Quote from: Istaria on March 19, 2015, 12:07:51 AM

Quote from: Soros Shorts on March 19, 2015, 12:04:17 AM

Quote from: Istaria on March 18, 2015, 11:58:29 PM

Quote from: Soros Shorts on March 18, 2015, 11:53:37 PM

Quote from: Istaria on March 18, 2015, 11:30:47 PM

Can I ask then, from the point of view of, say, my local coffee shop taking bitcoin for takeaway coffees.....is it generally safe for them to take an unconfirmed transaction?

If it were my coffee shop I would accept standard unconfirmed transactions with no detected double-spends after a 30 second monitoring period.

Why 30 seconds? How long after you scan the QR code or whatever would you see a problem? Would 10 seconds be enough? Or should it be 2 minutes? I am not selling coffee, I am just thinking from the point of view of a consumer standing in a coffee queue, or at a petrol pump or at a bookstore counter....30 seconds is a damn long time if they have a queue.

I guess somebody would have to do some kind of Monte Carlo simulation with double spends from different points of the Bitcoin network. Then you might be able to say something like "with the current network propagation delay a double spend made 10 seconds after the initial legit transaction has a 0.5% (or whatever %) chance to succeed". They you can adjust your business model to accommodate your risk.

mm....I think I need to know the maths of this a bit better. So the possibility of a double spend is reliant on time?

Ultimately all that matters is the mining node that confirms either one of the transactions sees the legit transaction first before the double spend transaction. From a statistical standpoint, the more nodes that see the legit transaction first the less likely the double spend will succeed.