JP2000259503A - Flash microcomputer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a password system difficult to be illegally decoded by the third person by using a password address, a password byte length and password data, which can be defined by an end user, without providing a password-only area on a user memory. SOLUTION: Concerning a flash microcomputer 10, the respective data of the password byte length and a password are successively stored from a defined password leading address on a flash memory (b) in advance. In this case, the password byte length of password information received from the outside is compared with the previously stored password byte length and when they are coincident, the next received password data are compared with the previously stored password data. In the case of coincidence in this comparison, the coincidence of password data is discriminated for the first time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microcomputer having a built-in flash memory, a so-called flash microcomputer, and more particularly to an improvement in a method of using a password to inhibit writing and reading of the flash microcomputer.

[0002]

2. Description of the Related Art On-board programming tools for on-chip flash memories for flash microcomputers have recently emerged. By using this kind of tool, device functions such as reading and changing data from and to the flash memory can be easily executed.

In this case, in order to prevent unauthorized writing and reading to the flash memory by a third party, the flash microcomputer determines whether the password matches, and reads or changes the memory on condition that the password matches. Some device functions are permitted to be executed.

[0004]

However, in the current flash microcomputer, there are the following problems with this password, and the password is easily illegitimately decrypted or a dedicated area must be prepared in the flash memory. There were challenges. Many password areas are defined as fixed addresses by the microcomputer. The password length is often a fixed length of about several bytes to 10 bytes. Since the password area is constant, if an attempt is made to define a longer password (the longer the password becomes, the more difficult it will be for unauthorized decryption), it is necessary to newly provide a dedicated area in the flash memory.

[0005] An object of the present invention is to solve such a problem, and a third embodiment uses a password address, a password byte length, and password data that can be defined by an end user without providing a dedicated password area in a user memory. It is an object of the present invention to provide a flash microcomputer that realizes a password scheme that is difficult for a user to illicitly decode.

[0006]

In order to achieve the above object, according to the present invention, a flash memory for storing various information and a control program for writing externally input information in the flash memory are provided. In a flash microcomputer provided with a central processing unit for reading and executing a control program from the stored memory and the memory and controlling each unit, the flash memory includes:
The password byte length and each data of the password are sequentially stored in advance from the defined password start address, and the password byte length of the password information received from the outside is compared with the previously stored password byte length. The received password data is compared with pre-stored password data, and the password is determined to be the same only when the password data matches.

[0007] According to such a configuration, the password byte length and password data set in advance can be set in an arbitrary area on the flash memory, and it is extremely difficult for a third party to illegally decode the password. .

Further, the password information stored in advance can be redefined, so that the user can set the password information independently without being known to the semiconductor manufacturer as the microcomputer maker. Can be.

In addition, by defining the minimum value of the password byte length as described in claim 3, it is possible to protect against illegally specifying a short password byte length.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a basic configuration diagram showing one embodiment of a flash microcomputer according to the present invention. The flash microcomputer 10 includes a central processing unit (hereinafter referred to as a microcomputer core) a for controlling each unit, an on-chip flash memory b,
It is composed of a memory c storing a control program WCP for controlling writing to the flash memory b and other controls and processes, and a serial interface (I / O) d for communicating with the writer 20 for the flash microcomputer.

The control program stored in the memory c is
Usually a fixed program, which includes a password matching function. The password match determination function is a function for determining whether the password information received from the writer 20 externally connected to the flash microcomputer 10 matches the password information stored in the flash memory.

In the conventional flash microcomputer, a data area of several bytes to about 10 bytes is defined in a user area in the flash memory, password information is stored in advance in the data area, and password information input from the writer 20 is stored in the data area. Is used to determine whether they match, but the present invention employs the following method.

As shown in FIG. 2, the password information required to set a password in advance is a head address e of the password, a password byte length f, and password data g. Note that all of these three pieces of information can be defined by the user, and can be set independently by the user without being known to the flash microcomputer manufacturer. In the flash memory b, the data of the password byte length and the password are sequentially stored after the address indicated by the head address e of the password.

The head address e of the password may be several kilos in the flash memory area b which is always used.
It can be set at any position (address) within a range of several hundred kilobytes. In this case, for example, in order to exclude, from the password start address, an area where data (program code) information in the area, such as a reset vector or an interrupt vector area, is relatively easily guessed, an invalid password start address is specified. Control program WCP to prevent
In this case, a gate can be set in the address area for the password start address.

A minimum byte length is also provided for the password byte length f, so that a password with an illegally short byte length specified by the control program WCP is protected from being accepted. Note that the password byte length f
Is 255 bytes here.

The operation in such a configuration will be described below. The password information input from the writer 20 is received via the serial interface d. The password information includes a password byte length and password data. The received password information is stored in the microcomputer core a
By the processing of the control program executed in step (1), a comparison is made with password information preset in a specific area according to the following algorithm.

The received password information is temporarily stored in the flash memory a. The data (the password byte length) of the head address of the information is compared with the password byte length data f set in advance. If the password byte lengths match, the next data of the received password information is compared with the password data g set in advance (judgment is made). The data length to be compared is the number of bytes specified by the password byte length. If the password data matches as a result of the password match determination as described above, the microcomputer core a permits subsequent processing, for example, execution of a device function or the like.

According to the present invention, the password information to be compared with the received password information is stored in an arbitrary area instead of a fixed area in the user memory. Can be realized.

It is useful for the end user to be able to arbitrarily define the password start address, the password byte length, and the password information of the password data in order to prevent unauthorized decryption. Input from the 20 side is complicated, and there is even a risk of erroneous input.

In such a case, if the password is stored in the form of a password file in the program on the writer 20 side, and this file is read and the password information is sent to the fresh microcomputer side, the password input operation can be simplified. Thus, erroneous input can be prevented.

It is to be noted that the above description of the present invention has been presented by way of illustration and example only of a particular preferred embodiment. Thus, it will be apparent to one skilled in the art that the present invention may be modified or modified in many ways without departing from its essentials. The scope of the present invention, which is defined by the description in the appended claims, is intended to cover alterations and modifications within the scope.

[0022]

As described above, according to the present invention, the following effects can be obtained. The password start address, password length, and password data have a user-definable structure, and the password start address can be specified at any position in a wide area in the flash memory.
The efficiency of unauthorized decryption of a password can be extremely reduced.

Since the storage location of the password information set in advance can be arbitrarily specified, data of an arbitrary byte length in a part of the user program area can be used as the password as it is, and the password area must be occupied. There is an advantage that there is no.

Long byte (eg, up to 255 bytes)
Can be specified, so that a password that is difficult to decipher can be easily set. By making the password byte length part of the password, a deeper password scheme was realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a flash microcomputer according to the present invention.

FIG. 2 is a diagram for explaining password information.

[Explanation of symbols]

 10 Flash microcomputer 20 Writer a Microcomputer core b Flash memory c Memory d Serial interface

Claims (3)

[Claims] 1. A flash memory for storing various information, a memory in which a control program for writing externally input information in the flash memory is stored, a control program is read from the memory and executed. In a flash microcomputer provided with a central processing unit for controlling each unit, a password byte length and password data are sequentially stored in advance in the flash memory from a defined password start address, and a password byte of password information received from outside is stored. The password is compared with the pre-stored password byte length, and if they match, the received password data is compared with the pre-stored password data. Configured to determine A flash microcomputer characterized by the following: 2. The method according to claim 1, wherein one, two or three of the head address, password byte length, and password data of the previously stored password are redefinable. The flash microcomputer described. 3. The flash microcomputer according to claim 2, wherein a minimum byte length of the password byte length is defined.