The present invention discloses a central certificate management system for thin client devices in data networks and has particular applications to systems having a large number of the thin clients serviced by a proxy server through which the thin clients communicate with a plurality of secure server computers over a data network. According to one aspect, the present invention provides a certificate management module that causes the server device to manage digital certificates for each of the thin client devices. To minimize the latency of obtaining certificates for each of the thin client devices, the certificate management module reserves a fixed number of free certificates signed by a certificate authority and their respective private keys in a certificate database and frequently updates the free certificate according to a certificate updating message. Whenever a user account is created for a thin client device, the certificate management module fetches one or more free certificates from the certificate database and associate the fetched certificates to the created account and meanwhile the certificate management module creates new free certificates with the certificate authority to fill in the certificate database. Apart from the tradition of obtaining certificates locally in client devices that normally have sufficient computing power, the present invention uses the computing resources in a server device to carry out the task of obtaining and maintaining certificates asynchronously in the proxy server and further. These and other features in the present invention dramatically minimize the demands for computing power and memory in thin client devices like mobile devices, cellular phones, landline telephones or Internet appliance controllers.