Authentication verifies that each timestamp has come from the intended time reference by analysing a set of agreed encryption keys that are sent along with the time information. NTP, using Message Digest encryption (MD5) to un-encrypt the key, analyses it and confirms whether it has come from the trusted time source by verifying it against a set of trusted keys.

The best solution is to use a specialist NTP server and receive an authoritative time reference via either the GPS network or radio transmissions (known as MSF in the UK or WWVB in the US).

NTP servers judge the distance of each network device from a timing source and organises them into Strata. These Stratum levels exist to prevent cycles and guarantee accuracy. Stratum 0 are devices such as reference clocks connected directly to a computer. Stratum 1 are computers attached to stratum 0 devices, while Stratum 2 are computers further out.

NTP is free to download via NTP.org and is continually supported and updated. The current version is v 4. A simplified version of NTP (SNTP) exists has less functions and is used in some devices and applications (and also included in older versions of Windows) where high accuracy timing is not as important.

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