JP2006164163A - Unauthorized rom use prevention device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an unauthorized ROM use prevention device that is used for preventing an unauthorized use for a general purpose ROM. <P>SOLUTION: The device, which prevents an unauthorized use for data on a ROM 3 on which data inverse-converted in a conversion cycle preset for each address area are recorded, enables a normal use for the ROM data and prevents an unauthorized use for the ROM data, by decoding and sending to the ROM 3 a request address for ROM data requested by a microprocessor 2, then in a data conversion cycle specification part 13, identifying an address area according to the request address to specify a conversion cycle corresponding to the address area, and next decoding or converting the ROM data acquired from the ROM 3 in response to the request address sent to the microprocessor 2 in the conversion cycle specified by the data conversion cycle specification part 13 before sending them to the microprocessor 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a ROM improper use prevention apparatus that decodes ROM data that has been inversely converted by a set method to decode it into a usable state in order to prevent unauthorized use of ROM data.

  In general, a ROM is often used as a storage medium for a program for operating a computer. The program stored in the ROM can be easily copied and used by a ROM writer or the like, and the fact is that illegal copying is rampant because of its ease. In order to prevent these illegal copies, there are techniques described in Patent Documents 1 and 2 below.

In the techniques described in Patent Documents 1 and 2, data obtained by performing reverse conversion of conversion performed when ROM data is output is recorded in the ROM in advance, and is output after performing predetermined conversion for each address area. The normal data can be read out with this.
JP 09-282234 A Japanese Patent No. 3464738

  However, these methods have been problematic in that they cannot be applied to general-purpose ROMs because the unauthorized copying is prevented by manufacturing the ROM using an LSI including a copy protection function, and the range of use is limited.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a ROM unauthorized use prevention device used for preventing unauthorized use of a general-purpose ROM.

  In order to achieve the above object, a ROM improper use prevention apparatus according to the present invention is an apparatus for preventing illegal use of ROM data in which data converted by a conversion method and the number of conversions set in advance for each address area is recorded. And a data conversion number specifying means for transmitting the address of the ROM data requested from the reading source to the ROM, determining an address area based on the address, and specifying a conversion method and a conversion number corresponding to the address area; ROM data obtained from the ROM in response to the transmission of the address to the ROM is converted by the conversion method specified by the data conversion count specifying means and the conversion count and decoded, and data decoding means for transmitting to the reading source It is characterized by providing.

  Since the ROM unauthorized use prevention apparatus of the present invention is provided between a general-purpose ROM and a microprocessor such as a general-purpose CPU, unauthorized use can be prevented even for a general-purpose ROM not equipped with a copy prevention function.

<Configuration of ROM Unauthorized Use Prevention Device 1>
A first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a block diagram showing the operation of the ROM unauthorized use preventing apparatus 1 according to this embodiment. The ROM improper use prevention apparatus 1 of the present embodiment includes a CPU 2 that is a general-purpose microprocessor as a reading source, and a ROM 3 in which data obtained by performing a reverse operation with a preset conversion method and number of conversions is written. And connected to. This conversion method is not limited as long as the data can be uniquely calculated by the inverse operation, and the number of conversions is set for each address area.

  The ROM unauthorized use prevention apparatus 1 receives a request address signal for requesting acquisition of data in the ROM 3 from the CPU 2 and transmits it to the ROM 3, and in response to the transmission of the request address signal, the ROM data signal obtained from the ROM 3 is received. It is converted into a usable state, and transmitted to the CPU 2.

  The ROM unauthorized use preventing apparatus 1 according to the present embodiment includes an address decoding unit 11, a reference address signal storage unit 12, a data conversion number specifying unit 13, three data conversion units 14, 15, 16 and a data selection unit. 17.

  The address decoding unit 11 receives and decodes the address signal transmitted from the CPU 2, and if the address is a specific address for specifying a reference address value for dividing the address area of the ROM 3, the address decoding unit 11 sends the reference signal to the reference address signal storage unit 12. In the case of a request address for requesting acquisition of ROM data, it is transmitted to the data conversion number specifying unit 13 and the ROM 3.

  The reference address signal storage unit 12 receives an address data signal having a number of bits usable as an address signal at a plurality of preset specific addresses. When a specific address decoded by the address decoding unit 11 is detected from the plurality of specific addresses, the address data signal input to the detected specific address is stored in the register as a reference address signal. The reference address signal storage unit 12 transmits the stored reference address signal to the data conversion count specifying unit 13.

  The data conversion number specifying unit 13 divides the ROM address area based on a plurality of reference address signals received from the reference address signal storage unit 12. Further, the number of conversions of the ROM data signal acquired from the ROM 3 is set for each divided area. When the request address signal is received from the address decoding unit 11, the address area corresponding to the request address signal is determined, thereby specifying the number of conversions and transmitting it to the data selection unit 17.

  The data converters 14, 15, and 16 convert the ROM data signal acquired from the ROM 3 according to a preset conversion method.

  The data selection unit 17 is a ROM data signal that is called by the ROM 3 and is not converted as it is, a ROM data signal that is converted once by the data conversion unit 16, and a ROM data signal that is converted twice by the data conversion units 16 and 17. And the ROM data signal converted three times by the data conversion units 16, 17 and 18 and select the ROM data signal converted by the number of conversions specified by the data conversion number specifying unit 13 from among them. , To CPU2.

<Operation according to the first embodiment>
The operation of the first embodiment of the present invention will be described below with reference to FIGS. FIG. 2 is a sequence diagram showing the operation of this embodiment, and FIG. 3 is an explanatory diagram showing an example of setting a reference address.

  First, a specific address 6759 signal for specifying a reference address value for dividing the address area of the ROM 3 by the user's operation is transmitted from the CPU 2 to the ROM unauthorized use preventing apparatus 1 (S1).

  The specific address 6759 signal is received by the address decoding unit 11 of the ROM unauthorized use preventing apparatus 1 (S2), decoded and transmitted to the reference address signal storage unit 12 (S3). In the reference address signal storage unit 12, an address 6759 decoded by the address decoding unit 11 is detected from a plurality of preset specific addresses, and an address data signal 8192 inputted to the specific address 6759 is used as a request address signal. Is stored in the register X as a reference address signal for comparison (S4).

  Similarly, the specific address 7311 signal transmitted from the CPU 2 is decoded by the address decoding unit 11 of the ROM unauthorized use preventing apparatus 1 and the address data 16384 signal input to the specific address 7311 of the reference address signal storage unit 12 is used as a reference. It is stored in the register Y as an address.

  On the assumption that the reference address signal is stored in the reference address signal storage unit 12, a request address signal for requesting data acquisition from the CPU 2 to the ROM 3 is transmitted to the ROM unauthorized use preventing apparatus 1 (S5). The request address signal received by the address decoding unit 11 of the ROM unauthorized use preventing apparatus 1 is decoded and transmitted to the ROM 3 and also transmitted to the data conversion number specifying unit 13 (S6, S7).

  When the request address signal is received by the data conversion number specifying unit 13, the reference address signal is acquired from the reference address signal storage unit 12, and the address area of the ROM 3 is divided based on the reference address signal, and data is divided for each divided address area. The number of conversions is set (S8).

  The setting of the number of data conversions will be described. FIG. 4 is a flowchart showing an embodiment of the operation of the address area determination unit for setting the number of data conversions from the reference address signal.

  First, it is determined whether or not the value of the register X and the value of the register Y acquired by the reference address signal storage unit 12 are 0 (S21). If neither is 0 (“YES” in S21), region determination processing is performed (S22). When the request address is A, no conversion is performed when A value <X value (S23), one conversion when X value ≦ A value ≦ Y value (S24), and two conversions when A value ≧ Y value. (S25) is set. (In ROM 3, the data that has been subjected to the inverse operation is written in advance when A value <X value, once when X value ≦ A value ≦ Y value, and twice when A value ≧ Y value. If either X or Y is 0, an error occurs (S26).

  In response to the transmission of the request address decoded to the ROM 3 from the address decoding unit 11 of the ROM unauthorized use preventing apparatus 1 in step S7 of FIG. 2, the corresponding ROM data signal is transmitted from the ROM 3 (S9, S10). The ROM data signal is acquired by the ROM unauthorized use preventing apparatus 1 (S11). In the ROM improper use prevention device 1, the ROM data signal as received, the ROM data signal that has been converted once by the data conversion unit 14, and the second conversion that has been converted by the data conversion unit 15 are performed. The converted ROM data signal and the ROM data signal converted three times converted by the data converter 16 are transmitted to the data selector 17 (S12).

  An embodiment of a conversion method in the data converters 14, 15, and 16 in this embodiment will be described with reference to FIG.

  Data before conversion is represented by 8 bits a0 to a7, and data after conversion is represented by 8 bits b0 to b7. This conversion method is performed by combining arbitrary bits and logical negation of arbitrary bits. In FIG. 5, a0 → b1, a1 → b2,... Are sequentially replaced, and a7 is replaced with a bit inverted by logical negation to b0.

  In this conversion method, 8 bits to be output are uniquely determined with respect to 8 bits that are arbitrarily input, and thus the inverse operation is easily calculated. Accordingly, the ROM 3 stores data converted in advance by a predetermined number of inverse operations.

  The data selection unit 17 selects a ROM data signal converted by the number of conversions determined by the data conversion number specifying unit 13 from each received ROM data signal (S13) and transmits it to the CPU 2. (S14). The CPU 2 can use the ROM data normally by receiving the data decoded by the conversion for each address area (S15).

  According to the present embodiment, when the ROM unauthorized use preventing apparatus 1 is used, even if a specific address value for setting an address area is fixed, the fixed address value is easily inferred by a third party. Can not be used illegally.

<Operation according to the second embodiment>
FIG. 6 shows a conversion method according to the second embodiment. Data before conversion is represented by 8 bits c0 to c7, and data after conversion is represented by 8 bits d0 to d7. The conversion method 2 is performed by exchanging arbitrary bits, combining exclusive OR, and using the root α of the Galois field GF (2 ⁸ ). In FIG. 6, c0 → d1, c1 → d2,... Are sequentially replaced, c7 is replaced with d0, and an exclusive OR with c1, c2, and c3 is obtained and replaced with d2, d3, and d4. Further, conversion is performed by multiplying 8 bits of d0 to d7 as a solution α of the Galois field GF (2 ⁸ ). This conversion may be performed as many times as the number of conversions to be calculated, or may be performed by using multiplication after the second time. These data conversion operations can be determined in advance according to the amount of hardware.

  Even in the conversion method according to the second embodiment, 8 bits to be output are uniquely determined with respect to 8 bits that are arbitrarily input, so that the inverse operation can be calculated. Therefore, the ROM 3 can store data converted in advance by a predetermined number of inverse operations. Thereby, the effect similar to 1st embodiment can be acquired.

<Other embodiments>
The number of bits of the reference address signal and the request address signal may be different. For example, when the value of the register X or Y is 16 bits and the request address signal is 8 bits, the reference address signal X or Y is every 8 bits. It is possible to determine whether it is zero.

  Further, when the ROM 3 is manufactured in large quantities for sale, the address data signal corresponding to the specific address signal can be changed for each set. In this case, a reset signal is transmitted from the CPU 2 to the reference address signal storage unit 12 of the ROM unauthorized use prevention 1 by the user's operation, and the stored address data is erased to input and store a new address data signal. Can be made. By changing the address data signal for each set, even if a specific set of address data signals is revealed to a third party, the address data signals cannot be used normally in other sets, and the ROM data is illegal. It is impossible to use.

  Also, for the same set of manufacture, it is possible to change the specific address signal set by the date of manufacture.

  Furthermore, it is possible to set to select the number of data conversion, conversion contents, conversion method, etc. in each area using any 2 bits of data corresponding to the specific address signal, and more reliably Unauthorized use can be prevented.

It is a block diagram which shows 1st embodiment of the ROM unauthorized use prevention apparatus of this invention. It is a sequence diagram which shows the operation | movement by 1st embodiment of the ROM unauthorized use prevention apparatus of this invention. It is explanatory drawing which shows the example of a setting of the reference address by 1st embodiment of ROM unauthorized use prevention apparatus of this invention. It is a flowchart which shows operation | movement of the address area | region determination part by 1st embodiment of the ROM unauthorized use prevention apparatus of this invention. It is explanatory drawing which shows the conversion method in the conversion part by 1st embodiment of ROM unauthorized use prevention apparatus of this invention. It is explanatory drawing which shows the conversion method in the conversion part by 2nd embodiment of the ROM unauthorized use prevention apparatus of this invention.

Explanation of symbols

1 ROM unauthorized use prevention device 2 CPU
3 ROM
DESCRIPTION OF SYMBOLS 11 Address decoding part 12 Reference address signal memory | storage part 13 Data conversion frequency specification part 14, 15, 16 Data conversion part 17 Data selection part

Claims (1)

A device for preventing unauthorized use of ROM data in which data converted by the conversion method and the number of conversions set in advance for each address area is recorded,
A data conversion number specifying means for transmitting an address of the ROM data requested from a reading source to the ROM, determining an address area based on the address, and specifying a conversion method and a conversion number corresponding to the address area;
The ROM data obtained from the ROM in response to the transmission of the address to the ROM is converted and decoded by the conversion method and the conversion count specified by the data conversion count specifying means, and transmitted to the reading source. Data decoding means for
A device for preventing unauthorized use of ROM, comprising:

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