The Basics of Password Cracking

In the 19^th century, Auguste Kerckhoff stated that everything about a system should be public knowledge except for the system’s key and this will maintain the overall effectiveness and security of a system. Kerckhoff’s principle remains relevant in terms of cyber security today. Today, passwords are the keys necessary to grant users access to entire software systems, databases, etc. Passwords make it possible to handle security breaches simply by changing the key instead of the entire system behind it; but if you want to prevent future breaches into your system how do you create a key that cannot be broken?

The best way to understand the thought process necessary to creating a secure password is to understand the methods hackers use to crack a password. Password crackers are primarily after root or administrative account passwords which grant the administrator full access and privileges to the operating system. They use systems which rapidly convert passwords into the system’s appropriate hash codes in order to find a match.

There are three methods a password cracker can use to unlock these hidden codes in order to gain unauthorized access to the system:

1. Dictionary Attack

The dictionary attack identifies passwords that are dictionary words. Many businesses and individuals use single dictionary words without combining them with numbers, symbols or upper and lower case letters. If an organization used a single dictionary word as a password, it may only take hackers a few minutes to break the codes.

2. Hybrid Dictionary Attack

Hybrid dictionary attacks take dictionary words and add characters to them, increasing the possibilities significantly and, as a result, increasing the amount of time needed to test them. Hackers create their own dictionaries too, including not just dictionary words but the most common passwords users choose. People use very common conventions when creating a password and hackers are well aware of this fact. They know most people will use a common dictionary word as the root of their password and then make it seemingly complex by beginning with capital letters and ending with numbers. This knowledge allows even a mediocre hacker to crack a password using a hybrid attack within the course of a day.

3. Brute Force

Finally, the brute force attack system guarantees success because it tests every combination of characters on the keyboard including letters, numbers and symbols. After the dictionary and hybrid attacks have been exhausted the brute force is the final attempt. This method will eventually crack the password; however, it can take years upon years to do so; therefore, taking it out of the usable timeframe.

Password Cracking Tools

In order to crack a system, hackers will use certain password cracking tools. Once installed, these systems can test possible hashes without human assistance and often times can go unnoticed by the user. Certain password cracking tools only work on particular operating systems and sometimes only provide one type of attack method.

The most effective and commonly used password cracking tools include:

Cain & Abel

A Windows-only recovery tool, it supports brute force and dictionary attack methods.

THC Hydra

A password recovery tool that uses brute force and dictionary attacks.

Medusa

A newly released password cracker, it is comparable to the THC Hydra in its brute force methods.

John the Ripper

A UNIX/Linux and Mac OS X password cracking tool, it comes in both a free community based version and a professional version.

L0phtCrack

The leading Windows cracking tool which uses brute force and dictionary attack methods.

RainbowCrack

Hash cracker that uses time memory trade off; after it pre-computes the cracking-time it is significantly faster at cracking the hash than a regular brute force cracker.

Brutus

A Windows only recovery tool, it uses dictionary attack methods.

If you are interested in learning more about password cracking, enroll in one of our award-winning cyber security training courses.