Parema: An unpacking framework for demystifying VM-based Android packers

Abstract

Android packers have been widely adopted by developers to protect apps from being plagiarized. Meanwhile, various unpacking tools unpack the apps through direct memory dumping. To defend against these off-the-shelf unpacking tools, packers start to adopt virtual machine (VM) based protection techniques, which replace the original Dalvik bytecode (DCode) with customized bytecode (PCode) in memory. This defeats the unpackers using memory dumping mechanisms. However, little is known about whether such packers can provide enough protection to Android apps. In this paper, we aim to shed light on these questions and take the first step towards demystifying the protections provided to the apps by the VM-based packers. We proposed novel program analysis techniques to investigate existing commercial VM-based packers including a learning phase and a deobfuscation phase.We aim at deobfuscating the VM-protection DCode in three scenarios, recovering original DCode or its semantics with training apps, and restoring the semantics without training apps. We also develop a prototype named Parema to automate much work of the deobfuscation procedure. By applying it to the online VM-based Android packers, we reveal that all evaluated packers do not provide adequate protection and could be compromised.