Services in a service-oriented architecture are designed to meet desired functional and non-functional requirements. Conformance of a service implementation to its functional requirements can be tested by observing the interface of the service but it is hard to enforce non-functional requirements such as data privacy and safety properties by monitoring the interface alone. Instead the implementation of the service need to be monitored for its conformance to the non-functional properties. A requirement's monitor can be deployed to check this conformance. A key problem is that such monitor must execute in an untrustworthy environment (at the service provider's location).;We argue that the integrity of the reported results of such a monitor crucially depends on the integrity of the monitor itself. Previous research results on trustworthy computing has shown that static properties, such as the checksum, of a remote program can be verified using a hardware-based mechanism called trusted platform module.;This thesis makes two contributions. First, we extend the traditional notion of a service-oriented architecture to accommodate the requirements for trust. Second, we propose a dynamic attestation mechanism that serves to support our extensions. To evaluate our approach, we have conducted a case study using a commercial requirements monitor and a collection of web service implementations available with Apache Axis implementation. Our case study demonstrates the feasibility of verifying the conformance of a web service executing in an untrusted environment with respect to a class of non-functional requirements using our approach. Lack of data privacy during online transactions is a major cause of concern among e-commerce users. By providing a technique to monitor such properties in a decoupled environment our work promises to address the issue of guaranteeing the privacy of confidential client data on the provider's side in a Service Oriented Architecture.