Password cracking is the process of attempting to gain Unauthorized access to restricted systems using common passwords or algorithms that guess passwords. In other words, it’s an art of obtaining the correct password that gives access to a system protected by an authentication method.
Password cracking employs a number of techniques to achieve its goals. The cracking process can involve either comparing stored passwords against word list or use algorithms to generate passwords that match
In this Tutorial, we will introduce you to the common password cracking techniques and the countermeasures you can implement to protect systems against such attacks.
What is password strength?
Password strength is the measure of a password’s efficiency to resist password cracking attacks. The strength of a password is determined by;
- Length: the number of characters the password contains.
- Complexity: does it use a combination of letters, numbers, and symbol?
- Unpredictability: is it something that can be guessed easily by an attacker?
Better to use the password strength indicator on passwordmeter.com when creating passwords.
Let’s suppose that we have to store our above passwords using md5 encryption. We will use an online md5 hash generator to convert our passwords into md5 hashes.
password: flower MD5 hash: 608f0b988db4a96066af7dd8870de96c
password: flower1$ MD5 hash: aa88158aa2735a70532bab723b0781ce
We will now use http://www.md5this.com/ to crack the MD5 hashes.
We can’t manage to crack the password which was longer, complex and unpredictable by this way.
Password cracking techniques
There are a number of techniques that can be used to crack passwords. We will describe the most commonly used ones below;
- Dictionary attack– This method involves the use of a wordlist to compare against user passwords.
- Brute force attack– This method is similar to the dictionary attack. Brute force attacks use algorithms that combine alpha-numeric characters and symbols to come up with passwords for the attack. For example, a password of the value “password” can also be tried as p@$$word using the brute force attack.
- Rainbow table attack– This method uses pre-computed hashes. Let’s assume that we have a database which stores passwords as md5 hashes. We can create another database that has md5 hashes of commonly used passwords. We can then compare the password hash we have against the stored hashes in the database. If a match is found, then we have the password.
- Guess– As the name suggests, this method involves guessing. Passwords such as qwerty, password, admin, etc. are commonly used or set as default passwords. If they have not been changed or if the user is careless when selecting passwords, then they can be easily compromised.
- Spidering– Most organizations use passwords that contain company information. This information can be found on company websites, social media such as facebook, twitter, etc. Spidering gathers information from these sources to come up with word lists. The word list is then used to perform dictionary and brute force attacks.
Spidering sample dictionary attack wordlist
1976 <founder birth year> smith jones <founder name> acme <company name/initials> built|to|last <words in company vision/mission> golfing|chess|soccer <founders hobbies>
Password cracking tool
These are software programs that are used to crack user passwords. We already looked at a similar tool in the above example on password strengths. The website www.md5this.com uses a rainbow table to crack passwords. We will now look at some of the commonly used tools
John the Ripper
John the Ripper uses the command prompt to crack passwords. This makes it suitable for advanced users who are comfortable working with commands. It uses to wordlist to crack passwords. The program is free, but the word list has to be bought. It has free alternative word lists that you can use. Visit the product website http://www.openwall.com/john/ for more information and how to use it.
Cain & Abel
Cain & Abel runs on windows. It is used to recover passwords for user accounts, recovery of Microsoft Access passwords; networking sniffing, etc. Unlike John the Ripper, Cain & Abel uses a graphic user interface. It is very common among newbies and script kiddies because of its simplicity of use. Visit the product website http://www.softpedia.com/get/Security/Decrypting-Decoding/Cain-and-Abel.shtml for more information and how to use it.
Ophcrack is a cross-platform Windows password cracker that uses rainbow tables to crack passwords. It runs on Windows, Linux and Mac OS. It also has a module for brute force attacks among other features. Visit the product website http://ophcrack.sourceforge.net/ for more information and how to use it.
Password Cracking Counter Measures
You can use the following methods to reduce the chances of the passwords been cracked
- Avoid short and easily predicable passwords
- Avoid using passwords with predictable patterns such as 11552266.
- Passwords stored in the database must always be encrypted. For md5 encryptions, its better to salt the password hashes before storing them. Salting involves adding some word to the provided password before creating the hash.
Hacking Activity: Hack Now!
1. Install and run Cain. Immediately when it opens you can see the first disturbing scene. All the cached passwords are shown in the “Protected Storage” tab. These include passwords from IE, Outlook or other HTTP transactions.
2. The “Network” tab is a scaled enumeration system, able of enumerating all Windows computers it can find on the local network.
3.The most interesting (IMHO) feature of Cain is in the “Sniffer” Tab. Cain allows you to ARPSpoof, Sniff and Brute force passwords all via one interface. Notice that the “Sniffer Tab” has 5 sub-tabs- Hosts, APR, DNS Spoofer, Routing and Passwords.
4. To start ARP Spoofing, you need to activate the sniffing daemon and the APR daemon. You do this by clicking on both the “Sniff” and “APR” buttons at the top of the window
5. Make sure you are in the “Sniffer” tab, and right click anywhere inside the tab. You should see a “Scan MAC addresses” option. Click it.
6. Choose the appropriate IP range that suits your local network and click “Ok”.
7. A quick scan should occur, giving you all the MAC addresses present in that subnet.
8. Once the scan is complete, move to the APR sub-tab at the bottom of the window.This is the window in which you choose the computers you want to attack. Now click on the blue “plus” sign at the top of the windows to add hosts to attack.
9. You should get the following screen:
10. Now we wait for the attacked host to enter password data to services such as FTP, HTTP, POP3, IMAP, and lots of others. In the following screenshot, an FTP password was intercepted.
11. We can see that the FTP session between 192.168.1.32 (Attacked Computer) and 126.96.36.199 (Netvision’s FTP server) was router via our computer. Now click on the “Passwords”see the captured passwords.
12. For encrypted passwords such as SMB (NTLM in it’s various flavours) you can send the password to a Brute Force session.
13. After sending the password to the cracker, click on the “Cracker” tab and start the required attack.
This was a quick tutorial about Cain’s ARP Spoofing ability. Apart from ARP Spoofing Cain can do lots of other wonderful things, just take time to *carefully* learn the application.
Let´s do a dictionary attack. You will need to download the dictionary attack wordlist here 10k-Most-Common.zip
- Right click on the account you want to crack. For this tutorial, we will use Accounts as the user account.
- The following screen will appear
- Right click on the dictionary section and select Add to list menu as shown above
- Browse to the 10k most common.txt file that you just downloaded
- Click on start button
- If the user used a simple password like qwerty, then you should be able to get the following results.
- Note: the time taken to crack the password depends on the password strength, complexity and processing power of your machine.
- If the password is not cracked using a dictionary attack, you can try brute force or cryptanalysis attacks.
- Password cracking is the art of recovering stored or transmitted passwords.
- Password strength is determined by the length, complexity, and unpredictability of a password value.
- Common password techniques include dictionary attacks, brute force, rainbow tables, spidering and cracking.
- Password cracking tools simplify the process of cracking passwords.