PoWs

Proof of Work (PoW) is a consensus mechanism used by several blockchain networks in which participants, known as miners, expend computational resources to solve cryptographic puzzles. The first miner to solve the puzzle earns the right to add a new block of transactions to the blockchain and receives a block reward in the network's native cryptocurrency. The approach secures the network by making block creation energy-intensive, so altering past blocks would require controlling a majority of the network's hashing power.

How it works: Each block header includes a nonce; miners repeatedly hash the block data with different nonces until they find a hash below a target threshold. The difficulty of the puzzle is adjusted periodically to keep block times approximately constant. When a valid hash is found, the new block is broadcast and other nodes verify it before appending it to their local copy of the chain. The chain considered valid is typically the one with the most cumulative difficulty, i.e., the "heaviest" chain.

Advantages and criticisms: PoW provides strong security through economic incentives and has a simple, battle-tested design that supports decentralization by allowing widespread participation. However, it is criticized for high energy consumption, potential centralization due to specialized hardware and cheap electricity, and environmental concerns. It is often contrasted with Proof of Stake (PoS), which aims to achieve consensus with staking instead of intensive computation.

Examples: Bitcoin and Litecoin are prominent PoW networks using different hashing algorithms (SHA-256 and scrypt, respectively). Ethereum originally used PoW but transitioned to PoS in 2022, raising PoW usage on the mainnet.