Abstract: A method for agreeing a communication key between communication subscribers of a wirelessly operating communication system is provided. The method for agreeing a communication key includes using a communication key to determine at least one further communication key for security-related services, and exchanging acoustic signals for agreeing the communication key being exchanged between the communication subscribers provided at a subsequent data transmission.

Abstract: A communication system is proposed which, as its communication elements (KE) has a gatekeeper (GK), a gateway (GW) coupled to the gatekeeper (GK) and at least one communication unit (KEH) coupled to the gateway (GW), with the communication system being set up so that, to register a communication relationship of the communication unit (KEH) in the communication system (KS), a request message (ANF) is transmitted from the communication unit (KEH) via the gateway (GW) to the gatekeeper (GK), which is checked in the gateway (GW) for authenticity and in the gatekeeper (GK) for authorization.

Abstract: A method for data communication in a cryptographic system containing a plurality of entities, includes the entities arranged in a hierarchical structure. If a current entity in the hierarchical structure is altered, those entities which are on the same hierarchical level as the current entity, and which are connected to the current entity's superordinate entity, are notified of the alteration.

Abstract: A method for data communication in a cryptographic system containing a plurality of entities is specified, in which the entities are arranged in a hierarchical structure. If a current entity in the structure is altered, those entities which are connected directly to the current entity's hierarchically superordinate entity are notified of the alteration.