You may be interested in this discussion http://forum.bitcoin.org/index.php?topic=2227.0 in which I show that a mining cartel with about 30% of the total hashing power can win more blocks than it deserves to by delaying their block solution announcements under certain circumstances.
ByteCoin
Topic: Is it possible for a miner to delay announcing a correct block solution? (Read 1070 times)
June 05, 2011, 05:19:53 PM
June 05, 2011, 12:38:00 PM
Yes, a hash of the hashes of the transactions is hashed in the block header, so if you add a transaction it invalidates your hash.
However, when the block reward decreases miners might only start mining with sufficient transaction fees piled up.
However, when the block reward decreases miners might only start mining with sufficient transaction fees piled up.
June 05, 2011, 12:34:19 PM
As far as I understood, solutions are only valid for transactions that are already known when the block was mined. So it is NOT possible to include more transactions, as this would change the needed solution.
thanks Sukrim, that makes sense. So no point delaying announcing a block once you find it as you can add new tx's to you're solution only the tx's that were included in the original solution.
June 05, 2011, 12:24:02 PM
As far as I understood, solutions are only valid for transactions that are already known when the block was mined. So it is NOT possible to include more transactions, as this would change the needed solution.
The only thing possible right now is a DoS "attack" by not submitting valid solutions to the network, so it takes longer until a solution is found.
This is useless in solo mode but creates problems in pooled mining currently, as pools rely on you solving difficulty 1 blocks as proof of work, with the hope, that some of these solutions might also solve more difficult blocks. If you withhold the more difficult ones, the pool will still think you do your work perfectly fine, but it will earn less, since your hashrate needs to be deducted from the pools hashrate.
This cannot even be verified via statistical analysis, as the chance to find a solution for the current difficutly is sooooo small, that it won't show up if you just withhold solutions which are also working for difficulty >= current diff.
The only thing possible right now is a DoS "attack" by not submitting valid solutions to the network, so it takes longer until a solution is found.
This is useless in solo mode but creates problems in pooled mining currently, as pools rely on you solving difficulty 1 blocks as proof of work, with the hope, that some of these solutions might also solve more difficult blocks. If you withhold the more difficult ones, the pool will still think you do your work perfectly fine, but it will earn less, since your hashrate needs to be deducted from the pools hashrate.
This cannot even be verified via statistical analysis, as the chance to find a solution for the current difficutly is sooooo small, that it won't show up if you just withhold solutions which are also working for difficulty >= current diff.
June 05, 2011, 12:22:00 PM
Sure you can delay sending out a block. You control the software.
But you put yourself at a disadvantage not only for losing the block reward, but also getting left behind in the block chain as others build on top of that block on their own.
But you put yourself at a disadvantage not only for losing the block reward, but also getting left behind in the block chain as others build on top of that block on their own.
June 05, 2011, 12:13:05 PM
Is it possible for a miner to delay announcing a correct block solution?
I was thinking about this and had a search but didn't find the answer.
I'm sure most are thinking why would you do this. If you have the block solution, release it immediately and collect the block reward. And currently that is obviously the best strategy. Get the 50BTC + whatever tx fees there are.
But my thoughts were about a time when the tx fee makes up a bigger proportion on average of the overall block reward.
Hypothetically, say after the block reward is halved to 25 BTC, imagine the tx fee is on average worth ~25 BTC per block. (Just using these numbers as an example, I know there are so many unknowns here about what the level of tx fees will be in the future). The average total tx fees per block will typically be proportional to the length of time since the previous block. Now put yourself in the position of the miner who gets lucky and finds the solution to a block very soon after the previous block was found, say within 10 seconds. The miner knows on average no one else is going to solve the block for another few minutes. Do you (can you?) delay announcing the block to the network for a some time (short enough that no one else will find the solution on average) to allow some fee paying tx's to build up in the queue of unconfirmed tx's? You have a choice, announce the solution immediately and get 25BTC + ~0BTC tx fees (say), or hold off for 2 mins say and get 25BTC + ~5 BTC tx fees but take the chance that someone else releases the solution before you.
If you can delay announcing the solution could this be a more profitable strategy? Does this really matter? If miners did delay announcing block solutions like I've discussed above it would mean the real network hash rate would be underestimated.
Maybe this is not possible at all or there could be some other misunderstanding on my part making the above moot.
I was thinking about this and had a search but didn't find the answer.
I'm sure most are thinking why would you do this. If you have the block solution, release it immediately and collect the block reward. And currently that is obviously the best strategy. Get the 50BTC + whatever tx fees there are.
But my thoughts were about a time when the tx fee makes up a bigger proportion on average of the overall block reward.
Hypothetically, say after the block reward is halved to 25 BTC, imagine the tx fee is on average worth ~25 BTC per block. (Just using these numbers as an example, I know there are so many unknowns here about what the level of tx fees will be in the future). The average total tx fees per block will typically be proportional to the length of time since the previous block. Now put yourself in the position of the miner who gets lucky and finds the solution to a block very soon after the previous block was found, say within 10 seconds. The miner knows on average no one else is going to solve the block for another few minutes. Do you (can you?) delay announcing the block to the network for a some time (short enough that no one else will find the solution on average) to allow some fee paying tx's to build up in the queue of unconfirmed tx's? You have a choice, announce the solution immediately and get 25BTC + ~0BTC tx fees (say), or hold off for 2 mins say and get 25BTC + ~5 BTC tx fees but take the chance that someone else releases the solution before you.
If you can delay announcing the solution could this be a more profitable strategy? Does this really matter? If miners did delay announcing block solutions like I've discussed above it would mean the real network hash rate would be underestimated.
Maybe this is not possible at all or there could be some other misunderstanding on my part making the above moot.
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