GPS and NTP are two very typical time sources when accurate clocks are required. However, each has an important failing. NTP does not provide authentication of the time source, and so may be vulnerable to spoofing. GPS doesn't work very well inside the walls of a datacentre.
Accurate time is an operational concern for any number of reasons, as well as being a security concern due to things like session token lifetimes, key expiration, rate limiting, time-of-day restrictions, and behavioural pattern analysis in support of anti-fraud measures. Clock retrogression introduces instability in some network protocols which may create exploitable scenarios; IRC privilege escalation or impersonation ("split riding") is the typical example.
It is also extremely important that this time be consistent with time obtained from standard sources, to avoid drift during network disruption (or exploitation by time service disruption).
Accordingly, what technology or technique can be used to supply accurate and trusted time (within one second preferably) in sync with UTC, where GPS and other radio clocks are ineffective, while avoiding the need to manually true the time source frequently?
Best Answer
NTP 4 provides authentication and some servers provide it.