Software Shell Technology

With the development of computer, its application has been deep into all aspects of our social lives. Along with the function of computer growing much stronger, the structure getting more complicated, the cost for developing software has been getting higher and higher. However, to duplicate the software nearly cost nothing, if the software developed by the researcher was taken by other people in illegal way, it will be a great loss to the software researchers and the investors. Therefore, to protect the legal rights of the software developer and maintain the healthy development of software industry, it is necessary to have software protection.Software protection can be realized by laws and by technologies. The law way mainly rely on the improvement of social legislation . This article will focus on how to protect software by using the packer technology. Packer is one important trend in research on software protection. Packer is to compress or encrypt the program which need to be protected, so that it can effectively prevent decompilation or illegal modification.This thesis focus on the packer for the exe file in Windows environment. The reason is because Windows system is the most popular operating system currently, to guarantee the safety for the shared software in Windows system appears more important. Based on that , this article attached great importance to analyze the structure of PE file in Windows , and introduced the packer software ,unpacker software, unpacking method and some important reverse analysis. In view of the feature of existing unpacker technology, this article did research on the reverse analysis theory such as junk code, code confusion, encrypt and compress, virtual machine and so on.The last part of this thesis works over the realization of the packers. In the aspect of the design and realization of packers, it emphasizes the construction of dynamic import tables and virtual machines. This software adopts a dynamic construction way to access the import tables. It not only points out the mechanism and process of building the dynamic import tables, but also explains its advantages and significance. This software makes use of the technology of virtual machines. It introduces the components of virtual machines, and it studies the theory and mechanism of using the virtual machines in packers. Furthermore, the virtual CPU environment, P-code, compiler, and interpreter are the main points of study in this article. The advantages and important significance of using virtual machines in the packers was also explained in this paper.