Anyone wishing to use Bitcoin can create one or more Bitcoin addresses, which are collected and tracked in "wallets". Wallets have public addresses and private keys. Anyone can send Bitcoins to a wallet using the public address provided by the owner of the wallet, while the private key must be entered by the wallet owner to send bitcoins. Securing and protecting the private key is the essence of wallet security. Wallets allow a user to complete transactions between addresses by requesting an update to the blockchain, the public transaction log. Wallets come in a variety of forms: apps for mobile devices and computers, hardware devices, and paper tokens. When making a purchase with a mobile device, the use of QR codes to simplify transactions is ubiquitous.
