The study deals with the most important elements of ubiquitous computing, that is, the toolkit to acquire, express and safely use the context information. To do so, we introduce CAST(Context-Awareness Simulation Toolkit) and show how it works. CAST generates users and devices in a virtual home domain, designates their relation and creates virtual context information. The created context information is reused by the request of application and put into use for context learning. Particularly, we have given a consideration to security in the process of context creation and its consumption. That is, we applied SPKI/SDSI to test if the created context information was valid information and if the application that called for the context had legitimate authority to do so. CAST not only captures virtual context information, but it also guarantees the safe sharing of the context information requested by the application.