In the next step, the master node sends a request to apply a proxy credential for the user instance, as depicted by Phase II(b) in Fig. 3. Since a proxy credential is the authentication information of a user instance on the slave nodes, it must be unique with each use case to avoid abusing, even for the same user instance but different jobs. For this purpose,the master node generates a random key pair {MN_Pub, MN_Prv}. This key pair is used later during the authentication phase between the master node and slave nodes. The master node retains the private key MN_Prv and sends the public key MN_Pub to the CA server.