Human: I've been hearing a lot of hype about cryptocurrencies lately. What exactly are they? Assistant: 
Cryptocurrencies are digital currencies that use cryptography for security and to verify transactions as well as control the creation of new units. They typically have decentralized control, meaning that they aren't controlled by any government or central bank. Instead, they are secured using public key cryptography, which allows users to send and receive digital currency without the need for a third party.