Proof of work (PoW)

Proof of work is a consensus mechanism in which participants (miners) compete to solve a computational puzzle to earn the right to add the next block. Solving the puzzle requires many guesses, which costs real electricity and hardware, but checking a solution is instant for everyone else.

That asymmetry is the point. To rewrite history, an attacker would have to redo the work for the blocks they want to change and then outpace the honest network, which on a large chain would cost enormous resources. Nodes always follow the valid chain with the most accumulated work.

Bitcoin, Litecoin, Dogecoin and Bitcoin Cash use proof of work. Critics focus on its energy consumption; supporters argue the energy is what anchors the system's security to the physical world. Ethereum used proof of work until it switched to proof of stake in September 2022.