Brute Force Attack

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A Brute Force Attack also known as an Exhaustive Search is a method of cracking a password where every possible combination is tried. Because of this, brute force attacks are always successful, however, they usually take so much time, they're not worth using.

A mechanical example of a brute force attack is trying every possible combination on a combination lock. This is a tedious process, as even a simple combination lock where the dial has only 30 places and the lock uses three numbers, would require 75 hours to check every combination if we assume it takes 10 seconds per attempt.

A similar system is used with password cracking on computers, where you first try password "a," then "b," and on to "z," then "aa," "ab," and so on. The number of passwords you need to try grows exponentially the longer the password gets.

Brute force attacks have legitimate uses, like when you've forgotten your password. However, they're mostly used for nefarious purposes.

Process

At its most basic level, a brute force attack is a three step process:

  1. Generate the next password.
  2. Try the password.
  3. If the password was not successful, go to step 1.

Step 2 is the most difficult step because many systems make it difficult to automate trying a password specifically to prevent brute force attacks.

Accelerating the Process

In computer systems, passwords almost always allow the letters a-z, capital A-Z, numbers 0-9, and a host of special characters like !@#$%^&*. If we assume 100 possible characters, and the password is at most eight characters long, it means we will have to try 10,101,010,101,010,101 total passwords. If we assume our PC can try 1,000,000,000 passwords a second, it will take about 116 days to try every password, and for a nine-character-long password, it would take over 32 years! So, why do password crackers even bother with brute force attacks? Because there are several ways to accelerate the process.

Ignoring Unlikely Characters

Unless the system requires an assortment of characters like a capital letter, number, or symbol, most users don't bother with them. Because of this, a brute force system can be setup to only try just the 26 lowercase letters. This results in only 208,827,064,576 possible

Simulating the Log In Process

Setting up a brute force attack requires being able to simulate the login process with a computer program. For programs that accept command-line arguments (like 7-Zip), this system is already in place. For web sites, it's best to simulate the web site programmatically, while other programs However, some programs require simulating a mouse click or keyboard keystroke which is not too difficult to do.