A cryptocurrency 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.Cryptocurrencies are classified as a subset of digital currencies and are also classified as a subset of alternative currencies and virtual currencies.Bitcoin became the first decentralized cryptocurrency in 2009.Since then, numerous cryptocurrencies have been created. These are frequently called altcoins, as a blend of bitcoin alternative. Bitcoin and its derivatives use decentralized control. as opposed to centralized electronic money/centralized banking systems.the decentralized control is related to the use of bitcoin's blockchain transaction database in the role of a distributed ledger.