Research On Algorithms Of Secure Network Coding Against Global Eavesdropping

With the development of society, people has entered an information age. Every day,there is a huge amount of information which needs to be transmitted via network. How to transmit information fast and safely becomes more and more important. The network coding properly meets the requirements of transmitting information fast and safely. When the network coding is used to transmit information,the nodes will mix the information received from input links and send the result through output links. So the transmission rate of the network coding can achieve the upper bound specified by the max-flow min-cut theorem. In addition, because the data is mixed at the intermediate nodes, eavesdroppers can not get the original data directly. So the network coding is more secure than the routing transmission.However, eavesdropping attacks may still cause information leakage. So it is necessary to study the secure network coding against eavesdropping attacks.In literature some secure network coding schemes have been proposed for achieving information-theoretic security,however,these schemes limit the number of eavesdropped channels and sacrifice some bandwidth due to use of extra random symbols. When eavesdroppers can eavesdrop on all the channels in the network, these schemes will leakage some of source messages, and therefore these schemes can not resist global eavesdropping attacks. In this thesis, two kinds of secure network coding schemes against global eavesdropping are proposed by studying the existing schemes against global eavesdropping.First,a secure network coding scheme against global eavesdropping based on encrypting source messages is proposed. For the network coding whose size of coding field is q,the proposed scheme generates two permutation sequences of length q.And then it mixes and replaces source messages by using the permutation sequences so that it can resist global eavesdropping attacks. The proposed scheme only encrypts source messages at the source node and has no change at intermediate nodes. Because of the simple encryption algorithm and no pre-coding operation,the scheme doesn't introduce extra bandwidth overhead and has high actual coding efficiency.Next, a secure network coding scheme against global eavesdropping based on hiding the pre-coding matrix is proposed. For the network whose multicast capacity is m, the proposed scheme generates a quasi-vandermonde matrix by using the first column of the source message matrix with m rows and n columns. Every row of the quasi-vandermonde matrix is permuted for generating the pre-coding matrix. The first column of the source message matrix is encrypted by using the AES algorithm and then transmitted together with the rest n-lcolumns which have been multiplied with the pre-coding matrix. The encryption volume of this scheme is m. The pre-coding matrix of this scheme can be further transformed into a sparse matrix and therefore the pre-coding complexity can be reduced from O(m2n)to O(mn). The simulation results show that the proposed low complexity scheme has high actual coding efficiency.