Courtroom Hash

The final evidence packet contains a short ciphertext and a note from the forensic lead:

• Pick three words recovered from earlier stages.
• Concatenate them as the Vigenère key.
• Lowercase, no separators.

Use the relevant recovered words from earlier stages as a Vigenère key, then decrypt the packet. The flag is the recovered phrase in lowercase, with words separated by underscores.

cipher = gviiysfjegwcwaceef
cipher_system = Vigenere
alphabet = a=0, b=1, ..., z=25