In high dynamic environments such as Internet or pervasive computing, different unknown services are provided. When two services communicate, they share properties to negotiate a provided service. By introducing trust, services rely on the identity of the participants, to evaluate a trust level and adapt this provided service. However, it is not always possible to verify identity. In this paper, we propose a service-to-service trust protocol based on services' description. By exchanging their descriptions, services build trust in each other and adapt the quality of the provided service through policies.