The growing success of WS-related technologies has resulted in a large number of providers, which implement services of varying degree of sophistication and complexity. While on the one hand the availability of a wide array of services has created a competitive and flexible market that suits well the needs of different type of users, on the other hand, it requires them to select among possibly hundreds of similar services. As such, Web service selection plays a crucial role in Web service lifecycle. Here, several application-dependent requirements might constrain the selection of the best service. In this paper, we study the privacy implications caused by the exchange of large amount of potentially sensitive data required by optimized strategies for service-selection. In particular, we propose a comprehensive framework to uniformly protect users' and service providers' privacy needs, at the time of service selection. We define a solution that allows matching of the search criteria against the Web services attributes in a private fashion such that both criteria and service attributes are kept private during the matching. Further, we propose an approach to protect service provisioning rules from unwanted disclosure, both from the user and the service provider's perspective. Our experimental evaluation and complexity analysis demonstrate that our algorithms are efficient.