python 3 txt文件数字签名和验证

from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.asymmetric import padding
from cryptography.hazmat.primitives.asymmetric import rsa
from cryptography.hazmat.primitives import serialization

private_key = rsa.generate_private_key(
    public_exponent=65537,
    key_size=2048
)
public_key = private_key.public_key()

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

signature = private_key.sign(
    data,
    padding.PSS(
        mgf=padding.MGF1(hashes.SHA256()),
        salt_length=padding.PSS.MAX_LENGTH
    ),
    hashes.SHA256()
)

with open('signature.txt', 'wb') as file:
    file.write(signature)

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

with open('signature.txt', 'rb') as file:
    signature = file.read()

try:
    public_key.verify(
        signature,
        data,
        padding.PSS(
            mgf=padding.MGF1(hashes.SHA256()),
            salt_length=padding.PSS.MAX_LENGTH
        ),
        hashes.SHA256()
    )
    print("Signature is valid.")
except:
    print("Signature is invalid.")