Re: ... prepaid meters & crypting
From: nobody (nobody_61@hotmail.com)
Date: 02/13/03
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From: nobody_61@hotmail.com (nobody) Date: 13 Feb 2003 09:38:12 -0800
"Kai" <nospamkai@webmail.co.za> wrote in message news:<3e4a4121.0@news1.mweb.co.za>...
> Hi Goup,
>
> I am new to cryptology, and just noticed something:
>
> I purchase electricity for my pre-paid meter. I
> get a 12 digit number, punch it in and voila, my units,
> in kWh are credited on the box.
>
> Now: assuming that the electricity is purchased in units
> with one decimal precision, is it going to be a complicated
> algorithm or not? Given that a single bedroom apartment
> without heating uses about 300kWh a month. That said,
> the minimum source information is already 4 digits ... (3+1)
> ... leaves 8 for hashing?
>
> I suspect that the card I use to purchase the electricity
> contains the public key ...
>
> Any ideas?
>
> regards
>
> Kai
On a similar note a lot of pre-paid mobile phone scratch cards are
open to attack. I cracked a system used by Zamcell and a number of
other African providers, which may be relevant given your email, in a
few hours and could generate any card after that. The error was
highlighted with the providers and a stronger system should now be in
place. To check if the old system is still in use simply take 2
consecutive cards and see what can be found, its quite easy.
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