Quote from: Ground Loop on August 31, 2010, 10:50:21 PM

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as in the 'neighbor kid moans the lawn' scenario

Your neighborhood sounds pretty fun. Shocked

Is it possible that 'testing' a bitcoin bill for double-spend could be done much faster than confirmation?

Certainly, if the receiver is willing to trust that his own client is up to date.

At least as well as the credit card companies can promise that the person who is holding the card didn't steal it.

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After all, you just want to know if the coin has been previously spent.

SO the cashier takes the bill with the 2D barcode, scans it, and the register confirms that the coin hasn't been previously spent (ie, the balance is real). The confirmations can come later if the merchant wants to extend some trust. Seems this wouldn't take any longer than a Visa authorization.

Quicker, actually; since the Point-of-sale system within the store could check that address against it's own client in milliseconds. Credit cards are usually assumed to be good for orders under $50 anyway.

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In a nutshell, my goal is to pay for something
1) Anonymously (thank you sir, you have no idea who I am.)
2) Spontaneously (I wasn't planning to spend bills at lunch, but here I am)
3) Off-line (I didn't bring my gadgets)
4) Minimal trust required (Give me physical goods, and you have reasonable confidence my bill is good.)

A completely separate discussion would be valid for discussing a quick way to share BTC addresses, IRL. Cut & Paste works fine. "Read your number to me" would not. A standard 2D sticker on the back of a register would be the ticket here. "BTC Accepted @" with a phone client that scans and pays.

Bluetooth in the register.