What is a Brute Force Attack?

A brute force attack consists of trying every possible code, combination, or password until you find the right one.

Determining the Difficulty of a Brute Force Attack

The difficulty of a brute force attack depends on several factors, such as:

How long can the key be?
How many possible values can each component of the key have?
How long will it take to attempt each key?
Is there a mechanism which will lock the attacker out after a number of failed attempts?

As an example, imagine a system which only allows 4 digit PIN codes. This means that there are a maximum of 10,000 possible PIN combinations.

Increasing Security Against a Brute Force Attack

From the example above, PIN security could be increased by:

Increasing the length of the PIN
Allowing the PIN to contain characters other than numbers, such as * or #
Imposing a 30 second delay between failed authentication attempts
Locking the account after 5 failed authentication attempts

A brute force attack will always succeed, eventually. However, brute force attacks against systems with sufficiently long key sizes may require billions of years to complete.

Brute Force Attacks vs. Dictionary Attacks

In most cases, a dictionary attack will work more quickly than a brute force attack. A brute force attack is, however, more certain to achieve results eventually than a dictionary attack.