Introduction! A cryptocurrency is a type of currency which uses digital files as money. Usually, the files are created using the same methods as cryptography (the science of hiding information). Digital signatures can be used to keep the transactions secure, and let other people check that the transactions are real. The first cryptocurrencies were made to be independent of government-issued currencies. Cryptocurrencies use 'decentralized control',[4] which means that they aren't controlled by one person or government. This is different to 'centralized' electronic money and central banks. The control of each cryptocurrency works through a distributed ledger (a list of transactions shared by everyone), usually a blockchain, that serves as a public financial transaction database.Bitcoin, first released as open-source software in 2009, is often called the first decentralized cryptocurrency.[ Since then, over 4,000 cryptocurrencies (sometimes called ' altcoins '