5 ms·

Double-spending seems problematic. You can't really wait 10-30 minutes before starting to dispense gas, the lines would be terrible.

mikeash 13y ago
I don't really see the problem. Start dispensing gas immediately. Have surveillance cameras with timestamps that tie into the transaction. In the unlikely event that you lose out to a double-spend, you have the culprit's face, his car, and his license plate and you can point the police to him. Let's not forget that until fairly recently (ten years ago or so?) it was common for gas stations to let you pull up and start pumping without any payment whatsoever. You went in and paid after you finished. There was occasional abuse, but it worked reasonably well overall.
- logfromblammo 13y ago
  You haven't had much experience reporting crimes to the police, have you? If you tell a cop that someone cheated you in a transaction involving BitCoin, I'm guessing that 80% will laugh at you and tell you to contact your insurance company and fill out an online property crime report with their automated city/county system before hanging up, 15% will actually open an investigation on your gas station for suspected money laundering or tax evasion, and 5% will actually follow up on your report as you seem to expect they should.
  - mikeash 13y ago
    There are dedicated laws for gas station drive-offs and as far as I know the police take it fairly seriously. In some states you can lose your driver's license for committing a drive-off. If gas stations managed to survive the era of ubiquitous post-pay transactions without being killed by drive-offs, you are not going to convince me that bitcoin double-spends, which are vastly more difficult to pull off than simply pulling up to the pump, pumping, and driving away, are somehow an insurmountable problem here.
    - logfromblammo 13y ago
      It is not an insurmountable problem, but the solution is not to let the police handle it. The police response does not prevent the station from losing money. It just prevents the same people from committing the same offense many times in a row. The reason you have to pre-pay now when you didn't before is that pay-at-the-pump points of sale make it possible to require it without losing business. Stations that had prepay-at-the-pump could lower their prices below stations that did not. The stations that did not have pre-pay did not die off because all the competition was in the same boat, using the same technology and exposed to the same risk. You can't avoid those economics. Your pay-by-BitCoin technical solution has to be the same order of magnitude time-wise on verifying the payment as credit card terminals. At the least, your transfer should be verified by the time the customer is filled up and ready to drive off. As such, the solution should probably be to take a big transaction to activate the pump, verify it while the pump is running, and issue a refund transaction for the unused amount after that verification and before the customer drives away. If the transaction fails due to a double spend, the person might still be on the premises long enough for an employee to request an alternate form of payment. Or use a coin with shorter transaction verification times.
      - mikeash 13y ago
        Or the solution could just be to not wait for validation. Yes, it will mildly increase fraud, and thus costs, but evidently not a huge amount. It could make bitcoin-gas more expensive than the regular kind, but so it goes. Given the difficulty of carrying out a real double-spend attack, I doubt it would happen with any sort of frequency.
        logfromblammo 13y ago
        As long as no other BitCoin-accepting pump can devise a better solution, whatever solution you have that works as well as a credit-card-accepting pump should be just fine.
- vilhelm_s 13y ago
  Good point.
- mpyne 13y ago
  > Let's not forget that until fairly recently (ten years ago or so?) it was common for gas stations to let you pull up and start pumping without any payment whatsoever. That's actually a bigger point than you seem to think. Gas stations deliberately stopped allowing this for a reason. Did the ability to defraud a gas station owner go away in the past 10 years and no one noticed? If so then surely they'd allow for pumping before payment today without Bitcoin.
  - mikeash 13y ago
    Prepay won because it's generally better, but postpay is still viable. Certainly the solution doesn't need to involve a 10-30 minute delay for validation before dispensing product.
- rahimnathwani 13y ago
  "it was common for gas stations to let you pull up and start pumping without any payment whatsoever" That's how it works in the UK. In many stations (at least in London) one of the people at the cash register has to press a button, but they do this after seeing you and (I guess) after they've confirmed that the number plate was correctly OCR'd.

mikeash 13y ago

I don't really see the problem. Start dispensing gas immediately. Have surveillance cameras with timestamps that tie into the transaction. In the unlikely event that you lose out to a double-spend, you have the culprit's face, his car, and his license plate and you can point the police to him. Let's not forget that until fairly recently (ten years ago or so?) it was common for gas stations to let you pull up and start pumping without any payment whatsoever. You went in and paid after you finished. There was occasional abuse, but it worked reasonably well overall.

logfromblammo 13y ago
You haven't had much experience reporting crimes to the police, have you? If you tell a cop that someone cheated you in a transaction involving BitCoin, I'm guessing that 80% will laugh at you and tell you to contact your insurance company and fill out an online property crime report with their automated city/county system before hanging up, 15% will actually open an investigation on your gas station for suspected money laundering or tax evasion, and 5% will actually follow up on your report as you seem to expect they should.
- mikeash 13y ago
  There are dedicated laws for gas station drive-offs and as far as I know the police take it fairly seriously. In some states you can lose your driver's license for committing a drive-off. If gas stations managed to survive the era of ubiquitous post-pay transactions without being killed by drive-offs, you are not going to convince me that bitcoin double-spends, which are vastly more difficult to pull off than simply pulling up to the pump, pumping, and driving away, are somehow an insurmountable problem here.
  - logfromblammo 13y ago
    It is not an insurmountable problem, but the solution is not to let the police handle it. The police response does not prevent the station from losing money. It just prevents the same people from committing the same offense many times in a row. The reason you have to pre-pay now when you didn't before is that pay-at-the-pump points of sale make it possible to require it without losing business. Stations that had prepay-at-the-pump could lower their prices below stations that did not. The stations that did not have pre-pay did not die off because all the competition was in the same boat, using the same technology and exposed to the same risk. You can't avoid those economics. Your pay-by-BitCoin technical solution has to be the same order of magnitude time-wise on verifying the payment as credit card terminals. At the least, your transfer should be verified by the time the customer is filled up and ready to drive off. As such, the solution should probably be to take a big transaction to activate the pump, verify it while the pump is running, and issue a refund transaction for the unused amount after that verification and before the customer drives away. If the transaction fails due to a double spend, the person might still be on the premises long enough for an employee to request an alternate form of payment. Or use a coin with shorter transaction verification times.
    - mikeash 13y ago
      Or the solution could just be to not wait for validation. Yes, it will mildly increase fraud, and thus costs, but evidently not a huge amount. It could make bitcoin-gas more expensive than the regular kind, but so it goes. Given the difficulty of carrying out a real double-spend attack, I doubt it would happen with any sort of frequency.
      - logfromblammo 13y ago
        As long as no other BitCoin-accepting pump can devise a better solution, whatever solution you have that works as well as a credit-card-accepting pump should be just fine.
vilhelm_s 13y ago
Good point.
mpyne 13y ago
> Let's not forget that until fairly recently (ten years ago or so?) it was common for gas stations to let you pull up and start pumping without any payment whatsoever. That's actually a bigger point than you seem to think. Gas stations deliberately stopped allowing this for a reason. Did the ability to defraud a gas station owner go away in the past 10 years and no one noticed? If so then surely they'd allow for pumping before payment today without Bitcoin.
- mikeash 13y ago
  Prepay won because it's generally better, but postpay is still viable. Certainly the solution doesn't need to involve a 10-30 minute delay for validation before dispensing product.
rahimnathwani 13y ago
"it was common for gas stations to let you pull up and start pumping without any payment whatsoever" That's how it works in the UK. In many stations (at least in London) one of the people at the cash register has to press a button, but they do this after seeing you and (I guess) after they've confirmed that the number plate was correctly OCR'd.