Drivechain ObservatoryConnecting…Waiting for data.
  1. 1What is a drivechain?
  2. 2Blocks: the heartbeat
  3. 3Slots and sidechains
  4. 4Creating a sidechain
  5. 5Deposits and the treasury
  6. 6Withdrawals by miner vote
  7. 7Blind merged mining
  8. 8How we know
Concept 7 of 8

Blind merged mining

How sidechain blocks get made, and how L1 miners get paid for them.

5 min read

Who makes sidechain blocks?

A sidechain needs someone to produce its blocks. With blind merged miningBlind merged mining (BMM)BIP301's way for L1 miners to earn sidechain fees without running sidechain software. (BIP301), L1 miners secure sidechain blocks and collect their fees without running any sidechain software.

The work is split. A sidechain user, who does run the sidechain, builds the next sidechain block. They then offer L1 miners a payment if the next L1 block commits to that sidechain block.

Blind merged miningA sidechain user builds a sidechain block and sends a bid on L1. The miner puts that block's hash in the L1 coinbase and collects the bid.1 · BMM Request: "I pay X if your block includes h*"Sidechain userbuilds side block h*L1 minerruns only L1 softwareL1 blockcoinbase: BMM Accept h*2 · commits toone h* and takes X3 · side blockis "found"
The miner never looks inside the sidechain block; that is why it is called "blind".

Bid and accept

  • BMM RequestBMM Request (M8)A sidechain user's L1 transaction offering miners a payment if the block commits to their sidechain block hash.. An L1 transaction from the sidechain user: "I pay this bidBidThe amount a BMM Request offers the L1 miner. if your block includes my sidechain block hash (h*)". It names the L1 block it builds on, so it is only valid in the very next block.
  • BMM AcceptBMM Accept (M7)A miner's coinbase commitment to one sidechain block hash per slot.. The miner writes one h* per sidechain into the coinbase, and can then collect the matching request's payment in the same block.

It is an auction held every block: sidechain users bid for the right to make the next sidechain block, and the miner picks one winner per sidechain.

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Open bids for the next block

UnknownThis value is missing, conflicting, or was read while the chain moved. Nothing is guessed to fill the gap.

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BMM commitments, L1 block by L1 block

UnknownThis value is missing, conflicting, or was read while the chain moved. Nothing is guessed to fill the gap.

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commitment (BMM Accept) none not observed
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Bids that were paid

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Recent commitments, in words

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Go deeper: what a sample of bids can and cannot tell you

The bids you see are the ones the monitor found when it last looked. Requests come and go between looks, so an empty sample does not prove nobody was bidding, and a bid that disappears was not necessarily paid. A paid bid is confirmed separately, from the block itself.

Check yourself

Why is it called blind merged mining?

Read the source

The rules in this lesson come from these documents and code:

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