The existing algorithms of Top-k query can not make full use of the powerful parallel throughput of Graphic Processing Unit (GPU) to timely return the query results. So, a segmented query algorithm based on Compute Unified Device Architecture (CUDA) model was proposed. By dividing the query process and using the strategy of segmented parallel process, the maximal calculation and comparison efficiency in query process could be obtained in this algorithm. The experimental results show that this algorithm has obvious performance advantages compared with four-thread parallel optimization algorithm on multi-core CPU. When the number of ordered lists is 6 and the traversal stride is 120, the optimal performance can be obtained which is 40 times faster than multi-core CPU algorithm.

The identity-based ring signcryptions have both high efficiency of identity-based cryptosystem and signcryption technology and the ambiguity of ring signature. In the fair exchange protocol based on signcryption proposed by Luo, et al (Luo M, Zou C H, Hu J, 〖WTBX〗et al.〖WTBZ〗Signcryption-based fair exchange protocol. Journal of Communications, 2010, 31(8A): 146-150), the fairness and efficiency are not good enough. The new scheme introduced a more efficient identity-based ring signcryption and dealt with the decryption and the signature-and-identity binding separately. A new fair exchange protocol was proposed based on this new scheme. The analysis shows that this scheme overcomes the fairness defect of the original scheme and has a better efficiency, which makes it a good application in electronic payment and contract signing.

By analyzing the certificateless verifiable ring signature scheme (LUO DAWEN, HE MINGXING, LI XIAO. Certificateless verifiable ring signature scheme. Computer Engineering,2009, 35(15): 135-137) and the verifiable proxy ring signature scheme (LUO DAWEN, HE MINGXING, LI XIAO.A verifiable proxy ring signature scheme.Journal of Southwest University for Nationalities:Natural Science Edition, 2009, 35(3):608-611), it was found that these convertible ring signature schemes were susceptible to non-repudiation attack, i.e., any member in the ring can impersonate others identity to sign the message and the verifier believed the signature was signed by the latter. To address the above problems, improved schemes were proposed by using the private key of the signer to have a secret value. The security analysis proves that the improved schemes overcome the security defect of the original scheme and satisfy all security requirements of verifiable ring signature.

In order to select text feature more comprehensively and improve the accuracy of the text feature selection, a new text feature selection method based on Invasive Weed Optimization (IWO) was proposed. The biggest advantage of IWO is that the offspring individuals are being randomly spread around their parents according to Gauss normal distribution, and the standard deviation of the random function is adjusted dynamically during the evolution process; thus, the algorithm explores new areas aggressively to maintain the diversity of the species in the early and middle iterations, and enhances the feature selection of the optimal individuals in final iteration. Such mechanism ensured the steady convergence of the algorithm to global optimal solution, and improved the accuracy of the text feature selection. The results of experiments indicate that this method can provide the entry of low weight value with feature selection opportunity, and ensure the feature selection advantage of the entry with high weight value, thereby enhancing the completeness and accuracy of the text feature selection.

Because the traditional anisotropic diffusion equation for image restoration only considers the gradient size, and produces false edges in color image inpainting, this paper proposed an image inpainting method based on structure tensor. Structure tensor was used as diffusion coefficient which can implement different diffusion processes in different regions. The experimental results show that the new method, in comparison with Total Variation (TV) and BSCB methods, improves the image inpainting results, and effectively inpaints color images.