Nakamoto consensus

Nakamoto consensus, introduced by Satoshi Nakamoto in the Bitcoin whitepaper of October 2008, is not a single algorithm but the combination of four pieces: proof of work (PoW), the heaviest-accumulated-work rule (popularly the longest chain), the economic incentives of the block reward and block propagation by gossip. Miners compete to solve a hashing puzzle, and nodes treat as valid the chain with the most accumulated work, not simply the one with more blocks.

It solved the double-spend problem for the first time in a trustless, permissionless setting. Its security rests on the honest-majority assumption: as long as more than 50% of hashrate acts honestly, the honest chain grows faster than any attacking chain. Finality is probabilistic, never absolute: a block is never 100% confirmed, but the probability of reversal falls exponentially with each block added on top, which is where the concept of confirmations comes from.

It is the historical starting point of the entire field of blockchain consensus. Bitcoin's genesis block was mined on 3 January 2009 and the network still uses it today. Variants such as Litecoin and Dogecoin share its principles, and Ethereum relied on it until The Merge in 2022. It is not a formal standard with an RFC or ISO, but a de facto specification. For anyone assessing on-chain infrastructure, it sets the contrast against the later proof-of-stake models.