Topic: Feature Suggestion for BitPay / Blockchain.info: Web POS Terminal (Read 2134 times)

Oh, Duh. I don't know why I forgot about that.

To sign a transaction in advance, one must know who they're paying.  The pre-signing idea was mainly to manipulate the denomination so the merchant doesn't have to return change - it still doesn't negate the need to deliver a private key.  In other words, if I want to give you 2BTC, then, instead of giving you private key A worth 10BTC, my phone could pre-sign a transaction against key A that sends 2BTC to key B and the other 8BTC back to me, and then I only give you key B.


Naw, sorry, without knowing who to pay, and if you're not giving a private key, it's not possible to pre-sign a useful transaction.  But you can still have the benefits of what you're after - you can always print bills and keep a copy of the private keys (either a paper copy or in a file).  If you lose the bills and can beat the thief to redeeming them using your copy, you'll get the money right back.

I like the idea of the QR code containing the signed transaction. This means that the private key can remain private?

Someone can show a QR on their phone or have bills printed with pre-signed transactions, either way. Isn't that more robust.

casascius: couldn't you just as easily print bills that contain signed transactions and then when they're scanned they just get sent out. No need to create provate keys either. The wallet could just print bills directly from the wallet. The money doesn't leave home until the bill is scanned and the transaction inserted.

Seems like a feature for blockchain.info. (I'd say the satoshi client except it would take ages to get it added and piuk is just so amazingly fast with features.)

I'm sure no offense was intended, but some may interpret this comment as sexist. As Bitcoin and BitPay are striving for legitimacy, acceptance, and wide-spread adoption in my opinion, it would behoove you and our community, as a whole, to not make grey-area, easily-misinterpreted comments like this. I say this with good intentions and only as suggestion. The Bitcoin community is male-dominated and we should work towards changing that.

Ok, I change my statement to: "That way the waiter don't have to stand there while you scan." (Plus taking up the phone and open the app.) I just think that the way they did it in the video was a bit "clumsy"...

But I think you are doing a great job Bit-Pay! Just telling you how it can be done even better (in my opinion)

Exactly.  Once the waiter gets the invoice, you scan it, and then you fumble around with your phone.  The waiter can walk away and do anything else during that time, and they get the on-screen alert when you send your payment.

I agree with this. Bitcoins are electronic and anything on paper is just for emergency. Scanning and handling private keys is dirty. Physical stuff can be counterfeited. The only trip should be from the coins shop to user's smart-phone.

Slightly off-topic - I would like to propose the QR scanner solution to be able also to scan & post raw transactions. The QR codes can carry up to some 2000 bytes, simple transactions are around 300 bytes. Even if some extravagant transactions don't fit into the code, I think it's still worth it because wallets then don't need to go online to make a payment. Foreseeing some specialized secure wallets, to which users feed necessary data at home, and then go spending. The wallet just reads destination address and amount from a POS terminal, and posts the resulting transaction back to POS. No need to go online because everything is transferred via QR codes, NFC, or Bluetooth. Maybe we are not there yet but one day this looks like a good idea to me.


BTW the waiter doesn't have to stand there while you pay (at least not while signing and sending tx).

This is very possible, assuming their POS terminal that prints the tickets is connected to the internet.  If you find a restaurant willing to pay the development costs, and run 3rd party software on their terminal, we can absolutely do it.

It would be better if the QR code was on the (paper) bill. That way the waiter don't have to stand there while you pay.

why doesn't anyone make an INTRANET version of a web terminal like that bit-pay version?

If these 2 girls can figure it out, I think anyone can.

It's hard to believe this was filmed 1 year ago.  It's been a busy year!

http://www.youtube.com/watch?v=YZ-pqo0cLcE

That is true for those of us in the community of computer-educated people who like to do as much as possible with their phone, and who have the means and the desire to own a smartphone, like me.  This idea is meant to bring Bitcoin to those not part of that community (a whole lot of people), and is meant as a complement to using smartphones for accepting payments and not a replacement.  If someone walks in with a smartphone, then by all means they can make their payment by scanning the merchant QR code the usual way.


It depends on how you prioritize the value of your resources.  Most of the time, it is silly for me to pay my bills by paper check instead of online, but there are occasions where a paper check is simply the best practical way.  Where paper is scarce and the time available to complete a transaction in a checkout line is not scarce, and a smartphone and wireless internet connection are reliably presumed to be available, then this statement is absolutely correct.  This proposal is for those frequent situations where the statement cannot be considered correct.


I fully agree with this, I have just assumed this is already possible outside the scope of what I have proposed.  For example, Bit-Pay specializes in this and already has apps that make this possible, and with BlockChain.info this is already constructively possible with a regular wallet or even a watching-only wallet.  I am suggesting that a new screen be added to enable another useful kind of functionality with a practical application, but of course not to suggest in any way that this is the only way one should accept BTC or that the other avenues should be removed.


I see this as a fantastic idea that could really go somewhere (the root idea the way I see it is it's smartphone payments without the smartphone needing internet access).  It sounds practical and convenient, but would need some refinement to work technically.  For example, the only way for a smartphone to convey permission to take an arbitrary amount like 2.347 BTC would be to sign a transaction for that amount to fund a fresh private key while keeping the change, and then offer both the private key and the funding transaction to the merchant.  That's a tall order of bytes to be crammed into a screen-size QR code (not impossible with the way smartphone screens are going, but definitely pushing the envelope on readability).  Or, the phone could just remember pre-denominated codes, just like having bitcoin bills but saved in phone memory instead of printed on paper.

OP - I like where your head is at, but any "solution" which presupposes widespread use of printing out one-time-use paper bills to pay for things is DOA

Payments are moving to the phone. It is silly and inefficient to print out paper just to take it somewhere and destroy it upon redemption. Any workable BTC POS system needs to enable the customer to pay from her phone.

I think a better solution, using your QR code scanning gun idea, is for the user to enter the final price on his phone in his BTC app. He enters for example 2.347 and hits "Offer Payment". The app then shows a QR code which allows the merchant to take 2.347 BTC from the account on the phone. This would require a common standard that POS terminals and mobile wallets would need to adopt.

+1, what is needed to put it in stores?

Most merchants have a smartphone with a QR scanner...

https://www.youtube.com/watch?feature=player_embedded&v=YZ-pqo0cLcE

I'm thinking the printable bill standard should be such that the qr code containing the private key also contains a change address specified at the time of the bill's creation.  Then there'd be no need to manually mess around with change at all at the point of sale.  The spender can also more easily avoid address reuse, since the bill creation program would by default just grab a new address from the wallet for change.

That's a great idea but wouldn't a broken casascius coin drilled and hooked onto a key chain make a great change address? I guess it would need a QR code sticker on it but a firstbits address is not too slow either. The problem would be printing a QR code small enough at high enough rez.

My hope is that users will print them themselves with free open-source software, and in less frequent cases, receive them as change from merchants.


A home-printed bill can easily be torn in half or cut with scissors and the private key left at home.  For more durability for someone willing to prepare, my suggestion is to carry a receiving address on their keychain (e.g. BitPay keyfob) so they always have a way to receive funds but not be carrying the private key.

Aren't people going to get all fuddled up with what's what? I'd have it so when you buy the bills/coupons they have a tear strip that has the change key on it. So they leave those at home when they go out to use the bills. That way whatever happens to the bills as long as they put the change on one of them they'll have it when they get home, and the key is never out in public.

Kind of like travelers checks. You leave the serial # at home so you can claim them later if stolen.

Bitcoin travelers checks could be useful if more places knew about them.

"Don't leave your computer without them."

I like it!