AutoCAD 2004 introduced the ability to digitally sign drawing files when they are saved, but very few people use this feature. Even fewer use the time stamp feature that goes along with it. Time stamping a digital signature is important when it’s not only important to know *who* signed it, but also *when* they signed it.
For time stamping to be reliable and trustworthy, you need an independent (and trustworthy) third party to provide the time stamp, along with a verifiable receipt so that anyone can verify the authenticity of a claimed time stamp in the event of a future dispute.
Since the inception of the digital signature feature, AutoCAD has included three default time servers for this purpose. Unfortunately, none of the three are accessible any more. If you need to digitally sign drawing files with a time stamp, you’ll have to modify this list of time servers.
The list of time servers is maintained in a file named timesrvr.txt in the AutoCAD installation folder. You can edit the file with notepad, and the format is obvious and straightforward when you view the file.
If you just want to play around with time stamps, try adding the following to the end of the file (you do not need to restart AutoCAD to see the new servers):
NIST A [Maryland] (time-a.nist.gov)
NIST B [Maryland] (time-b.nist.gov)
As of this writing, both of these NIST servers are available and working, but you get what you pay for. For officially incorporating time stamped digital signatures into your workflow, I recommend subscribing to a commercial time service with guaranteed uptime and a web based time stamp verification console. I can’t recommend one, because I have never used a commercial time service myself, but a good place to start is the list of public time servers maintained by NTP.org at http://support.ntp.org/bin/view/Servers/.
FWIW, here is URL containing list of all NIST time servers:
http://tf.nist.gov/tf-cgi/servers.cgi
and more on the keeper of official NIST time here:
http://www.visitkarpathos.com/articles/?article=17
> Modern electronic systems, such as electronic navigation or
> communications systems, depend increasingly on precise time and time
> intervals,” Dr. Matsakis said. “Examples would be the ground-based
> LORAN-C navigation system and the satellite-based Global Positioning
> System.
With 22 timeservers, software which can hop among servers should not
encounter a situation where all are down, unless massive areas of the
Internet are down, in which case other issues may very well take
precedence.:)
In fact, I've used Atomtime:
http://www.atomtime.com for many years to sync my PC clocks to NIST, and never
encountered a problem other than my own Internet connection being down.
I don't know anything about "commercial" time servers, but my guess is
they just resell USNO time.
Why pay for it again? You already paid last April 15 (and the year
previous, etc.).
I expect the NIST time servers (which, as you point out, are not really "free" because US taxpayers pay for them) are sufficient for most applications. However, commercial time servers should theoretically offer some guarantee, and in any case, someone to blame when there's a problem. For some applications, that is more important than cost.