Overview
We are given two text files. The first contains hint ciphertext, and the second contains the encrypted flag.
Reconnaissance
Decrypting the first file using a Caesar cipher with a shift of 3 yields: "This is the first level. Code is the key."
Exploitation Strategy
We take the key word Code from the decrypted hint and apply Vigenère decryption on the second file, which exposes the flag.
Solution Code
1. Shift first file by 3 -> Key is 'Code'
2. Decrypt second file using Vigenere with key 'Code' -> STG{crypt0_i5_thalav4l1}Flag
STG{crypt0_i5_thalav4l1}