Roy Smith wrote: > Peter Hansen <[EMAIL PROTECTED]> wrote: > >>I guess as long as the NTP client is set up to ensure the time >>adjustments are smaller than some value X, it would be acceptable. > > > NTP is generally capable of keeping the various system clocks on a LAN > within a few ms of each other, and within a few 10's of ms over the > Internet from GPS, WWV, or similar international time references. > > >>I'll have to look into how to set up Windows XP to prevent users from >>changing the time on their own, assuming that's possible. > > > On a single-user system like Windows, you pretty much have to assume the > user can do anything. They can turn off NTP, reset the clock, reboot the > system, uninstall your software, whatever. > > If you could check to see that NTP is running, it doesn't prove anything. > A malicious and determined user could set up another machine as a NTP > server to synch against, and even configure that machine to look like it > was a stratum-1 reference (i.e. an atomic clock). > > At some point, you need to decide if you trust the system administrator to > supply you with an accurate system clock or not. If you don't, and it's > really important that you have an accurate time reference, you've got an > interesting engineering problem on your hands.
A couple of quick thoughts: (1) stupidity is much more prevalent than malice in that environment. (2) Peter, if your app has something else to measure e.g. it is processing zillions of rows from a database, grab the [UTC] wall time every N things, and apply plausibility checks to the speed N/delta(wall) -- if it goes negative or "too high" or "too slow", holler fer a mountie. -- http://mail.python.org/mailman/listinfo/python-list
