Patent ID: 7200234

Claim:
A method for communicating an information string between a source entity and a destination entity, the method comprising the acts of: encrypting said information string through a time-sequence of encrypting keys that are each valid only in a predetermined associated time interval within said string, for allowing as based on said time-sequence of encrypting keys said destination entity to decrypt said information, presenting the destination entity with control information regarding a changeover instant between two particular encryption keys, in said information string, singling out a data block at a predetermined localization in said string, which localization is known to said destination entity, encrypting said data block with an encryption key, forming a fingerprint of said encrypted data block, transmitting to said destination entity said fingerprint at said predetermined localization instead of said encrypted data block, and transmitting to said destination entity an out-of-band control message for indicating that an update occurred, said information string and said out-of-band control message being at different channels, wherein said control message contains said data block after encrypting, but before forming of the fingerprint.