How to Use the Command 'fcrackzip' (with Examples)

‘fcrackzip’ is a utility designed to crack and recover lost passwords from ZIP archives. It is an open-source tool available for Unix-like operating systems, allowing users to retrieve otherwise inaccessible data in compressed files by exposing the password through various techniques like brute-force attacks and dictionary attacks. This tool is highly valuable for users who need to access secure zip files when the password is forgotten, all while emphasizing the importance of data recovery and ethical usage.

Use Case 1: Brute-force a password of 4 to 8 alphanumeric characters

Code:

fcrackzip --brute-force --length 4-8 --charset aA1 archive

Motivation:

This use case is particularly useful when you suspect that the ZIP archive password consists of alphanumeric characters and you are aware of the potential length range of 4 to 8 characters. When traditional memory reliance methods fail, executing a structured brute-force attack makes recovering the password feasible.

Explanation:

• --brute-force: This flag initiates the brute-force method, attempting all possible combinations within the given parameters.
• --length 4-8: Specifies the length range of the password as between 4 and 8 characters. This criterion constrains the search area, increasing efficiency.
• --charset aA1: Limits the character set to include only lowercase (a), uppercase (A), and numeric (1) characters, which helps in narrowing the cracking scope to what’s most likely.
• archive: Represents the target ZIP file for the password recovery process.

Example Output:

PASSWORD FOUND!!!!: pw == A1b2 

Use Case 2: Brute-force a 3-character password with lowercase and special characters

Code:

fcrackzip -v --brute-force --length 3 --charset a:$% archive

Motivation:

When you know that the ZIP archive password includes special symbols in addition to lowercase characters, a more targeted attack is necessary. Additionally, using a 3-character password is plausible in scenarios where shorter passwords were encouraged for simplicity, making recovery not overly time-consuming.

Explanation:

• -v: Enables verbose mode, providing detailed output and progress updates during the cracking process, which is useful for monitoring.
• --brute-force: Executes a brute-force attack.
• --length 3: Limits the password length to exactly three characters, streamlining efforts to check only the needed possibilities.
• --charset a:$%: Explicitly includes only lowercase letters (a) and special characters ($, %) in the character set, based on known patterns or configurations.
• archive: The target ZIP file is specified for password recovery.

Example Output:

Trying passwords, elapsed time: 00:00:03
PASSWORD FOUND!!!!: pw == a%$

Use Case 3: Brute-force a password with lowercase and special characters

Code:

fcrackzip --brute-force --length 4 --charset a! archive

Motivation:

This example suits situations where you are sure that the password comprises lowercase letters and special characters, and the length is precisely four. It helps when attempting to retrieve simple passwords that include basic symbolic complexity.

Explanation:

• --brute-force: Conducts a brute-force approach.
• --length 4: Specifies the necessity for the password to be four characters long.
• --charset a!: Implies that the keyspace includes only lowercase letters (a) and the exclamation mark (!).
• archive: The ZIP file source for the attempted password retrieval.

Example Output:

PASSWORD FOUND!!!!: pw == a!b!

Use Case 4: Brute-force a 5-digit numeric password starting at ‘12345’

Code:

fcrackzip --brute-force --length 5 --charset 1 --init-password 12345 archive

Motivation:

This application becomes practical if you suspect or remember the alphanumeric structure forms of the password start from ‘12345’, common in cases where users follow a numeric sequence. By setting an initial guess, you expedite the process.

Explanation:

• --brute-force: Implements a brute-force search.
• --length 5: Restricts search to passwords of exactly five characters.
• --charset 1: Includes only numeric digits in the search space permutations.
• --init-password 12345: Starts the brute-force attempt at ‘12345’, based on an intuitive first guess to streamline the process.
• archive: Represents the archive to be decrypted.

Example Output:

PASSWORD FOUND!!!!: pw == 12347

Use Case 5: Crack a password using a wordlist

Code:

fcrackzip --use-unzip --dictionary --init-password wordlist archive

Motivation:

Employing a wordlist to crack a password is effective when you have a list of potential passwords saved as strings known to the user. This scenario is efficient if the wordlist contains common terms or phrases theorized as user passwords.

Explanation:

• --use-unzip: Uses the unzip method, which is more reliable and accurate for checking potential passwords.
• --dictionary: States that the program should use a dictionary (wordlist) instead of generating the passwords.
• --init-password wordlist: Specifies the file containing the line-by-line password guesses.
• archive: Denotes the ZIP file whose password will be located.

Example Output:

PASSWORD FOUND!!!!: pw == forgotlasttime

Use Case 6: Benchmark cracking performance

Code:

fcrackzip --benchmark

Motivation:

Benchmarking the performance of ‘fcrackzip’ is crucial when you need to understand how well your current setup can handle password cracking tasks. It assesses the potential time requirement and the system’s capacity.

Explanation:

• --benchmark: Initiates a built-in test to evaluate the speed and performance efficiency of the tool on the current hardware setup. This command runs test cycles and outputs the cracking speed.

Example Output:

Trying all files: benchmark test complete - guessed 3400 passwords in 60 seconds.

Conclusion

The ‘fcrackzip’ tool offers diverse methods to tackle the challenge of forgotten or lost passwords in ZIP archives. Whether opting for a brute-force method or employing a wordlist approach, understanding the varied use cases and corresponding commands can simplify this complex process. Each example above illustrates a practical scenario, providing guidance on using the tool effectively and acknowledges the need for continuous ethical consideration in applying such tools.