Collaborative filtering is the most popular personalized recommendation technology at present. However, the existing algorithms are limited to the user-item rating matrix, which suffers from sparsity and cold-start problems. Neighbours' similarity only considers the items which users evaluate together, but ignores the correlation of item attribute and user characteristic. In addition, the traditional ones have taken users' interests in different time into equal consideration. As a result, they lack real-time nature. Concerning the above problems, this paper proposed a nonlinear combinatorial collaborative filtering algorithm consequently. In order to obtain more accurate nearest neighbour sets, it improved neighbours' similarity calculated approach based on item attribute and user characteristic respectively. Furthermore, the initial prediction rating fills in the rating matrix, so makes it much denser. Lastly, it added time weight to the final prediction rating, so then let users' latest interests take the biggest weight. The experimental results show that the optimized algorithm can increase prediction precision, by way of reducing sparsity and cold-start problems, and realizing real-time recommendation effectively.

The security weakness of structured multi-signature scheme with signers' intentions was pointed out. It is that the signers' intentions could be modified by an inner or outer attacker, thus the security of this type of signature is tampered. By using a more secure signing algorithm to sign the signers' intentions, the problem was solved. The improved scheme not only has all the necessary security properties of this type of signature, but also has improvement in efficiency - shorter signature size, more efficient in communication and signing computation. The shortage of the new scheme is some decrease in the efficiency of verification.

With proxy multisignature, many original signers can delegate their signing power to a proxy signer in such a way that the proxy signer can sign any message on behalf of them. In blind signature, the signer cannot make a linkage between the blind signature and the identity of the requester. Therefore, they are easily applied in electronic commerce. Based on Schnorr signature scheme, a new proxy blind multisignature scheme was proposed. One proxy signer can generate a proxy blind multisignature on behalf of many original signers. This scheme satisfies the security properties of both the blind signature scheme and the proxy multisignature scheme. It has advantages such as low computation load, high efficiency and security, and that the length of signature does not increase when the new original signers join in.