I was a bit concerned about clicking the fob for no good reason. I
assume each click is a different number. I only use it for ebay and
paypal. [Incidentally, they jacked the price from $5 to $30.]
Now a phone has accurate network time, so they could get really tricky
with the time as part of the code.
I was meditating a bit on the power grid synchronization. If all the
sites but one are in sync, then the generator whose sync is being hacked
will have a hard time trying to feed the grid while being out of phase.
This should be detectable electronically in the generator interface. If
the timing is moved slowly, the the "conflict" would build slowly as well.
In the dark ages, I TAs an electronics class set up for non electrical
engineers. I considered it kind of brutal since they tried to cover just
about everything in one class. Well it included what we used to call
"motors and rotors". [I suspect this isn't even taught anymore.] One of
the lab experiments was to sync a generator to the mains. Now the
generator was driven by a motor from the mains, so this wasn't
particularly difficult. You would put a meter between your generator and
the mains and drag on the shaft a bit until the phase error was zero,
then turn the switch to connect them.
Things were going OK but then I heard a nasty sound and the lights
flickered a bit. It turns out some curious students wanted to see what
happened if the generator and mains were out of phase. Well, the mains wins.
It is apparently hard to move the grid.
On 12/3/2012 8:12 PM, Jim Lux wrote:
On 12/3/12 6:34 PM, Hal Murray wrote:
li...@lazygranch.com said:
I have one of those key fobs. Does the code somehow inform the power
the be
about the drift in the built in clock? Or is the time element of the
code so
sloppy that the drift is acceptable?
The magic number changes every second or so.
Every 30 seconds or every minute.. I've seen both. My fob is once a
minute, the iPhone "soft fob" is 30 seconds.
You only have to scan a few
seconds either side of the correct time to find a valid match. Every
time
the server gets a match it can update its memory of the fob time to
reduce
its searching in the future.
Exactly, the maximum time difference is a settable parameter.
You could measure/compute the drift too. I don't know if that's worth
the
effort. It would probably change with temperature so seasonal or
lifestyle
changes could throw the prediction way off.
I don't think they do that.. I think it's a "reset when validated"...
[I have no inside knowledge. I could be totally wrong, but that seems
reasonable to me. They may have a better approach.]
It's all described on the RSA website..
Hmm.. I suspect I could time my fob once a day, and see how many
seconds a day it drifts.. without a timed camera it would be hard to get
tighter than 1 second resolution..
the iPhone one almost certainly uses the internal clock in the phone.
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