If the bitcoin protocol were changed so that the merkle root from block N-1 were replaced in block N by the two roots of blocks N-2 and N-3, then it would become possible to mine 2 blocks at a time in parallel and increase the block frequency compared to the time each block took to propagate. Each block would still get confirmed by 6 of the following 7 blocks. The block size variance could be controlled by requiring that transactions with odd hashes go into odd-numbered blocks and vice-versa. What would be the limitations of this variant protocol compared to the existing Bitcoin protocol, assuming nobody considered one confirmation to be much better than zero?

  • I don't think I understand your proposal. There are five fields in a Bitcoin block header: version, prevblock, merkle root, timestamp, and nonce. Which one are you proposing to modify, and how?
    – Nick ODell
    Commented Jul 16, 2015 at 4:52
  • 1
    prevblock, by replacing it with two fields based on blocks N-2 and N-3.
    – Pr0methean
    Commented Jun 8, 2017 at 3:12

1 Answer 1


Objections that come to mind initially, I'm sure there are more:

  1. You don't want to split the hashing power into two halves because that would make it easier for an adversary to get 51% of that halve: 25% of the total or even less if the halves are not exactly 50-50.

    The idea behind Proof of Work is to concentrate as much work as possible behind one and the same chain and make that the level-to-beat by an attacker.

  2. If you force odd transactions into odd blocks (and vice versa) then you still have 10 minutes block times for all transactions.

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