Quote from: Littleshop on August 06, 2011, 12:19:52 PM

Quote from: boaz2020 on August 06, 2011, 12:01:19 PM

Quote from: willphase on August 06, 2011, 11:10:09 AM

I'm surprised that, even with 1 block confirmations, stealing bitcoins in the way that Tom describes would be feasible without a considerable amount of compromised computing power. If my understanding is correct, for an attack to succeed an attacker would have to compute 2 blocks containing their false transactions before the rest of the network computes one. This computation could be done offline so the attacker could wait until they have been lucky and computed these blocks before publishing them, but it would still require a non-insubstantial amount of compute or waiting a long time before being able to make the attack.

I'm not saying that pools are involved in this, but if even a small pool was involved, then this attack would be a lot more believable.

Will

I'm pretty sure it would work something like this.

1.) Peer directly to the bitcoind running on MyBitcoin.
2.) Solve the next block with your dubious transactions.
3.) Wait for someone else to solve the block you solved.
4.) After the same block was found, but before MyBitcoin's bitcoind hears it, announce your dubious block to MyBitcoin.
5.) That is 1 confirm, funds will now show up. Transfer the funds out, the next block on the network will orphan your dubious one.

Step 2 is a problem, not impossible, but would require a substantial mining investment. If i took all of my $X000 investment in mining gear I would be able to do that about once a month and it would not be guaranteed each time I solved a block.

No, I'm not saying you have to generate two successive blocks.
Just generate a given block first.

By dubious transactions, I mean legitimate coins sent to MyBitcoin that will get reversed once your block gets orphaned, but only after the funds are confirmed on MyBitcoin.