Consensus & Finality

Proof of Work, Proof of Stake, reorgs and how many confirmations are enough.

8 min read·4 quiz questions

Proof of Work

Miners burn electricity searching for a hash below a target. Bitcoin retargets difficulty roughly every two weeks for ~10 minute blocks; Dogecoin targets ~1 minute and is merge-mined with Litecoin.

Proof of Stake

Validators lock capital and are slashed for misbehaviour. Ethereum finalises epochs (~12.8 minutes); Solana uses Tower BFT with sub-second slots and fast optimistic confirmation.

Reorgs and confirmations

A reorg happens when the network switches to a heavier chain, dropping recently included transactions. That is why exchanges wait for a chain-specific number of confirmations before crediting deposits.

•Bitcoin: ~6 confirmations for large value.
•Ethereum: wait for finalised, not just latest.
•L2s like Base: soft confirmations are fast, L1 finality is slower.

Key terms

Reorg: Reorganisation where blocks previously in the chain are replaced.
Slashing: Penalty burning part of a validator's stake for provable misbehaviour.
Finality: Point after which reverting a block is economically infeasible.
Merge mining: Reusing one PoW effort to secure two chains, as with LTC and DOGE.

Chapter quiz

4 questions · pass mark 75%

1. What secures Bitcoin's ordering of blocks?
2. Slashing exists to…
3. A reorg means…
4. Why wait for finality rather than one confirmation?

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