Abstract
Raptor Codes is the most popular AL-FEC Codes, and it has excellent efficiency in unstable transmit environment. Raptor Codes will depart an object into many blocks and use its coding algorithm to repair the lost part of the packet. It can avoid retransmitting the lost packets again in unicast and multicast. Therefore, there are many applications adopting Raptor Codes. In this thesis, we propose a method which can improve the confidentiality with low cost so that it can avoid main disadvantages and provide more advantages of the traditional method. In our method, we import three parameters which are shift number, shift index number, and padding set. These parameters protect each other to gain more security. We will elaborate how the parameters work in encoder and decoder, and analyze the security in the worst case. Furthermore, we analyze the overhead time and explain it is between 0.0037% and 0.0076% in our experiments. Moreover, the method we provided in this thesis can also improve the security by increasing the number of shift index numbers. But the relation of the symbols may be the weakness in our method. It needs further analysis to estimate the actual increasing rate to the security.