Withdrawals by miner vote

Withdrawals travel in bundles

To move coins back to L1, sidechain users request withdrawals on the sidechain. The sidechain periodically combines many requests into one withdrawal bundleWithdrawal bundleMany withdrawals from one sidechain combined into one L1 transaction. It pays everyone or no one.: a single L1 transaction that pays everyone. A bundle pays all of its withdrawals or none of them.

Propose (M3), then vote (M4)

A miner puts the bundle up for a vote with an M3M3 · Propose bundleA coinbase message that puts a withdrawal bundle up for a vote. It counts as the first vote. message. Miners vote on its M6 idM6 idThe identifier miners vote on for a bundle: the id of a "blinded" copy of the withdrawal transaction without its treasury input, which usually does not exist yet when voting starts., an identifier of the payout transaction, not on the transaction itself. Being proposed counts as its first vote.

From then on, each block carries an M4M4 · ACK bundlesA coinbase message with each block's withdrawal votes: upvote one bundle per sidechain, abstain, or raise an alarm. vote for every sidechain that has bundles pending. For each one, the miner can:

• Upvote one bundle. It gains a vote; the sidechain's other pending bundles each lose one.
• Abstain. Nothing changes. A block without an M4 counts as abstaining.
• Raise an alarm. Every pending bundle of that sidechain loses a vote.

Votes never drop below zero.

Pay out (M6), or expire

Once a bundle has more votes than the threshold, the payout transaction (M6M6 · WithdrawThe L1 transaction that pays out an approved bundle and returns the rest of the coins to a new treasury output.) can be included in a block. It spends the treasury, pays the withdrawals, and returns the rest to a new treasury output. A bundle that grows too old without passing is dropped and pays nothing.

It is a public countdown. Everyone can watch the votes for months before a single coin leaves, so a dishonest withdrawal cannot happen quietly.