A communication method includes receiving by a SGSN a context request message from a mobility management entity (MME), obtaining by the SGSN an authentication vector-related key, and calculating by the SGSN a root key according to the authentication vector-related key. In addition, the method further includes sending by the SGSN a context response message including the root key to the MME, wherein the MME derives a NAS protection key according to the root key.