Focused on the problems of extra bandwidth overhead and high computational complexity to realize secure network coding against wiretapping, a secure networking coding scheme based on double chaotic sequences was proposed. Firstly, the first-dimentional data of source information was encrypted by using Cat-Logistic sequence. Then, sparse pre-coding matrix was constructed by the encrypted data. Finally, the rest vectors were linearly and randomly mixed up with the pre-coding matrix, realizing anti-wiretapping. Compared with the traditional Secure Practical netwOrk Coding (SPOC) scheme, the proposed scheme does not indroduce extra source coding redundancy by constructing sparse pre-coding matrix, reducing bandwidth overhead. The theoretical analysis and experimental results show that the proposed scheme not only has lower coding complexity but also improves network security and the transmission efficiency.

To solve the problem that the construction algorithm of multi-source multicast network coding costs long convergence time, a deterministic layered construction algorithm based on network coding was proposed. On the basis of existing studies, a virtual source was used for virtual trial. Firstly, the nodes with non-full rank local coding matrix were determined layer-by-layer by decision tree algorithm. Then, the local encoding coefficients of the upper transform nodes were reconstructed and a new encoding vector was generated. Finally, the new encoding vector was transmitted to the lower node corresponding to it, and the local coding matrix of the lower node was full rank, so a feasible coding scheme was obtained to realize network coding. Moreover, when redundant data is found in some links, pruning branches method was implemented to improve bandwidth utilization. The algorithm only needs one virtual trial multicast in comparison with the Sink Nodes Feedback Deterministic Network Coding (SNFDNC), and the simulation results show that the convergence time of the proposed algorithm is shorter in the medium scale network, and the average transmission rate of multicast communication is further improved.

Concerning the problems of the existing network coding schemes against global wiretapping attack such as large amount of computation, low bandwidth efficiency and low security, a secure network coding scheme by double encryption based on chaotic sequences was proposed. Firstly, a key was used to encrypt the last dimensional transmission data and the chaotic sequences were disturbed by the data itself while encrypting. Then, another key and a random number key were used to generate coding coefficient matrix, while the chaotic sequences were disturbed by m sequence. Finally, the obtained coding coefficient matrix was used for the linear combination of encrypted messages and unencrypted messages against global wiretapping attacks. Since the coding coefficient matrix was generated by the keys, the coding coefficients were not needed to be transmitted in the channel. Compared with the traditional Secure Practical Network Coding (SPOC) scheme, the proposed scheme saves the bandwidth overhead of the transmission of coding coefficients in the network. The analysis and experimental results show that, the proposed scheme improves the safety performance of network, which ciphertext-only attacks and known plaintext attacks can all be resisted. And the proposed scheme can also improve the transmission efficiency, and its algorithm complexity is moderate.

Concerning the shortcomings in improving the sensing ability and reducing the amount of data transmission of the conventional dual-threshold cooperative spectrum sensing under the communication environment of uncertain noise, an improved dual-threshold cooperative spectrum sensing algorithm based on two-step fusion was introduced in Fusion Center (FC). Firstly, this algorithm got rid of the negative influences of some drop-out users by filtering all cognitive users. Then set the dual-threshold adaptively according to the uncertainty of the noise to strengthen the sensing adaptability of system under uncertain noise circumstance. Finally, by adopting a strategy of two-step fusion in FC, this algorithm made a compromise between the high detection ability and low amount of the data transmission. Compared with the conventional dual-threshold spectrum sensing algorithm, the theoretical analysis and simulation indicate that the proposed algorithm can not only avoid the cognitive failure and enhance the cognitive performance on the condition of a low data transmission, but also show an obvious improvement under a high noise uncertainty.

In order to solve the problems of digital image encryption algorithm including scheme complexity and poor security, a DNA fusion image encryption algorithm based on chaotic system was proposed. Firstly, the image was scrambled by Baker transform to obtain the DNA sequence. Then, Logistic map was used to generate chaotic sequence. Finally, the DNA sequence was encrypted. The method has good sensitivity to initial values and strong ability of anti-statistical and anti-differential attacks. The simulation results show that the algorithm is not only simple, but also has good encryption effect and high security.