[Cryptography] Best internet crypto clock
agr at me.com
Sun Oct 12 10:18:21 EDT 2014
Sent from my iPhone
> On Oct 9, 2014, at 1:52 AM, Tom Mitchell <mitch at niftyegg.com> wrote:
> A free running tick counter that never overflows is a good thing. Freedom
> from time of day issues leap seconds and more make it easy. The frequency
> choice is open and precision and accuracy is open. An external map of ticks to
> historic real world time (and temperature) is interesting in the right context.
A simple counter with no overflow would work, of course, but Inexpensive cpu clock chips, like the DS-1307 family, provide a 99 year range with one second resolution and have all the circuitry for dual supply (5 VDC and battery) with very low power (500 na) operation on battery. Another possible advantage over a straight counter: yy-mm-dd-hh-ss in a time stamp is a lot easier to explain to a judge and jury than a long hexadecimal constant.
Here's a data point. I installed a cheap digital video recorder for a surveillance system just over four years ago. It's not connected to the Internet and I never adjusted the clock since installing it. I had to pull a clip off of it last week and the clock was 44 minutes fast. That's about a minute a month.
So if the device grabbed the current NIST beacon signed it with its internal clock and had the resulting certificate time stamped by an external authority once a month, that should be enough to establish minute accuracy.
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