| The security of mobile communication has always been a critical part, which needs to be considered carefully, no matter in ancient communication systems or in modern communication systems. Therefore, the recent research of LTE (Long Term Evolution) system also has to pay attention to the security problem since it is a main indicator of communication system reliability. In this thesis, the research focuses on the security of the access layer of LTE system-the PDCP (Packet Data Convergence Protocol) layer. In most of the existed LTE systems, the main algorithms that are used in PDCP layer are AES (Advanced Encryption Standard) algorithm and SNOW3G algorithm. With the development of communication technology, the ZUC (Zu Chongzhi) algorithm developed by China has become the third standard algorithm for access layer of LET system.The main task of this thesis is applying the ZUC algorithm of PDCP layer in LTE system, strengthening communication system security by improving the nonlinearity of the algorithm, establishing a transmission system of a LTE system, and simulating the system performance before and after the improvement of ZUC algorithm.The main works and outcomes of this thesis are as follows:Firstly, the LFSR (Linear Feedback Shift Registers), bit recombination and F function of ZUC algorithm have been realized by C language programming.Secondly, the ZUC algorithm has been improved. The algorithm security has been increased by improving its nonlinearity. The work has been divided into two parts:one is using FCSR (Feedback with Carry Shift Registers) instead of LFSR; the other adding two S boxes of AES and keeping the existed two S boxes of ZUC algorithm.Thirdly, the base station transmission system in the LTE system has been built and the testing of the system performance before and after the improvement of ZUC algorithm has been completed, including system establishment, PDCP layer throughput test and mobility management test. |
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