fcrackzip

What is fcrackzip?

fcrackzip is a lightweight, fast password cracker specifically designed for ZIP archives. It supports two attack modes — dictionary (wordlist) and brute-force — and uses the unzip utility to verify candidate passwords. It is commonly encountered in CTF forensics and password attack challenges where a protected ZIP file must be cracked to access its contents.

Installation

# Update packages
sudo apt update

# Install fcrackzip and unzip (unzip is needed to verify passwords)
sudo apt install fcrackzip unzip -y

# Verify installation
fcrackzip --version

Basic Usage

# Dictionary attack using rockyou.txt (most common CTF approach)
fcrackzip -u -D -p /usr/share/wordlists/rockyou.txt protected.zip

# Brute-force attack — lowercase letters, length 1 to 6
fcrackzip -u -b -c a -l 1-6 protected.zip

# Brute-force — alphanumeric (lowercase + digits), length 4 to 8
fcrackzip -u -b -c aA1 -l 4-8 protected.zip

# Brute-force — all printable characters
fcrackzip -u -b -c '!a' -l 1-5 protected.zip

# Verbose output (show each attempt)
fcrackzip -u -v -D -p /usr/share/wordlists/rockyou.txt protected.zip

Key Flags

• -u — Use unzip to verify the correct password (always include this)
• -D — Dictionary attack mode
• -p — Path to the wordlist file
• -b — Brute-force attack mode
• -c a — Charset: a = lowercase, A = uppercase, 1 = digits, ! = special chars
• -l — Password length range (e.g. -l 4-8)
• -v — Verbose mode, show each candidate tried

Common Use Cases

• CTF (Capture The Flag) forensics and password attack challenges
• Recovering passwords from ZIP files you own
• Authorized penetration testing engagements
• Internal security audits involving archived data

Further Reading

Practice on legal targets like TryHackMe, HackTheBox, or hackzia.site labs. Always read the official documentation before using in a live engagement.