Design And Improvement Of STB Graphic Library And CAS

In recent years, because of the well-known advantages of digital television technology, transition from analog television to digital television has become quicker obviously. Base on the situation, STB (Set-Top Box ) will become the bridge between analog television and digital television, so "High Definition Digital Television STB" become a focus for both commerce and academic research. Therefore exploit and design STB software with friendly user interface and good CAS (Conditional Access System) have important academic values and practical meanings.This paper is based on the project—High Definition Digital Television STB. The main task of this project is to develop a high definition digital television STB with personal video recorder and conditional access functions. This paper mainly explains how to design a wonderful software system of STB, and how to build a graphic library, and the design of the CAS, and how to crack the program on the E~2PROM of a smartcard.The key for user interface is the graphic library, which is composed of graphic figures and texts. This paper explains how to build a graphic library include many kinds of two-dimensional mapping function and some examples about the ultimate application functions. After that, a new algorithm for drawing ellipse is introduced to the graphic library of STB in this paper. The new algorithm can generate serial pixels at one step. So, it is faster than the conventional algorithms (such as Midpoint algorithm).CAS allows authorized users to receive encrypted programs. This system can also achieve digital programming copyright protection and digital pay TV problems. But because of the absence of a uniform standard for CAS on the encryption system , the STB as the terminal receive equipment in digital television system becomes the key point that is affecting the development of digital television industry. Generally speaking, the STB smart card belongs to the CAS. Therefore, the principle and mechanisms of CAS are described firstly; then designed the entire CAS, elaborated on the role of smartcards in the system, cracked the programs in a smartcard. The binary file on E~2PROM of smartcard will be read out and be anti-compiled to source codes, execute the source file by software control in PC just like they are executed in smartcard, thereby realize the process of disassembling and simulation. The arithmetic has been realized based on the standard C language and is working fairly well in source file renewing and STB developing.The software system of STB is easily maintained and upgraded because the structure is hierarchical. Besides, the modularization allows each part of the software have its own function. Based on the theory and technology, a STB with friendly user interface has been completed; the design and improvement to CAS will impetus the development of encrypt TV, pay TV, and the development of smartcards itself.