Bitcoin functions using public-key cryptography, in which a user generates a pair of cryptographic keys: one public and one private. Only the private key can decode information encrypted with the public key; therefore the keys' owner can distribute the public key openly without fear that anyone will be able to use it to gain access to the encrypted information. (The private key, however, must be kept secret and secure.) The public key can be used as an "address" to which other users can send Bitcoins. Anyone wishing to use Bitcoin can create one or more Bitcoin addresses, which are collected and tracked in "wallets". Anyone can send Bitcoins to 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. If the private key for an address is not kept secret, the Bitcoins may be stolen; theft has been documented on numerous occasions.
