In pervasive computing environments, service discovery is an essential step for computing devices to properly discover, configure, and communicate with each other. We introduce a user-centric service discovery model, called PrudentExposure, which automates authentication processes. Traditional authentication approaches requires much users’ involvement. PrudentExposure encodes hundreds of authentication messages in a novel code word form. Moreover, we discuss how a progressive and probabilistic model can protect both users’ and service providers’ privacy. Perhaps the most serious challenge for pervasive service discovery is the integration of computing devices with people. In a challenging case, both users and service providers want the other parties to expose sensitive information first. Our model protects both users and service providers.