Quote from: midnightlightning on March 13, 2013, 05:17:00 PM

The buyer would have to trust the cash register app to not hang on to the private key long-term, and not create additional transactions beyond what's agreed upon, but that's what we as buyers do every time we use a POS device for a normal credit card.

Isn't that why credit cards have chargebacks, and the associated fees? I think Bitcoin can be much more competitive if you don't copy that part of the credit card system.

Here in the Netherlands, hardly anyone uses credit cards; most people don't even have one. Instead, electronic POS payments are typically done with a card known as a "PIN" card (actually a Maestro card), which is a debit card directly linked to your bank account. Transactions are non-reversible (or at least hard-to-reverse, I'm not really sure). the customer doesn't have to pay a transaction fee, and when looking at how eager shops are to tell you you can pay with PIN, they don't have to pay too much either. An essential security feature is that the customer has to enter his secret "PIN" code into the POS terminal; if the POS terminal is untampered, the PIN code is never shared with the shop owner or anyone else.

There is increasing news about POS terminals and ATMs being tampered by criminals, who obtain the PIN code in that way, and then either also obtain the card information (by reading the magnetic stripe) or (with newer, more secure cards) simply steal the card. The fundamental problem here is that the authentication (entering the PIN code) happens on someone else's device.

I think security can actually be a lot better if authentication happens on a device owned by the customer. This has the additional feature that the customer can choose the security method (PIN number, passphrase, voice recognition, fingerprint, whatever). Smartphones might be good enough for this purpose, but since they're also used for so many other things, they're vulnerable to hacking. A separate device, slightly resembling a pocket calculator, would give a really good level of security.