Brute force attack

Brute Force Attack is the most widely known password cracking method. This attack simply tries to use every possible character combination as a password. To recover a one-character password it is enough to try 26 combinations (‘a’ to ‘z’). It is guaranteed that you will find the password

.. but when? How long will it take? The two-character password will require 26*26=676 combinations. The number of possible combinations (and therefore required time) grows rapidly as the length of the password increases and this method quickly becomes useless. Do you ready to wait for two months while your 9-character password is cracked? What about one hundred years for an 11-character password? Besides the maximal length of the character set you should also specify the character set i.e. the list of characters that will be included in the combinations. The longer the character set is, the longer the required period of time is. Here is the problem: usually you have no idea of what characters are present in the password. On the one hand, you should specify all possible characters. On the other hand, this can slow things down very much. Unfortunately, there are no common ways to determine what character set to use. It is more a question of luck and intuition. The only thing I can recommend is to begin with trying short passwords using the full character set. Then you can increase the length of password simultaneously decreasing the character set to keep the required time good acceptable.

If the password is case sensitive (this is the most common situation), there is another problem with the case. 

There are three options: 

1) you can assume that the password was typed in lower case (this is most likely). In this case, the required time will stay the same but if the password contains upper case letters it will not be recovered. 

2) you can try all combinations. 

The password is guaranteed to be found, but the process slows down significantly. A 7-character lower case password requires about 4 hours to be recovered but if you would like to try all combinations of upper case and lower case letters, it will require 23 days. 3) The third method is trade-off. Only the most probable combinations are taken into consideration, for example "password", "PASSWORD" and "Password". The complicated combinations like "pAssWOrD" are not. In this particular case the process slows down to one third of original speed but there is still a possibility to fail. 

You can reduce the amount of time required using faster computers (only the CPU speed is important. The amount of RAM, the performance of the hard drive and other hardware don’t affect the brute force speed), using several computers, choosing the fastest password crackers or tuning the brute force parameters wisely and accurately.