KR101284676B1 - Cryptography-based copy protection system and method for android apps - Google Patents

Abstract

PURPOSE: An encryption-based user authentication/android application illegal copy prevention system and a method thereof allow only legitimate users to launch an android application by utilizing the odex file format and pre-encoding the files to be stored. CONSTITUTION: A Dalvik virtual machine (VM) extracts an encoded classes.dex from an apk file and generates an odex file by using a decoding module. An encoding module stores the odex file, performing an encoding process, and stores the processed file in a mobile device. If a legitimate user who has paid to use an application, the decoding module decodes the odex file. The encoding/decoding modules of the Dalvik VM perform a checksum investigation and an offset adjustment on the dex file and the odex file in order to encode and decode the files before and after the optimization/verification processes (classes.dex-decoding-Optimization/Verification-odex-encoding).

Description

Cryptography-based Copy Protection System and method for Android Apps}

The present invention relates to an encryption-based user authentication and Android app piracy prevention system and method thereof, and more specifically, to distribute the app in an encrypted state by using encryption technology, only a legitimate user at the time of execution The present invention relates to an encryption-based user authentication and an Android app piracy prevention system and method for decryption and execution.

The present invention was carried out as a result of the 2011 copyright technology development project of the Ministry of Culture, Sports and Tourism and the Korea Copyright Commission.

With the recent rapid expansion of smartphones, the application of smartphones called "apps" is also increasing rapidly.

The American Dialect Society chose “app” as the word of the year in 2010, and as of March 2011, Apple's iPhone has more than 350,000 apps, and Google's Android The number of apps has also surpassed 250,000, especially for Android, which is growing more rapidly.

In the case of digital information, such as apps, it is possible to create an unlimited number of copies identical to the original without losing information, and app piracy is currently prevalent due to the lack of proper app piracy prevention technology.

The number of illegal smartphone apps caught in the second half of 2010 amounted to 26,261 points, and games also exceeded 3741 points. In most cases, this is the use of copyrighted content without permission or illegal distribution.And while Android provides a module for managing licenses, there is a technique that can be circumvented. Even if it finds illegal copying or copyright infringement, the legal response is not easy.

Currently, most existing anti-piracy technologies are based on Digital Rights Management (DRM).

However, DRM is used as a monopoly market building tool by some operators because of its closedness that lacks compatibility between technologies.

In the Android Market, paid apps currently account for about 40% of all apps.

However, there are apps that can receive paid apps without just paying, and there are many ways to receive them through blogs or web pages on the web.

Google provides the License Verification Library (LVL) for license management of Android paid apps, but there is a technique to circumvent it, and even if the copyright holder confirms illegal copying or copyright infringement in online-based distribution environment, It is not easy to respond.

In addition, as another conventional technology, Korean Laid-Open Patent Publication No. 2011-0038152 relates to a system and method for generating forensic marking image data from source material. The generated forensic mark is a forensic marking parameter that is changed for each copy of the source image data. Changes between copies and copies are described using marking techniques.

Therefore, it is necessary to develop a new system and method that can improve the security of the app and form the right distribution culture through the development of copyright protection technology.

In order to solve the above problems, the present invention, the Android app copy protection system is an encryption-based user authentication and Android app piracy prevention system that can prevent illegal downloads in the Android environment that can be easily rooted and relatively illegal app download and The purpose is to provide a method.

The present invention extracts encrypted classes.dex from an Apk file in a Dalvik VM and generates an odex file through a decryption module added to the Dalvik virtual machine, and inserts it before storing the odex file. Performing encryption through one encryption module and storing it in a mobile device; and decrypting the odex file through a decryption module when only a legitimate user executes the app.

In the present invention, in order to perform encryption and decryption before and after optimization and verifycation of the encryption / decryption module in the Dalvik virtual machine, the dex file goes through an execution sequence of 'classes.dex-decryption-Optimization / Verifycation-odex-encryption'. And checksum check and offset correction of the odex file.

The invention further comprises the step of dexZipExtractEntrytoFile () function called in dalvik / dexopt / Optmain.c to use the encryption / decryption module in the dalvik directory in the Android source to obtain the classes.dex file from the Apk file. .

The present invention further comprises the step of converting the decrypted classes.dex file into an odex file in a function called dexContinueoptimization () of dalvik / vm / dexprepare.c.

The present invention further comprises the step of encrypting the odex file by inserting an encryption module after optimaze, verify, offset adjustment and dexoptHeader are written to store the generated odex file in an encrypted state and the odex file is generated.

The present invention further includes the step of executing the app using the classes.dex file in / data / dalvik-cache when the user clicks the icon of the app to execute the App.

The present invention is to encrypt the Dalvik VM (Dalvik VM) to extract the encrypted classes.dex from the Apk file to create an odex file through the decryption module, and to store the odex file, and then to encrypt and store in the mobile device Module and a decryption module for decrypting the odex file when only a legitimate user executes the app.

The encryption / decryption module in the Dalvik virtual machine performs a dex file and an odex file through an execution order of 'classes.dex-decryption-optimization / Verifycation-odex-encryption' to perform encryption and decryption before and after optimization and verifycation. Checksum checks and offsets are fixed.

To use the encryption / decryption module in the dalvik directory in the Android source, the dexZipExtractEntrytoFile () function called in dalvik / dexopt / Optmain.c gets the classes.dex file from the Apk file.

The decrypted classes.dex file is generated by converting it into an odex file in a function called dexContinueoptimization () of dalvik / vm / dexprepare.c.

In order to store the generated odex file in an encrypted state, after optimaze, verify, offset adjustment, and dexoptHeader are written and the odex file is generated, an encryption module is inserted to encrypt the odex file, and the generated odex file is / data / dalvik Store it in -cache as data @ app @ [filename] @ classes.dex.

When the user clicks the icon of the app to execute the app, the app is executed using the classes.dex file in / data / dalvik-cache, and the part calling the dex file is dalvik / analysis / vm / dvmOpenCachedDexFile () function in dexprepare.c. Since the odex file is stored in an encrypted state, after decryption is performed through the decryption module added to this part, the odex file is returned and used to execute the App.

According to the present invention, since the encrypted app is stored in an encrypted state when it is stored as an odex file, unlike a normal app, only a legitimate user who pays the fee can be executed.

According to the present invention it is possible to improve the security of the app and to form the right distribution culture through the development of copyright protection technology.

1 is a view showing the entire flow of encryption-based user authentication and Android app piracy prevention system according to the present invention.
Figure 2 (a), (c) is an encrypted Apk File installation flow chart according to the present invention,
(b) A diagram showing an odex file format.
3 is a diagram illustrating an encrypted Apk File installation process according to the present invention;
4 illustrates a modified Dalvik VM directory and method in accordance with the present invention.
5 is a view showing an App execution process through an encrypted Odex file according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, the server 100 includes a subscription / authentication service module 10 including a subscription service module 12 and an authentication service module 14, and a module 20 using RSA and AES keys. The device 200 further includes an authentication and download module 30 and an encryption module 40.

Here, AES (Advanced Encryption Standard) is a US standard 128-bit block cipher that uses 128/192 / 256-bit secret keys and 10/12/14 rounds depending on each key.

AES is designed to be safe against attack methods known to the block cipher algorithm so far, and since the implementation is efficient in terms of speed and ease of implementation, the present invention allows the AES algorithm to be used for application encryption.

And to secure the AES secret key that encrypts the application, public key encryption algorithm RSA is used. RSA is based on a large integer of 1024 bits or more.

It is performed by a modulo operation and maintains high security because the prime factorization of large integer coefficients is very difficult. Therefore, encrypting the AES secret key with RSA can compensate for the disadvantages of AES with relatively low security.

The authentication and download module 30 may further include a subscription request module 32, an authentication request module 34, and a download module 36.

That is, the encryption-based user authentication and Android app piracy prevention system according to an embodiment of the present invention extracts encrypted classes.dex from an Apk file and generates an odex file through a decryption module added to the Dalvik virtual machine. It is divided into a machine (Dalvik VM), an encryption module that stores the odex file, encrypts and stores it on a mobile device, and a decryption module that decrypts the odex file when only a legitimate user executes the app.

Specifically, Figure 2 (a) is a process of downloading and installing the encrypted Apk file from the server.

General Apk file extracts classes.dex file from Apk file in Dalvik VM and executes optimized and verifiy.

The installation process is terminated by saving it to the system.

2 (b) is a flowchart illustrating a process of extracting and decrypting encrypted classes.dex from an Apk file.

The encrypted part is the classes.dex file in the Apk file, and the rest of the classes.dex file except the header part is actually encrypted.

The decryption module added to the Dalvik VM decrypts this part, and the decrypted classes.dex file creates an odex file through a series of processes after optimization and verify.

As shown in FIG. 2 (c), after the encryption is performed through the encryption module inserted before the generated odex file is stored, it is stored in the mobile device. When the saving is completed, all installation processes are terminated.

Unlike regular apps, encrypted apps are stored in an encrypted state when they are saved as odex files, so only authorized users who have paid for them can run them.

When the user clicks the icon to run the app, the app will be decoded so that the app can be used.

As shown in FIG. 3, in order to install an encrypted app, an encryption / decryption module in the Dalvik VM should be added.

The most important part here is that encryption and decryption must be performed before and after optimization and verifycation. Only after the execution order of `` classes.dex- decryption-Optimaiztion / Verifycation-odex-encryption '', the checksum check and offset correction process of dex file and odex file can be passed without error.

.

Figure 3 shows the modifications actually made to use the encryption / decryption module in the dalvik directory in the Android source.

4 shows a modified Dalvik VM directory and method in accordance with the present invention.

The dexZipExtractEntrytoFile () function called in dalvik / dexopt / Optmain.c according to the present invention is a part of obtaining classes.dex file from Apk file.

The function exists in dalvik / libdex / ZipArchive.c and inserts a decryption module here to decrypt the obtained classes.dex file.

In addition, the classes.dex file decoded according to the present invention is generated by converting it into an odex file in a function called dexContinueoptimization () of dalvik / vm / dexprepare.c.

To save the generated odex file in encrypted state, optimaze, verify, offset adjustment, and dexoptHeader are used to create the complete odex file.

The odex file created according to the present invention is stored in the form of data @ app @ [filename] @ classes.dex in / data / dalvik-cache.

As shown in FIG. 5, when the user clicks the icon of the app to execute the app, the app is executed using the classes.dex file in / data / dalvik-cache.

According to the present invention, the part calling the dex file is the dvmOpenCachedDexFile () function in dalvik / analysis / vm / dexprepare.c, and since the odex file is stored in an encrypted state, decryption is performed through a decryption module added to this part. After executing, it returns odex file and is used to execute App.

Hereinafter, an encryption-based user authentication and an Android app piracy prevention method according to an embodiment of the present invention will be described in detail.

First, an encrypted classes.dex is extracted from an Apk file in a Dalvik VM and an odex file is generated through a decryption module added to the Dalvik virtual machine.

In addition, the encryption is performed through the encryption module inserted before the odex file is stored and then stored in the mobile device.

If only a legitimate user runs the app, the decryption module decrypts the odex file.

In addition, in order to perform encryption and decryption before and after optimization and verifycation, the encryption / decryption module in the Dalvik virtual machine runs dex file and odex through the execution sequence of 'classes.dex-decryption-Optimization / Verifycation-odex-encryption'. Checksum checks and offsets of files.

Also, to use the encryption / decryption module in the dalvik directory in the Android source, the dexZipExtractEntrytoFile () function, which is called in dalvik / dexopt / Optmain.c, obtains the classes.dex file from the Apk file.

Here, the decrypted classes.dex file is generated by converting it into an odex file in a function called dexContinueoptimization () of dalvik / vm / dexprepare.c.

In order to store the generated odex file in an encrypted state, optimaze, verify, offset adjustment, and dexoptHeader are written to encrypt the odex file by inserting an encryption module after the odex file is generated, and the user executes the App. If you click on the icon of the app, you run the app using the classes.dex file in / data / dalvik-cache.

100: Server
10: Subscription / Authentication Service Module
12: subscription service module
14: authentication service module
20: module using RSA, AES keys
30: Authentication and Download Module
40: encryption module
200: device

Claims (12)

Extracting encrypted classes.dex from an Apk file in a Dalvik VM and generating an odex file through a decryption module added to the Dalvik virtual machine;
Performing encryption through an encryption module inserted before storing the odex file and storing the encrypted file on a mobile device;
Decrypting the odex file through a decryption module when only a legitimate user who has paid the fee is executed;
Encryption-based user authentication and Android app piracy prevention method characterized in that it comprises a. The method of claim 1,
In order to perform encryption and decryption before and after optimization and verifycation, the encryption / decryption module in the Dalvik virtual machine goes through the execution order of 'classes.dex-decryption-Optimization / Verifycation-odex-encryption'. Checking the checksum and correcting the offset;
Encryption-based user authentication and Android app piracy prevention method, characterized in that further comprises a. The method of claim 1,
Obtaining a classes.dex file from an Apk file by a dexZipExtractEntrytoFile () function called in dalvik / dexopt / Optmain.c to use an encryption / decryption module in the dalvik directory in the Android source;
Encryption-based user authentication and Android app piracy prevention method, characterized in that further comprises a. The method of claim 2,
Converting the decrypted classes.dex file into an odex file in a function called dexContinueoptimization () of dalvik / vm / dexprepare.c;
Encryption-based user authentication and Android app piracy prevention method, characterized in that further comprises a. 5. The method of claim 4,
Encrypting the odex file by inserting an encryption module after optimaze, verify, offset adjustment, and dexoptHeader are written to store the generated odex file in an encrypted state and the odex file is generated;
Encryption-based user authentication and Android app piracy prevention method, characterized in that further comprises a. The method of claim 1,
If the user clicks on the icon of the App to execute the App, executing the App using the classes.dex file in / data / dalvik-cache;
Encryption-based user authentication and Android app piracy prevention method, characterized in that further comprises a. A Dalvik VM which extracts encrypted classes.dex from an Apk file and generates an odex file through a decryption module;
An encryption module for storing the odex file, performing encryption, and storing the odex file in a mobile device;
A decryption module for decrypting the odex file when only a legitimate user who has paid the fee is executed;
Encryption-based user authentication and Android app piracy prevention system, characterized in that comprises a. The method of claim 7, wherein
The encryption / decryption module in the Dalvik virtual machine,
In order to perform encryption and decryption before and after optimization and verifycation, the checksum check and offset of dex and odex files are modified through the execution sequence of 'classes.dex-decryption-optimization / verificationcation-odex-encryption'. Encryption based user authentication and Android app piracy prevention system. The method of claim 7, wherein
Encryption-based user authentication and Android, in which the dexZipExtractEntrytoFile () function called in dalvik / dexopt / Optmain.c gets a classes.dex file from an Apk file to use the encryption / decryption module in the dalvik directory in the Android source. App anti-piracy system. 9. The method of claim 8,
The decrypted classes.dex file is an encryption-based user authentication and Android app piracy prevention system, characterized in that generated by converting to the odex file in a function called dexContinueoptimization () of dalvik / vm / depreprere.c. The method of claim 10,
In order to store the generated odex file in an encrypted state, after optimaze, verify, offset adjustment, and dexoptHeader are written and the odex file is generated, an encryption module is inserted to encrypt the odex file, and the generated odex file is / data / dalvik Encryption-based user authentication and Android app piracy prevention system, characterized in that stored in the form of data @ app @ [filename] @ classes.dex in the -cache. The method of claim 7, wherein
When the user clicks the icon of the app to execute the app, the app is executed using the classes.dex file in / data / dalvik-cache, and the part calling the dex file is dalvik / analysis / vm / dvmOpenCachedDexFile () function in dexprepare.c, and since the odex file is stored in an encrypted state, it is used to execute the app by returning the odex file after decrypting through the decryption module added to this part. Encryption based user authentication and Android app piracy prevention system.

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