If that would be true, bitcoin would be completely USELESS, but that is NOT the case.

First, the miner has no guarantee that his/her BAD block will be first to get into the chain. For that he needs a lot of processing power today and even more if we ever get to have bitcoins "on the street" for instant shop payments. The cost/benefit ratio assures that mining attacks are not worth unless for huge transactions that nobody will expect to be instantaneous.

Second, more difficult it is to get a second or more consecutive blocks in the chain is WAY difficult, you will need to monopolize >51% processing power.

Third, I wouldn't believe that other peers and miners would accept a malformed block that contains a double spending like 2 transactions saying that output X is used more than once.

Forth, "inventing" transactions it not feasible without the private key of the bitcoin previous output holder. What is the chance that you guess right a key of 32bytes, even if you know it has to conform to some rules to be a key you are talking about 2 exp 100 posibilities or more... good luck with that!


THE ATTACK I was talking about DOES NOT NEED ANY MINERS, it is cheap and can be carried out with 5 or 10 peers. making bitcoin report (and I would say punish) double spending detections would make this attack impossible just by waiting a few seconds, that could longer depending of the size of the transaction so to keep the cost/benefit attack ratio over a safe value.

I repeat the question.
Is double spending reported when detected?

It not... Why not?
It seems too stupid NOT to report it and also not to punish the transaction issuer.

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