JP3865347B2 - Watermark insertion method and system for program - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a watermark insertion method and system that can identify the source of fraud when there is fraud due to illegal copying of a computer program.
[0002]
[Prior art]
With the development of computerization and the spread of computers, the importance of computer programs is increasing. The most notable feature of a computer program is its digital information itself, which is the productivity that makes it possible to produce copies of the same quality as the original at high speed and at low cost. However, while having such advantages, there is a risk that unauthorized use such as unauthorized copying, theft of program codes and algorithms, and alteration are easily performed. From this background, it is considered necessary to create an environment that can prevent unauthorized use of computer programs (software) by non-creators.
[0003]
As a main software protection method currently proposed, for example, as disclosed in Japanese Patent Application Laid-Open No. 8-95777 “Software Usage Control Device”, various contents are distributed for a fee through a network, so-called “super distribution” And a method using special hardware (server computer), and a method of applying copy protection as disclosed in Japanese Patent Application Laid-Open No. 10-27123 “Copy protection method of computer software”. It is done.
[0004]
[Problems to be solved by the invention]
However, the “super-distribution” method has a problem that costs increase. Also, a method using a recording medium such as copy protection has a problem that it cannot be used when distributing a computer program via a network. In order to create an environment that can be reassured by the creator, it is necessary to provide the software itself with a tamper-resistant property that is low-cost and resistant to tampering and theft. However, in reality, since a computer program is digital information, it can be easily copied and it is considered difficult to prevent unauthorized use.
[0005]
The object of the present invention is not to prevent unauthorized use itself, but by providing a mechanism that allows a computer program to easily identify the source (unauthorized copy person) when unauthorized use is detected. An object of the present invention is to provide a method and system for inserting a watermark into a computer program that can prevent unauthorized use by non-persons with an inexpensive configuration.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, the idea of a digital watermark technique that is currently used as a technique for preventing unauthorized use of images and the like is applied to a computer program. The digital watermark method is one of technologies for protecting copyrights such as images and sounds as disclosed in, for example, Japanese Patent Application Laid-Open No. 9-191394 “Electronic watermark insertion method”. This is a technique for preventing unauthorized use such as diversion of image data and unauthorized reproduction by embedding ID information in the data.
[0007]
The digital watermark technique has the following features:
1. 1. Data is not degraded by embedding ID When the user removes the embedded ID, the data deteriorates (the user cannot remove the ID).
[0008]
The watermark insertion method for a program according to the present invention selects several instruction sentences that do not affect the specifications of the program from the source code of the program into which the watermark is to be inserted, and does not affect the specifications of the program. In addition, after inserting the calculation formula for the dummy variable, the command statements are randomly exchanged, and the order of the exchanged command statements is stored as watermark information.
[0009]
The “watermark” in the present invention inserts information that does not affect the specification of the program and is meaningful to the creator, but meaningless to the user side or does not know that it exists. It is. In the present invention, as a method of “watermark”, a method is adopted in which a dummy variable is inserted, and the command statements in which the dummy variable is inserted are randomly replaced.
[0010]
The “watermark information” is information representing the method of the “watermark” inserted by the above method, and in the present invention, information on the order of the exchanged command statements is employed.
[0011]
An example of a replaceable command statement is a variable assignment statement. The dummy variable is used to make it difficult for an unauthorized user to analyze the program and to prevent falsification of the watermark.
[0012]
The calculation formula for the dummy variable refers to a variable used in a replaceable command statement. Furthermore, in order to make it more difficult for an unauthorized user to analyze the program, the generated assembler code may be obfuscated when the source code is compiled after replacing the statement. Obfuscation refers to, for example, IEICE Transactions Vol. J80-D-I No. 7 “Proposal of a method to obfuscate a program containing a loop” (Kadota, Takada, Torii) This is a transformation that makes the analysis difficult while maintaining the program specifications.
[0013]
By the above means, when an unauthorized user replaces a command statement in an attempt to tamper with the “watermark”, the dummy variable calculation formula refers to the variable used in the command statement in which the dummy variable calculation formula is replaced. The result will change. Therefore, for unauthorized users, if the “watermark” is tampered with, it becomes difficult to know whether or not the program specification is maintained, and the act of tampering even at the expense of the program specification must be abandoned. It is possible to suppress unauthorized use.
[0014]
On the other hand, even if the “watermark” can be tampered with, the creator immediately discovers that it has been tampered with by analyzing the altered program and comparing it with the watermark information stored on the creator's side. can do.
[0015]
Further, by adding a user ID for each distribution destination to the “watermark information” and storing it, even if a large number of illegal copies are circulated, the “watermark information” of the illegal copies is taken out, and the “watermark” By examining the user ID corresponding to “information”, the unauthorized copy source can be immediately identified. As a result, unauthorized use of a computer program by a person who is not the creator can be suppressed.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0017]
FIG. 1 is a system configuration diagram showing an embodiment of a watermark insertion system to which the present invention is applied.
[0018]
The watermark insertion system 110 of this embodiment includes an input unit 111, a display unit 112, an output unit 113, a central processing unit 114, a watermark insertable area detection unit 115, a watermark insertable area storage unit 116, a watermark insertion unit 117, watermark information. The storage unit 118 and the watermark extraction unit 119 are configured to perform processing such as detection of a watermark insertable area, watermark insertion, and watermark information extraction.
[0019]
The input unit 111 is for inputting a source code of a program into which a watermark is to be inserted. The display unit 112 is for displaying watermark information and the like. The output unit 113 is for outputting an executable program into which a watermark is inserted. The central processing unit 114 controls processing such as detection of a watermark insertable region, watermark insertion, and watermark extraction.
[0020]
The watermark insertable area detection unit 115 detects a portion where a watermark can be inserted from the source code of the program. The watermark insertable area storage unit 116 stores a portion of the program source code into which a watermark can be inserted. The watermark insertion unit 117 inserts a watermark into the program source code and compiles the source code. The watermark information storage unit 118 stores information on the inserted watermark. The watermark extraction unit 119 extracts a watermark from the executable program.
[0021]
The watermark insertion system 110 of the present embodiment performs the following three characteristic processes.
[0022]
(1) Detection of watermark insertable area (2) Watermark insertion (3) Extraction of watermark The watermark insertable area detection process is a process for detecting a place where a watermark can be inserted in a program to be inserted, Before the watermark is actually inserted into the program to be inserted, it is performed only once at the beginning. The watermark insertion process is a process for embedding an ID for identifying a distribution-destination user. Each time a program to be distributed is distributed to the user, management of the creator or management of the administrator who has been delegated by the creator is performed. Do it below.
[0023]
The watermark extraction process is a process for specifying the user to whom the program is distributed, and is performed when investigating unauthorized use of the program. An example of a case where it is desired to specify a distribution destination of a program is a case where an illegal copy of the program is circulated and the source of the illegal copy is to be determined. The three processes will be described in detail below.
[0024]
First, the watermark insertable area detection process will be described with reference to the watermark insertable area detection flowchart of FIG.
The program creator inputs the source code of the program into which the watermark is to be inserted from the input unit 111 (step 21).
When the source code of the program is input, the central processing unit 114 uniquely assigns a program ID to the input program (step 22).
When the program ID is assigned, the central processing unit 114 sends the source code to the watermark insertable area detecting unit 115. The watermark insertable area detection unit 115 analyzes the sent source code and detects a set of command statements that do not affect the program specifications even if they are replaced with each other (step 23).
[0025]
FIG. 3 is an explanatory diagram of the watermark insertable area detection process in step 23. In FIG. 3, an imperative sentence 31, an imperative sentence 32, and an imperative sentence 33 are assignment statements that refer to different variables. Therefore, even if the command statement 31, the command statement 32, and the command statement 33 are interchanged with each other, the specification of the program is not affected.
When a replaceable command sentence is detected, the watermark insertable area detection unit 115 sends the information of the command sentence to the central processing unit 114 as a watermark insertable area. The central processing unit 114 sends the sent watermark insertable area and the program ID of the program including the watermark insertable area to the watermark insertable area storage unit 116 (step 24).
[0026]
FIG. 4 is an example of watermark insertable area information stored in the watermark insertable area storage unit 116. The watermark insertable area information 40 includes a program ID 41 for identifying a program, an original source code 42 of the program, and a watermark insertable area 43 representing a replaceable command statement.
[0027]
FIG. 5 shows an example of the watermark insertable area 43, which is composed of a source line number 51 in the source code of a replaceable command statement, a replaceable command statement 52, and a code ID 53 for identifying the command statement. Has been. The example of FIG. 5 corresponds to the command statement of FIG.
In the example of FIG. 3, there is only one watermark insertable area 43, but there may be two or more. However, in that case, it is necessary to devise the notation of the code ID 53 (eg, A1, A2,..., B1, B2,...) So that it is possible to identify which command statements can be interchanged. is there.
[0028]
When the watermark insertable area information 40 is sent, the central processing unit 114 displays the program ID assigned to the display unit 112 (step 25) and ends the process. The program ID is information input by the program creator so that the watermark insertion system 110 can identify the program into which the watermark is to be inserted during the watermark insertion process. Therefore, the program creator needs to record the displayed program ID.
[0029]
Next, watermark insertion processing will be described with reference to the watermark insertion flowchart of FIG.
The program creator inputs the program ID of the program into which the watermark is to be inserted and the user information of the program distribution destination from the input unit 111 (step 61).
When the program ID and the user information are input, the central processing unit 114 refers to the watermark insertable region information 40 from the watermark insertable region storage unit 116 based on the input program ID, and the watermark insertable region information 40 is sent to the watermark information insertion unit 117 (step 62).
[0030]
When the watermark insertable area information 40 is sent, the watermark inserting unit 117 inserts a calculation formula related to the dummy variable between the command sentence that can be exchanged based on the watermark insertable area information 40 and the command sentence (step). 63). The dummy variable is used only for preventing falsification of the watermark. The dummy variable calculation formula refers to the variable used in the replacement statement. Note that the calculation result of the dummy variable is not related to the program specification or the watermark information itself.
When the calculation formula is inserted, the watermark insertion unit 117 randomly replaces the replaceable command statement (step 64).
[0031]
FIG. 7 is an explanatory diagram of the watermark insertion process in step 63 and step 64. The command statement 71, the command statement 72, and the command statement 73 are watermark insertion possible areas. In step 63, a calculation formula 74 regarding the dummy variable is inserted between the command statement 71 and the command statement 72. Further, a calculation formula 75 related to the dummy variable is inserted between the command statement 72 and the command statement 73. The calculation formula 74 and the calculation formula 75 refer to the variables a, b, and c used in the command statement 71, the command statement 72, and the command statement 73. In step 64, the command statement 71, the command statement 72, and the command statement 73 are replaced at random.
[0032]
When the statements are replaced, the watermark insertion unit 117 compiles the source code (step 65).
When the source code is compiled, the watermark insertion unit 117 sends the order information of the replaced instruction sentence to the central processing unit 114 as watermark information. The central processing unit 114 sends the sent watermark information, the program ID corresponding to the watermark information, and the input user information to the watermark information storage unit 118 for storage (step 66).
[0033]
FIG. 8 is an example of the watermark information 80 stored in the watermark information storage unit 118. The watermark information 80 is composed of a program ID 81 for identifying a program, command statement order information 82 indicating the order of replaced command statements, a user ID 83 for identifying a program distribution destination user, and additional information 84. ing. The user ID 83 is uniquely assigned when the watermark information storage unit 118 stores and saves the watermark information 80. Examples of the additional information 84 include the name, address, telephone number, and mail address of the distribution destination user.
[0034]
FIG. 9 is an example of the command statement order information 82. The command statement order information 82 includes a code ID 91 of the command statement, an assembler code 92 corresponding to the command statement, and an assembler line number 93 of the assembler code.
When the watermark information 80 is sent, the watermark information storage unit 118 checks whether the program ID 81 and the command statement order information 82 in the watermark information 80 overlap with the already stored watermark information 80 (step 67). ).
If it is duplicated, the process returns to step 65 to replace the statement.
If there is no overlap, the watermark information storage unit 118 adds the user ID 83 to the sent watermark information 80 and stores and saves the watermark information 80 (step 68).
[0035]
By this duplication check process, a different watermark is inserted for each user ID, and the watermark information is stored in the storage unit 118.
[0036]
When the watermark information 80 is stored, the central processing unit 114 outputs the executable program into which the watermark is inserted from the output unit 113 (step 69), and the process is terminated. The executable program inserted with the watermark in this way is distributed to the user.
[0037]
Next, processing for extracting a watermark from an executable program distributed to a user will be described with reference to the watermark extraction flowchart of FIG.
The creator of the program inputs from the input unit 111 an executable file of the program whose watermark is to be extracted (step 101). Further, the program ID is input from the input unit 111 (step 102).
[0038]
When the executable program and the program ID are input, the central processing unit 114 takes out the watermark information 80 corresponding to the program ID stored in the watermark information storage unit 118 based on the input program ID, It is sent to the watermark extraction unit 119 together with the execution format program (step 103). In this case, when a program with the same program ID is distributed to a plurality of users, all watermark information 80 having that program ID is extracted and sent to the watermark extracting unit 119.
[0039]
When the executable format program and watermark information 80 are sent, the watermark extraction unit 119 disassembles the executable format program, analyzes the order of the command statements used for the watermark, and generates the command statement order information 82. In this case, the range of the command sentence used for the watermark is known from the range of the assembler line number 93 in the command sentence order information 82 in the watermark information 80 extracted from the watermark information storage unit 118.
[0040]
If the command statement order information 82 is generated, the watermark extraction unit 119 compares the generated command statement order information 82 with the command statement order information 82 in the watermark information 80 extracted from the watermark information storage unit 118, The watermark information 80 having the command sentence order information 82 that matches (or has the same meaning) is selected and extracted, and the selected and extracted watermark information 80 is sent to the central processing unit 114 (step 104).
[0041]
FIG. 11 is an explanatory diagram of the watermark extraction process in steps 103 and 104. When the executable program is disassembled, the order of the instruction sentences is analyzed, and the instruction sentence order information 82 is generated. Then, the generated command statement order information 82 and the command statement order information 82 in the watermark information 80 extracted from the watermark information storage unit 118 are collated, and the command statement order information 82 in which both match (or have the same meaning). Is selected and extracted, and the user ID 83 and additional information 84 in the selected and extracted watermark information 80 are extracted.
[0042]
The central processing unit 114 displays the extracted user ID 83 and additional information 84 on the display unit 112 (step 105), and ends the process.
[0043]
As described above, in this embodiment, the order of the statements is inserted into the program as a watermark. Therefore, in order for an unauthorized user to alter the watermark without changing the program specifications, it is necessary to replace the command statement in the watermark insertable area. However, if the command statement in the watermark insertable area is replaced, the calculation result of the dummy variable changes. In the example of FIG. 7, the calculation result of the dummy variable d is “2” before the command statement replacement, but the calculation result of the dummy variable d is “−4” after the command statement replacement. For this reason, even if an unauthorized user replaces the instruction text in the watermark insertable area, it becomes difficult for an unauthorized user to know whether the program specifications are maintained after the instruction replacement, and at the expense of the program specifications. Therefore, it is necessary to give up the act of tampering until it is possible to substantially prevent unauthorized use.
[0044]
On the other hand, even if the “watermark” can be tampered with, the creator immediately discovers that it has been tampered with by analyzing the altered program and comparing it with the watermark information stored on the creator's side. can do.
In addition, by adding a user ID for each distribution destination to the “watermark information” and storing it, even if a large number of illegal copies are available, the “watermark” of the illegal copy is taken out and the “watermark” is supported. By checking the user ID to be used, the unauthorized copy source can be immediately identified. As a result, unauthorized use of a computer program by a person who is not the creator can be suppressed.
Further, if obfuscation is performed after watermark insertion, it becomes even more difficult for an unauthorized user to analyze the program, which is more effective in suppressing unauthorized use.
In the above embodiment, a computer program executable by the central processing unit 114 is a watermark insertable area detection function, a watermark insertable area storage function, a watermark insertion function, a watermark information storage function, and a watermark extraction function in the watermark insertion system 110. However, it is possible to record all or part of the programs constituting these functions on a storage medium such as a CD-ROM or to provide the program creator for a fee via a communication medium such as the Internet. be able to. By executing the above functions on the program creator's computer, it is possible to insert a unique “watermark” into the computer program created by each program creator to prevent unauthorized use and contribute to copyright protection. it can.
[0045]
【The invention's effect】
As described above, if the watermark insertion method of the present invention is used, it is necessary to give up the act of tampering even at the expense of the program specifications, and it becomes possible to suppress unauthorized use with an inexpensive configuration. .
Even if the “watermark” can be tampered with, the creator analyzes the altered program and confirms that it has been tampered with by checking the “watermark information” stored on the creator side. It can be discovered immediately.
Furthermore, by adding a user ID for each distribution destination to the “watermark information” and storing it, even if a large number of illegal copies are available, the “watermark” of the illegal copy is taken out and the “watermark” is supported. By checking the user ID to be used, the unauthorized copy source can be immediately identified. As a result, unauthorized use of a computer program by a person who is not the creator can be suppressed.
Further, if obfuscation is performed after watermark insertion, it becomes even more difficult for an unauthorized user to analyze the program, which is more effective in suppressing unauthorized use.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram showing an embodiment of the present invention.
FIG. 2 is a watermark insertion possible area detection flowchart in the embodiment of FIG. 1;
FIG. 3 is an explanatory diagram of a watermark insertable area detection process in the embodiment of FIG. 1;
FIG. 4 is a diagram showing watermark insertable area information in the embodiment of FIG. 1;
FIG. 5 is a diagram showing a watermark insertable area in the embodiment of FIG. 1;
FIG. 6 is a watermark insertion flowchart in the embodiment of FIG. 1;
FIG. 7 is an explanatory diagram of watermark insertion processing in the embodiment of FIG. 1;
FIG. 8 is a diagram showing watermark information in the embodiment of FIG. 1;
FIG. 9 is a diagram showing a command statement order in the embodiment of FIG. 1;
FIG. 10 is a watermark extraction flowchart in the embodiment of FIG. 1;
FIG. 11 is an explanatory diagram of watermark extraction processing in the embodiment of FIG. 1;
[Explanation of symbols]
80 ... watermark information, 82 ... command sequence information, 83 ... user ID, 110 ... watermark insertion system, 111 ... input unit, 112 ... display unit, 113 ... output unit, 114 ... central processing unit, 115 ... watermark insertable area Detection unit 116... Watermark insertable region storage unit 117 117 watermark insertion unit 118 118 watermark information storage unit 119 watermark extraction unit

Claims (5)

Watermarking area detector mounted on the computer accepts the source code of the watermark insertion target program from the source code, takes out a plurality of instruction statement has no effect on the design of the programs even out of sequence, the statement A first step of storing the description line in the first storage means as a watermark insertable area;
The watermark insertion means implemented in the computer inserts a calculation formula related to the dummy variable between the instruction sentence and the instruction sentence in the watermark insertable area stored in the first storage means, and randomly inserts the instruction sentences. A second step of storing in the second storage means as the watermark information, the order information of the exchanged instruction sentence and the identification information for each distribution destination of the executable program compiled from the source code with the exchanged instruction sentence;
A method for inserting a watermark into a program.   The watermark extracting means mounted on the computer takes the executable program as an input, disassembles the inputted executable program, analyzes the order of the instruction sentences, and analyzes the order information of the instruction sentences as a result of the analysis. And a third step of collating with the order information of the replacement instruction sentence in the watermark information stored in the second storage means, and extracting the watermark information related to the input executable program. A method for inserting a watermark into the program according to Item 1. A source code of a watermark insertion target program is received, a plurality of instruction statements that do not affect the program specifications even if the order is changed are extracted from the source code, and a description insertion line of the instruction statement is used as a watermark insertion possible area. Watermark insertable area detection means for storing in the storage means;
A calculation formula related to a dummy variable is inserted between a command sentence and a command sentence in the watermark insertable area stored in the first storage means, the command sentences are exchanged at random, and the order information of the exchanged command sentences And watermark insertion means for storing, in the second storage means, identification information for each distribution destination of the executable program obtained by compiling the source code in which the instruction statement is replaced, and watermark information to the program. Insertion system.   The execution format program is set as an input, the input execution format program is disassembled, the order of instruction statements is analyzed, and the order information of the analysis result instruction statements and the second storage means are stored. 4. The watermark insertion system for a program according to claim 3, further comprising: a watermark extracting unit that compares the order information of the replacement command statement in the watermark information and extracts the watermark information related to the executable program. A recording medium recording a watermark insertion program for inserting a watermark into a program,
A source code of a watermark insertion target program is received, a plurality of instruction statements that do not affect the program specifications even if the order is changed are extracted from the source code, and a description insertion line of the instruction statement is used as a watermark insertion possible area. A first step of storing in the storage means;
A calculation formula related to a dummy variable is inserted between a command sentence and a command sentence in the watermark insertable area stored in the first storage means, the command sentences are exchanged at random, and the order information of the exchanged command sentences A second step of storing, in the second storage means, identification information for each distribution destination of the executable program obtained by compiling the source code in which the command statement is replaced, as watermark information;
The execution format program is set as an input, the input execution format program is disassembled, the order of instruction statements is analyzed, and the order information of the analysis result instruction statements and the second storage means are stored. A recording medium on which is recorded a program that causes a computer to execute a third step of collating the order information of the replacement command in the watermark information and extracting the watermark information related to the input executable program.

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