Summary: A digital equivalent of paper banknotes. Just like paper banknotes, cryptocurrencies allow users to maintain privacy in digital commercial transactions while ensuring that value is transferred from one party to the other. Cryptocurrencies achieve these properties through various cryptographic techniques. There are two types of cryptocurrencies. The first type has a trusted central institution for issuing digital coins and for preventing double spending. The second type of cryptocurrency is based on peer-to-peer networks; for example Bitcoin (see illustration)