Or just use python script that i've found in internet
import base64 as b
with open("enc_flag", "r") as file:
cipher = file.readlines()
cipher = "".join([i.strip() for i in cipher])
plain = b.b64decode(cipher).decode()
while "picoCTF" not in plain:
plain = b.b64decode(plain).decode()
print(plain)
