If two miners find a valid block for the same height, the block with the largest difficulty is selected and the other one is rejected by the network (orphaned), regardless of their discovery timestamp.

Are there situations where it would make sense for a miner to keep mining towards an already published block, in the hope of finding a more difficult block that could replace it? Could it be turned into a threat to the network?

  • is this unique from the consensus protocol used in bitcoin? If not, the answer probably exists in bitcoinland somewhere. – Ginger Ale Mar 28 '17 at 1:58
  • Same reasoning applies. The numbers will differ since Monero has a different block time, hash rate distribution, etc, but the principle is the same. – user36303 Mar 28 '17 at 18:36

Assuming that the network is healthy which means there are many competing miners for a block. It would not make sense for a miner to keep mining an already published block because by the time it will be able to find that block the blockchain is already longer compared to his chain. Even if there are nodes that would accept it the network will always select the longest blockchain.

For example, if we assume that the said miner can find a block every 1 hour and blocks are being found every 2 minutes in the entire network. The worst scenario is when it just mined a block. This means it is impossible for him to grab the block from an hour ago because there are already 30 blocks ahead of it.

Therefore, the best case to steal a publish blocked would be that when the miner found a block an hour ago. There is a chance for that miner to keep mining for that block and be able to be accepted. However, its chances diminishes as the blockchain increases. In this case every 2 minutes. Probably at 2 blocks that miner would not be able to submit its block and accepted in the network.

This would cost a lot for that miner since it has only a very small window to publish an already submitted block. It would be profitable to just be a good miner and find the next block which has more probability of mining it rather than mining with an already published block.

In another case if the network is not healthy and that miner can mine blocks faster than the entire network it would be a different story. But this only happens when the network is at its infancy.

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