Abstract: This invention generally relates methods, computer program code, data processing apparatus, and signals for certifying data, in particular by means of an electronic signature. Embodiments of the invention can be implemented on a user terminal without the need for dedicated hardware or software and may be termed “zero-footprint” data certification methods. A method of providing an electronic signature to-a-server; the method including receiving data for said server at a proxy system for said server; reading said received data to identify a signature request; obtaining a signature for a portion of said received data associated with said request responsive to said request, and providing said signature from said proxy system to said server. The use of a signature-enabled reverse proxy enables the use of a zero footprint user terminal, that is without the need to add additional functionality to the terminal for the purposes of signature creation in the context of a distributed application architecture.