Study Of Software Protection Technique Based On CPLD

Software Protection is a needed work for protecting software engineers' benefits as well as an important component of software engineering. After analysis of protecting and cracking encryption technique of software,the paper presents a software protection technique using CPLD(Complex Programmable Logic Device).Because the software for protection is mainly used in a real-time checking subsystem in an industry system,and needs faster speed of data transport,so the PCI(Peripheral Component Interconnect) interface criterion is utilized in the Software Protection card. The basis of Software Protection with CPLD is to design circuits according to PCI local bus criterion and the goal of software protection. In this paper the functions and principles of Software Protection card are introduced,and the circuit diagrams are also presented.The technique of Software Protection studied in this paper is realized by designing CPLD in the Software Protection card. After introduction of techniques of designing circuit with CPLD,some types of software protection technique involving code replanting are implemented in the card.Because in Windows 98 operation system,software and hardware resources are managed in a virtualized way to guarantee the system's safety,the device driver of the Software Protection card is developed to ensure its software protection ability. So,the technique of developing Virtual Device Driver with VtoolsD is presented after a brief introduction of Windows98 virtual machine structure and primary knowledge of VxD. Four main aspects of development of Virtual Device Driver are analyzed. They are device initialization,communication of Win32 application process and VxD,access of VxD to hardware and hardware interruption process in VxD.