JPH0664842B2 - Data tampering check method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a data tampering check system for cards such as prepaid cards in which data tampering is important, and particularly to a direction for adding recorded information such as a laser card. A recording medium that can only be tampered with (hereinafter referred to as "write-once recording medium").
Called) data tampering check method.

[Conventional technology]

The laser card is for extracting information by making a hole in a recording medium with a laser beam and optically detecting the presence or absence of the hole at the time of reproduction based on the intensity of reflection of the irradiation laser beam.
This laser card is a kind of the write-once type recording medium in which falsification of data can be made only in the direction of making a hole (increasing a hole).

As a conventional data check method, for example, Japanese Patent Laid-Open No.
As disclosed in Japanese Patent Laid-Open No. 188159, by having a low number of BCCs (block check characters), the validity of read data is checked by a combination of a plurality of check methods.

In the data check method disclosed in Japanese Patent Laid-Open No. 57-140050, the total value of certain items related to the contents of data is calculated and used as the check data. Is obtained and collated with the above-mentioned check data.

[Problems to be solved by the invention]

Each of the above-mentioned conventional techniques has a problem that the reliability of data tends to be improved by complicating the data check method, and the burden on the check data creation and the check circuit increases.

The present invention has been made in view of the above circumstances, and an object of the present invention is to solve the above-mentioned problems in the conventional system, and to perform data tampering check and validity check in the above-mentioned write-once type recording medium. It is to provide a data tampering check method that can be easily performed.

[Means for solving problems]

In order to achieve the above object, the data tampering check method of the present invention is a system for recording and reproducing data by using a write-once type recording medium, and when recording the data on the recording medium, the recorded data is recorded as normal or Based on the total number of negative bits, create numerical data that decreases by additional recording to the recorded data, and use this numerical data as the first of the recorded data.
The check data is recorded together with the record data, and at the time of reproducing the data from the recording medium, it is created by the same procedure as the first check data creating procedure based on the total number of positive or negative bits of the reproduced data. It is characterized in that the data tampering check is performed based on the equality between the second check data and the first check data.

[Action]

In order to simplify the description, a laser card will be taken as a specific example of the write-once type recording medium described above, and an example of a method for creating check data based on the number of positive or negative bits of recorded data will be described below. As an example, check data using a one's complement of the number of positive bits of the recording data will be taken as an example.

That is, in the present invention, when data is recorded on the laser card, the shake data, which is a one's complement of the number of positive bits of the record data, is recorded together with the record data. Since a laser card cannot repair a bit that has been pierced once, tampering with the data pierces the hole. That is,
You can only increase the number of holes. Therefore, if the data on the laser card is tampered with by a third party, the number of positive bits (here, holes are positive bits) increases, but the check data is the one's complement of the number of positive bits. Therefore, if the check data is tampered with, the value will be smaller than the regular value. This makes it possible to check whether the recorded data on the laser card has been tampered with only by checking that the number of positive bits of the read data is equal to the one's complement of the check data.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows an embodiment of the present invention. It is a block diagram which shows a data tampering check mechanism.

In the figure, 10 is a positive bit counting unit that counts the number of positive bits of write data 1, 11 is a bit inverting unit that generates a 1's complement of the number counted by the positive bit counting unit 10, and 12 is write data. 1 and a laser card writing section for writing the check data created by the bit inverting section 11 in the recording section 14 in the laser card 13, and 17 is a data section 15 constituting the recording section 14 in the laser card 13 and A laser card reading unit that reads data from the check data unit 16,
Reference numeral 18 is a positive bit counting section for counting the number of positive bits of the data section 15 read by the laser card reading section 17, and 19 is a one's complement number of the check data section 16 read by the laser card reading section 17. A bit inversion unit 20 and a different value detection unit 20 for checking whether or not the number counted by the positive bit counting unit 18 and the one's complement number generated by the bit inversion unit 19 are equal to each other are shown.

FIG. 1 is a flow chart showing the operation of the data tampering check mechanism of this embodiment constructed as described above. The operation of this embodiment will be described below based on this.

When recording data on the laser card 13, the number of positive bits of the write data 1 is counted by the positive bit counting unit 10 (step 21), and the number is checked by inverting each bit by 1, 0 by the bit inverting unit 11. Data for use is created (step 22), and the writing data 1 is written in the recording part 14 in the laser card 13 by the laser card writing part (step 23). In this case, the write data 1 is in the data section 15 of the recording section 14 and the check data is in the check data section.
It will be recorded separately in 16.

The state of the recorded data is shown in FIG. 3 by taking the case of a data length of 8 bits as an example. As shown in Fig. 3, the data section
The data "1010" obtained by inverting 1,0 of the binary number "0101" of the number "5" of 1 of 15 is the data of the check data portion 16. In order to tamper with data in this state, as described above, the bit that has been punched cannot be restored due to the recording method of the laser card, so the bit of 0 (non-perforated state) is set to 1 (perforated state). I have no choice.

Here, 0 is a non-perforated state and 1 is a perforated state, but this may be reversed.

That is, when the data is tampered with, the data section 15 has 1 bit increased. However, since the check data portion 16 is data in which the number of 1 bits in the data portion 15 is inverted, if the 0 bit in this is altered to 1, the normal number of positive bits in the data portion 15 is changed. Will be less than. Therefore, it is impossible to falsify the check data portion 16 in accordance with the data portion 15.

Therefore, by checking whether or not the number of positive bits of the data part 15 and the data composed of the 1's complement of the check data part 16 are equal, it is possible to check the presence or absence of falsification. This will be described in detail below.

The hole is a positive bit, the number of data bits is DB, the number of positive data bits is PD, and the number of check data bits is CB (where CB ≧ [log ₂ DB] +1 and [log ₂ DB] is
the maximum integer not exceeding log ₂ DB), when the CD numerical values indicated by the check data, a ^{CD = (2 CB + 1 -1} ) -PD ···· (1). Due to the recording method of the laser card, data tampering can only be done in the direction of making holes. Therefore, if all the bits of data are perforated, they cannot be tampered with. Therefore, PD
<In the case of DB, the number of positive bits of the altered data PD ′
Is PD ′ = PD + x ₁ (2) (0 <x ₁ ≦ DB−PD, x ₁ is an integer). The 'numerical CD indicated by the check data alteration in accordance with the' PD, CD '= (2 CB + 1 -1) is _{-PD-x 1 ···· (3)} , before tampering check data When compared with the numerical value CD shown, CD'-CD = -x ₁ <0 ... (4). As shown in equation (4), it is necessary to falsify so that the numerical value indicated by the check data is smaller than that before falsification, but falsification can only be done by making holes, that is, increasing the positive bit. In this case, the numerical value indicated by the check data must be increased.
Therefore, it is impossible to falsify the check data in accordance with the data, and whether the number of positive bits of the data part 15 and the data composed of the 1's complement of the check data part 16 are equal or not. By checking whether or not there is tampering, it is possible to check.

On the reading side of the laser card, when reading the write data recorded in the laser card 13, the data section 15 is read by the laser card reading section 17 from the recording section 14 in the laser card 13.
And the check data section 16 are read together (step 3
1), a value obtained by counting the number of positive bits of the data part 15 by the positive bit counting part 18 (step 32) and a value obtained by inverting the check data part 16 by the bit inverting part 19 (step
33) is given to the different value detection unit 20. The different value detection unit 20 checks whether the received values are equal (step 34), and if they are not equal, tampering occurs or an error detection signal 3 (see FIG. 2) is generated as a read error occurrence (see FIG. 2). Step 35). If the two are equal, the error detection signal 3 is not generated and the read data 2 (see FIG. 2)
Indicates that the data is equivalent to the write data 1 at the time of writing and is normal data that has not been tampered with.

According to the present embodiment, it is easy to falsify the data in the laser card by utilizing the fact that the bit which is once pierced cannot be restored due to the recording method of the laser card and the falsification of data can only be done in the direction of making a hole. There is an effect that the existence check can be realized.

In the above description, an example in which the perforations are positive bits has been described, but the same applies when the perforations are negative bits. Further, the check data may be created by a method other than the one's complement method shown above. Further, it goes without saying that the present invention can be applied to the above-mentioned write-once type recording medium other than the laser card shown in the above embodiment.

〔The invention's effect〕

As described above, according to the present invention, even if any data is tampered with in a write-once type recording medium such as a laser card, it is possible to perform a complete process by simply recording, reproducing, and calculating data and check data. It is possible to carry out detection.

[Brief description of drawings]

FIG. 1 is a flow chart showing the operation of a data tampering check mechanism according to an embodiment of the present invention, FIG. 2 is a block diagram of the data tampering check mechanism of the embodiment, and FIG. 3 is recorded in a recording section in a laser card. It is a figure which shows the appearance of the data. 10: Positive bit counting unit, 11: Bit inverting unit, 12: Laser card writing unit, 13: Laser card, 14: Recording unit, 15: Data unit, 16: Check data unit, 17: Laser card reading unit, 18 : Positive bit counting unit, 19: Bit inversion unit, 20: Different value detection unit.

Claims (1)

[Claims] 1. In a system for recording and reproducing data using a write-once recording medium, when recording data on the recording medium, the recording data is recorded based on the total number of positive or negative bits of the recorded data. Numerical data that decreases by additional recording is created, and the numerical data is recorded as the first check data of the recording data together with the recording data. When the data is reproduced from the recording medium, the positive or negative of the data to be reproduced is recorded. The first based on the total number of bits
The data tampering check method is characterized in that the data tampering check is performed by the equivalence between the second check data created by the same procedure as the check data creation procedure and the first check data.