Design Of A Cryptographic System On BeiDou Data

Beidou navigation satellite system has been independently developed by China and worked as the third mature navigation system. With the increasing of the Beidou navigation satellite applications, its safety has obtained increasing concern. It is often needed to encrypt the Bei Dou data in the application of some Beidou Navigatio Satellite System, so as to prevent an unauthorized third party from obtaining the message during data transmission. Now encryption system is divided into symmetric encryption and asymmetric encryption. The main application of symmetric encryption is to encrypt data to ensure data security. The primary application of asymmetric encryption is to sign data to ensure the source of message. On the basis of characteristics of the Beidou data, we use block cipher algorithm to encrypt data, and choose the RSA algorithm to sign data. The cryptographic system can effectively ensure the security of Bei Dou data.For the encryption part, we choose AES algorithm with improved key expansion to encrypt Bei Dou data. First, the data are divided into blocks with 128 bits. Then each block is encrypted by the block cipher algorithm. During the process, in order to enhance the strength of resistance to attack, we make the generation of round keys be related to the first two round keys instead of the previous key to improve the key expansion algorithm. Each block of data is effected by Add Roundkey followed by nine rounds of operations, which consist of Sub Byte, Shift Row, Mix Column, and Add Roundkey. At the tenth round of operation, Sub Byte, Shift Row and Add Roundkey will be done. Then the encrypted message is obtained. We choose the impossible-differential attack and the Biclique attack to validate these encrypted data. The results show that the encrypted data can resist these attacks.We further adopt a lightweight algorithm RECTANGLE to encrypt the Bei Dou data for portable devices which demand less resource comsumption. First the data are divided into blocks with 64 bits. Then each block is encrypted by the block cipher algorithm. The encryption process consists of 25 operations which include Add Roundkey, Sub Column and Shift Row. The Addroundkey operation is also needed after 25 operations, then the encryption process is completed. We choose the differential attack and the related-key differential attack to validate these encrypted data. The results show that the encrypted data can resist these attacks.During the signature of the cryptographic system, we adopt asymmetric algorithm RSA to sign the Bei Dou data, which can ensure the source of message and the non-repudiation of message.The cryptographic system designed in this thesis can ensure the safety and non-repudiation source of Beidou data. We implement the designed cryptographic system in software by C language in VC6.0.