Nakamoto Consensus
Bitcoin's consensus design: the longest valid chain wins, with security from proof-of-work and probabilistic finality.
Nakamoto consensus is the mechanism Satoshi introduced with Bitcoin: nodes accept the longest valid chain (the one with the most accumulated proof of work) as truth, and security comes from the economic cost of out-working the honest network. It solved distributed consensus among anonymous, permissionless participants — the breakthrough that made Bitcoin possible.
Its finality is probabilistic: a transaction becomes exponentially harder to reverse with each block added on top (hence waiting for “confirmations”), rather than instantly final as in BFT systems. This trade-off — openness and simplicity in exchange for slower, probabilistic finality — defines Bitcoin’s conservative design and distinguishes it from the faster, more complex consensus models that followed.