What is Proof of Work?

How do thousands of computers agree on who paid whom, without a bank in the middle? In Bitcoin, the answer rests on a computing contest: mining.

Miners bundle transactions into a candidate block and try different values again and again until they find a digital fingerprint (hash) that meets the network’s difficulty target. Picture a padlock that opens only with certain combinations: there’s no shortcut, it takes many attempts. The more computing power someone has, the more attempts they can make.

Finding the solution takes work, but checking it is easy. When a miner finds a suitable hash, it broadcasts the block to the network. Nodes check both the proof of work and the transactions. A block with invalid transactions is rejected, no matter how much electricity was spent on it. For a valid block that joins the accepted chain, the miner can collect the block reward and the transaction fees.

Why it matters

PoW makes changing the history expensive. In Bitcoin, nodes follow the valid chain with the most accumulated work, not simply the one with the most blocks. To replace old transactions, someone would have to redo the corresponding work and overtake the chain that everyone else keeps building.

If you receive crypto, this explains why transaction confirmations matter. The more blocks are added after the one that contains your transaction, the harder it becomes to reverse. You don’t need to mine to use such a network.

What to watch out for

This security comes at a cost in electricity and equipment. Access to cheap power and specialized machines can also favor the concentration of mining. We believe a fair assessment of PoW needs both sides: the protection it offers and the resources it consumes.

It isn’t invulnerable. Someone who controls the majority of the computing power could attempt to reorganize recent blocks or double-spend their own coins. That doesn’t let them sign transactions from your wallet or arbitrarily bypass the network’s rules.