This came to mind after seeing Max Keiser mentioning that Scotland, if it did become independent, should embrace Bitcoin as its currency;

This obviously is tongue-in-cheek, but it got me thinking: For Bitcoin to become adopted by the masses, it would need to be easy to use in brick-and-mortar shops and act like current credit/debit cards.

Having your private key printed as a QR Code on a credit card-like piece of plastic is obviously very risky – as soon as someone steals this, kiss goodbye to your finances – but an incomplete private key, paired with a manual PIN code-like process could work.

What do you think of the following process when buying something at the supermarket?
1)   The cashier completes the scanning of the goods as normal, marking the purchase as a Bitcoin purchase (working much like current Point Of Sales (POS) systems, with the amount and recipient entered in).
2)   The card reader asks to see your QR code (which is your Private Key minus the last 6 characters).
3)   The card reader then asks you to punch in these last 6 characters to complete the key.
4)   The POS checks available funds in the associated Public Address and initiates the transfer.
5)   Nothing about the Private key is recorded.
6)   You get a receipt with the transaction address/code.

Software at home, or local services, could manage addresses and printing of these key cards. If a card is lost or stolen, the user could transfer the BTC to a new address using said software (which keeps track of the Private Key, much like a wallet) or via a backup card kept safe.

- Does this sound like a viable solution for “the masses” to adopt Bitcoin for day-to-day use?
- Would holding back the last 6 or so characters be enough to secure the Private Key?
- Could replacing some of the numeric characters with underscores be a better way of using a “PIN” as security? i.e. the code 5KQo_nY_PtyHG_K_BosGHkw_pdkRoaBHFCa_cGmyWWjJLq32sPg would have the PIN 382329
- The POS would need to be set up to return the "change" of the transaction to the same spending address associated with the card.

Thoughts?