Bitcoin (₿) is a decentralized digital currency, without a central bank or single administrator, that can be sent from user to user on the peer-to-peer bitcoin network without the need for intermediaries.[7] Transactions are verified by network nodes through cryptography and recorded in a public distributed ledger called a blockchain. The cryptocurrency was invented in 2008 by an unknown person or group of people using the name Satoshi Nakamoto.[8] The currency began use in 2009[9] when its implementation was released as open-source software.[6]:ch. 1 Bitcoin Prevailing bitcoin logo Prevailing bitcoin logo Denominations Plural bitcoins Symbol ₿ (Unicode: U+20BF ₿ BITCOIN SIGN (HTML ₿))[a] Ticker symbol BTC, XBT[b] Precision 10−8 Subunits  1⁄1000 millibitcoin  1⁄100000000 satoshi[2] Development Original author(s) Satoshi Nakamoto White paper "Bitcoin: A Peer-to-Peer Electronic Cash System"[4] Implementation(s) Bitcoin Core Initial release 0.1.0 / 9 January 2009 (12 years ago) Latest release 0.21.1 / 2 May 2021 (2 months ago)[3] Code repository https://github.com/bitcoin/bitcoin Development status Active Website bitcoin.org Ledger Ledger start 3 January 2009 (12 years ago) Timestamping scheme Proof-of-work (partial hash inversion) Hash function SHA-256 Issuance schedule Decentralized (block reward) Initially ₿50 per block, halved every 210,000 blocks[7] Block reward ₿6.25[c] Block time 10 minutes Block explorer Many implementations Circulating supply ₿18,660,000 (as of 20 March 2021) Supply limit ₿21,000,000