| Software update over network not only reduces the software vendor's cost of maintaining the software system greatly, but also provides the software users more convenient update service. But there are many security problems in the process of software update in distributed systems, all the software update systems available don't provide a complete security solution to these problems. Moreover most of the software systems nowadays are based on components, many software systems are consisted of components produced by different software vendors. The requirements of software components on their hosting environments and their interdependencies bring many problems when being deployed: how to check the deployment constraints, how to solve the dependencies between different versions of each component, how to choose the needed components.This paper focuses on the two fields of software update in distributed environment: the security problem and the constraint and dependence checking when deploying software update. Firstly, on the basis of the analysis of the security policy in the software update, a new security solution is presented for the security policy. Then the security solution for a software update system built in Web service is implemented via XML signature and Encryption techniques and so on, and some experiments are conducted to test and analyze the performance of the different implementations which adopt different encryption algorithms, so that one can choose the security technology in practice according to his own requirement. Secondly, this paper presents a software update description format to describe software update unit, and models the constraints and dependences in a standardized form. And a software update algorithm is designed, which uses the update description to conduct the update process. This algorithm can implement the constraint checking and dependence checking in the process of update, and reduce the network load effectively. |
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