Roadmap › Blockchain & Web3 Fundamentals › Module: Blockchain Fundamentals
Lessons in this course (15)
3. Consensus mechanisms
Basic★ Must knowLesson 3 of 15
| Mechanism | How blocks are produced | Examples | Trade-offs |
|---|---|---|---|
| Proof of Work | Miners compete to solve a hash puzzle; most cumulative work wins | Bitcoin, Litecoin | Very secure and simple; high energy use; slow |
| Proof of Stake | Validators lock stake; chosen to propose/attest; misbehaviour is slashed | Ethereum (since 2022), Cardano, Solana (PoS + Proof of History) | Energy-efficient, faster finality; complexity, stake concentration |
| Delegated PoS | Token holders vote for a few block producers | EOS, TRON | Fast; more centralised |
| PBFT / BFT variants | Known validators vote in rounds | Hyperledger Fabric (ordering), Tendermint/CometBFT (Cosmos) | Instant finality; limited validator count |
| Proof of Authority | Approved identities sign blocks | Private networks, some testnets | Fast; centralised trust |
Ethereum PoS numbers: validators stake 32 ETH (Pectra raised the max effective balance to 2,048 ETH); a slot is 12 seconds, an epoch is 32 slots (6.4 minutes); finality after ~2 epochs.
51% attack — controlling the majority of hash power (PoW) or stake (PoS) allows reorganising recent blocks/double spending (not stealing arbitrary funds). Double spending is prevented by consensus on transaction order.
Blockchain trilemma (Vitalik Buterin): hard to maximise decentralisation, security and scalability at the same time — hence layer-2 solutions.