Bitcoin is a peer-to-peer electronic cash system that allows participants to digitally transfer units of bitcoin without a trusted intermediary. Bitcoin combines a public transaction ledger (blockchain), a decentralized currency issuance algorithm (proof-of-work mining), and a transaction verification system (transaction script). Bitcoin has a supply cap of 21 million bitcoin, 95% of which will be mined by the year 2025. Bitcoin relies on Nakamoto consensus, or consensus implied by the longest blockchain that has accumulated the most computational effort.