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Author Topic: Fake Bitcoins?  (Read 14387 times)
vector76
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August 23, 2011, 12:14:35 AM
 #41

My understanding is that blocks that are not on the best chain are still relayed, otherwise people will get stuck on the wrong chain.  So even if the block were only sent to the target, the target should have relayed it and the rest of the network should have seen it.  The network does not know which fork will be extended next, so everyone will have to have both.

An "innocent" fork that occurs by pure chance should have the characteristic that all transactions in the abandoned block are included either in the "true" block of the same height, or in the next block.  I think reversing a transaction will require a transaction in an abandoned block to be invalidated in the "true" fork due to a double-spend.  It seems unlikely that such a transaction reversal could happen by accident.
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August 23, 2011, 12:32:36 AM
 #42

In the case that there are two equal-difficulty-sum chains, the node processes whichever block it received first.  They won't discard the second block, but they won't be trying to extend it if they saw the other one first.   If MBC is behind Tor and the attacker studied the network latencies well, most miners will see the "legit" block first, and that "legit" chain will most definitely get extended first.  (I'm using "legit" here, because I don't know any other way to refer to the non-attacker chain... there is, of course, nothing wrong with the attacker's block except that that chain is unlikely to get extended)

If transactions carry over between from invalidated chains, then the attacker should send himself a small transaction using one of the outputs he used in the huge deposit transaction, to be included in the "legit" block while he waits for it.  By doing this, he guarantees that the large deposit is DOA on the new chain in case the nodes decide to carry it over.  Otherwise, it's possible that the deposit will be transferred to the new chain and the double-spend fails.


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