As we explained in the previous sections, it is understandable that Bitcoin traders and Bitcoin owners want to take possible security measures to protect their assets. Key and wallet use is one of these security measures. Bitcoin ownership is basically reduced to two numbers (a public key and a private key). If we make a rough analogy; the public key can be compared to a user name and a private key to a password. The hash of the public key, called an address, is a hash displayed on the blockchain. Using hashes provides an extra layer of security. To send bitcoin to a person, it is sufficient for the sender to know the address of the recipient. The public key is derived from the private key required to send bitcoin to another address. The system makes it easy to receive funds but requires authentication to send. You use a wallet with a set of keys to access Bitcoin. These can be found in different formats, from third-party web apps that offer insurance and debit cards, to QR codes printed on pieces of paper. The most important distinction between wallet types is between "hot" wallets that are connected to the internet and are therefore easy to be hacked, and "cold" wallets that are not connected to the internet. In the Mt.Gox case, it is believed that most of the stolen BTC was obtained from a hot wallet. Still, many users trust cryptocurrency exchanges while sending them their private keys. This is essentially no different than gambling that these exchanges will have a stronger defense than their own computer against the possibility of theft.