The authors proposed a new Android repackaging method based on Android app characteristics. The new method can repackage apps without decompiling nor modifying the code and also supports packed apps. The method leverages multiple new code injection techniques to attach code to the app. Then, it adds a hook framework to provide capabilities to modify the code behaviors. Finally, the app’s behaviors will be changed during runtime, thus the app is repackaged. A prototype framework is also implemented. The experiments demonstrate that the framework is compatible to different Android platforms and multiple packers. This research has proved that the current packing techniques have some flaws and the method can be used in dynamic code analysis, defense policies deployment and app modification.

The authors propose a practical and accurate cross site script prevention method based on delimiters for UTF-8 encoded web applications. Only trusted delimiters are tainted into corresponding UTF-8 shadow bytes, and these tainted shadow bytes are automatically propagated in web applications and can be directly delivered into output pages. Cross site script is prevented by analyzing the tainted delimiters and HTML context of output pages. A prototype called XSSCleaner is implemented on PHP. The evaluation shows that XSSCleaner can accurately protect web applications from real world cross site script attacks with an average overhead 12.9%.

A formal definition and analysis on the hierarchical key management is presented for permission management and access control problem in the role hierarchy. Based on one-way hash function, a practical hierarchical key management scheme is proposed. This scheme allows the role to select its master key by itself, and constructs the hierarchical permission relationship with secure hash function and public parameters. The process of key generation and derivation is simple and effective in this proposed scheme, which satisfies the security requirement of the hierarchical permission management. Compared with other present schemes, the new scheme optimizes the efficiency of key derivation and storage overhead. The dynamic access control of hierarchical role can be adapted in this new scheme.

Adaptive playout algorithm is an important component of the Internet multiparty real-time communication system. The authors bring forward a new adaptive playout algorithm in the multiparty real-time communication fields based on the consideration of the impact of the packet loss dependency using E model tool. The aim of the algorithm is to give the best voice feeling to users as well as the best voice quality. The experiment results prove the validity of the algorithm. The algorithm can reduce the packet loss probability and delay significantly, and reduce the consecutive packet loss simultaneously.