What is password cracking?


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What is password cracking? #1
A well-designed password-based authentication system doesn’t store a user’s actual password. This would make it far too easy for a hacker or a malicious insider to gain access to all of the user accounts on the system.

Instead, authentication systems store a password hash, which is the result of sending the password — and a random value called a salt — through a hash function. Hash functions are designed to be one-way, meaning that it is very difficult to determine the input that produces a given output. Since hash functions are also deterministic (meaning that the same input produces the same output), comparing two password hashes (the stored one and the hash of the password provided by a user) is almost as good as comparing the real passwords.

Password cracking refers to the process of extracting passwords from the associated password hash. This can be accomplished in a few different ways:

Dictionary attack: Most people use weak and common passwords. Taking a list of words and adding a few permutations — like substituting $ for s — enables a password cracker to learn a lot of passwords very quickly.
Brute-force guessing attack: There are only so many potential passwords of a given length. While slow, a brute-force attack (trying all possible password combinations) guarantees that an attacker will crack the password eventually.
Hybrid attack: A hybrid attack mixes these two techniques. It starts by checking to see if a password can be cracked using a dictionary attack, then moves on to a brute-force attack if it is unsuccessful.

Most password-cracking or password finder tools enable a hacker to perform any of these types of attacks. This post describes some of the most commonly used password-cracking tools.