Abstract: According to an embodiment of the present disclosure, a method of key-management by a group management server in Mission Critical Systems (MCX) between an initiating party and a receiving party is provided. The method comprises generating a master key, the master key being designated for an ad-hoc communication, allocating an identifier to the generated master key, and transmitting a transmission message signed by an initiating MCX entity including the master key to a receiving MCX entity.

Abstract: A method for sharing a reason cause for a mission critical communication (MCX) communication over pre-established session in an MCC network is provided. The method includes transmitting, to the server, a call initiation request to initiate a call, wherein the call initiation request includes first information on a session type and second information on a resource list, receiving, from the server, a mission critical pre-established session control (MCPC) connect message including a security message, determining whether an authentication for the security message is successful, and transmitting, to the server, a first MCPC acknowledgement message including a reason cause field to inform a reason for terminating the call in response to determining that the authentication for the security message is not successful.

Abstract: According to an embodiment of the present disclosure, a method of key-management by a group management server in Mission Critical Systems (MCX) between an initiating party and a receiving party is provided. The method comprises generating a master key, the master key being designated for an ad-hoc communication, allocating an identifier to the generated master key, and transmitting a transmission message signed by an initiating MCX entity including the master key to a receiving MCX entity.