stores the correspondence between the secret tt and the receiver 4 identified with a service provider number mid arrow 102 within the framework of the invention an unambiguous secret could also be generated by the receiver 4 or the sender 1 and kept anonymous vis u00e1 vis the further exchange 3 in order to register the sender 1 sends a registration message 105 to the first exchange 2 the registration message 105 is preferably sent as other messages for example as ussd message sms or ss7 signaling data the secret tt agreed upon with the receiver is contained in the message 105 the first exchange 2 handles the registration message 105 like all other messages and replaces the sender identifying data msisdn with a first alias identification cid step 106 if no alias identification corresponds to this msisdn a new correspondence is generated and stored permanently in all further messages from this sender the msisdn will be replaced with the same alias identification the adapted registration message 107 is then forwarded to the further exchange 3 this installation recognizes the secret tt and thus knows that this message must be forwarded to the receiver mid arrow 109 if the secret tt is unknown to the further exchange 3 the registration message must contain the receiver 39 s identification mid the secret tt has properties allowing the further exchange 3 to recognize the receiver 4 for example a table in the exchange 3 can be provided in which a correspondence between each secret and the different receivers 4 is stored alternatively predefined series of secrets can be associated with specific receivers the exchange 3 then replaces the first alias identification cid with a newly generated alias identification cmid dependent on the receiver mid arrow 108 this correspondence is stored so that.