According to one embodiment of the invention, a method is provided for receiving a timestamp from a caller via a telephone connection; receiving a device identifier from the caller, in which the device identifier identifies a device; determining a cryptographic key based on the device identifier; determining...http://www.google.es/patents/US6959387?utm_source=gb-gplus-sharePatente US6959387 - Method and apparatus for verifying secure document timestamping
Method and apparatus for verifying secure document timestamping
