Fiat currency is centralized one that is controlled by the government and it is a legal currency . Cryptocurrency is a decentralized currency and is not controlled by a third party influence or any government and it is not accepted as a legal currency . In fiat currency the government decides how much currencies to be circulated and in cryptocurrency  everyone has the same right and this is done in internet . Today there is no currencies backing with gold only ink printed papers Cryptocurrency is a global free system using blockchain technology .