バイトコードモディフィケーションによるJAVAモバイルコードの動的な検証方法の研究

摘要

Mobile code program can be transmitted via network from a remote source to alocal system and be executed on that local host. And such programs may raise thesecurity problems of the host because they could interact with the resources of thelocal host and malicious or defective programs will tamper data or release secureinformation of the local host. The Java language has been used widely in theimplementation of mobile code systems because of its portability, security andplatform-independency. In our research, we are heading for building a verificationapproach with high precision in order to protect the host security in mobile codesystems.Compared with the security mechanisms such as access control andauthentication, the Secure Information Flow theory is a useful mechanism for thesecurity protection, especially for the confidentiality protection. In the traditionalinformation flow analysis, the source code is taken as the analysis object. While inmobile code systems, the host executing the mobile code can only get the bytecodeof the programs. Therefore, we analyzed the bytecode’s information flow in ourresearch.Though several approaches have used the information flow analysis, thoseapproaches neglected the characteristics of security demand in mobile code systemsand did not achieve satisfying verification precision. In our approach, we make itclear that what are the subjects and objects in mobile code systems, and put forwardthe appropriate security model. We assign security-levels to the data of thelocal-host and clearance-level to the third-party hosts. Then we trace theinformation flow during the mobile code and check whether a data-leaking is raised　when the mobile code tries to send data to a third-party host.Furthermore, different from static approaches that verify the mobile code beforethe JVM executes the bytecode, our approach is a dynamic approach that verifiesthe mobile code when the JVM is executing the bytecode. Before the mobile codeis sent to the JVM, we analyze the information flow in the bytecode and insertproper instructions implementing the verification function into the originalbytecode. Thus when the JVM executes the modified bytecode, the verificationfunction is done as while as the original function of the mobile code. The dynamicapproach can get the runtime information during the mobile code execution (suchas which branch of the implicit information transferring will be executed, whetheran instruction will throw an exception or not, and so on), and it can achieve betterverification precision than static ones.In addition, we also discuss the information flow during the exception handlingin our research, which is almost impossible for static verification approaches. Weanalyze what kind of information flow can be caused during the exception handlingof Java mobile code, and put forward the corresponding verification bytecode forthe information flow caused by exception handling. Since our approach can dealwith the verification of the exception handling in bytecode, the verificationprecision and practicality of our approached are improved further.