What Is zip2john?
zip2john is part of the John the Ripper suite, used to extract password hashes from ZIP files.
In CTF challenges, ZIP archives are frequently password-protected to hide flags. zip2john allows you to convert the ZIP file into a hash format that John the Ripper can attempt to crack.
Key points:
- Works on standard and encrypted ZIP files
- Extracts hash without decrypting the archive
- Enables brute-force or dictionary attacks on ZIP passwords
Basic Usage
- Extract the hash from the ZIP:
zip2john protected.zip > zip_hash.txt
- Crack the password using John the Ripper:
john zip_hash.txt
- Once cracked, John will display the password used to encrypt the ZIP file.
- You can then unzip the archive:
unzip -P <password> protected.zip
How zip2john Is Used in CTF Challenges
1. Detecting Password-Protected ZIP Files
If zipinfo or unzip -l indicates:
Encrypted: yes
Use zip2john to extract the password hash.
2. Extracting Password Hashes for Cracking
zip2john converts ZIP encryption into a format suitable for John:
zip2john challenge.zip > hash.txt
- This allows dictionary or brute-force attacks
- Supports older ZIP encryption and AES-encrypted ZIPs
3. Integration With Other Tools
zip2john is often used together with:
- John the Ripper → crack password
- zipinfo → check if ZIP is encrypted
- unzip → extract decrypted files once password is found
Example workflow:
zipinfo challenge.zip zip2john challenge.zip > hash.txt john hash.txt unzip -P $(john --show hash.txt) challenge.zip
Common Patterns in CTF ZIP Challenges
| Pattern | Description | How zip2john Helps |
|---|---|---|
| Flag in password-protected ZIP | Challenge requires decrypting ZIP | Extract hash to crack password |
| Simple password | Dictionary-based passwords (like “CTF2025”) | John can quickly find password |
| Complex password | Longer or mixed-character passwords | Use wordlists or rules in John |
| Multiple ZIP layers | ZIP inside ZIP | Extract each ZIP’s hash and crack sequentially |
| Known pattern | Password hint in challenge text | Combine hints with dictionary attacks |
Recommended Workflow in CTF
- Check if the ZIP is encrypted:
zipinfo challenge.zip
- Extract the hash:
zip2john challenge.zip > zip_hash.txt
- Crack the password with John the Ripper:
john zip_hash.txt
- Use the discovered password to extract the files:
unzip -P <password> challenge.zip
- Analyze extracted files for flags:
- Use
strings,binwalk, orexiftoolfor hidden data - Look for common CTF flag patterns like
FLAG{…}
zip2john is an essential tool in CTF forensics, allowing you to handle encrypted ZIP files efficiently and extract hidden flags without manually guessing passwords.
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