Bitcoin is a decentralized digital currency without a central bank or single administrator. It can be sent from user to user on the peer-to-peer bitcoin network without the need for intermediaries. 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. Its implementation was released as open-source software in 2009 and began to be used then.