
Rock the Cash Box: Writing a Host Processor for a ATM - jrwr
https://medium.com/@spiceywasabi/7724332663d2
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lykr0n
It was amazing to watch the effort Wasabi and Jrwr put into reverse
engineering these ATMs. This write up is no where reflective of the head
banging these people did to figure this stuff out.

Fun Fact. George (the dog pictured in the bottom of the post) is the laziest
husky you will ever encounter. But he is cute.

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jonny383
I _loved_ reading this article. I felt strangely transported back twenty or so
years...

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ncmncm
I found it hard to discover what they were even trying to achieve. I _think_
they are saying they needed to make the pi pretend to be both a modem, and the
server on the other side of the modem. But not all is clear. What generated
"RING RING"? Normally the modem would say that, if there were one.

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outworlder
I think the Raspberry is taking the role of the "financial institution", not
the modem. The writeup seems to indicate they have an actual modem on both
sides, but I couldn't find out how they are connected.

You don't really need an actual phone line, but you would have to add a
dialtone, and simulate the ringing. If you controlled both sides, you could
disable dial tone detection, and just "answer" whenever you please, and wire
the two modems. But they don't seem to have modified the ATM, just changed
some settings. So that's out, and we do have some sort of phone line. But
simulating a line would be a project into itself and, if they went through
such lengths, I would expect that to be noteworthy enough to be mentioned.

That, and given their unfamiliarity with modems, makes me think they actually
have a phone line and are really dialing.

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snuxoll
Assuming you have adequate control over the local network to deal with jitter
one could just use SIP ATA’s with everything set to use G.711 (uncompressed
PCM audio) and make modems quite happy to believe they are on a traditional
POTS line.

You would need to know how to setup Asterisk or something similar to do this,
but it’s not a Herculean effort either.

Alternatively, POTS PBX devices exist as well and would work fine - though
they’re harder to come by these days.

