HackThisSite — Basic Mission 6

---

Understanding the Cipher

Tested with qwerty123 → got qxgux~79;

The pattern:

• Position 0 → shift by 0 (no change)
• Position 1 → shift by 1
• Position 2 → shift by 2
• ...and so on (operates on ASCII values)

encrypted_char = original_char + position
original_char  = encrypted_char - position

---

Decryption

Encrypted password: 05g9f;<= (or 05g9f;<; — use whatever shown on your level page)

Apply: original = encrypted_char_ASCII - position

Quick Python to decode:

Run it → get the plaintext password → submit.

---

Root Cause

A custom, weak cipher with a fully predictable pattern. The encryption tool itself is publicly available on the same page — making it trivial to test inputs and reverse-engineer the algorithm.

---

Key Takeaway

Never roll your own encryption. Custom ciphers are almost always breakable by pattern analysis. Use proven, standard algorithms.