Deep packet inspection (DPI) is widely used in detecting abnormal traffic and suspicious activities in networks. With the growing popularity of secure hypertext transfer protocol (HyperText Transfer Protocol over Secure Socket Layer, HTTPS), inspecting the encrypted traffic is necessary. The traditional decryption-and-then-encryption method has the drawback of privacy leaking. Decrypting encrypted packets for inspection violates the confidentiality goal of HTTPS. Now, people are faced with a dilemma: choosing between the middlebox’s ability to perform detection functions and protecting the privacy of their communications. We propose OTEPI, a system that simultaneously provides both of those properties. The approach of OTEPI is to perform the deep packet inspection directly on the encrypted traffic. Unlike machine and deep learning methods that can only classify traffic, OTEPI is able to accurately identify which detection rule was matched by the encrypted packet. It can facilitate network managers to manage their networks at a finer granularity. OTEPI achieves the function through a new protocol and new encryption schemes. Compared with previous works, our approach achieves rule encryption with oblivious transfer (OT), which allows our work to achieve a better balance between communication traffic consumption and computational resource consumption. And our design of Oblivious Transfer and the use of Natural Language Processing tools make OTEPI outstanding in terms of computational consumption.
Clustering ball spinning (CBS) forming is a novel approach to manufacturing a complex curved surface. In order to explore the forming limit of magnesium alloy in the CBS forming process, the modified GTN model was incorporated into the FE simulation to analyze the damage evolution. The theoretical analyses are conducted to investigate the deformation mechanism and to explore the stress state in the CBS forming process. The numerical results show that the modified GTN model can predict the result more accurately compared with the standard GTN model, and the damage parameters for GTN model are determined by the experiments. Besides, the forming limit of AZ31 magnesium alloy can be improved by CBS forming method. To explore the reason for the increased forming limit, the microstructure of curved surface was tested by electron backscattered scattering detection (EBSD). The results demonstrate that the deformation of magnesium alloy plate by the CBS method is dominated initially by the extension twinning, and non-basal slip systems are activated with the development of forming process.
Kinetic characteristics of chain drive system were investigated in this paper and some corresponding mathematical models were established. In accordance with the theory of chain drive, based on the multi-body dynamics software platform, a dynamic analysis model of timing bushing chain system for diesel engine was established. Chain tension force, chain contact force and chain fluctuation in a rotation cycle at different running speeds were analyzed. By analysis and evaluation these results, the kinematic and dynamic characteristics of the chain drive system during the operation could be effectively recognized, this research results can provide a basis for production tests.
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