One of the core challenges facing the design of electronic currency is the problem of double spending. If electronic currency is merely information, free from the limitations of tangible paper and metal, how can we prevent people from easily copying and pasting it, spending it however they like, just like copying text? The traditional solution is to use a central clearinghouse to aggregate all transactions into a real-time ledger, so that if someone has just spent an electronic currency, they cannot use it again.