Given a client/server application, how can the server entrust the integrity of the remote client, albeit the latter is running on an un-trusted machine? To address this research problem, we propose a novel approach based on the client-side generation of an execution signature, which is remotely checked by the server, wherein signature generation is locked to the entrusted software by means of code integrity checking. Our approach exploits the features of dynamic aspect-oriented programming (AOP) to extend the power of code integrity checkers in several ways. This paper both presents our approach and describes a prototype implementation for a messaging application.