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Dictionary attack is a common cybersecurity threat where attackers use predefined lists of common passwords to gain unauthorized access. Understand how it works, see examples, and discover effective ways to protect your accounts with strong passwords and multi-factor authentication.
Dictionary attack definition
A dictionary attack is a method of breaking into a password-protected system by systematically entering every word in a predefined list of words, called a “dictionary.” The idea behind this attack is that many people use simple, common passwords that are likely to be found in the dictionary.
This attack is applicable in two situations:
- In cryptanalysis, to discover the decryption key for obtaining the plaintext from a ciphertext
- In computer security, to bypass authentication and access the control mechanism of the computer by guessing passwords
Methods to improve the success of a dictionary attack:
- Use of several different dictionaries, such as technical and foreign dictionaries, which increases the number of possibilities
- Use of string manipulation along with the dictionary (e.g., if the dictionary contains the word “system,” string manipulation creates anagrams like “metsys,” among others)
How a Dictionary Attack Works:
Creation of a Dictionary:
- The attacker creates or obtains a list of common passwords. This “dictionary” can include actual words, common passwords (like “123456”, “password”, “qwerty”), names, or even phrases.
- This list might also include variations of words with numbers or special characters (e.g., “password1”, “p@ssword”, “welcome123”).
Automated Guessing:
- The attacker uses an automated tool or script that systematically attempts each word in the dictionary as the password for a targeted account.
Matching:
- If the correct password is in the dictionary, the tool will find it, allowing the attacker to gain access to the account.
Outcome:
- If the password is strong and not found in the dictionary, the attack will fail. But if the password is common or weak, the attack is likely to succeed.
Example of a Dictionary Attack
Imagine an attacker trying to break into an online account where the user’s password is “welcome123.”
- The Attacker’s Dictionary:
- The attacker has a list of common passwords, which might look like this:
123456
password
welcome
welcome123
qwerty
123456789
letmein
iloveyou- Notice that “welcome123” is included in this list because it’s a commonly used password.
- The Attack:
- The attacker runs an automated tool to try each password in the list against the account.
- The tool tries “123456”—it fails.
- It tries “password”—it fails.
- It tries “welcome”—it fails.
- Finally, it tries “welcome123″—and it succeeds! The attacker now has access to the account.
- Result:
- Because the user chose a common password, the dictionary attack was successful.
Foreign Dictionary Attack:
A foreign dictionary attack is similar but involves the use of dictionaries or word lists in foreign languages. This can be effective if a user has chosen a password based on words from a non-English language. For example, if the user’s password is “bonjour” (which means “hello” in French), and the attacker is using a French word list, they might successfully crack the password.
Example of a Foreign Dictionary Attack:
Suppose an attacker knows that a target is French-speaking and thus might use French words as passwords. The attacker might use a dictionary that includes common French words like:
- “amour” (love)
- “chocolat” (chocolate)
- “bonjour” (hello)
If the target’s password is “chocolat,” the attacker would be able to crack it using this method.
sring manipulation algorithms for dictionary attack
Dictionary attacks often leverage specific string manipulation algorithms to increase their effectiveness. These algorithms modify the original dictionary words in various ways to cover more potential password combinations. Below are some common string manipulation techniques and algorithms used in dictionary attacks:
1. Appending Numbers
- Algorithm: Append numbers to the end of each word.
- Example:
- Word:
password - Manipulated:
password1,password123,password2023
- Word:
2. Character Substitution (Leet Speak)
- Algorithm: Replace certain letters with numbers or special characters that look similar (often referred to as “leet” or “1337” speak).
- Example:
- Word:
password - Manipulated:
p@ssw0rd,pa$$w0rd,p4ssword
- Word:
3. Case Variation
- Algorithm: Change the case of letters in the word, often focusing on the first letter or applying title case.
- Example:
- Word:
password - Manipulated:
Password,PASSWORD,pAssword
- Word:
4. Prepending Characters
- Algorithm: Add characters to the beginning of the word.
- Example:
- Word:
password - Manipulated:
1password,!password,2023password
- Word:
5. Concatenation
- Algorithm: Combine two or more dictionary words together to form a longer password.
- Example:
- Words:
hello,world - Manipulated:
helloworld,worldhello,hello123world
- Words:
6. Reversing the Word
- Algorithm: Reverse the order of characters in the word.
- Example:
- Word:
password - Manipulated:
drowssap
- Word:
7. Insertion of Special Characters
- Algorithm: Insert special characters within the word at random or predefined positions.
- Example:
- Word:
password - Manipulated:
pass@word,pa$$word,pass.word
- Word:
8. Doubling Characters
- Algorithm: Repeat certain characters in the word.
- Example:
- Word:
password - Manipulated:
paassword,passwoord,passwword
- Word:
9. Shuffling Characters
- Algorithm: Shuffle the order of characters within the word.
- Example:
- Word:
password - Manipulated:
apswsord,pwsasord
- Word:
10. Hybrid Approaches
- Algorithm: Combine two or more of the above techniques to create complex password variations.
- Example:
- Word:
password - Manipulated:
P@ssw0rd123,2023P@ssw0rd!
- Word:
Best tool for the dictionary attack
Several tools are popular for conducting dictionary attacks, each with its strengths and use cases. Here are some of the best tools, depending on the context:
1. John the Ripper
- Overview: John the Ripper is a widely-used password cracking tool that supports various attack modes, including dictionary attacks. It’s highly customizable and can handle different hash types.
- Best For: Cracking Unix/Linux passwords, Windows LM/NTLM hashes, and others.
- Key Features:
- Extensive support for different hash types.
- Can combine dictionary attacks with brute force.
- Supports wordlist manipulation and rules.
- Platform: Cross-platform (Linux, Windows, macOS).
2. Hashcat
- Overview: Hashcat is one of the fastest password-cracking tools available, supporting various attack modes, including dictionary attacks. It’s known for its ability to leverage GPU acceleration, making it extremely fast.
- Best For: Cracking a wide range of hash types quickly, including bcrypt, SHA-256, MD5, and more.
- Key Features:
- GPU acceleration for high-speed cracking.
- Supports hybrid attacks, combinatorial attacks, and mask attacks alongside dictionary attacks.
- Highly customizable rule-based attacks.
- Platform: Cross-platform (Linux, Windows, macOS).
3. Hydra
- Overview: Hydra is a powerful tool for performing dictionary attacks against network services. It’s commonly used for testing the strength of passwords for remote services.
- Best For: Brute force and dictionary attacks against online services like SSH, FTP, HTTP, MySQL, and more.
- Key Features:
- Supports a wide range of protocols and services.
- Parallelized to perform attacks quickly.
- Can be combined with proxy servers for anonymization.
- Platform: Cross-platform (Linux, Windows, macOS).
4. Aircrack-ng
- Overview: Aircrack-ng is a comprehensive suite of tools for assessing Wi-Fi network security. It’s widely used for performing dictionary attacks on WPA/WPA2-PSK passwords.
- Best For: Cracking Wi-Fi passwords using captured handshake data.
- Key Features:
- Captures network handshakes and performs dictionary attacks on them.
- Supports various wireless network protocols.
- Works well with large wordlists.
- Platform: Primarily Linux, but also supports Windows and macOS.
5. Cain & Abel
- Overview: Cain & Abel is a password recovery tool for Microsoft Windows that offers various features, including dictionary attacks. While not as powerful as Hashcat or John the Ripper, it is user-friendly and provides various attack methods.
- Best For: Recovering passwords on Windows, including LM and NTLM hashes, and performing dictionary attacks.
- Key Features:
- User-friendly interface.
- Supports various network sniffing and password recovery methods.
- Capable of dictionary attacks on Windows passwords.
- Platform: Windows.
6. Medusa
- Overview: Medusa is a speedy, parallel, and modular brute-forcer, which makes it an excellent tool for dictionary attacks against various protocols.
- Best For: Network-based dictionary attacks, especially on remote services.
- Key Features:
- Modular architecture, supporting different protocols like FTP, HTTP, SMB, etc.
- Supports parallel attacks, making it faster.
- Simple and scriptable for automated attacks.
- Platform: Linux, Windows, macOS.
Which Tool is the Best?
The “best” tool depends on what you’re trying to achieve:
- For cracking password hashes: Hashcat is generally the best due to its speed, especially when using GPUs.
- For network services: Hydra or Medusa are excellent choices.
- For Wi-Fi networks: Aircrack-ng is specialized for this purpose.
- For a general-purpose, cross-platform tool: John the Ripper is very versatile and works well in various scenarios.
How to Protect Against Dictionary Attacks:
Use Strong Passwords:
- Avoid common words, phrases, or patterns. Instead, use a combination of upper and lower-case letters, numbers, and special characters.
- Example: “P@ssw0rd!234” is much stronger than “password123.”
Long Passwords:
- Longer passwords are harder to guess. Aim for at least 12 characters.
Multi-Factor Authentication (MFA):
- Even if an attacker guesses your password, MFA (like a code sent to your phone) adds an additional layer of security.
Password Managers:
- Use a password manager to create and store complex, unique passwords for each of your accounts.
Conclusion:
A dictionary attack exploits the tendency of people to choose simple, easy-to-remember passwords. By understanding how this attack works and taking steps to create strong, unique passwords, you can significantly reduce the risk of falling victim to it.
