A cryptocurrency (or crypto-currency) is a digital asset designed to function as a means of exchange using powerful cryptography to secure financial transactions, control the creation of additional units and verify the transfer of assets. Cryptocurrencies use decentralized control as opposed to centralized systems of digital money and central banks . Decentralized control of each cryptocurrency works through a distributed ledger technology, typically a blockchain, that serves as a public database of financial transactions.  Bitcoin, published for the first time. As open-source software in 2009, it is generally considered the first decentralized cryptocurrency. Since the publication of Bitcoin, more than 4,000 altcoins have been created (alternative variants of Bitcoin or other crypto-currencies). The decentralized cryptocurrency is produced collectively by the entire cryptocurrency system, at a rate defined during the creation of the system and known to the public. In centralized banking and economic systems such as the Federal Reserve, boards of directors or governments control the supply of foreign currency by printing fiduciary money units or by requiring additions to the digital banking records. In the case of decentralized cryptocurrency, businesses and governments can not produce new units and have not yet provided support to other companies, banks or companies with measured asset values. The underlying technical system on which the decentralized crypto-currencies are based was created by the group or the individual named Satoshi Nakamoto.  In May 2018, there were more than 1,800 cryptocurrency specifications.  Within a cryptocurrency system, the security, integrity, and balance of the ledgers is ensured by a community of suspicious and mistrustful miners who use their computers to help validate and time stamp them. transactions, adding them to the ledger according to a particular timestamp scheme. Most cryptocurrencies are designed to gradually reduce the production of this currency, limiting the total amount of this currency that will be in circulation. Compared to ordinary currencies held by financial institutions or kept in cash, crypto-currencies may be more difficult for law enforcement to seize. This difficulty comes from the use of cryptographic technologies.