JPH0245829A - Method and circuit for detecting permission-free access of computer program stored in medium - Google Patents

Abstract

PURPOSE: To prevent the unapproved copying of an unapproved user by providing a circuit for detecting that a code is accessed by a sequential order which is not a normal non-sequential order. CONSTITUTION: A go-by flag 103 corresponding to a pre-branch address array 102 is set when the pre-branch address of the array 102 is accessed. That is, in a branch address array 104, an address to be accessed after the pre-branch address is accessed in normal non-sequential access and to be accessed before the access of the pre-branch address in simply sequential access is stored. A comparator circuit 107 checks whether or not valid access is performed by the flag 103 of the array 102 every time the address in the array 104 is accessed, and when it is not performed, instructs an error function generation circuit 110 and turns output data from a ROM 109 to incoherent data.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the field of software copy protection, and more specifically, how software is accessed by authorized users and how unauthorized users The present invention relates to a method and apparatus for providing copy protection using the assumption that there is a fundamental difference between the way software code is accessed.

[Conventional technology]

The software industry is plagued by the problem of software being copied by unauthorized users. The act of copying software causes the software producer to suffer damage in that the software cannot be sold because the software has been copied.

The inventors are aware of numerous methods for copy protection of computer program code. For example, how to link the execution of a program to the serial number of a specific computer,
A method involves physically damaging a floppy disk at a predetermined location before writing a computer program to the disk, and then having the software verify the existence of the damaged portion before allowing the computer program to run. used.

However, the inventors are unaware of how to take advantage of the inherent differences in the way authorized and unauthorized users access software.

[Summary of the invention]

This specification describes methods and apparatus for preventing unauthorized copying of software. The invention is based on the fundamental difference between the way software code is accessed by authorized users and the way software code is accessed by unauthorized users.

Authorized users who wish to run software code may do so by reference to the procedures published with the code. Using those procedures, authorized users begin executing the code. Execution of computer program code occurs not sequentially, but in some non-sequential order known to the software developer at the time the software developer wrote the source code. However, that information
It is unavailable to unauthorized users who do not have access to the computer's source code. The present invention recognizes the fundamental differences in the way software is accessed by authorized and unauthorized users and exploits these differences in the way the code is protected. Accessing the code in a sequential order rather than the normal non-sequential order causes the error generator to mess up subsequent data read from the data source.

To utilize the above method of the present invention, the software developer inserts several trap addresses.

The code was chosen so that executing the code in its normal execution order would always skip over those trap addresses. Trap addresses are used to trap unauthorized users attempting to dump code sequentially from beginning to end. Dumping the code sequentially like that also dumps trap addresses. When the trap address is dumped, the error generator is activated. The error generator then messes up all subsequent data read from the data source. Unauthorized users do not know which addresses will mess up the data being copied. Unauthorized copying of the contents of the protected code is therefore futile.

In a preferred embodiment of the invention, read-only memory is used to store computer program object code! J
(ROM) or similar storage device is used.

In addition to storing computer program object code in the ftROM, circuitry is provided to store the four arrays used by the method of the invention.

The first play, called the trap branch array, stores a set of addresses to jump to during normal execution of the computer program. The second one, called the pre-branch array,
stores the address to branch to each address in the trap branch array. The pre-launch array also stores an indicator that corresponds to each pre-launch address and is set each time that pre-launch address is accessed. Each time an address in the trap branch array is accessed, the circuit of the present invention determines whether the indicator corresponding to the pre-plant address corresponding to the trap branch address has been set.

As explained in more detail later in the Examples section, the indicator is set during normal execution of the code, but the indicator is set during sequential access of the code, as is done during copying of the code. Not set.

The present invention also discloses a third array called a clear branch array. The clear branch array contains addresses that are accessed during a successful access to code after the corresponding trap branch address is accessed. Circuitry is provided to reset the corresponding indicator flag after accessing an address in the clear branch array.

Furthermore, a fourth play is also disclosed that is stored in the ROM and has an address in the ROM storage space that is not accessed during normal execution of the code but is accessed during sequential copying.

Various alternative embodiments are also disclosed to make it more difficult for pirates to defeat copy protection technology and copy software.

This specification describes methods and apparatus for preventing unauthorized copying of computer programs.

In the following description, numerous details are set forth, such as program code, in order to provide a thorough understanding of the present invention.

However, it will be apparent to one skilled in the art that the invention may be practiced without such specific details.

In other instances, well-known processes and structures are not described in detail in order to avoid obscuring the present invention in unnecessary detail.

The present invention discloses a method for protecting convenience store software from unauthorized copying. This method takes advantage of non-order access to the computer software while the computer software is normally running by an authorized user. An unauthorized user attempting to copy the code will attempt to access the code sequentially.

As a first aspect of the invention, each first address set is R
A method and apparatus for setting an indicator when accessed within an OM is disclosed. As each second set of addresses is accessed, a check is made to determine whether the corresponding indicator has been set. During normal execution of the program code, the indicator is set before accessing the second address. However, if the code were to be accessed sequentially, the indicator would not be set and the circuit of the present invention would prevent coveys.

As a second aspect of the invention, a method and apparatus for maintaining a set of addresses in ROM is disclosed. The retained addresses are not accessed during normal execution of the computer program stored in the ROM, but are accessed when the code in the ROM is accessed sequentially. A circuit is disclosed by the present invention for detecting access to a retained memory address and preventing copying of a computer program stored in a ROM after the access is detected.

〔Example〕

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

The above first aspect of the invention can be better understood with reference to the accompanying drawings. All computer programs have logical branches, but only the software developer and others who have access to the source code know the exact location of the branches. Unless an unauthorized user accesses the source code, the location of the branch cannot be easily accessed by that user. One method disclosed by the present invention of protecting computer software is by using trap branches. The principle of a trap branch is that addresses in procedure B can be accessed during program execution if and only if procedure A has already been executed. An unauthorized user does not know the correct order of execution of the procedures, so when copying code sequentially, he accesses procedure B without accessing procedure A first.

In modern high-level programming languages, several constructs are available to modify the flow of control in a computer program. Examples of such constructs are the Go To statement and the rtr THEN E
t,sgJ structure and the CASE,'( statement. However, any number of structures used for branching in computer programs may be utilized without departing from the spirit of the invention.

Table 1 shows examples of computer program code that can be utilized in accordance with the present invention. The code shown in Table 1 is used to implement aspects of the invention.
Use LSEJ structure.

Table 1 PROCEDURE X: //ITRAP BRANCHI/ PROCEDURE Y: IF (condition) TI (EN CALL puocgoouEX; /:
PREB rib species 1γELSE CALL, puocgoo
ug x;2009 CA[,L C0N
TINUE PROCEDURE; /, cLJC
^J1 BRANCH umbrella/In the normal table execution of the code in Table 1, PROCEDURE
can be executed if and only if the r IF THENJ statement at line 2003 has been executed first.

Referring to the accompanying drawings, which show a block diagram of a circuit that can be utilized in accordance with the present invention, the circuit has a pre-launch address array 102. The pre-launch address play has a plurality of pre-launch addresses 101 and an indicator or "go-by flag" 103. Pre-plant address 101 has an address such as the address of the rp THENJ statement in row 2003 of Table 1. Each time address 101 in pre-plant address array 102 is accessed,
A corresponding go-pai flag 103 is set.

The circuit of the present invention also includes a trap branch array 104. This trap branch array is row 5o of Table 1.

has multiple trap branch addresses such as PROCED[]RgX in . A trap-plant address is one that is accessed during normal execution of a computer program only after accessing the corresponding pre-plant address, even though the trap-plant address normally occurs before the pre-plant address in the program code sequence. This is the address.

Each time an address in the trap-plant address is accessed, a check is made to determine if the corresponding go-pay flag 103 has been cassetted. Setting the go-by flag 103 indicates that the corresponding pre-launch address 101 has been accessed or "passed."

A comparison circuit 107 is coupled to trap branch array 104 and pre-branch array 102 to perform the comparison of whether an address in trap branch array 104 was accessed prior to the access in pre-branch array 102 . Comparison circuit 101 further receives as input the address to be accessed in ROM1Q9. The address is received by comparison circuit 107 and ROM 109 via address line 108 almost simultaneously.

Comparison circuit 107 includes circuitry that indicates whether a valid access has been attempted. Comparison circuit 107 is coupled to ROM 109 to indicate whether a valid address access has been attempted. As long as the comparison circuit 107 indicates that a valid access has been made, j5, ROM1
09 outputs valid data on line 1 in response to address input.
11.

Comparison circuit 107 is also coupled to error function generation circuit 110. A signal from the comparator circuit 107 indicating that a trap state or an error state has occurred is supplied to the false function generating circuit 11G. In response to receiving that signal, error function generating circuit 110 provides an output that disrupts the data output provided by ROM 109 on line 111.

In one embodiment of the present invention, the error function generation circuit 110
also takes as input a random number that is used to mess up the data output. Generally, the error function generation circuit can implement functions such as ERRORFtlNCTION (current date, current address, programmable input).

The large number of programmable inputs makes decoding the output values extremely difficult. It will be apparent to those skilled in the art that any feature that disrupts or renders the data output from ROM 109 unusable is useful in the present invention.

The preferred embodiment of the present invention also has a clear branch array 106 coupled to the pre-branch array and comparator circuit 107. The clear branch array 106 in row 2009 of Table 1 is [CALLCoNTINUEpuoc
It has multiple addresses corresponding to entries in the pre-branch array 102, such as the address of the EouhgJ statement. Each time an address in clear branch array 106 is accessed, the corresponding go-by flag 103 is reset. Assuming that the code is accessed in normal table execution order, the trap branch play address is accessed and the clear array address is accessed 9 seconds later.

A trap address array 105 can be used as a second means for preventing copying in the present invention. Table 1 shows an example of computer programming code that can be utilized in accordance with the present invention in connection with trap address array 105.

Chapter ■ Table line number statement annotation 1000 1F 1=I X:UNtVER8
AL TRUTH 1001 THEN DUMY vhRxAnLE=o:
1002 ELSE DUMY VARIABJ=
L 〆, TRAP ADDRESS */Trap address array 105 has a plurality of addresses in the address space of ROM 109 that are not accessed during normal execution of a program. For example, in Table ■, row 1000
When the statement [IF 1=IJ is executed, the statement rTHEN DU at line 1001
MY VARIABLE = always results in OJ being executed. During normal program execution, the statement ra
Lsg DUMY vpnxhsr, E=x'' is never executed, but it will be accessed during sequential copying of program code. :X in line 1002
f-Tome 7 “THEENDUMYvARIABLE =
Accessing the address of IJ will result in comparator circuit 107 signaling an error condition and messing up the data output provided on line 111 as described above.

The circuit shown in FIG. 1 can be implemented using discrete components or can be implemented using a gate array or similar device. Additionally, the ROM 109 may be a normal read-only memory or an electrically erasable read-only memory.
(PROM), Electrically Erasable Programmable Read Only Memory (EEPROM), Programmable Read Only Memory (PROM), Masked ROM
Alternatively, it may include similar devices such as flash EFROM.

Different from the embodiments described above, several methods and devices are available to improve protection. For example, a first pre-branch array has an entry corresponding to a trap branch array, a second pre-branch array has an address corresponding to a fourth pre-branch array, and a third pre-branch array has an entry corresponding to a fourth pre-branch array. A nested pre-branch array can be used to have addresses corresponding to two pre-branch arrays. Each pre-branch array has an address and a go-by flag. Any access to an address in the second pre-branch array! Valid only when the corresponding go-by flag in the pre-branch array of 3 is set. Any access to an address in the first pre-branch array is valid only when the corresponding go-by flag in the second pre-branch array is set. Any table access to an address in the trap branch array is valid only when the corresponding go-by flag in the first pre-branch array is set.

As a second example, a trap branch is a substitute for one address υ
can have a range of addresses.

A third example of an improved protection method and device includes delaying messing up data due to a random number of memory accesses after an invalid access has been made.

As a fourth example, the error function generating circuit 110 has a self-destruct mechanism. That fourth example makes decoding of copy protection techniques even more difficult. The self-destruct function can be implemented in several ways. For example, in a ggPROM, a self-destruct mechanism can be implemented by asserting an array signal that erases all EEFROM code. masked R
In OM, self-destruction can be accomplished by irreversibly damaging the circuit by blowing an electronic fuse, permanently disconnecting control lines and other critical equipment.

Such a self-destruct mechanism can be designed to be activated only after n trap alarms have been detected.

As disclosed by the present invention, the use of pre-branch arrays and trap branch arrays and the use of trap address arrays to detect unauthorizedness may be performed independently or in conjunction with each other. It can be made to work. Implementing these mechanisms in conjunction with each other makes the work of unauthorized users even more difficult.

Thus, methods and apparatus for detecting and preventing unauthorized access of computer software have been described.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the circuit of the present invention. 101... Comparison circuit, 109... ROM. 110...Error function generation circuit.

Claims (6)

[Claims] (1) (a) determining the addresses on the medium that are accessed in the normal execution order of a computer program stored on the medium; and (b) the step of determining the addresses that are accessed in the execution order of the computer program stored on the medium; responsively providing a signal indicating that a valid access has occurred; (d) providing a signal indicating that an invalid access has occurred in response to the determination of addresses being sequentially accessed; A method for detecting unauthorized access of a computer program stored on a medium. (2) storing at least one pre-launch address;
and at least 1 corresponding to the pre-launch address, indicating that the pre-launch address has been accessed.
a pre-plant array memory means for storing at least one trap-plant address; a read-only memory coupled to an address input line and a data output line for storing said computer; a comparator coupled to the address input line, the pre-plant array memory means, and the trap-plant array memory means for comparing the pre-plant address and the trap-plant address with an address provided to the address input line; A circuit for detecting unauthorized access of a computer program, comprising: means for detecting unauthorized access of a computer program. (3) a trap address array memory means for storing at least one trap plant address; a read-only memory coupled to an address input line and a data output line for storing said computer program; and said address input line and said trap branch address; and comparator means coupled to address array memory means for comparing said trap address with an address provided to said address input line. (4) detecting when a first address location in the medium is accessed; and setting an indicator to indicate that the first address location is accessed; detecting when a second address location is accessed; and checking the indicator when the second address location is accessed to determine whether the first address location is accessed. A method for detecting unauthorized access of a computer program stored on a medium, comprising: (5) detecting when a first address location on a medium is accessed; and detecting when the computer program is output from the medium in response to accessing the first location; 1. A method for detecting and preventing unauthorized access of a computer program stored on a medium, comprising the steps of: (6) read-only memory (ROM), electrically erasable read-only memory (EEPROM), erasable and programmable read-only memory (EPROM), and programmable read-only memory (PROM);
in a method for detecting and preventing unauthorized copying of computer program purpose code residing in a device selected from a group of ROM firmware devices comprising a masked ROM; such that the first location is accessed before, and
designing a computer program such that the second location is accessed before the first location during sequential access of the computer program object code; and a third location is accessed during execution of the computer program object code. configuring the computer program object code so that it is not accessed but is accessed during sequential accesses of the computer program object code; detecting when the first location on the device is accessed; setting an indicator to indicate that a first location has been accessed; detecting when the second location on the device is accessed; and detecting when the second location is accessed. checking a sign to determine whether the first location has been accessed; and the second location has been accessed and no sign is set to indicate that the first location has been accessed. If the third location is accessed, the ROM is characterized by comprising: a step of changing the information output from the device; and a step of changing the information output from the device if the third location is accessed. A method for detecting and preventing unauthorized copying of computer program purpose code residing on a device selected from a group of firmware devices.