A method for sending registered secure messages via a messaging system to a receiver device that is to be tested includes: supplying first secure and still serialized messages from message packages for processing in a reproduction unit; in the first messages, reducing the data volume of the serialized messages; deserializing the reduced first messages and creating second secure messages by adding a second counter value in each case or, where applicable, by replacing a first counter value with the second counter value, and creating and adding a second authenticator in each case by using the second counter value, the encryption information, and the key, and by using the communication description or the information obtained by applying a data interpretation algorithm; and serializing the second secure messages and sending corresponding message packages to the receiver device to be tested.