JP2014052955A - Security token, data falsification detection method, and computer program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a security device capable of detecting that data is falsified when a laser attack is made to falsify data stored in a memory.SOLUTION: When reading data from a data file with an error detection code is attached thereto to perform processing, control means 10 of a security token 1 reads prescribed data from the data file in a case that the data file is stored in a readable and writable memory, verifies the error detection code from the data file subjected to writing back data after writing back the read data to an original place, and executes data falsification detection processing for determining that the read data is falsified in a case that an error exists in the data file.

Description

  The present invention relates to a security token mounted with a semiconductor integrated circuit, and more particularly to a technique for improving tamper resistance against a laser attack that changes data stored in a memory using a laser.

  Security tokens mounted with semiconductor integrated circuits are used for applications requiring high security. For example, an IC card, which is one of the security tokens, has already been put into practical use for cash cards and credit cards in financial applications. In addition, the use of a USB key with a chain, which is one of security tokens, as a device for generating a one-time password used for user authentication is under consideration.

  Security data used for applications requiring high security contains security data that cannot be leaked to the outside in accordance with the application of the security token, but various security attacks aimed at obtaining security data Laws have been devised, and security tokens are required to be tamper resistant to the security attack method.

  One of the newly devised security attack methods is laser attack. Laser attacks are recorded in a readable / writable memory by irradiating a laser to the readable / writable memory of a semiconductor integrated circuit mounted on a security token, and temporarily changing the state of the readable / writable memory to a high energy state. By deliberately changing the stored data, the security data is obtained by comparing the output obtained from the security token when the laser is irradiated with the output obtained from the security token when the laser is not irradiated. It is a security attack method.

  FIG. 6 is a diagram for explaining a laser attack. As shown in FIG. 6A, when reading temporarily used data (here, the first byte) from a readable / writable memory, a normal value (here, 11h) is normally used. Read out.

  However, when reading data from a readable / writable memory, if the location where the data to be read is stored is irradiated with a laser, the data at the location where the laser was irradiated changes to a different value, and the normal value The value which is not is read.

  The danger of such a laser attack has been pointed out for some time, but it is technically difficult to irradiate the laser only to the smallest area of readable and writable memory, the effectiveness of the laser attack is low, and no countermeasures are considered necessary. It was.

  However, in recent years, the laser irradiation technology has improved dramatically, making it possible to irradiate the laser only to the minimum range of readable and writable memory, and the laser attack has become a reality, so countermeasures against the laser attack can also be taken. It came to be required.

  As a countermeasure against the laser attack method in Patent Document 1, the present applicant encrypts the security data even in the case of encrypting the security data stored in the electrically rewritable nonvolatile memory of the security token. An invention that can prevent leakage of a scramble key used when performing the process is disclosed.

JP 2010-258630 A

  However, the above-described invention is an invention for preventing leakage of the scramble key used when encrypting the security data, and is not an invention for detecting that the security data has been tampered with by a laser attack.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a security device, a data falsification detection method, and a computer program that can detect that data has been falsified when a laser attack is performed and data stored in a memory is falsified. .

  In a first invention for solving the above-described problem, when data is read from a data file to which an error detection code is added and processed, the data file is stored in a readable / writable memory. After reading the predetermined data and writing the read data back to the original location, verify the error detection code of the data file after the data is written back, and if the data file has an error, the read data is It is a security token characterized by comprising control means for executing data falsification detection processing for determining that falsification has occurred.

  Further, according to a second invention, in the security token according to the first invention, when the control means reads the data from the data file, the data file is stored in a predetermined memory. After the data file stored in the memory is copied to the RAM, the error detection code of the data file copied to the RAM is verified, and the data file copied to the RAM is copied to the RAM only when there is no error. Processing is performed using a data file, and the data alteration detection processing is executed when data is read from the data file copied to the RAM.

  Furthermore, when the CPU of the security token reads the data from the data file to which the error detection code is added and performs processing when the data file is stored in a readable / writable memory, the third invention After reading the predetermined data from the file and writing the read data back to the original location, the error detection code of the data file after the data is written back is verified, and the data file is read if there is an error A data falsification detection method that performs data falsification detection processing for determining that data has been falsified.

  Furthermore, a fourth invention is the data falsification detection method according to the third invention, wherein when the CPU of the security token reads the data from the data file, the data file is stored in a predetermined memory. After the data file stored in the predetermined memory is copied to the RAM, the error detection code of the data file copied to the RAM is verified, and only when the data file copied to the RAM has no error The data falsification determination processing is executed when data is read from the data file copied to the RAM.

  Furthermore, in the fifth aspect of the present invention, when data is read from a data file to which an error detection code is added and processing is performed, if the data file is stored in a readable / writable memory, predetermined data is read from the data file. After reading and writing back the read data to the original location, the error detection code of the data file after the data is written back is verified, and if there is an error in the data file, it is determined that the read data has been tampered with This is a computer program for causing the security token CPU to function as a control means for executing the data falsification detection process.

  Further, in a sixth aspect of the present invention, when the CPU of the security token reads data from the data file, if the data file is stored in a predetermined memory, the data file stored in the predetermined memory Is copied to the RAM, the error detection code of the data file copied to the RAM is verified, and only when there is no error in the data file copied to the RAM, processing is performed using the data file copied to the RAM, It is a computer program for functioning as the control means for executing the data falsification determination process when data is read from the data file copied to a RAM.

  According to the present invention described above, when data is read from a data file to which an error detection code is added and processed, if the data is tampered with by a laser attack, data that is not a normal value is written back to the data file. Since the verification of the error detection code of the data file after the data is written back fails, it can be detected that the data read from the data file has been tampered with.

The figure explaining a security token. The figure explaining a data file. The figure explaining data falsification detection processing. The figure used for description of the effect of invention. The figure explaining the operation | movement performed before a data alteration detection process. The figure explaining a laser attack.

  From here, the security token according to the present invention will be described.

[First Embodiment]
FIG. 1 is a diagram illustrating a security token 1 according to this embodiment. The security token 1 according to the present embodiment is a device used in a computer system that requires high security. As illustrated in FIG. 1, a semiconductor integrated circuit 2 is mounted on the security token 1 according to the present embodiment.

  As such a security token 1, in addition to an IC card and a USB key, an SD card equipped with an operating system for an IC card such as TinySmart already sold by the present applicant can be used.

  As shown in FIG. 1, a semiconductor integrated circuit 2 mounted on a security token 1 includes a RAM 21 (Random Access Memory) that is a volatile memory as a readable / writable memory in addition to a CPU 20 (Central Processing Unit) that is a microprocessor. ) And an electrically rewritable nonvolatile memory EEPROM 23 (Electrically Erasable and Programmable Read Only Memory), and a ROM 22 (Read Only Memory) as a non-writable memory. Are connected via an address bus 24 and a data bus 25.

  In FIG. 1, the electrically rewritable nonvolatile memory is described as the EEPROM 23, but the electrically rewritable nonvolatile memory may be FeRAM. Further, the security token 1 includes a random number generator (Random Number Generator) for generating a random number, a cryptographic coprocessor (Cryptographic Co-processer) specialized for a calculation function of a predetermined cryptographic algorithm (for example, DES), an external device However, these peripheral circuits are not shown in FIG. 1 because they are not related to the present invention.

  FIG. 2 is a diagram for explaining a data file stored in a readable / writable memory. In the first embodiment, a readable / writable memory (here, RAM 21 and EEPROM 23) of the semiconductor integrated circuit 2 mounted on the security token 1 has a data file containing data used when processing a command received from an external device. Is stored, and an error detection code (CC: CheckCode) calculated from all data contained in the data file is added to the end of this data file.

  As described with reference to FIG. 6, if the data used by the CPU 20 of the semiconductor integrated circuit 2 is read from the data file and subjected to a laser attack, the data read by the CPU 20 of the semiconductor integrated circuit 2 is not a normal value. The security token 1 according to the embodiment includes a control unit 10 that executes data falsification detection processing that detects falsification of data using an error detection code added to a data file, and executes the data falsification detection processing. The CPU 20 functions as the control unit 10 when the computer program for executing the program is executed by the CPU 20.

  FIG. 3 is a diagram for explaining data alteration detection processing executed by the control means 10 in the first embodiment. When the control means 10 of the security token 1 reads data used for processing from the data file stored in the readable / writable memory (S1), the control means 10 reads the read data in the original readable / writable memory. A process of writing back to the place is executed (S2).

  Next, the control means 10 recalculates the error detection code of the data file after the data is written back, and compares the error detection code added to the data file to which the data is written back, thereby writing the data. The error detection code of the returned data file is verified (S3).

  Next, the control means 10 branches the process according to the verification result of the error detection code of the data file (S4). If the verification of the error detection code is successful, it is determined that the data has not been falsified, and the subsequent processes (S5), this procedure ends, and if the verification of the error detection code fails, it is determined that the data has been falsified, the subsequent processing is interrupted (S6), and this procedure ends.

  From here, the effect of invention is demonstrated. FIG. 4 is a diagram used for explaining the effects of the invention.

  In FIG. 6, the place where the laser is irradiated is a readable / writable memory. However, even if the address bus 24, the data bus 25 or the CPU 20 of the semiconductor integrated circuit 2 is irradiated with the laser, the CPU 20 (control means) There is a possibility that the data read in 10) is not a normal value.

  FIG. 4A is a diagram for explaining a case where the read data is irradiated with laser at the timing when the CPU 20 reads the data from the readable memory. In this case, the data stored in the readable memory is not a normal value, and the data read by the CPU 20 from the readable / writable memory is not a normal value.

  FIG. 4B is a diagram illustrating a case where the laser is irradiated to the address bus 24, the data bus 25, or the CPU 20 at a timing when the CPU 20 reads data from a readable memory. In this case, the data stored in the readable / writable memory remains at a normal value, but the data read by the CPU 20 from the readable / writable memory is not a normal value.

  When the CPU 20 irradiates the address bus 24 with a laser at a timing of reading data from a memory from which data can be read, data is read from an address that is not a normal value, so the data read from the memory that the CPU 20 can read and write is not a normal value.

  Further, when the laser is irradiated onto the data bus 25 at a timing when the CPU 20 reads data from a readable memory, the data changes on the data bus 25 and the data delivered to the CPU 20 via the data bus 25 is a normal value. Therefore, the data read from the memory that the CPU 20 can read and write is not a normal value.

  In addition, when the CPU 20 is irradiated with laser at the timing when the CPU 20 reads data from the readable memory, the data stored in the CPU 20 changes, so the data read from the memory that the CPU 20 can read and write is a normal value. Disappear.

  In either case of FIGS. 4A and 4B, the data read from the readable / writable memory by the CPU 20 no longer has a normal value, and the non-normal data is written back to the data file in the readable / writable memory. Therefore, when the error detection code of the data file is verified after the data is written back, the verification of the error detection code fails and the CPU 20 can detect that the data has been falsified.

[Second Embodiment]
The second embodiment is a mode in which it is possible to cope with the case where data to be read is stored in a non-writable memory (in this case, ROM 22) in the first embodiment. Although the data stored in the ROM 22 is unlikely to change due to the laser attack, when the address bus 24, the data bus 25, or the CPU 20 is irradiated with the laser, even if the read data is stored in the ROM 22, the CPU 20 The data read out is not a normal value.

  FIG. 5 is a diagram for explaining an operation performed by the control unit 10 in the second embodiment before the data alteration detection process. In the process of FIG. 5, when reading the data from the data file, the control unit 10 of the security token 1 first checks the type of memory in which the data file is stored (S10).

  The control means 10 branches the process depending on the type of memory in which the data file is stored (S11), and the type of memory in which the data file from which data is read is stored is not a predetermined type (here, ROM 22). Then, the data alteration detection process described with reference to FIG. 3 is executed (S15).

  Further, when the type of the memory in which the data file from which data is read is stored is a predetermined type (here, ROM 22), the control means 10 is stored in a predetermined type of memory (here, ROM 22). The data file is copied to the RAM 21 which is one of the readable and writable memories (S12).

  Next, the control means 10 verifies the error detection code of the data file copied to the RAM 21 to determine that there is no laser attack at this point (S13).

  Next, the control means 10 branches the process according to the verification result of the error detection code (S14), and when the verification of the error detection code fails, the control means 10 interrupts the subsequent processes (S16). ) To finish this procedure.

  If the verification of the error detection code is successful, the control means 10 continues the processing using the data file in the RAM 21, and when data is read from the data file in the RAM 21, the data falsification detection described with reference to FIG. Processing is executed (S15).

  Note that the contents of the second embodiment can be applied not only to the ROM 22 that cannot be written but also to the EEPROM 23 that takes a long time to write by including the EEPROM 23 in a predetermined type.

DESCRIPTION OF SYMBOLS 1 Security token 10 Control means 2 Semiconductor integrated circuit 20 CPU
21 RAM
22 ROM
23 EEPROM
24 address bus 25 data bus

Claims (6)

  When processing is performed by reading data from a data file to which an error detection code is added, if the data file is stored in a readable / writable memory, predetermined data is read from the data file and the read data is restored to the original data. After writing back to the location, the error detection code of the data file after writing back the data is verified, and if there is an error in the data file, a data falsification detection process is performed to determine that the read data has been falsified A security token comprising a control means.   When the data is stored in a predetermined memory when reading data from the data file, the control means copies the data file stored in the predetermined memory to the RAM and then copies the data file to the RAM. The error detection code of the data file is verified, and only when there is no error in the data file copied to the RAM, processing is performed using the data file copied to the RAM, and the data is copied from the data file copied to the RAM. The security token according to claim 1, wherein the data alteration detection process is executed when reading.   When the CPU of the security token reads data from the data file to which the error detection code is added and performs processing, when the data file is stored in a readable / writable memory, the predetermined data is read from the data file, Data that verifies the error detection code of the data file after the data is written back after the read data is written back to the original location, and determines that the read data has been tampered with if there is an error in the data file A data falsification detection method characterized by executing falsification detection processing.   When the CPU of the security token reads data from the data file, if the data file is stored in a predetermined memory, the CPU copies the data file stored in the predetermined memory to the RAM, The error detection code of the data file copied to the RAM is verified, and only when there is no error in the data file copied to the RAM, processing is performed using the data file copied to the RAM, and from the data file copied to the RAM, 4. The data falsification detection method according to claim 3, wherein the data falsification detection process is executed when reading data.   When processing is performed by reading data from a data file to which an error detection code is added, if the data file is stored in a readable / writable memory, predetermined data is read from the data file and the read data is restored to the original data. After writing back to the location, the error detection code of the data file after writing back the data is verified, and if there is an error in the data file, a data falsification detection process is performed to determine that the read data has been falsified A computer program for causing a security token CPU to function as control means. When the data is stored in a predetermined memory when reading data from the data file, the control means copies the data file stored in the predetermined memory to the RAM and then copies the data file to the RAM. The error detection code of the data file is verified, and only when there is no error in the data file copied to the RAM, processing is performed using the data file copied to the RAM, and the data is copied from the data file copied to the RAM. 6. The computer program according to claim 5, wherein the data alteration determination process is executed when reading.

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