Bruce Schneier

# Schneier on Security

A blog covering security and security technology.

## September 14, 2006

### Defeating a Coin-Op Copy Machine

dragonfrogSeptember 14, 2006 2:58 PM

I remember as a young punk, getting free calls from certain payphones by closing a circuit betweent the mic in the handset and the metal of the coin slot.

I doubt that would work anymore, but you never know...

electronSeptember 14, 2006 3:18 PM

I can't wait for the countermeasure that puts 2OO volts on the red and black wires.

And the college policy change that says carrying a paper-clip is evidence of intent to hot-wire photocopiers.

zoobnoobieSeptember 14, 2006 3:27 PM

Now, *that's* a h4xx0r! Perfect follow-on from your previous post, Bruce.

grumpcastdotcomSeptember 14, 2006 3:36 PM

I remember another coin phone trick from my young days. Back when pay phones had three coin slots (nickel, dime and quarter) it was easy to drop a nickel and at exactly the right time, bang the coin return button. The nickel would bounce twice and the phone would think it was a dime.

If you were really good, you could do the same thing with a penny in the nickel slot.

Gary in DCSeptember 14, 2006 3:53 PM

This is an old one, updated. 20 years or so ago, the Bates College library copiers had little counter boxes distributed at the circulation desk. They noted the count, then you plugged into the side of the machine. Hit "copy" and the counter incremented by one. Take it back and pay for the copies you made.

Problem (feature?) was, that there was a time interval between hitting "copy" and the increment of the counter. You could pull the counter out during that interval and get an uncounted (free) copy. If you practiced, you could lightly balance the counter box against its contacts and very slightly move it to break contact during your window of opportunity. An interesting point of failure for what ought to have been a pretty simple system. Alas, no ACID-tested transactions in the mechanical counter.

We had a soft drink machine in the dorm that would take a penny and give you a soda and 15 cents change. I was called in as the resident mathematician to tell them how many nickels they would have to feed back in to keep the machine from running out of change. (When the exact change light was on, it wouldn't take pennies any more.)

kiwanoSeptember 14, 2006 4:08 PM

damn, by the time i got into phreaking, you guys' young days had long passed and the best way i'd found to fake out payphones was to take one of the many non-functional redboxes out there, call the operator complaining that the phone was eating your coins without giving you credit for them, and playing the appropriate tones when asked to insert coins (to test the phone).

(please note that the statute of limitations has long since passed on any of the times that i may have done this, even though it probably still works)

Yet another old coin-op trick, although this one's a little more on the evil side... A quantity of salt water squirted down the coin slot of some older soda machines would short the system out and cause it to empty all of its change into the coin return.

Many a bus ride paid for in soggy nickels back in the bad ol' days...

hehe, I remember some paid copiers back at school.. they were so very proud to introduce magnetic stripe cards for all payments (copiers, cafeteria, some secretary fees), and the tech guy who installed the card readers on the copiers boasted that the cards are impossible to manipulate and talked a bit about checksums and encryption and blah.. but the company who designed the system made two mistakes: the card readers on the various machines are unable to talk to each other, and they only keep a minimal transaction record (a day or two for tracking down mis-billings).
While the cards only gave out gibberish when being read with a normal swipe reader, it was no problem to charge one card on the regular payment terminal and then duplicate its stripe onto cheap blank cards. Sure, some vending machines might reject the card if they "remembered" that the value was lower a day ago and the last-recharge-date entry wasn't changed (thus meaning it wasn't recharged on the regular terminal), but all other machines accepted the cards without problems, and a day or two later the value records were gone anyway.

In the late 60's, we used to push a 6"x1/2" stiff piece of paper down the dime slot of a pay phone. Depositing a penny in the nickle slot would then register as a dime. Oh, pay phone calls cost only ten cents.

another_bruceSeptember 15, 2006 1:10 AM

when i was a wee lad, i could scotch-tape dental floss to the side of a quarter and...

AnonymousSeptember 15, 2006 10:46 AM

Wow. I always like to learn from my elders, but I never remember a nickel being worth a damn.

I think my generation is the last one to really know the glory of hoarding quarters for the arcade.

RvnPhnxSeptember 15, 2006 1:02 PM

Hmmm......, What about the glory of hoarding quarters so that you could actually dry your underwear? I found it actually cost less to drive an hour to my grandmother's house and do my laundry there--and that is before one calculates in the other benefits of doing so.
At one point my housemate had enough quarters in a surplus army duffel that it could have qualified as a lethal weapon.
It wasn't until campus added electronic dryer payments that they got hacked.

None of the above compared to the case of people making collect calls to a payphone in Columbia in my opinion though.

Clive RobinsonSeptember 15, 2006 9:13 PM

@Anonymous

"I never remember a nickel being worth a dam"

The expression "not worth a dam" actually refered to a small Indian coin (the Dam) that was of very very little worth.

So even with todays very weak USD a nickel is still likley to be worth several dams ;)

However you might find the following amusing,

http://plateaupress.com.au/wfw/tinker.htm

AnonymousMarch 31, 2009 8:11 AM

TODAY KIDS ARE RIPPING OFF THE PUBLICSIMPLY WITH A 2 OR3 COTTON BALLS WITH THREAD WRAPPED AROUND IT. a A SMALL COBALT MAGNET HANGS JUST ABOUVE THE REACH OF ANYONES FINGERS TRYING TO RETRIEVE THEIRE COIN--S WHEN THEY GET A BUSY SIGNAL OR HANGUP ON THE ANSWERING MACHINE. A LITTLE PIECE OF COAT HANGER WITH ANOTHER COBOLT MAG ATTACHED PULLS IT OUT---THEY DO THIS TO SEVERL PAYPHONES IN ONE AREA THEN GO COLLECT AND RESET

THE BAD SPELLERMarch 31, 2009 8:18 AM

SORRY FOR THE SPELLING IN LAST POST--MAGNETS--DOESN'T ANYONE REMEMBER WHEN PAYPHONES HAD A BLACK BOX ONDER THE METAL SHELF UNDER THE PHONE--REMOVE ONE SCREW IN MIDDLE CUT YELLOW WIRE PUT BOX BACK--COME BACK LATER OPEN BOX TOUCH YELLOW WIRE ALL COINS COME OUT OF COIN RETURN---THE COINS THAT WERE SUPPOSED TO COME BACK

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