By studying the algorithms of single pattern matching, five factors that have effect on time complexity of the algorithm are analyzed. The five factors are: sorting the characters of pattern string in an increasing order of using frequency, utilizing already-matched pattern suffix information, utilizing already-matched pattern prefix information, utilizing the position factor which is absorbed from quick search algorithm, and utilizing the continue-skip idea which is originally proposed by this paper. Combining all the five factors, a new single pattern matching algorithm is implemented. It’s proven by the experiment that the effciency of new algorithm is the best of all algorithms.
Privacy is a critical requirement in distributed data mining. Cryptography-based secure multiparty computation is a main approach for privacy preserving. However, it shows poor performance in large scale distributed systems. Meanwhile, data perturbation techniques are comparatively efficient but are mainly used in centralized privacy-preserving data mining (PPDM). In this paper, we propose a light-weight anonymous data perturbation method for efficient privacy preserving in distributed data mining. We first define the privacy constraints for data perturbation based PPDM in a semi-honest distributed environment. Two protocols are proposed to address these constraints and protect data statistics and the randomization process against collusion attacks: the adaptive privacy-preserving summary protocol and the anonymous exchange protocol. Finally, a distributed data perturbation framework based on these protocols is proposed to realize distributed PPDM. Experiment results show that our approach achieves a high security level and is very efficient in a large scale distributed environment.
This paper presents a concrete democratic group signatme scheme which holds(t,n)-threshold trace- ability.In the scheme,the capability of tracing the actual signer is distributed among n group members.It gives a valid democratic group signature such that any subset with more than t members can jointly reconstruct a secret and reveal the identity of the signer.Any active adversary cannot do this even if he can corrupt up to t-1 group members.
Growing numbers of users and many access policies that involve many different resource attributes in service-oriented environments cause various problems in protecting resource. This paper analyzes the relationships of resource attributes to user at- tributes based on access policies for Web services, and proposes a general attribute based role-based access control(GARBAC) model. The model introduces the notions of single attribute ex- pression, composite attribute expression, and composition permis- sion, defines a set of elements and relations among its elements and makes a set of rules, assigns roles to user by inputing user’s attributes values. The model is a general access control model, can support more granularity resource information and rich access control policies, also can be used to wider application for services. The paper also describes how to use the GARBAC model in Web services environments.
