Reliable Clock Synchronization for Eletronic Documents

Trusted time sources are required to insert time stamps in electronic documents. A signed and time stamped electronic document is equivalent to a traditional paper document and is legally recognized. Clock synchronization protocols of the sort provided by Network Time Protocol (NTP) do not satisfy all requirements to assure that a time source is trustworthy. This paper proposes the use of an external Certificate Authority (CA) to issue digital certificates to all computer systems that want to synchronize their clocks using NTPv4 protocol. The use of external auditors and a Time Stamp Authority (TSA) based on relative techniques to make this kind of service trustworthy is also proposed. All modules inserted will not affect the normal operation of NTP protocol.