extent that those skilled in the art of the present invention can understand the contents of the invention and implement the invention. The embodiment described below is an embodiment in which the portable device according to the present invention is an IC card, and is only one embodiment of the present invention, and the present invention is not limited to the embodiment described below. Various modifications and changes are possible.

  FIG. 1 is a diagram for explaining an IC card 1 according to the present embodiment. The IC card 1 according to the present embodiment is a contact type, and an IC module 1a in which an IC chip 2 is molded is mounted on a card base having the same size as a cash card or a credit card.

  In FIG. 1, the IC card 1 is illustrated as a contact type, but the IC card 1 is a non-contact IC card that performs wireless communication with a terminal device that is not illustrated, or two communication functions of contact communication and wireless communication. It may be a dual interface IC card provided with

  In addition, regardless of the shape of the IC card 1, the IC card 1 is not the same shape as the cash card, but is a SIM (Subscriber Identity Module) or USIM (Universal Subscriber Identity Module).

  As shown in FIG. 1, the IC chip 2 mounted on the IC card 1 includes a central processing unit 20 (CPU: Central Processing Unit) having a calculation function and a function of controlling a circuit and a memory of the IC chip 2. I / O circuit 21 used for data input / output with an external device, random access memory 22 (RAM: Random Access Memory) which is a volatile memory, read only nonvolatile memory 23 (ROM: Read Only Memory), An EEPROM 24 (EEPROM: Electrically Erasable Programmable Read-Only Memory) which is an electrically rewritable nonvolatile memory, a coprocessor circuit 25 which is a circuit specialized for DES cryptographic operations, and an RNG circuit 26 which is a circuit for generating random numbers (Random Number Generator) and the like, and the CPU 20 and memories and circuits other than the CPU 20 are connected via a data bus 27 and an address bus 28. It has been.

  The ROM 23 and the EEPROM 24 of the IC chip 2 are loaded with an operating system and applications as computer programs that operate on the IC card 1, and are reset to restart the IC card 1. The system sets a work area for storing dynamic data generated after the operating system or application operates in the memory (RAM 22 or EEPROM 24) of the IC chip 2, and then uses the RNG circuit 26 to generate a random number. An offset value within a predetermined range is generated using an external random number.

  In a general IC card, the storage position of dynamic data in the work area is determined at the design stage of the computer program. Therefore, even if reset, the storage position of dynamic data in the work area does not change. In the IC card 1 of the embodiment, the size of the work area is set larger than the actually required size, and when the IC card 1 is reset, an offset value within a predetermined range is generated by a random number, and the computer program operates. When the IC card 1 is reset, a value obtained by adding the offset value and the relative position to the start address of the work area is used as the physical address for storing the dynamic data generated thereafter. The physical address where the target data is stored is changed.

  FIG. 2 is a diagram for explaining addressing of dynamic data. In this embodiment, the structure of the machine language code that uses dynamic data is based on an operation code that describes an instruction for processing the dynamic data and an offset value that is generated each time the IC card 1 is reset. The physical address where dynamic data is stored is described in the offset value generated when the IC card 1 is reset and the operand. It is a value obtained by adding the relative positions.

  Therefore, if the operating system generates an offset value using the random number acquired from the RNG circuit 26 when the IC card 1 is reset, the dynamic data is generated each time the IC card 1 is reset. Since the physical address in which the data is stored changes, it becomes difficult to specify a memory cell in which a malfunction that becomes a stepping stone for the decryption of confidential data occurs, so that tamper resistance against laser attacks can be improved. .

  In this embodiment, the physical address of the work area for storing dynamic data generated after a computer program such as an operating system operates is changed because the PIN (Personal Identification Number) is added to the dynamic data. This is because the IC card 1 includes a lot of data that is liable to malfunction.

  FIG. 3 is a diagram for explaining the effect of the present invention. In FIG. 3, the size of the work area is 256 bytes that is 8 bytes larger than the actually required size (here, 248 bytes), and is generated using a random number each time the IC card 1 is reset. The range of the offset value is a value obtained by subtracting “1” from the numerical value of the actually required size (here, 246) from the numerical value of the size of the work area (here, 256) (here, 7). It becomes the following numerical value (here, any of 0-7). The reason why “1” is further subtracted from the value obtained by subtracting the numerical value of the actually required size from the numerical value of the size of the work area is to include “0” in the values that the offset value can take.

    FIG. 3A is a diagram in which an offset value generated by using a random number every time the IC card 1 is reset is set to “0”, and is the top physical address of the work area (here, 0x0000). Since the value obtained by adding the offset value (here, “0”) to 0x0000 is 0x0000, the dynamic data is stored from 0x0000. In FIG. 3A, since dynamic data is stored from 0x0000, dynamic data is not stored from 0x00F8 to 0x00FF.

  FIG. 3B is a diagram when the offset value is “2”, and the value obtained by adding the offset value (here, “2”) to the top physical address (0x0000) of the work area is 0x0002. , Dynamic data is stored from 0x0002. In FIG. 3B, since dynamic data is stored from 0x0002, dynamic data is not stored from 0x0000 and 0x0001, and from 0x00FA to 0x00FF.

  For example, even if 0x0002 is subjected to a laser attack in the state of FIG. 3A, if the IC card is reset and enters the state of FIG. 3B, it is stored in 0x0002 in FIG. 3A. Since the dynamic data that has been stored is stored in 0x0004 in FIG. 3 (b), the attacker loses its meaning even if the same memory cell is repeated many times, and becomes a starting point for decryption of the confidential data. It becomes difficult to specify a memory cell in which a malfunction occurs.

1 IC card 2 IC chip

Claims (2)

A relative position based on an offset value is described in an operand of a program code that uses dynamic data generated after a computer program operates, and the dynamic data is stored as a physical address for storing the dynamic data. Using the value obtained by adding the offset value and the relative position within a predetermined range generated using a random number at the time of activation to the start address of the work area set in the memory for storing , the dynamic data A portable device characterized in that a physical address to be stored is changed by a random number . A method of changing a storage position of dynamic data, wherein when a mobile terminal is activated, a step of generating an offset value within a predetermined range using a random number, the mobile terminal is generated after a computer program is operated As a physical address for storing dynamic data, a relative address described in an operand of a program code that uses the dynamic data, a head address of a work area set in a memory for storing the dynamic data, and the look including the step of using a value obtained by adding the offset value, the physical address for storing the dynamic data, characterized in that is possible to change by a random number, stored position changing how dynamic data.

Images