5 ms·

The pool operators could launch 'double spend' attacks. Essentially with > 50% of the hashing power, a bad operator is able to generate a chain faster than the

The pool operators could launch 'double spend' attacks. Essentially with > 50% of the hashing power, a bad operator is able to generate a chain faster than the rest of the network. They can hold back this longer chain in secret, execute some transactions on the honest chain, then broadcast their chain (which doesn't have those transactions included) to the network. The network will use the evil chain since it is the longest, and since those transactions are not included, whoever accepted them beforehand has been ripped off. It worries me that it's this hard to convince miners to leave a pool. If I wanted to kill Bitcoin and had a few million to spare, I'd open a pool with no fees PLUS a bonus of 1 or 2% from my own pocket. Good luck getting people to leave that pool.

btcwatcher 13y ago
Who would want to kill bitcoin apart from governments? (They can just outlaw it.) It's not possible to short it yet, is it?
jackgavigan 13y ago
There are rumours that that double-spend attacks have already been tried or experimented with by someone linked to the Ghash.io pool: https://bitcointalk.org/index.php?topic=327767.0 https://bitcointalk.org/index.php?topic=327767.0
flatline 13y ago
There is even some evidence that double-spending attacks have already happened. You don't strictly speaking need 51%, that majority just ensures that your chain will win out over time. The original bitcoin paper[1] details the probabilities involved for nodes controlling < 51%, if anyone is interested it is a short and good read. It could be even worse than that however. Another post on BCT[2] talks about a "time warp attack", where at 51% node could effectively mine all remaining bitcoins in one fell swoop. [1] http://bitcoin.org/bitcoin.pdf http://bitcoin.org/bitcoin.pdf [2] https://bitcointalk.org/index.php?topic=114751.0 https://bitcointalk.org/index.php?topic=114751.0

btcwatcher 13y ago

Who would want to kill bitcoin apart from governments? (They can just outlaw it.) It's not possible to short it yet, is it?

jackgavigan 13y ago

There are rumours that that double-spend attacks have already been tried or experimented with by someone linked to the Ghash.io pool: https://bitcointalk.org/index.php?topic=327767.0 https://bitcointalk.org/index.php?topic=327767.0

flatline 13y ago

There is even some evidence that double-spending attacks have already happened. You don't strictly speaking need 51%, that majority just ensures that your chain will win out over time. The original bitcoin paper[1] details the probabilities involved for nodes controlling < 51%, if anyone is interested it is a short and good read. It could be even worse than that however. Another post on BCT[2] talks about a "time warp attack", where at 51% node could effectively mine all remaining bitcoins in one fell swoop. [1] http://bitcoin.org/bitcoin.pdf http://bitcoin.org/bitcoin.pdf [2] https://bitcointalk.org/index.php?topic=114751.0 https://bitcointalk.org/index.php?topic=114751.0