A cryptocurrency (or crypto currency) is a digital asset designed to work as a medium of exchange using cryptography to secure the transactions and to control the creation of additional units of the currency.[1] Cryptocurrencies are a subset of alternative currencies, or specifically of digital currencies.
Bitcoin became the first decentralized cryptocurrency in 2009.[2] Since then, numerous cryptocurrencies have been created.[3] These are frequently called altcoins, as a blend of bitcoin alternative.[4][5] Bitcoin and its derivatives use decentralized control[6] as opposed to centralized electronic money/centralized banking systems.[7] The decentralized control is related to the use of bitcoin's blockchain transaction database in the role of a distributed ledger.[8]