Quote from: riggasconi on January 23, 2011, 12:14:02 PM

Why, if the ROI of such an attack is positive ?

I don't think it is positive.

The rest of my post gave a bunch of reasons why the return is lower than at first glance. Many types of merchants would be immune, many would be warned, etc. Shops are not going to mindlessly ship their entire stock without making sure nothing weird is going on. Even if they aren't savvy they are likely to know other bitcoin merchants. "Huh, all of your stuff was just bought too? Cool, I guess we're rich now."

Bitcoin price is up about 6x since I got here and difficulty is up over 90x.

The value of attack calculation is hard, but you aren't even looking at the right numbers. The attacker doesn't just get to turn bitcoins into cash via magic. He's going to flood exchanges and tip people off by buying to many sneakers. A lot of what you can do with bitcoin doesn't help him at all, so he can get a lot of credits at A Tale in the Desert, so what, doesn't help him at all. He can bet at bitcoinsportsbook, so what? The only thing valuable to him is the exchanges and they are likely to be the most alert to weird stuff.

The point is that you have to match the whole thing, but you only get a subset of a certain type of good. Except for a few exceptions you will get at most the total of bids at all exchanges.

In the future it will be even harder to get a hold of enough goods and money to justify the attack. Many of the goods will be meals and nights in a hotel. How many of those can you get?