Task 2 : Attacks Against Encrypted Files

How Attackers Recover Weak Passwords

Attackers don't usually try to "break" the encryption itself because that would take far too long with modern cryptography. Instead, they focus on guessing the password that protects the file. The two most common ways of doing this are dictionary attacks and brute-force (or mask) attacks.

Dictionary Attacks

In a dictionary attack, the attacker uses a predefined list of potential passwords, known as a wordlist, and tests each one until the correct password is found. These wordlists often contain leaked passwords from previous breaches, common substitutions like password123, predictable combinations of names and dates, and other patterns that people frequently use. Because many users choose weak or common passwords, dictionary attacks are usually fast and highly effective.

Mask Attacks

Brute-force and mask attacks go one step further. A brute-force attack systematically tries every possible combination of characters until it finds the right one. While this guarantees success eventually, the time it takes grows exponentially with the length and complexity of the password.

Mask attacks aim to reduce that time by limiting guesses to a specific format. For example, trying all combinations of three lowercase letters followed by two digits.

By narrowing the search space, mask attacks strike a balance between speed and thoroughness, especially when the attacker has some idea of how the password might be structured.

Practical tips attackers use (and defenders should know about):

• Start with a wordlist (fast wins). Common lists: rockyou.txt, common-passwords.txt.

• If the wordlist fails, move to targeted wordlists (company names, project names, or data from the target).

• If that fails, try mask or incremental attacks on short passwords (e.g. ?l?l?l?d?d = three lowercase letters + two digits, which is used as a password mask format by password cracking tools).

• Use GPU-accelerated cracking when possible; it dramatically speeds up attacks for some algorithms.

• Keep an eye on resource use: cracking is CPU/GPU intensive. That behaviour can be detected on a monitored endpoint.

Answer the questions below

What is the flag inside the encrypted PDF?

THM{Cr4ck1ng_PDFs_1s_34$y}

What is the flag inside the encrypted zip file?

THM{Cr4ck1n6_z1p$_1s_34$yyyy}

If you enjoyed diving into this challenge and sharpening your offensive-security skills, you’re going to love what’s coming next. I regularly publish practical walkthroughs, real-world cybersecurity techniques, and deep-dive tutorials designed to level up your hacking game.

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