In order to improve the transmission efficiency of information between vehicles in the city and realize the information sharing between vehicles, aiming at the problem that the current multi-hop unicast routing algorithm based on geographical location forwarding in the Vehicular Ad-hoc NETwork （VANET） does not consider the specificity of the urban scene and cannot adapt to the high dynamicity of vehicles in the city, so that the data packets between vehicles may spread on the wrong path, resulting in high packet loss rate and long delay, a new greedy routing algorithm based on path exploration was proposed. Firstly, taken the data packet transmission delay as the standard, artificial bee colony algorithm was used to explore multiple routing paths planned by the digital map. Then, the multi-hop forwarding method of data packets between vehicles was optimized. Simulation results show that, compared with Greedy Perimeter Stateless Routing (GPSR) protocol and Maxduration-Minangle GPSR (MM-GPSR) improved algorithm, in the best case, the data packet arrival rate of the proposed algorithm increases by 13.81% and 9.64% respectively, and the average data packet end-to-end delay of the proposed algorithm decreases by 61.91% and 27.28% respectively.

Appending chunk attack is an important attack to threaten the security of cross-user deduplication for cloud data,which works by appending a random number of non-duplicate chunks to the file to be detected,making it impossible for cloud service providers to determine the true existence of the file. Therefore,the existence privacy of cloud data cannot be protected by general ways of response obfuscation methods. To deal with this problem,a new response obfuscation based secure deduplication method with resistance against appending chunk attack was proposed. By calculating the number of appending chunks,counting the number of non-duplicate chunks and comparing these two to determine the minimum number of redundant chunks involved in the response,so as to achieve the obfuscation. As a result,the existence of the checking file was not able to be judged by the attacker according to the response with little extra communication overhead. Security analysis and experimental results show that,compared with the state-of-the-art in this field,the proposed method achieves higher level of security with smaller amount of overhead required,or improves security significantly with comparable or slightly increased overhead.

In the existing time bank system, the issuance and settlement functions of time dollar are completely centralized on a central node. This central way not only suffers from many security problems including single point failure of central node and data tampering, but also has some problems such as lack of transparency in time dollar issuance and circulation, the dependance on centralized settlement agency in time dollar settlement process. In order to solve these problems, a public welfare time bank system based on blockchain was proposed. Firstly, the issuance function and settlement function of time dollar were separated from the central node. Then, the separated issuance function was gradually decentralized, and the separated settlement function was directly decentralized by the use of advantages of blockchain such as distributed decentration, collective maintenance and the feature of not easy to tamper, after that Public Welfare Time Blockchain (PWTB) was formed. Finally, PWTB used blockchain to decentralize the time bank system from a single node maintaining ledger to the collective maintaining distributed shared ledger, so the issuance and circulation of time dollar became open and transparent, and the settlement of time dollar did not rely on a central node. The security analysis shows that the PWTB can achieve safe information transmission and storage as well as safe data sharing.

In Software Defined Network (SDN), Dynamic Host Configuration Protocol (DHCP) flood attack packets can actively enter the controller in reactive mode, which causes a huge hazard to SDN. Aiming at the promblem that the traditional defense method against DHCP flood attack cannot keep the SDN network from control link blocking caused by the attack, a Dynamic Defense Mechanism (DDM) against DHCP flood attacks was proposed. DDM is composed of a detection model and mitigation model. In the detection model, different from the static threshold detection method, a dynamic peak estimation model was constructed by two key parameters - DHCP average traffic seed and IP pool surplus to evaluate whether the ports were attacked. If the ports were attacked, the mitigation model would be informed. In the mitigation model, the IP pool cleaning was performed based on the response character of Address Resolution Protocol (ARP), and an interval interception mechanism was designed to intercept the attack source, mitigating the congestion and minimizing the impact on users during interception. Simulation experimental results show that the detection error of DDM is averagely 18.75%, lower than that of the static threshold detection. The DDM mitigation model can effectively intercept traffic and reduce the waiting time for users to access the network during the interception by an average of 81.45%.

To avoid conflict incurring in airport taxiway and ease air traffic controller load, a control strategy of taxiway conflict based on sensor network was proposed. The dynamic model of taxiway based on sensor network was proposed according to taxiway movement process and the taxiway movement controlling regulations are defined, then the problems of taxiway conflict are transformed into state forbidden problems. Controllers were designed using the partial correlation matrix method and logical mutual exclusion method for state forbidden problems, and a way is proposed for control command of lights decided based on the state of transition. Taxiway conflict can be avoided and guided automatically using navigation light. A simulation was provided to testify the effectiveness of the control strategy finally.