JPH0268641A - Security protective system of integrated circuit - Google Patents

Abstract

PURPOSE: To simplify constitution and to completely protect the security of data processing conditions by selecting a conversion mode based on security data held in a security data holding circuit backed up by a battery. CONSTITUTION: A conversion circuit 3 for mutually converting an external data code and an internal data code by one of the plural conversion modes is provided and the conversion mode is selected based on the security data held in the security data holding circuit 5 backed up by the battery. Thus, since the conversion mode is selected by specifying the security data, even in the integrated circuit of the same form, which of conversion modes is used is unknown and the security is maintained more completly. Thus, the security of the data processing conditions is completely maintained and the constitution is simplified since address signals are used as they are.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION This invention relates to a system for providing operational security in a semiconductor integrated circuit incorporating a data processing circuit such as a microprocessor or microcontroller.

When an integrated circuit according to the prior art is used for anti-theft control 1, management of confidential information, etc., the operation status may be detected by a third party, or
It is necessary to prevent the software from being controlled by a third party, and in the past, in order to make it difficult for outsiders to decode the software, it was necessary to newly develop a dedicated integrated circuit and software compatible with it. It is being done.

In this case, new development requires a huge amount of time and expense, so it is necessary to use off-the-shelf integrated circuits and software, convert the address code and data code internally, and use the converted codes externally. ,
This generally makes it impossible to detect the internal operating status.

Problems to be Solved by the Invention However, when converting address codes and data codes, a conversion circuit is required for each code.

As the configuration becomes more complex and each conversion mode is single,
However, there is a shortcoming in which the operation status can be easily clarified.

Therefore, it is an object of the present invention to provide a security protection system for an integrated circuit that is simple in structure, uses a plurality of conversion modes, and does not allow easy identification of operating conditions.

Means for Solving the Problems In order to achieve the above object, the present invention provides a conversion method for mutually converting an external data code and an internal data code in one of a plurality of conversion modes in the above-mentioned integrated circuit. The present invention is characterized in that a conversion mode is selected based on confidential data held in a confidential data holding circuit backed up by a battery.

In the method described above, the conversion mode is selected by specifying the confidential data, so even if the integrated circuits are of the same type, it is unclear which conversion mode is being used. Retention takes place.

EXAMPLES Hereinafter, the present invention will be explained in detail with reference to figures showing examples.

FIG. 1 is a block diagram showing a general configuration, in which a microprocessor (hereinafter referred to as CPU) 1 is built in a semiconductor integrated circuit 2, which sends an address signal ADS from an address terminal ADH, and a control terminal CNT. It sends out various control signals CTS, accesses the data signal DTS through the data terminal DAT, and executes a predetermined data processing operation.

In this case, an off-the-shelf one is used as the CPU, while the conversion circuit 3, its control unit 4, and confidential data holding circuit 5 are integrated into the same integrated circuit 2 as peripheral circuits.
The conversion circuit 3 has a plurality of conversion modes, and uses one of these modes to perform mutual conversion between an external data code and an internal data code used by the CPU 1. The holding circuit 5 holds confidential data, which specifies the conversion mode of the conversion circuit 3, and based on this, the control unit 4 controls the conversion circuit 3.
The conversion status is selected.

Note that a volatile memory or the like is used as the confidential data holding circuit 5, which is backed up by a battery B, and continues to hold confidential data even if the main power supplies VDD and SS are cut off.

This is because if a fixed memory such as a ROM is used as the confidential data holding circuit 5, the contents must be specified during the manufacturing process, which makes it easy for confidential data to leak, and the contents can be detected through destructive observation. In order to prevent this, a volatile memory such as a register is used.

FIG. 2 is a block diagram showing details of FIG.
U1 operates based on a clock pulse CLK supplied from the outside, and sends out a control signal CTS as well as an address signal ADS, which is sent via a buffer circuit 6 to simplify the configuration. The external data signal DTSe is accessed according to the address specification, and the received data signal is sent through the buffer circuit 7.
The sending data signal is passed through the buffer circuit 8 to the data signal D.
We are giving and receiving TSe.

Furthermore, the data signal DTSe and the internal data signal DTSi used by the CPU 1 have different codes, and the conversion circuit 3 mutually converts them.
The data signal DTSi to the PU 1 is given to the CPU 1 via the buffer circuit 9 which exhibits an inhibiting effect, while the data signal DTSe sent from the conversion circuit 3 to the outside is sent to the multiplexer lO which selects conversion or non-conversion. The signal is sent to the buffer circuit 8 via the buffer circuit 8.

On the other hand, the conversion circuit 3 includes a ROM data scramble circuit 11 that scrambles data from an external ROM and a first ram data scramble circuit that scrambles data from an external RAM as a method for converting the code of the data signal DTSe into a data signal DTSi. 12 and external RAM
a second ram data circuit 13 that descrambles data to
The scrambling circuit 11 stores a plurality of conversion tables, and the scrambling circuit 12 stores a plurality of conversion tables.
A plurality of conversion tables are also stored in the scramble circuits 12 and 13, and the confidential data holding circuit 5 specifies which conversion table to use in correspondence with each other. is to be carried out. The above specification is achieved by changing the circuit configuration for each scrambling method based on a combination of programmed confidential data.

Note that when converting the data signal DTSe to the data signal DTSi, a multiplexer 14 is provided to select which one to use or not to convert, and the data signal DTSi is sent to the CPU 1 via this multiplexer 14. be done.

Further, the scramble circuit 11 is supplied with an address signal ADSc scrambled by conversion via an address converter 15 that converts the address signal ADS.
It is also controlled by and is involved in selection of the conversion table in the scramble circuit 11.

The confidential data holding circuit 5 includes a multistage register 16 backed up by a battery B, and a write circuit 17 that writes confidential data to the register 16. By setting the data into the register 16, the scrambling circuit 12.13
Conversion table storage and conversion memories 11 to 13
The conversion table to be used for is specified.

On the other hand, the control unit 4 outputs the address signal ADS and CP
The buffer circuit 9. Control multiplexers 10, 14, etc.
At the time of sending out the data signal DTSi, the output of the multiplexer 14 is blocked, and the state of mutual conversion between the data signal DTSe and the data signal DTSi is selected.

Therefore, the data signal DTSe is scrambled by conversion in the conversion circuit 3, and the data signal DTSi
As a result, the CPU 1 performs data processing, but since a plurality of conversion tables are prepared in each of the scramble circuits 11 to 13, the code conversion of the data signals DTSa and DTSi is performed using a plurality of conversion modes. One of these is specified by the confidential data of the confidential data holding circuit 5, and the conversion mode is selected based on the control of the control unit 4.

Further, in the control unit 4, the multiplexer 10.14
When controlling the multiplexer 10.14, the selection status of the multiplexer 10.14 is determined by combining these conditions based on the address signal ADS, the confidential data from the confidential data holding circuit 5, and the clock signal from the CPU 1. If the data is composed of 108 bits, the combination will be 210B valves 3.245 x 1032, and even if this is verified by computer processing, assuming that one combination is processed in 1 μSec, it will take 10 times to verify all combinations. -' X 3.245
It takes 103z(see) 410'' (years) and is virtually impossible to decipher by verification.

Note that the register 16 of the confidential data holding circuit 5 cannot store confidential data unless a predetermined entry procedure is followed, and an optical sensor is built into the main part of the integrated circuit 2, and this can be detected by opening the package. It detects external light and destroys the status held in the register 16, making it impossible to decipher confidential data by internal observation.

Therefore, since the address signal ADS is not converted, the configuration is simplified and the external data signal DT
It is clear in what conversion mode Se is currently converted into the internal data signal DTSi, and the confidentiality of the data processing situation can be completely protected.

Effects of the Invention The present invention is as described above, and includes a conversion circuit that converts an external data code and an internal data code in one of a plurality of conversion modes, and performs conversion based on the confidential data of the confidential data holding circuit. By selecting the mode, it is impossible to clarify the conversion status, and the confidentiality of the data processing status can be completely maintained. Also, since the address signal is used as is, the configuration is simple. ,
A remarkable effect can be obtained in securing the security of various integrated circuits.

1...Microprocessor 3...Conversion circuit 5... Confidential data retention circuit 2...Integrated circuit 4...Control unit

Claims (1)

[Claims] 1. In a semiconductor integrated circuit with a built-in data processing circuit, a conversion circuit that mutually converts an external data code and an internal data code using one of multiple conversion modes is provided to maintain confidential data backed up by a battery. A security protection method for an integrated circuit, characterized in that the conversion mode is selected based on confidential data held in the circuit.