Bitcoin is a decentralized digital currency. Bitcoin 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 entity under the name Satoshi Nakamoto. The currency began use in 2009, when its implementation was released as open-source software. : ch. 1 The word "bitcoin" was defined in a white paper published on October 31, 2008. It is a compound of the words bit and coin.