A cryptocurrency wallet stores the public and private keys which can be used to receive or spend a cryptocurrency. A wallet can contain multiple public and private key pairs. As of January 2018, there are over thirteen hundred cryptocurrencies; the first and best known is bitcoin. The cryptocurrency itself is not in the wallet. In case of bitcoin and cryptocurrencies derived from it, the cryptocurrency is DE centrally stored and maintained in a publicly available ledger. Every piece of cryptocurrency has a private key. With the private key, it is possible to digitally sign a transaction and write it in the public ledger, effectively spending the associated cryptocurrency.