1. An apparatus for transferring medical security-critical data records from a transmission station to at least one receiver station via a digital network, comprising: an input data interface, configured to capture the security-critical data records to be transferred; a context capture unit, configured to capture a planned processing context for the security-critical data records; and a processor, including a rulebook machine configured to store a multiplicity of predefinable and variable rules for dynamically calculating a pseudonymization function on the basis of the processing context that has been read in, configured to apply the determined pseudonymization function to the sections of the data to be transferred that are determined as critical to security and configured to produce a pseudonymized data record for the purpose of the transfer.