In smart environments, pervasive computing contributes significantly in improving daily life activities for users by providing personalized services to dependent people. Nevertheless, those environments do not guarantee a satisfactory level for protecting the user privacy and ensuring the trust between communicating entities. Context-based security is an emerging approach to cope with the new security problems introduced by the high level of dynamicity and heterogeneity that characterize pervasive environments. Although the fact that pervasive environments rise the security challenges, they also bring new opportunities due to the ubiquitous technologies and ambient intelligence which provide valuable contextual information about the user and its environment: user's identity, interaction history with services, location, preferences, type of requested services, time/date of service request.