Apparatus and method for functionally securely transfer data in a two-sided data exchange of safety-related data between two communication partners (A, B), wherein a mapping is defined, which assigns to a consumer ID a provider ID of the same end point in the case of each bidirectional connection, and the mapping is made known to the two end points a priori, where the mapping could consist of the one's complement or alternatively of the two's complement, and wherein the connection between the data provider and the data consumer is established as described, the data consumer receives the address identification of the data provider via an additional side channel, for example, and after the connection has been established, the identification of the data provider can be securely checked.