JPH0475137A - Data processor - Google Patents

Abstract

PURPOSE:To protect the secrecy of software by preventing the embezzlement of a program by providing a code conversion means at the preceding stage of an instruction register, and setting an instruction code differently at every user. CONSTITUTION:The code conversion means 11 is provided just before the instruction register 13, and also, such configuration is provided that it is controlled whether or not conversion by the code conversion means 11 should be performed by a signal, and the validity/invalidity of the code conversion means 11 or a code conversion system itself is dynamically varied corresponding to the progression of the program. Therefore, no instruction is executed correctly until matching with the code conversion system by hardware or firmware in a microprocessor is taken even when only the imitation of a program or the switching of a ROM is performed. In such a way, it is possible to protect the secrecy of the software by preventing the embezzlement of the program.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a data processing technology and a technology that is particularly effective when applied to security protection of programs in a microcomputer system. Regarding effective techniques.

[Prior Art] Conventional microprocessors sequentially read program instruction codes stored in semiconductor memory such as ROM (read-only memory) and RAM (random access memory), and then write them as they are. Load into internal instruction register. Then, the loaded instruction is decoded by an instruction decoder, a microaddress corresponding to the instruction code is formed, and the ROM containing the microprogram is stored.
A common method was to access the , read and decode the control word to form a control signal, and use this control signal to operate the execution unit to execute the instruction ([Co., Ltd. Asakura Shoten, June 1981). (Refer to pages 405 to 449 of "Integrated Circuit Application Handbook," published on March 30, 2013).

[Problem to be solved by the invention] For single-chip microcontrollers in which the memory for storing programs is built on the same chip as the processor, reading out instruction codes to the outside of the chip is prohibited. By doing so, you can protect your secrets. However, in a microprocessor that does not have an internal program memory, the instruction code is exposed, so the program stored in the external ROM can be easily decoded, making it impossible to protect the secret. Furthermore, even if the program itself is not decoded, the system can be operated simply by replacing the ROM with the desired program. Therefore, there is a problem in that it is easy to imitate a system that has been developed at a great deal of cost and time.

Therefore, the present applicant provided an instruction code conversion means in the front stage of the instruction register in the microprocessor that captures and holds instruction codes read from external memory, and made the parenthesis code conversion means programmable. He then developed and proposed an invention that enabled the code conversion method to be changed for each user (Japanese Patent Application Laid-Open No. 63-26653).
3).

This invention relates to an improvement on the prior invention, and its purpose is to more effectively prevent program theft and protect the security of software without impairing the versatility of the microprocessor.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means for Solving the Problems] Representative inventions disclosed in this application will be summarized as follows.

In other words, the code conversion means is provided immediately before the instruction register, and whether or not conversion is performed by the code conversion means can be controlled by a signal, and the enable/disable of the code conversion means or the code conversion method itself can be controlled in the progress of the program. It is designed to dynamically change depending on the situation.

[Operations] According to the above-mentioned means, the instruction codes constituting the program stored in the external memory are inversely converted and stored in advance, so if the conversion method of the code is not known, it becomes completely meaningless. Since the code is dynamically converted during the operation of the microprocessor, it becomes even more difficult to decipher the instruction code, and even if you simply imitate the program or replace the ROM, the code conversion method by the software or firmware inside the microprocessor will not work. Unless there is matching, the correct instructions will not be executed, thereby preventing program theft and achieving the above purpose of protecting the security of software.

[Embodiment] An embodiment in which the present invention is applied to a microprocessor will be described below.

The microprocessor 10 includes an instruction register 13 that captures and holds an instruction code read from a memory 30 such as a ROM in which a program is stored via an external data bus 20; The control unit 14 decodes the command code and generates an appropriate control signal. Various general-purpose registers, arithmetic logic units,
An execution unit 15 consisting of a dedicated register such as an accumulator is operated to execute processing corresponding to the read instruction. The control unit 14 is constituted by a ROM (microprogram ROM) in which a microprogram consisting of a group of microinstructions corresponding to a random logic circuit or an instruction code is stored.

In this embodiment, a code converting means 11 comprising, for example, a logic gate or a switching circuit is provided before the instruction register 13.
is provided. Further, corresponding to the code converting means 11, a specifying means 12 such as a flip-flop is provided for specifying whether or not to perform conversion. This designation means 12 receives a signal from an external terminal 16 or a signal from the control unit 1.
The code conversion means 11 can be set to "1" or "0" by the control signal from the data bus 20, and when the designation means 12 is set to "1", the output signal causes the code conversion means 11 to take in the code from the data bus 20. The instruction code is converted and supplied to the instruction register 13, and if the specifying means 12 is set to "0", the instruction code is stored in the instruction register 13 as is.

Here, assuming that the hardware or microprogram of the control unit 14 is common to all microprocessors of the same type, the final instruction codes entered into the instruction register 13 must all be the same.

Therefore, in the system using the microprocessor of this embodiment, the original instruction code entered in the instruction register 13 is created in advance using a code that is converted in the opposite way to the conversion executed by the code conversion means 11. By storing the program in an external memory 3°, desired instructions can be executed. This makes it difficult to decipher the program just by checking the instruction code stored in an external ROM, etc., and it is possible to protect the security of the user program.

Moreover, in this embodiment, the setting state of the specifying means 12 is dynamically changed during program execution.

As a specific method, an address register and a comparator are provided in the control unit 14, and the comparator constantly checks whether the instruction fetch address outputted to the outside is within the address range set in the address register. Specifying means 1 only when an instruction within a predetermined address range is fetched
There is a method of rewriting the state of 2 and causing the code converter 11 to convert the instruction code.

Another method for dynamically changing the setting state of the specifying means 12 during program execution is to
A method of preparing a dedicated command (not disclosed) for switching the command and inserting the command into the program as appropriate to randomly rewrite the specifying means 12, or providing a counter for counting command cycles in the control unit 14, There is a method of periodically rewriting the specifying means 12 to enable or disable the code converter 11.

Furthermore, as another method, there is a pure software method in which the control unit 14 decodes the instruction and rewrites the specifying means 12 so that only the instruction code among the fetched instruction codes is converted, and the operands and data are not converted. Conceivable.

Of course, a signal for resetting the designating means 12 may be input from the outside using the external terminal 16 provided on the chip.

FIG. 2 shows an example of the configuration of the code conversion means 11.

FIG. 2(A) is the simplest example, where the instruction code is n
If it is a bit configuration, n EOR gates 01 to O
Code converting means 11 is constituted by FFO and one flip-flop FFO.

In this embodiment, when the flip-flop FFO is set to "1", the input code is inverted and output, and when the flip-flop FFO is set to "0", the input code is output as is. The state is supplied to the instruction register 3.

In FIG. 2(B), one flip-flop FFO and
A pair of buffers yBF that operate complementary to each bit
11. BFl2 to BFnl, BFn2 are provided, and when the flip-flop FFO is set to "1", the buffers BF12 to BFn2 are activated, and the input bits B to Bn are exchanged and sent to the instruction register. supply

In the embodiment shown in FIG. 2(C), a register consisting of flip-flops FFI to FFn corresponding to the logic gate G1=Gn to which each bit 81 to Bn is input is provided as the specifying means 12. Code conversion can be executed according to the setting status of . In other words, a logic gate whose corresponding flip-flop is set to ``0'' forces the input bit to be fixed to ``0'' and outputs it, and when the flip-flop is set to ``1'', the input bit remains unchanged. Output and supply to the instruction register. As a result, the input code is converted into a completely different code if the settings of the register 12 are different.

In the embodiment shown in FIG. 2C, the same type of logic gate is used for all bits, but a different logic gate may be used for each bit.

On the other hand, as the setting means 12, in addition to a flip-flop, for example, an EPROM element or an EEPROMEPR
Programmable non-volatile elements such as OM elements and ROM elements may also be used. In that case, data may be written into the nonvolatile element by the manufacturer, or may be written by the user.

Further, the code conversion means 11 is configured with an arithmetic logic unit instead of the logic gate circuit shown in FIGS. 2(A) to (C), and the arithmetic logic unit You may also specify the type of operation in . Moreover, for users who wish to protect the confidentiality of their programs from manufacturers by providing a register to specify the type of operation, only the types of operations that are possible in the arithmetic unit are provided as information, and a register that specifies the type of operation is provided to the non-volatile register. By entrusting writing to the user, more reliable security protection is possible.

Furthermore, if the control unit 14 is configured with a rewritable EPROM, a keyword is stored in the microprogram ROM, and a volatile register is used as the register 12, so that the microprogram ROM can be stored in the microprogram ROM at the time of system startup, etc. The key code in the program ROM may be stored in the register 12.

Furthermore, a first-in, first-out cache memory capable of storing a plurality of instruction codes may be provided between the code conversion means 11 and the instruction register 13.

In this way, while the instruction taken into the instruction register 13 is decoded and executed, the next instruction code following the instruction is read from the external memory and converted by the code conversion means 11, By storing it in a cash register, the time required for code conversion can be ignored, and an instruction execution speed almost equivalent to that of a conventional microprocessor without code conversion means can be obtained.

As explained above, in the above embodiment, the code conversion means is provided immediately before the instruction register, and the configuration is such that whether or not the code conversion means performs conversion can be controlled by a signal. Since the conversion method itself is dynamically changed according to the progress of the program, the instruction codes that make up the program stored in external memory are inversely converted and stored in advance, so they become completely meaningless.
Moreover, as the code is dynamically converted during the operation of the microprocessor, it becomes even more difficult to decipher the instruction code, and even if you simply imitate the program or replace the ROM, it will not match the code conversion method using the hardware or firmware inside the microprocessor. Unless there is a code, correct instructions will not be executed, preventing program theft and ensuring software security.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the above Examples and can be modified in various ways without departing from the gist thereof. Nor. For example, in the above embodiment, it has been explained that the code conversion means 11 is composed of a logic gate or an arithmetic unit in order to perform dynamic code conversion, but the present invention is not limited thereto. For example, the code conversion means may be a PLA (programmable logic
It can also be constructed using a programmable ROM (array) or programmable ROM.

In addition, instead of configuring the code conversion means with a buffer circuit that switches a plurality of signal paths as shown in FIG. It may be possible to change and transmit.

In the above explanation, the invention made by the present inventor was mainly applied to microprocessors, which is the background field of application. It can be used generally in microcomputers and other data processing devices that capture and execute instructions.

[Effects of the Invention] The effects obtained by typical inventions disclosed in this application are briefly explained below.

In other words, since the code conversion method can be changed for each user, it is possible to make the instruction code different for each user, and the code conversion method can be changed dynamically during program execution, which increases the versatility of the microprocessor. It is possible to prevent program theft and protect the security of software without damaging the software.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a microprocessor according to the present invention, and FIGS. 2 (A), (B), and (c) are logic circuit diagrams showing an example of the configuration of code conversion means. 10...Microprocessor, 20...External data bus, 13...Instruction register, 14...Control unit, 15...Execution unit, 11...Code conversion means. (see Figure 1 and Figure 2)

Claims (1)

[Scope of Claims] 1. Code converting means provided before an instruction register that captures and holds an instruction code read from an external memory, and whether the code converting means is enabled or disabled or an instruction code conversion method. 1. A data processing device comprising: a designation means for designating. 2. The data processing apparatus according to claim 1, wherein the specifying means is configured such that the setting state is changed by a control signal supplied from a control unit during program execution. 3. The data processing apparatus according to claim 1, further comprising an external terminal for externally changing the setting state of the specifying means.