Authentication

Forms of Authentication

• Something you know: passwords
• Something you have: smart card
• Something you are: fingerprint

Salt

• Pick a random number—12 bits, for Unix—and use it to modify the password-hashing algorithm
• Store the salt (unprotected) with the hashed password
• Prevent the same password from hashing to the same value on different machines or for different users
• Makes dictionary of precomputed hashed passwords much more expensive
• Doesn’t make the attack on a single password harder; makes attacks trying to find some password 4096× harder

Shadowed Password File

In the Linux operating system, a shadow password file is a system file in which encryption user password are stored so that they aren't available to people who try to break into the system.

Two Factor authentication

Two-factor authentication provides unambiguous identification of users by means of the combination of two different components. These components may be something that the user knows, something that the user possesses or something that is inseparable from the user.