Authentication is an important process of a internet service for authenticating users. For example, when you register an account for Yahoo mail, you will be asked for an ID and password so that only you can access to your email account. That means Yahoo will save your ID and your password in their servers so that they can compare with your input later. Your ID can be saved in clear text but the password will not be never saved under clear text. Yahoo uses its own algorithmus to make a hash of your password. For example your password is “123456789”, then Yahoo may save it as format “25f9e794323b453885f5181f1b624d0b”. In this way only you know the password and if the server is attacked, your password will be still safe. Furthermore password hash protects you from losing password through snipping on network connection.