KR102193017B1 - Method for Software Copyright Protection using Method Generation based Watermarking - Google Patents

Abstract

The present invention relates to a software copyright protection technique using method generation-based watermarking, which uses method overloading and overriding to increase the concealability of watermarks, and uses opaque predicates to prevent execution performance degradation due to the watermarks. A method of the present invention comprises the processes of: generating overloading methods; generating overriding target classes and methods; and generating a method call statement to which an opaque predicate is applied.

Description

Method for Software Copyright Protection using Method Generation based Watermarking}

The present invention relates to a software copyright protection method using watermarking based on method generation in which a software watermark is applied to various applications used in smart devices such as a smart phone or a tablet PC.

Because of the convenience and various functions of a smartphone, it has become a device that is universally used regardless of gender and age, and the penetration rate has rapidly increased as the years go by, and as of 2018, two out of three adults around the world use smartphones.

As the number of smartphone users increases, smartphone app developers want to increase revenue by developing apps that users want. However, there are cases of illegally copying and using apps without purchasing them through normal procedures, and the damage caused by illegally copied apps amounts to $4 billion per year.

Digital watermarking is mainly used to prove content copyright. Similarly, a software watermarking technique has been proposed for copyright protection of software.

Software watermarking is a technology that inserts and extracts a watermark including copyright holder information in software. Using watermarks, developers can prove copyright to programs and prevent damage caused by reckless theft and duplication.

Here, software watermarking can be divided into a static software watermark and a dynamic software watermark according to a software watermark extraction method.

Static software watermarks are stored in a static form in a file, and the embedded watermark can be extracted at any time regardless of the program execution status. Existing studies in Korea have proposed a method of inserting static software watermarks in low-level language-based static watermarking and software watermarking techniques based on function calling conventions to protect intellectual property rights. A method of inserting was proposed.

Dynamic software watermarks have a feature that a watermark can be extracted when a program is always running. A hidden watermark may appear during program execution by key input or mouse movement [12], or it can be implemented by using the features of the data structure used in the program or inserting it into the heap or stack data area.

Codejam is a static watermarking system provided by the Korea Copyright Commission. Codejam works by adding variables to be used for watermarking in the original source code in the source code.

1 is an exemplary code for the operation of a conventional Codejam system. Variables w and t, which were not in the original source (a), were added to the modified source (b), and the constants 1, 1353, 350, 4, 156, and 494, which were used in the operation of these variables, were used for watermarking. I can.

However, such a conventional Codejam system has two problems.

First, it is vulnerable to code optimization. Since the variables w and t are actually variables not related to the program operation, the watermark can be deleted because they can be removed through data dependency analysis.

Second, since the source added to embed the watermark is actually executed, there is a problem in that execution performance is degraded depending on the amount of watermark.

Korean Patent Publication No. 10-2011-0072112 (Publication date 2011.06.29) Domestic Patent Publication No. 10-2015-0087075 (Publication date 2015.07.29)

Accordingly, in order to improve the problem of the watermark system of the prior art, the present invention increases the concealability of the watermark by using method overloading and overriding, and water using an opaque predicate. Its purpose is to provide a software copyright protection method using watermarking based on method generation that prevents execution performance degradation due to marks.

The software copyright protection process using method generation-based watermarking to achieve the object of the present invention is a software copyright protection method equipped with watermarking based on method generation of an application stored in the operating system area of the memory of a smart device capable of installing an application. The method of claim 1, wherein the smart device comprises: a first step of generating an overloading method by analyzing an original method parameter of an application software source code stored in a memory; A second process of generating an overriding method by analyzing a class inheritance structure of the software source code of the application; And a third process of generating a method call statement in which an unclear predicate is applied to each overloading method and the overriding method generated in the first and second processes.

The first process includes 11 steps of selecting the target method to be overloaded; 12 step of analyzing an argument of the method to be overloaded; And a 13 step of generating a method suitable for an overloading rule according to the analysis result in step 12.

The second process includes 21 steps of selecting a target method to be overridden; 22 step of analyzing the class to be overloaded; And a 23 step of generating a method suitable for the overriding rule.

In the third process, in the process of applying an unclear predicate to the overloading method, a predicate whose result is true is used for calling the original method by randomly extracting a set from the unclear predicate set, and connecting the generated method call to the predicate whose result is false. And inserting watermark information into a method that is not executed in a region to which the unclear predicate is applied.

In the third process, in the application of the unclear predicate to the overriding method, the overriding unclear predicate area is designated using a selector, and the method defined in the remaining subclasses excluding the actually used superclass method in the designated unclear predicate area Watermark information is inserted into the device.

The software copyright protection method using method generation-based watermarking according to the present invention duplicates the method with the same name as the existing method by using method overloading and overriding, so that the original method and the fake method created for the watermark are distinguished. Because it is difficult, it has the effect of enhancing concealability, and it is not easy to find and delete all watermarks of copyright holders because watermarks containing author information can be duplicated and included in several methods, and overloading or overriding Since the method is composed of the original code similarly, it has the effect of taking a long time to check the original.

In addition, an opaque predicate refers to a conditional expression that is difficult to distinguish between true or false.Since such an opaque predicate is used, it is possible to prevent a fake method containing watermark information from being recognized as a dead code and deleted. In addition, disabling the watermark by the automatic analysis tool can be prevented, and since the fake method is not actually executed, it has the effect of preventing execution performance degradation.

In addition, if the watermarking technique is used, copyright information can be checked when illegal copying is suspected or a program is actually stolen, and there is an effect of preventing illegal copying attempts in advance.

Due to these effects, it is possible to safely maintain the software copyright information of the application.

1 is an exemplary code display diagram for the operation of a codejam system according to the prior art,
2 is a configuration diagram of an operating system area of a memory of a smart device for implementing the present invention,
3 is a flowchart of a software copyright protection process using method generation-based watermarking according to an embodiment of the present invention;
4 is an exemplary diagram of method overloading by the method overloading generator in FIG. 3,
5 and 6 are exemplary diagrams of methods for comparing before and after method overloading,
7 is an exemplary diagram of method overriding by a method overriding generator,
8 and 9 are exemplary diagrams of methods for comparison before and after method overriding,
10 is a table showing an embodiment of an unclear predicate in FIG. 3,
11 is an exemplary diagram of an overloading method before an unclear predicate is added in FIG. 3,
12 is an exemplary diagram of an overloading method to which an unclear predicate is applied in FIG. 3,
13 is an exemplary diagram of an overriding method before an unclear predicate is added in FIG. 3,
14 is an exemplary diagram of an overriding method to which an unclear predicate is applied in FIG. 3,
15 is a chart showing the measurement of source and apk file sizes according to the number of method overloading,
16 is a graph display diagram for FIG. 15,
17 is a table showing the result of measuring the file size by generating method overriding,
18 is a diagram showing the diagram of FIG. 17 as a graph,
19 is a table showing results of measuring execution time overhead due to the number of unclear predicates,
20 is a diagram showing the table of FIG. 10 as a graph.

The features and effects of the present invention described above will become more apparent through the following detailed description in connection with the accompanying drawings, and accordingly, those of ordinary skill in the technical field to which the present invention pertains can easily implement the technical idea of the present invention. I will be able to.

The present invention will be described in detail in the text by illustrating specific embodiments, as various changes can be made and various forms can be applied.

However, this is not intended to limit the present invention to a specific form disclosed, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention.

Hereinafter, a software copyright protection method using method generation-based watermarking according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

First, FIG. 2 is a diagram showing an operating system region of a memory of a smart device for implementing the present invention, and a smart device 100 such as a smartphone, a smart pad, a tab book, and a notebook mounts an operating system in the built-in memory region. , It installs various applications based on the installed operating system.

When an application is installed on the smart device 100 as described above, analysis of the application is difficult and the risk of watermark exposure is reduced due to the method generated by overloading and overriding in software.

3 is a flowchart of a software copyright protection process using method generation-based watermarking according to an embodiment of the present invention as follows.

The operation of the method generation-based watermarking system according to an embodiment of the present invention is largely performed in two stages. First, in Step 1, the method overloading and the overriding generation module operate.

The overloading generation module analyzes the original method parameters to create an overloading method, and the overriding generation module analyzes the class inheritance relationship to create the overriding class and method.

In step 2, a method call statement using an unclear predicate is generated in the result of step 1. Here, the unclear predicate is used when overloading an unclear predicate extracted from a previously stored unclear predicate list or generating an overriding method call statement.

Hereinafter, each step will be described in detail with reference to examples of the overloading or overriding method of FIGS. 4 to 14.

4 is a representative example of method overloading, where a number of methods of the same name are generated, but the number or types of parameters must be different so that method calls can be statically bound at compile time.

In order to insert a watermark arbitrarily using the method overloading technique, it is necessary to generate a number of overloading methods.

In order to create the overloading method, first, a target method to be overloaded must be selected, second, an argument of an overloading target method must be analyzed, and third, a method suitable for the overloading rule must be created.

In the present invention, two selectors were used:'// OVERLOADING {'indicating the start point of the overloading target method and'// OVERLOADING }'indicating the end point so that the method to be overloaded can be easily selected. In other words, the overloading generator has the advantage of simplifying the method creation process because it does not need to parse the entire source code by reading the original source code, but analyzes the method parameters only for the selected area and creates a method.

5 and 6 are exemplary diagrams before and after overloading using an overloading region selector. In FIG. 5, method m is selected as the method to be overloaded, and as a result, three methods are created in the form of overloading m method as shown in FIG. It can be confirmed. In the example, the number of methods to be created through overloading is set to 3, but it can be changed as many times as desired.

7 is a representative example of method overriding. In other words, in the class inheritance relationship, a method with the same name as the method of the super class must be created in the subclass, and the number and type of parameters must all match so that the method call can be dynamically bound at runtime.

In order to create the overriding method, first, a target method to be overridden must be selected, second, an overloading target class must be analyzed, and third, a method suitable for the overriding rule must be created.

In the present invention, the'// OVERRIDING {'and'// OVERRIDING }'selectors are used to easily select an overriding target method similar to overloading.

8 and 9 are exemplary diagrams before and after overloading using an overriding region selector. That is, you can check the result of creating three subclasses and three overriding methods by creating a class inheritance relationship. The number of subclasses and methods to be created through overriding can be arbitrarily changed.

As such, each method created by the overloading and overriding generator is a method that did not exist in the original and is a fake method that does not actually run.

Therefore, execution performance is not degraded by fake methods, and it is used as a place where desired watermarks can be inserted arbitrarily.

However, methods that are not actually called during the source optimization process can be recognized as dead code and deleted. Therefore, we use an unclear predicate to prevent the created fake method from being deleted.

10 is an exemplary list of unclear predicates, which are expressions that are difficult to determine true or false by static analysis, and can be used for the purpose of hiding codes used for watermarking. If an unclear predicate is used, it is difficult to determine whether it is actually executed, so the watermark can remain without disappearing even in the optimization by static analysis.

If the overloading or overriding method is created, a process of adding an unclear predicate is required. A set is randomly extracted from the unclear predicate set, a predicate whose result is true is used for calling an original method, and the generated method call is connected to a predicate whose result is false. Since true and false can be reversed using the NOT operation, all data in an unclear predicate set can be used.

11 and 12 are exemplary diagrams before and after applying an unclear predicate to method overloading, respectively. In FIG. 11, a selector'// OVERLOADING OPAQUE {'was added at the start position to select a region to which the unclear predicate is to be applied, Added'// OVERLOADING OPAQUE }'to the end position.

The source of the fourth line in FIG. 12 is the original, and other sources are sources automatically generated by the unclear predicate generator. That is, the original source is always executed, and the three method call statements from line 5 are not executed because the result of the unclear predicate is always false.

However, unnecessary method calls that were intentionally inserted cannot be deleted by static analysis. The reason is that it uses an unclear predicate that makes it difficult to know the result. Therefore, watermark information can be inserted into the m methods other than the first m method that is actually executed.

The method of applying an unclear predicate to the overriding method is similar to the method used in overloading. However, method overriding requires class inheritance, so when adding an unclear predicate, it should be applied to the part of creating a class.

13 and 14 are examples before and after applying an unclear predicate to method overriding, respectively. In FIG. 13, a desired area was designated using the'// OVERRIDING OPAQUE' selector, and the source of the 5th line in FIG. 14 is The original and other sources are those generated automatically by the unclear predicate generator.

Therefore, watermark information can be inserted into the method m defined in'SuperClass1' and'SuperClass2' except for the method m of'SuperClass' that is actually used.

The method generation-based watermarking system implemented through the above process used the java language, and to evaluate this,'JetBoy' was used among sample projects included in the Android SDK as an example.

15 is a chart measuring the size of source and apk file according to the number of method overloading, and FIG. 16 is a graph chart for this. Referring to this, the Java source file increased by the creation of the overloading method and the apk file built in release mode Is the size of.

It can be seen that as the number of overloading methods generated by the watermarking system increases, the size of the source file and the size of the apk file increase.

Due to the nature of overloading, as the number of method creation increases, the number of method parameters increases, causing a problem that the size of the source file increases rapidly. However, the apk file built in release mode was not large compared to the original. For example, even when 200 overloading methods were created, the size of the source file increased more than 6 times, but the apk file remained at 1.037 times.

FIG. 17 is a table measuring source and apk file sizes according to the number of method overriding generations, and FIG. 18 is a graph chart for this. Referring to this, as the number of overriding methods increases, the size of the source file and the size of the apk file Was increased, but the proportion was not large when compared to the original. For example, even when 200 overriding methods were created, the size of the source file was 1.972 times and the apk file remained at 1.006 times.

It can be seen that the file size overhead is less for the method creation by overriding than the method creation by overloading.

In the case of overriding, only the class inheritance relationship is added and the parameter does not change, so there is no reason to become more complicated than the original method when a method is created by overriding.

However, since the methods created by overloading must have different types and numbers of parameters, the number of parameters continuously increases, so the size of the source file has increased significantly compared to overriding.

Therefore, if you are sensitive to the increase in the size of the source file or apk file, it would be desirable to apply the overriding method creation technique.

19 and 20 are tables and graphs showing results of measuring execution time overhead due to the number of unclear predicates.

Even if a method is added by overloading and overriding, the result of the conditional expression of the unclear predicate is false, so it is not actually executed. Therefore, the execution time overhead is not the execution time of the overloading or overriding method, only the execution time of the conditional expression of the unclear predicate is added.

To measure the time, the'currentTimeMillis()' method was used, and this method can be measured only in milliseconds, so it was converted into nanoseconds after repeated executions 1,000,000 times. As a result, the execution time increased in proportion to the number of unclear predicates. Even if 200 unclear predicates were added, the increased time was only 49 nanoseconds, so the performance degradation is considered to be negligible.

As described above, the software copyright protection method using method generation-based watermarking according to an embodiment of the present invention is not limited by this embodiment, although it has been described by a limited embodiment and drawings. Of course, various modifications and variations are possible within the scope of the technical spirit of the present invention and the scope of the claims to be described below by a person having knowledge of.

100: memory

Claims (7)

In the method of protecting software copyright by mounting method generation-based watermarking in an application stored in the memory of a smart device capable of installing an application,
The smart device includes: a first process of generating an overloading method by analyzing the original method parameter of an application software source code stored in a memory;
A second process of generating an overriding target class and method by analyzing a class inheritance structure of the software source code of the application; And
And a third process of generating a method call statement to which the unclear predicate is applied by adding an unclear predicate to a front end of each method call statement of each overloading method generated in the first and second processes and the method call statement of the overriding method. Software copyright protection method using watermarking based on method generation. The method of claim 1,
The first process includes 11 steps of selecting the target method to be overloaded;
12 step of analyzing an argument of the method to be overloaded; And
13 step of generating a new method that satisfies the overloading rule according to the analysis result in step 12; including,
The overloading rule is a method of the same name, and the number or type of parameters must be different from each other. The method of claim 1,
The second process includes a 21 step of selecting a target method to be overridden from a plurality of methods included in the overriding target class;
22 step of analyzing the overriding target class; And
Including; but, the step of creating a method suitable for the overriding rule 23;
The overriding rule is that a method with the same name as a method of a super class must be created in a subclass in a class inheritance relationship, and the number and type of parameters must match so that the method call can be dynamically bound at runtime.
The software copyright protection method using method generation-based watermarking, characterized in that the super class is a method already existing in the original source. The method of claim 1,
In the third process, in the process of applying an unclear predicate to the overloading method, a subset is randomly extracted from the unclear predicate set, and the unclear predicate set whose result is true is added to the front end of the original method call statement, and the unclear predicate whose result is false A software copyright protection method using method generation-based watermarking, characterized in that the set is added to the front end of the generated method call statement. The method of claim 4,
Software copyright protection method using method generation-based watermarking, characterized in that watermark information is inserted into a method that is not executed because a false unclear predicate is applied among unclear predicates in an area to which a selected unclear predicate is applied among the software source codes of the application. . The method of claim 1,
In the third process, in the application of an unclear predicate to the overriding method, an overriding unclear predicate region is designated using a selector,
Insert watermark information into the methods defined in the remaining subclasses except for the superclass method in the specified unclear predicate area,
The overriding unclear predicate area is an area to generate an unclear predicate for a method conforming to an overriding method rule,
The selector plays a role of selecting the beginning and the end of the region to which the overriding unclear predicate is to be applied,
The method of the super class is a method that already exists in an original source that operates when a program is executed. The method of claim 1,
In the third process, the unclear predicate for each overloading method and the overriding method is extracted from a previously stored unclear predicate list and used.

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