If the makers have any intelligence at all this device will be essentially
uncrackable. It is almost certainly a simple EEROM with an "I squared C"
interface or similar . If so, then reading it will be technically easy.
However, the information therein can easily be encoded in a large number of
different ways to make it EXTREMELY hard to decode.

It is possible that you may be able to "reload" such a device by, when it
is relatively empty, writing a code which you found in it when it was
relatively full. However, if I was producing such a system I would do one
of a number of things to dissuade you from doing this such as eg

- Tracking each key by an internal ID and keeping a log of the results.Some
systems don't actually change the keys internal data at all - they just
record in the main system that a certain key has $X of credit and then
decrement it as required. When the key is 'refilled" what they are doing is
simply using the key to record whose account should be updated. In this
sort of system your credit total is absolutely uncrackable by tampering
with the key. The best you could hope for is to stumble across someone
else's ID. Any decent system will ensure that you are almost certain to
stumble across an invalid code first and alert the operator. If one wanted
to lure hackers to their doom such a system could encrypt the users id plus
some random junk which varied each time plus eg a date etc. A hacker would
see the data varying and perhaps try to change it to an old value. The
first time would be the last time.

- Storing some information along with the credit (all encapsulated) that
allows some sort of tracking of the credit total. All this would be
encrypted. Again, the chances of alerting the system would be much much
(much ...) higher than achieving a valid alteration.

If 'I" had written the system I'd like to think that any hacker would
rapidly become much more personally acquainted with the management. What's
the chance that the person who designed this system had similar ideas?

----------
> From: Kevin <kevinau@INTERCHG.UBC.CA>
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: Unknown chip -- thanks! (was Help with
unknownmicrocontroller)
> Date: Sunday, 12 July 1998 23:20
>
> >Might this "key" have anything to do with operating photocopiers or
> >washing machines perhaps? Fix the number so you only have to buy one
key,
> >or even better sell them to all your friends.
>
>
> Yes, you are correct, except this "key" is responsible for dispensing
golf
> balls at a driving range.
>
> >I have a friend who made one of those magnetic card duplicating
machines,
> >bought a photocopier card, and ran off a load of copies for all his
> >mates (you can use out of date credit cards, or buy blank ones).
>
>
> I started out just being curious of what was inside this key, so I opened
it
> and found this one tiny piece of chip inside.  Wanting to know more about
> the working of this chip, I began reading books, searching the net, and
> asking questions.  Now I will not stop searching until I find a way to
> interact with this chip...
>
> So many things to learn...
>
> --
> Kevin