allows the destination entity to decrypt the information as based on the time sequence of encrypting keys furthermore the destination entity is presented with control information regarding a changeover instant between two particular encryption keys in particular the following steps are taken in said information string singling out a data block at a predetermined localization in the string relative to a changeover that is known to the destination entity encrypting the data block with an actually valid encryption key forming a fingerprint is formed of the encrypted data block transmitting the fingerprint at the predetermined localization instead of the encrypted data block and transmitting an out of band control message for indicating that an update occurred application_number US 24476202 A description 0015 fig1 illustrates a basic sketch of a secured link at left unsecured content 20 is being routed inside the transmitter environment so that protection of this content may be provided by mechanical blocking of unauthorized access undertakings and the like block 22 represents the encryption at the sender entity that will produce secured content 24 next to a certain amount of control information 30 generally the transfer rate of control information stream 30 will be much lower than that of content stream 24 the control information may serve various purposes next to the encryption procedures to be disclosed hereinafter such as message synchronization addressing and other functions that by themselves would not need inherent protection against eavesdropping in the context of the present invention the control includes information that supports detection of the transition from.