Now a days, a new family of web applications 'open applications’, are emerging (e.g., Social Networking, News and Blogging). Generally, these open applications are non-confidential. The security needs of these applications are only client/server authentication and data integrity. For securing these open applications, effectively and efficiently, HTTPI, a new transport protocol is proposed, which ensures the entire security requirements of open applications. Benefit of using the HTTPI is that it is economical in use, well-suited for cache proxies, like HTTP is, and provides security against many Internet attacks (Server Impersonation and Message Modification) like HTTPS does. In terms of performance HTTPI is very close to the HTTP, but much better than HTTPS. A Web service is a method of communication between two ends over the Internet. These web services are developed over XML and HTTP. Today, most of the open applications use web services for most of their operations. For securing these web services, security design based on HTTPI is proposed. Our work involves securing the web services over SOAP, based on the HTTPI. This secure web service might be applicable for open applications, where authentication and integrity is needed, but no confidentiality required. In our paper, we introduce a web service security model based on HTTPI protocol over SOAP and develop a preliminary implementation of this model. We also analyze the performance of our approach through an experiment and show that our proposed approach provides higher throughput, lower average response time and lower response size than HTTPS based web service security approach.