Fingerprint, control signal for new encryption key

摘要

For transmitting an information string from a source entity to a destination entity the information is encrypted through a time-sequence of encrypting keys that are each valid only in a predetermined associated time interval within the string. This 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.