A computing device (such as a client device) includes an application processing module for execution and storage of non-protected “normal” client software applications. The computing device may also include a secured processing module for execution and storage of one or more trusted software applications. A trusted software application generally has an associated client application in the application processing module which is configured to interface with the trusted application in the secured processing module. The protection facilities in the secured processing module are only available to trusted applications and their associated client applications. In particular, the functionality and capabilities of existing trusted applications are currently not available to other normal applications in the application processing module of the computing device. This is especially problematic in implementations where it is not possible to install new trusted applications or to extend existing trusted applications with new functionality. The present invention seeks to overcome this problem.