In our security framework, the CA server is an important component that issues proxy credentials and slave credentials. Since the Gfarm file system, which is the underlying file system of G-Hadoop, applies the GSI security mechanism and has already a CA server, we simply reuse this server as the CA server of the proposed security framework. In addition, the slave nodes in G-Hadoop have their own GSI certificate for the Gfarm file system. This GSI certificate is also simply used as the slave credential.