Vigenere

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

cat cipher.txt

Cipher text: rgnoDVD{O0NU_WQ3_G1G3O3T3_A1AH3S_2951c89f}

It says it is a Vigenere cipher (from title) and in the description it says the key is "CYLAB".

Flag: picoCTF{D0NT_US3_V1G3N3R3_C1PH3R_29...}