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Hacking the Hacker by Roger A. Grimes

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21Password Hacking

Hacking passwords has always been a popular activity for cyber attackers, although the newer methods have evolved from simple password guessing. The Hollywood notion of the hacker is someone who sits in front of a logon screen and simply guesses the correct password out of thin air. Although this does happen, it is fairly rare. Real password hacking usually involves a lot more guesses or no guessing at all.

Authentication Components

To understand passwords, you really have to understand authentication systems in general. The user (or device), also known as the security principal or subject, must submit something (such as a text label, a certificate, and so on) that uniquely identifies them and their logon to the authentication system service. For most traditional password scenarios, this is a label known as a username.

The subject must then be able to prove ownership of the label, which is usually done by submitting another bit of information tied to the label that only the subject and the authentication system knows and agrees upon. This is what the password is. When the user submits the correct password associated with the username, that proves the subject controls the username, and the system allows them access (in other words, they are authenticated) and may track them while they are accessing the system (which is called accounting or auditing). Most operating systems also ensure that the subject is supposed to access the objects they are trying to ...

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