• Journal of the Korea Institute of Information Security & Cryptology
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• v.23 no.4
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• pp.743-755
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• 2013

In recent years, the malicious apps with malicious code in normal apps are increasingly redistributed in Android market, which may incur various problems such as the leakage of authentication information and transaction information and fraudulent transactions when banking apps to process the financial transactions are exposed to such attacks. Thus the financial authorities established the laws and regulations as an countermeasures against those problems and domestic banks provide the integrity verification functions in their banking apps, yet its reliability has not been verified because the studies of the safety of the corresponding functions have seldom been conducted. Thus this study suggests the vulnerabilities of the integrity verification functions of banking apps by using Android reverse engineering analysis techniques. In case the suggested vulnerabilities are exploited, the integrity verification functions of banking apps are likely to be bypassed, which will facilitate malicious code inserting attacks through repackaging and its risk is very high as proved in a test of this study. Furthermore this study suggests the specific solutions to those vulnerabilities, which will contribute to improving the security level of smartphone financial transaction environment against the application forgery attacks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.4
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• pp.700-708
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• 2015

A software birthmark is the set of characteristics of a program which can be used to identify the program. Many researchers have studied on detecting theft of java programs using some birthmarks. In case of Android apps, code obfuscation techniques are used to protect the apps against reverse-engineering and tampering. However, attackers can also use the obfuscation techniques in order to conceal a stolen program. A birthmark (feature) of an app can be alterable by code obfuscations. Therefore, it is necessary to detect Android app theft based on the birthmark which is resilient to code obfuscation. In this paper, we propose an effective Android app birthmark and app theft detection through the proposed birthmark. By analyzing some obfuscation tools, we have first selected parameter and the return types of methods as an adequate birthmark. Then, we have measured similarity of target apps using the birthmarks extracted from the apps, where some target apps are not obfuscated and the others obfuscated. The measurement results show that our proposed birthmark is effective for detecting Android app theft even though the apps are obfuscated.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.29 no.1
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• pp.45-55
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• 2019

DEX file and share objects (also known as the SO file) are important components that define the behaviors of an Android application. DEX file is implemented in Java code, whereas SO file under ELF file format is implemented in native code(C/C++). The two layers - Java and native can communicate with each other at runtime. Malicious applications have become more and more prevalent in mobile world, they are equipped with different evasion techniques to avoid being detected by anti-malware product. To avoid static analysis, some applications may perform malicious behavior in native code that is difficult to analyze. Existing researches fail to extract the call relationship which includes both Java code and native code, or can not analyze multi-DEX application. In this study, we design and implement a system that effectively extracts the call relationship between Java code and native code by analyzing DEX file and SO file of Android application.

• Journal of Software Assessment and Valuation
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• v.10 no.1
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• pp.19-26
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• 2014

In this paper, we propose a method for protecting Android applications against reverse engineering attacks. In this method, the server encrypts the original executable code (DEX) included in an APK file, inserts into the APK file a stub code that decrypts the encrypted DEX later at run-time, and distributes the modified APK file. The stub code includes an integrity validation code to detect attacks on itself. When a user installs and executes the APK file, the stub code verifies the integrity of itself, decrypts the encrypted DEX, and loads it dynamically to execute. Since the original DEX is distributed as an encrypted one, we can effectively protect the intellectual property. Further, by verifying the integrity of the stub code, we can prevent malicious users from bypassing our method. We applied the method to 15 Android apps, and evaluated its effectiveness. We confirmed that 13 out of them operates normally.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06a
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• pp.116-118
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• 2012

안드로이드 앱 시장이 활성화되면서, 안드로이드 앱의 불법복제나 역공학 공격으로 인한 피해가 증가하고 있다. 앱 불법복제는 앱 판매 수익의 저하뿐만 아니라 개발자의 의지를 뺏고 개발 노력에 대해 상대적 박탈감을 주게 된다. 자바 프로그램의 경우 역공학으로 인해 바이트 코드에 존재하는 핵심 알고리즘이 쉽게 노출되어 지적재산권이 유출될 수 있다는 점에서 개발자나 개발사에게 심각한 위협이 되고 있다. 본 논문에서는 안드로이드 환경에서 앱에 대한 역공학 공격의 위협을 보이고, 역공학 방지 기법인 RACC를 제안한다. RACC는 보호할 핵심 클래스를 앱으로 부터 추출하여 바이트 코드 형태로 안전한 원격 서버에 관리하여 수행하며, 스마트폰(클라이언트)에는 저장하지 않는다. 스마트폰 앱이 해당 핵심 클래스를 호출하면, 그 호출이 원격 서버로 전송되어 수행된 후 결과가 스마트폰에 반환된다. 이처럼 핵심 클래스 코드가 클라이언트에 직접 노출 없이 원격지에서 관리되고 수행됨으로써 역공학 공격을 원천적으로 방지한다.

• Journal of Korea Society of Digital Industry and Information Management
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• v.11 no.2
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• pp.47-54
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• 2015

The popularity and adoption of smart-phones has greatly stimulated the spread of mobile malware, especially on the popular platforms such as Android. The fluidity of application markets complicate smart-phone security. There is a pressing need to develop effective solutions. Although recent efforts have shed light on particular security issues, there remains little insight into broader security characteristics of smart-phone application. Now, the analytical methods used mainly are the reverse engineering-based analysis and the sandbox-based analysis. Such methods are can be analyzed in detail. but, they take a lot of time and have a one-time payout. In this study, we develop a system to monitor that mobile application permissions at application update. We had to overcome a one-time analysis. This study is a service-based malware analysis, It will be based will be based on the mobile security study.

• Proceedings of the Korea Information Processing Society Conference
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• 2014.04a
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• pp.353-356
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• 2014

역공학 방지 기법이 적용되지 않은 어플리케이션은 악의적인 역공학에 취약할 수밖에 없다. 악의적인 역공학은 사회적으로 여러가지 손실을 가져온다. 그러므로 역공학 방지 기법을 적용하여 어플리케이션을 보호해야 한다. 역공학 방지 기법은 다양하며, 크게 자바 소스 난독화, Smali 코드 조작, Dex 파일 포맷 조작, 그리고 Zip 파일 포맷 조작 기법으로 나눌 수 있다. 자바 소스 난독화는 코드의 가독성을 떨어트려 안드로이드 어플리케이션의 역공학을 어렵게 하는 기법이다. Smali 코드 조작 기법은 Goto 문 추가, 예외 처리 재귀 기법 등을 통하여 역공학을 막는 기법이다. Dex 파일 포맷 조작 기법에는 클래스명 길이 변경, 헤더 크기 변경 등을 통해 역공학을 어렵게 만드는 기법이다. Zip 파일 포맷 조작 기법은 Zip 파일 포맷에서 헤더 값을 조작하여 마치 암호화된 것처럼 보이도록 만드는 기법이다. 본 논문에서는 이러한 다양한 기법들에 대해서 설명하고 이를 비교 분석한다.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.34 no.1
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• pp.61-70
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• 2024

As users use various services along with the rapid increase in Internet services, it may be difficult to manage accounts. To solve these difficulties, various password management applications are emerging. From a forensic point of view, password management applications can provide clues to obtain criminal evidence. The purpose of this paper is to acquire the data stored by the user in the password management application. To this end, we propose a better way to decrypt the encrypted data through reverse engineering, evaluate the security of the application to be analyzed, and safely store the data.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.05a
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• pp.184-186
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• 2022

Recently, as interest in personal information protection has increased, various apps for personal information protection have emerged. These apps protect data in various formats, such as photos, videos, and documents containing personal information, using encryption and hide functions. These apps can have a positive effect on personal information protection, but in digital forensics, they act as anti-forensic because they can be difficult to analyze data during the investigation process. In this paper, finds out PIN, an access control function, through reverse engineering on Calculator - photo vault, one of the personal information protection apps, and files such as photos and documents to which encryption and hide were applied. In addition, the vulnerability to this app was analyzed by research decryption for database files where logs for encrypted and hide files are stored.