from Crypto.PublicKey import RSA
from Crypto.Signature import pss
from Crypto.Hash import SHA256

with open("alice_public.pem", 'rb') as file:
    alice_pub = RSA.import_key(file.read())

with open('sigtext', 'rb') as file:
    data = file.read()

m = data[:18]
sig = data[18:]

h = SHA256.new(m)

verifier = pss.new(alice_pub)

try:
    verifier.verify(h, sig)
    print("Signature is valid")

except (ValueError, TypeError) as e:
    print("Signature is invalid")