Enforcing time-based transaction policies on devices lacking independent clocks

摘要

A system and a method for operating a device that is not capable of independently maintaining a local time clock to enforce a time-based transaction policy that requires a reliable time reference. The device establishes a secure communications channel to one or more network-attached time sources and inquires of each of the network-attached time-sources as to the current time using the secure communications channel. The device receives the current time from the network-attached time-sources and uses the received current times to estimate a current calendar time and to compute a reliability index associated with the estimated current calendar time. The device uses the estimated current calendar time and reliability index to enforce the time-based transaction policy.