7 ms·

So a dollar bill is an inexpensive (on the scale of crime) sheet of paper pre-printed with a unique number that's somewhat difficult to forge. If you rip it up

by p1mrx 7y ago

So a dollar bill is an inexpensive (on the scale of crime) sheet of paper pre-printed with a unique number that's somewhat difficult to forge. If you rip it up, that number won't be used again. How are they making use of this feature set? I'd like to see a diagram with arrows and stuff.

bproctor 7y ago
Took me a bit to understand, courier doesn't have the bill, the drop does. Boss: "Courier, deliver this money to <address>, code is 12345678" Courier: at <address>, "Hey Drop, what is the code?" Drop: "Code is 12345678" Courier: "That's correct, Here's you're money" Drop: Tears bill in half and hands part with serial number to Courier as proof
- cpeterso 7y ago
  Why would the Drop need to retain half the serial number? They have received the goods.
  - yesbabyyes 7y ago
    I'm not sure the drop retains half the serial number? GP claims the drop rips the bill in half, and hands the part with the (full, I seem to recall US dollar bills have the serial number on the bottom left) serial number to the courier. The courier can prove they delivered to the right drop, and the bill being ripped in half will ensure it won't be used again.
    - RaceWon 7y ago
      > I seem to recall US dollar bills have the serial number on the bottom left Our money (US Currency) has two (of the same) serial numbers on each bill; one on the lower left and one on the upper right for dollar bills. Other denominations also have two; one on each side of the front of the bill, however they are in opposite places i.e. upper left, and lower right--at least the current bills in my wallet are that way.
  - bartwe 7y ago
    Ensuring the code isn't reused, to put in a ledger, to avoid some kind of replay attack, having someone pretend to be the courier and get the key to then replay to the real courier. Dunno, probably many many things avoided by making the key not usable but still verifiable.
    - qrbLPHiKpiux 7y ago
      Very important to never reuse a code, or one time pad. Perfect forward secrecy.
    - trickstra 7y ago
      I can think of only one scenario when it would make sense to destroy the bill - if the Drop is still able to present the whole bill after the Courier says they delivered the package, that is a proof the Courier is lying or got played and didn't verify the code. Drop is the one who has motivation to keep the bill intact, Courier uses the bill as proof of delivery, and cuts it in half just to be safe that someone from the Drop won't stop them at gunpoint after the delivery, stealing the whole bill.
  - p1mrx 7y ago
    Well, the Drop can take the bills back to the bank. "The corners fell off. Can I have some fresh ones?"
    - steevdave 7y ago
      But they can't use that specific one again, it doesn't matter if they take the bill to a bank and get new ones, because the serial numbers won't be the same.
    - inlined 7y ago
      I doubt a Drop cares enough about $1 to repeatedly engage in suspicious behavior with a bank
      - p1mrx 7y ago
        That's the joke.
  - afiori 7y ago
    In a criminal organization security and accountability are a more complex topic, but I would say that this way the one serial number the drop keep is a proof of identity, while the serial number the courier keep is a receipt.
- rohan_shah 7y ago
  Yes you're right. It's called "havala" in India and is common among traders of all goods. People do this because having more than ~3000$ cash (in Rupees) is illegal, but people use it anyway. So I can tell you that the Drop has the note. And yes, here the whole note (bill) is given to the courier by Drop as receipt, not by tearing in half. And I don't think even there people tear the serial number into half. Just the note.
  - Razengan 7y ago
    > People do this because having more than ~3000$ cash (in Rupees) is illegal Wait, really? Do you mean no one is allowed to keep that much money in a safe in their house etc., or what? Why?
    - Bograff 7y ago
      I'm not up to date on the issue but India had an issue with black money and people hoarding cash without reporting the income. The laws were passed to combat that IIRC.
    - caymanjim 7y ago
      Is this really that surprising? Having more than roughly $10,000 cash in the US is nearly illegal, in that you're guilty until proven innocent and the police can just take it until you prove that it was obtained legally. You may not be charged with a crime, but you're still going to lose the money. The courts are slowly inching away from this unconstitutional insanity, but a duffel bag of cash is still going to end up turning into a new Hummer for whatever local police squad finds it.
      - heelix 7y ago
        Hah. So years back, I was going to buy a car. Went to the bank and they wanted (what I considered to be) a ridiculous service fee for a cashiers check. Fine... I'll take cash from my account! Ah, need a couple days to do that sort of thing... I, was miffed and stubborn as hell... so I did just that. Came back, got fingerprinted, and picked up my pile of cash to go buy the two year old 996. The dealership, when time came to close, absolutely freaked when I pulled out the cash. Another set of IRS forms... and sorted it after several phone calls.
andromeduck 7y ago
It's actually pretty cool. So for starters there's disambiguation since all serials are unique, you won't have carriers knowingly delivering to the wrong drop assuming the drop keeps possession of the bill since it's globally unique. You have some plausible deniability if found, "it's just money in my wallet, picked up at mcdonalds" and it's easy to hide/dispose of. If you're really smart you could also list a handful of possible serials for extra plausible deniability and hold/disperse the others such that the mechanism is still very likely to work due to the difficulty of finding a particular bill in circulation. Even when caught you may have some additional protection when the goods being immediately exchanged are otherwise legal, legal in the absence of money changing hands or difficult to establish in the absence of money or another component. Assuming the actual transaction is reasonably atomic, which it should be unless there's a fight or something, the the carrier can always prove that they delivered to the correct drop if they have a physical copy of the agreed upon serial while the drop can prove that they didn't receive a delivery if they can reproduce an undamaged copy of the whole bill. The ripping of the bill itself could plausibly serve as a step in a multi step process where the carrier may demand that the bill be ripped after the serial and goods are confirmed but before not yet exchanged so that the drop can't claim that a delivery was not at least attempted on the part of the courier. We could also do it with two bills, one from each party such that each party can have some proof that a transaction was or wasn't completed and with the right party in the case of a double exchange. The upfront cost of forging passable $1 bills is too high to be economical to pull off just for these low volume transactions, especially after the logistical cost of injecting the bills or otherwise tricking someone to using a fake as well as keeping a copy on hand but even if you achieved that. You'd also have to contend with the fed's coming after you for forging currency if the bills you distributed ever got into public circulation in any significant quantity so it should be pretty secure as long as they're sourced from a fairly high volume location like mcdonalds or something. The entropy might be somewhat useful too in bookkeeping like maybe using only bills ending with a 0 are for small cash transactions, 1 for large cash transactions, 2 is for drugs A, 3 for drug B etc... Entropy might be important but there are much easier sources.

by p1mrx 7y ago

bproctor 7y ago

Took me a bit to understand, courier doesn't have the bill, the drop does. Boss: "Courier, deliver this money to <address>, code is 12345678" Courier: at <address>, "Hey Drop, what is the code?" Drop: "Code is 12345678" Courier: "That's correct, Here's you're money" Drop: Tears bill in half and hands part with serial number to Courier as proof

cpeterso 7y ago
Why would the Drop need to retain half the serial number? They have received the goods.
- yesbabyyes 7y ago
  I'm not sure the drop retains half the serial number? GP claims the drop rips the bill in half, and hands the part with the (full, I seem to recall US dollar bills have the serial number on the bottom left) serial number to the courier. The courier can prove they delivered to the right drop, and the bill being ripped in half will ensure it won't be used again.
  - RaceWon 7y ago
    > I seem to recall US dollar bills have the serial number on the bottom left Our money (US Currency) has two (of the same) serial numbers on each bill; one on the lower left and one on the upper right for dollar bills. Other denominations also have two; one on each side of the front of the bill, however they are in opposite places i.e. upper left, and lower right--at least the current bills in my wallet are that way.
- bartwe 7y ago
  Ensuring the code isn't reused, to put in a ledger, to avoid some kind of replay attack, having someone pretend to be the courier and get the key to then replay to the real courier. Dunno, probably many many things avoided by making the key not usable but still verifiable.
  - qrbLPHiKpiux 7y ago
    Very important to never reuse a code, or one time pad. Perfect forward secrecy.
  - trickstra 7y ago
    I can think of only one scenario when it would make sense to destroy the bill - if the Drop is still able to present the whole bill after the Courier says they delivered the package, that is a proof the Courier is lying or got played and didn't verify the code. Drop is the one who has motivation to keep the bill intact, Courier uses the bill as proof of delivery, and cuts it in half just to be safe that someone from the Drop won't stop them at gunpoint after the delivery, stealing the whole bill.
- p1mrx 7y ago
  Well, the Drop can take the bills back to the bank. "The corners fell off. Can I have some fresh ones?"
  - steevdave 7y ago
    But they can't use that specific one again, it doesn't matter if they take the bill to a bank and get new ones, because the serial numbers won't be the same.
  - inlined 7y ago
    I doubt a Drop cares enough about $1 to repeatedly engage in suspicious behavior with a bank
    - p1mrx 7y ago
      That's the joke.
- afiori 7y ago
  In a criminal organization security and accountability are a more complex topic, but I would say that this way the one serial number the drop keep is a proof of identity, while the serial number the courier keep is a receipt.
rohan_shah 7y ago
Yes you're right. It's called "havala" in India and is common among traders of all goods. People do this because having more than ~3000$ cash (in Rupees) is illegal, but people use it anyway. So I can tell you that the Drop has the note. And yes, here the whole note (bill) is given to the courier by Drop as receipt, not by tearing in half. And I don't think even there people tear the serial number into half. Just the note.
- Razengan 7y ago
  > People do this because having more than ~3000$ cash (in Rupees) is illegal Wait, really? Do you mean no one is allowed to keep that much money in a safe in their house etc., or what? Why?
  - Bograff 7y ago
    I'm not up to date on the issue but India had an issue with black money and people hoarding cash without reporting the income. The laws were passed to combat that IIRC.
  - caymanjim 7y ago
    Is this really that surprising? Having more than roughly $10,000 cash in the US is nearly illegal, in that you're guilty until proven innocent and the police can just take it until you prove that it was obtained legally. You may not be charged with a crime, but you're still going to lose the money. The courts are slowly inching away from this unconstitutional insanity, but a duffel bag of cash is still going to end up turning into a new Hummer for whatever local police squad finds it.
    - heelix 7y ago
      Hah. So years back, I was going to buy a car. Went to the bank and they wanted (what I considered to be) a ridiculous service fee for a cashiers check. Fine... I'll take cash from my account! Ah, need a couple days to do that sort of thing... I, was miffed and stubborn as hell... so I did just that. Came back, got fingerprinted, and picked up my pile of cash to go buy the two year old 996. The dealership, when time came to close, absolutely freaked when I pulled out the cash. Another set of IRS forms... and sorted it after several phone calls.

andromeduck 7y ago

It's actually pretty cool. So for starters there's disambiguation since all serials are unique, you won't have carriers knowingly delivering to the wrong drop assuming the drop keeps possession of the bill since it's globally unique. You have some plausible deniability if found, "it's just money in my wallet, picked up at mcdonalds" and it's easy to hide/dispose of. If you're really smart you could also list a handful of possible serials for extra plausible deniability and hold/disperse the others such that the mechanism is still very likely to work due to the difficulty of finding a particular bill in circulation. Even when caught you may have some additional protection when the goods being immediately exchanged are otherwise legal, legal in the absence of money changing hands or difficult to establish in the absence of money or another component. Assuming the actual transaction is reasonably atomic, which it should be unless there's a fight or something, the the carrier can always prove that they delivered to the correct drop if they have a physical copy of the agreed upon serial while the drop can prove that they didn't receive a delivery if they can reproduce an undamaged copy of the whole bill. The ripping of the bill itself could plausibly serve as a step in a multi step process where the carrier may demand that the bill be ripped after the serial and goods are confirmed but before not yet exchanged so that the drop can't claim that a delivery was not at least attempted on the part of the courier. We could also do it with two bills, one from each party such that each party can have some proof that a transaction was or wasn't completed and with the right party in the case of a double exchange. The upfront cost of forging passable $1 bills is too high to be economical to pull off just for these low volume transactions, especially after the logistical cost of injecting the bills or otherwise tricking someone to using a fake as well as keeping a copy on hand but even if you achieved that. You'd also have to contend with the fed's coming after you for forging currency if the bills you distributed ever got into public circulation in any significant quantity so it should be pretty secure as long as they're sourced from a fairly high volume location like mcdonalds or something. The entropy might be somewhat useful too in bookkeeping like maybe using only bills ending with a 0 are for small cash transactions, 1 for large cash transactions, 2 is for drugs A, 3 for drug B etc... Entropy might be important but there are much easier sources.