Abstract: A method implemented by a client transmitting entity included in a 3GPP MCS (3rd Generation Partnership Program Mission Critical Services) standard network, the client transmitting entity being configured to transmit a plurality of contents intended for at least one client receiving entity included in the network, the client transmitting entity and the client receiving entity being affiliated with a same communication group, the method including generating, by the client transmitting entity, a group user key identifier, the group user key identifier being specific to the communication group and being used to encrypt the content, the generation being repeated each time a predetermined event takes place.

Abstract: A method implemented by a client transmitting entity included in a network according to the 3GPP MCS standard, the client transmitting entity being configured to transmit content intended for a client receiving entity included in the network and being affiliated with a same communication group, the method including selecting a security context from among: a security context with endpoint diversity formed by: a long master key identifier formed by the GMK-ID and the DMK-ID, or a short master key identifier formed by the GMK-ID or a short master key identifier formed by the GUK-ID or no master key identifier. A security context without endpoint diversity formed by: a short master key identifier formed by the GMK-ID or no master key identifier.