In password protection, salt is a random string of data (two characters, in traditional crypt implementations) used to modify a password hash.

Salt is added to make it impossible (or at least more difficult) for an attacker to break into a system by pre-compiling large dictionaries of password strings and then comparing them to the crypted strings from the password files. In effect, adding a 2-character salt to a password hash makes more than 600 possible combinations of the same actual password.

One of the side effects of salt is that it causes an actual password to generate two different encrypted strings (when two different salts are used), so multiple users can accidentally choose the same password without making that fact obvious to any user with read access to the crypted strings.

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