Re: Cryptographic strength in Wireless Alarm Systems?



Mark Lomas wrote:
Why all this discussion of jamming? Surely the sensible way of designing an
alarm is to use absence of a signal as the trigger.

The challenge is that sensors usually are battery-operated and don't
have enough power to transmit continuously. They can only afford
to transmit on a periodic basis. I think I mentioned earlier that
I believe there is a European standard that calls for each sensor to
broadcast a heartbeat once every 15 minutes (or more often), and the
failure to receive a heartbeat is an alarm condition. One limitation
is that this delays detection of a breakin by 15 minutes, which may
be enough time for a burglar to break in, have at it, and flee before
the alarm is triggered. For instance, an intruder could snoop on the
wireless communications, map out the location of all the sensors (by
triangulating their heartbeat signals), predict the time at which each
heartbeat will be sent, wait until just after one heartbeat is sent,
and then jam that sensor's communications, giving themselves 15 minutes
to do their worst before the jamming is detected.
.



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