The Design And Improvement On Algorithms About Trust Relationship Evaluation Based On Path Algebra

There are some new requirements between the security principals in the open computing system. We must find a new mechanism, which can set up and evaluate trust relationships. Trust management involves the specification of trust requirements, the analysis of these requirements to ascertain possible conflicts and the use of risk and experience information to aid in the on-line monitoring of these trust relationships. But how to supervise and administer trust relationship is still not resolved, especially in open computing systems. This dissertation presents evolvement of trust management in recent years, analyzes the factors of trust management models, and points out some problems in past models. In order to meet the requirement of trust management in open computing system, we bring forward a subjective trust relationship evaluation model based on path algebra, and define an efficiency described method of security credential and policy.This dissertation expatiates on the background, motivation and requirement of trust management, discusses the context and mathematic property of trust. We also discuss the existing trust management model and their shortages, such as description and measurement of trust and evaluated mechanisms is not reasonable, analyses method for trust evidence is complex, trust commend is subjective, and validation of trust relationship only rely on the third part. Consequently, we design digital certificate management system in particular, present basic class and interface of the system, and adopt X.509 certificate as basic credential for authentication and authorization. We also define the described method of security credential and policy as the foundations of trust relationship evaluation.The former evaluated method of trust has the problem of adaptability, and therefore we put forward an algorithm of trust relationship combination based on path algebra. This algorithm analyses the whole trust status of trust network, and converts subjective trust measurement into relative objective value of trust evaluation. This dissertation also ameliorates the algorithm of trust relationship combination to adapt certain trust environment that has no definite trust measurement.We have experimented and verified the efficiency and security of the algorithm of trust relationship combination in Web application environment, and reviewed somefactors, such as malevolent recommended trust, evaluated precise of principals and noisy in trust evaluation that may influence trust combination computation. The data of the experiment indicates that the algorithms of trust relationship combination can obtain evaluated value of trust relationship objectively and precisely.