Vigenere | picoCTF 2022 Solutions

Description

A ciphertext is provided along with the key CYLAB. Use any Vigenère decoder to recover the plaintext flag.

Setup

Download cipher.txt from the challenge artifacts.

Open the file to view the encrypted string.

Feed the ciphertext into a Vigenère decoder (CyberChef, dCode, etc.) with key CYLAB.

wget https://artifacts.picoctf.net/c/160/cipher.txt

cat cipher.txt

Step 1Identify the cipher
The problem statement explicitly names Vigenère. Tools like CyberChef → From Vigenere make decoding trivial.
Step 2Apply the key CYLAB
Enter CYLAB as the key and paste `rgnoDVD{O0NU_WQ3_G1G3O3T3_A1AH3S_2951c89f}` as the input. The decoder outputs the correct picoCTF flag.

picoCTF{D0NT_US3_V1G3N3R3_C1PH3R_29...}

Vigenère is not secure-once the key is known, decoding is instantaneous.