digital certificate

The transmission of (sensitive) data between server and client should be secured, in particular against eavesdropping and man-in-the-middle attack. The client accesses data (which is stored on the server) over HTTP through specific web interface. Hence, the client-server communication should be adapted to HTTP over TLS/SSL (i.e. HTTPS). There is no possibility to receive an officially issued digital certificate from one of the well-known certification authorities (CA). The solution should be simple, and the implementation may not take longer than ca. 2 hours.