With Asi Interface Des Data Encryption-channel Coding

The appearance of the Data Encryption Standard(DES) is an important thing in the history of cryptology, the DES is the first opening encryption algorithm which is widely used in the history of cryptology. The DES encryption algorithm has stood the long test from when it became the encryption standard in 1976 to now, it is proved by much practice that the security of the DES encryption can satisfy the voluminous need of security. Until now, there is no better decryption method except trying every possible key and find the only one at last.This dissertation introduces the design of a transport stream DES encryption system, it can encrypt data according to the packet of the transport stream, the system is implemented based on FPGA EP1C6T144C8 and Verilog HDL. According to the demands of mobile communication system of Unilik, the input data which will be encrypted is come from Asynchronous Serial Iinterface(ASI) and the output data which has been encrypted must be sent to the ASI, so the DES encryption system include the receiver and the transmitter of ASI. Data from ASI receiver is send to FPGA and encrypted in the FPGA, then data which has been encrypted is send to ASI transmitter from FPGA. Keeping the integrity of the transport stream packet frame is necessary to the latter function modules (channel encoder, modulator etc), so the 4 bytes header of the packet should not be encrypted. The 188 bytes transport stream packet is divided into two parts: one is the 4 bytes header, the other is the 184 bytes payload. The 4 bytes header is not encrypted, the 184 bytes payload is grouped by 8 bytes, 8 bytes is 64 bits which is the right input of the DES encryption algorithm. The payload data which has been encrypted is combined with the 4 bytes header which is not encrypted into a new 188 bytes transport stream packet. DES is a symmetry key cryptography, the security of DES is depend on the security of key, if the key is not safe enough, it should be replaced immediately. In order to change the key easily, design a interface between RS232 and the FPGA in the DES encryption system is necessary, then the user can change the key using a computer. After connectting the DES encryption system into the mobile communication system, the work of encryption and decryption is normal, the speed of encryption(decryption) is 192Mbps, exceeds the demand of 32Mbps.The last part of this dissertation introduces the theory of the Reed-Solomon codes, energy dispersal and the convolutional interleaving codes, the RS codes can correct the random error during the communication. The interleaving codes can disperse the data according to special rules, change the burst interference channel into random interference channel. The channel codes can improve the error-correcting capability of communication equipment. Acocording to the theory, this dissertation describes the design of RS(204, 188), I=12, M=17 convolutional interleaving codes and energy dispersal based on FPGA; and presents the right test result by using embedded logic analyzer SignalTapⅡ.