US Patent 7213149 Message authentication

For the authentication of messages communicated in a distributed system from an originator to a destination a keyed-hashing technique is used according to which data to be authenticated is concatenated with a private (secret) key and then processed to the cryptographic hash function. The data are transmitted together with the digest of the hash function from the originator to the destination. The data comprises temporal validity information representing the temporal validity of the data. For example the setup key of a communication is therefore only valid within a given time interval that is dynamically defined by the communication originator. After the time interval is exceeded the setup key is invalid and cannot be reused again.