Bitcoin Forum

Is it possible to make a system where I tap my bitcoin debit card on a POS terminal and transfer BTC to a merchant? I'm not talking about something like a BitPay card which converts BTC to fiat and uses traditional payment processing; I'm talking about using the bitcoin network so that the transaction is in a block ~10 minutes later.

Hypothetically speaking, how would this work? The card would be provided by a third-party service, is it possible to have this and still be in complete control of my keys? How could my tap on a terminal lead to a bitcoin transaction that's broadcasted through the network? Would you need to pre-load keys and addresses onto the card, or could the tap somehow authorize the card company to transfer the bitcoin ownership (I can't see how this is possible if they don't have your keys)?

Are we better off just using smartphones and other devices for transactions?

I really want to emphasize that I want to control my keys. I'm sure this would be possible if I transferred my BTC to a third-party and they could sign off the transaction whenever I authorize it with my card, but that's not the point. If they can do that, it's not my bitcoin.

if you are using a "card" and a "POS terminal" then it doesn't matter what happens in the background since you have already given up control over your bitcoins to a centralized party that is now holding your money (bitcoin in this case) and is processing your transactions and can decide where you spend them and when you spend them. there is just no other way that this can work.

if you want it in any other way then you have to use "bitcoin" instead of anything else like a "debit card", and you do that with your smart phone, on your laptop,... since it is a "digital" currency not a physical one.

I used to have a Shift card linked to Coinbase but I'm not sure if they still offer them.
Shift looked like a Visa credit card and functioned with a pin (so like a debit/bank card)

There are a lot of payment method like pay with BTC and it converts to USD. But what about your saying, it is not seem easy. Firstly, we have to find a lot of places where accept Bitcoin for payment.

I am always telling this, merchants doesn't accept Bitcoin as a payment yet, because of volatility. It is including so many price risks. Remember about a month ago BTC price has just lost its value almost halfly. No one wants this for a payment.

This is a good idea but it still violates the principles of bitcoin because it relies on the fiat-based system...credit card companies (they're the fucking worst!) to clear the transactions. So you're not circumventing the system we all hate, you're continuing to support it. Visa still gets paid on every transaction.

There's a company called Tradeshift (https://tradeshift.com/) that's building an ecosystem for merchants to tap into that serves as a middleman between the cryptocurrency used for payment and the currency the merchant wishes to get paid. Tradeshift clears the transaction and is also part of the crypto community, not the Fed world.

Now, I don't know if they a have a debit card or if any debit card has signed up for their system - but when one is available this will be the best, truest option!

The Tradeshift guys made a great showing at the Blockchain Hub at Denver Startup Week back in September 2018.

I am little bit confuse about your topic exactly what you want to know or explain. Most likely you want to ask to use Bitcoin on marchants transaction and you want to spend Bitcoin directly. That's why need Bitcoin visa card. If I am not wrong then it's sound like centralization. Why you need visa card for transaction? Why we need make Bitcoin centralized? On the other hand you want spend directly Bitcoin, it's not possible because volatility of Bitcoin price. Whatever you think eventually you have to spend it on USD. No way to use directly Bitcoin since its not physical money.

It is possible if the merchants support it, but until then, the operator of the POS terminal decides whether they'd give out the merchants bitcoin or fiat for your purchases. Debit/credit card companies still has the upper hand on such situations, so I don't really see how this one pans out. Also, why go the route of a debit card if the merchant accepts bitcoin, when you can just use a mobile wallet and pay the merchant directly with your bitcoins? That wouldn't be so hard and confusing IMO.

i feel skeptical about this.  if regular atm cards can be hacked, there's a possibility that it might happen on the bitcoin debit card.

I am sure that it is possible to do in our world of technology is progressing very quickly and the development team to do it will not be difficult,but the question is whether they need to do it? I think Yes since bitcoin was created as a form of payment and therefore need to issue a debit card.

using a merchants physical technology (the NFC tap to pay card reader) yes its possible..
but here is some out of the box thinking

why does it need to be a plastic card that has to be sent through the mail box..
why not just use a phones NFC chip.

then a user has more control and can be set up and running just by downloading a wallet app on their phone that utilises 'tap to pay' (like applepay does) but while keeping the private key secure on the phone and only a signed tx is sent over NFC.

this then solves
1. no need to mail out cards (no user delay waiting for postman)
2. no need to produce cards (no cost to some business to offer such a thing)
3. no need to distribute cards (no cost to some business to offer such a thing)
4. user privacy (no delivery addresses, no concern user has that business has a copy of privkey before distribution)
5. user control using smart phone instead of trust using dumb plastic
6. smart phone is capable of creating signed tx unlike dumb plastic
7. tapping a smartphone is same as tapping plastic card, so shopping experience is the same at checkout

I understand that you want to pay a merchant similar to debit/credit card but using bitcoin ? I guess that will be possible in the future but right now it will be possible only through mobile app based wallets. But you and merchant must need to wait for at least 10 minutes to settle down everything. It means we need LN kind of third party support for quicker transaction which will be using bitcoin as mode of payment.

But, I am sure that what you are imagining will be going to happen like you will go to a shop where the merchant will be accepting bitcoin payments and you will be holding some device (which may look like the exact debitcard). After shopping and billing merchant will show you some QR code in their computer screen, once you scan that it will display merchant's BTC addy and the exact BTC amount you need to pay for your purchases. You just click and confirm that transaction using your fingerprint in that device and a peep sound in merchant computer's indicates that the transaction is completed. This is going to happen anytime soon, start preparing for that.

Please note that specialized device may be your smart phone itself but we need solutions for trusting transactions with zero confrontation or anything similar to that. Then only paying in bitcoin will be feasible for real time purchases.

It might be possible somehow in the future? I guess there are some people who are working on it right now for it to make into the public? As there are only few stores that acveot bitcoin as a payment I think it won't gonna work.

You brought up some good points franky, I agree using a phone would be much better; but what would you do if tap didn't work? Sometimes it fails and you have to insert your card into the chip reader or use the magstripe. Assuming the merchant doesn't have a QR code at their disposal, how else would you send to the address? Typing out the bitcoin address is way too risky and it would obliterate user experience right?

I was hoping there could be a system where the POS terminal could be a raspberry pi (or anything really) with the merchant's bitcoin client running, as long as it could extract the necessary information from the card to create and broadcast a transaction. I don't think it's possible because I don't know how you would be able to find spendable UTXO and be able to sign transactions (without some third-party doing this for you through an account).

From what I understand, when I use wallet software my wallet finds UTXO that belongs to any of my addresses and spends all of it, returning whatever is left over to another address I own. I don't see how that could be done on my end through a card and it shouldn't be possible for a merchant to do that unless I expose my private key, which would defeat the purpose of using bitcoin. That's kind of annoying, I really wanted a debit card that said bitcoin on it  :P

In theory yes but in fact no
Bitcoin will be always exchanged to any other national currency
It is the same when i use euro card in my country
Euro is exchanged to my country currency
Exchange btc to fiat will be very costly much better idea to have wallet when you can keep both fiat and bitcoin and exchange both way with low cost
Wallet or service what will also offer cards

Yes, typing out the bitcoin address is way to risky but most of the crypto credit or debit card issues by the crypto currency payment companies work like the normal card issued by the bank and I believe getting one from a licence company or institution wont be a problem due to franky statement.

finding UTXOs is not the problem. it just requires either running a full node or communicating with one (which can be in a lot of different ways and all it requires is a computer with internet access!). the problem is with the "signing" part which requires your private keys and obviously your "private" keys are private and should not be on a card! and YOU should be the one that does the signing with the private keys not the terminal. so in order to sign you need to be using a computer device (like your smart phone) that does it internally without revealing anything to the merchant.
the other thing that you pointed out in the second paragraph is another problem. you should NOT reuse addresses as much as you can, this means sending the change to a NEW address instead of the old one which again requires a wallet application on your device.

if a merchant accepts BTC then as a backup ofcourse they would have a QR code laminated near the cashier desk.. accepting btc = having a QR code as standard transaction etiquette .. i dont think anyones manually had to type in a bitcoin address for atleast 5 years now.

ive done hundreds of transactions with 'brick-n-mortar' merchants and never needed to manually type an address.. and thats been since 2012

but yea QR codes are to bitcoin, what magnetic strip is to debit cards.. old school backup