encryption.py

from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes, serialization
from cryptography.hazmat.primitives.asymmetric import padding, rsa


def create_decryptor(private_location, public_location):
    try:
        with open(private_location, "rb") as key_file:
            private_key = serialization.load_pem_private_key(
                key_file.read(),
                password=None,
                backend=default_backend()
            )
    except FileNotFoundError:
        with open(private_location, "wb") as key_file:
            private_key = rsa.generate_private_key(
                public_exponent=65537,
                key_size=2048,
                backend=default_backend()
            )
            key_file.write(private_key.private_bytes(
                encoding=serialization.Encoding.PEM,
                format=serialization.PrivateFormat.TraditionalOpenSSL,
                encryption_algorithm=serialization.NoEncryption()
            ))

    with open(public_location, "wb") as public_file:
        public_key = private_key.public_key()
        pem = public_key.public_bytes(
            encoding=serialization.Encoding.PEM,
            format=serialization.PublicFormat.SubjectPublicKeyInfo
        )
        public_file.write(pem)

    def decrypt(ciphertext):
        return private_key.decrypt(
            ciphertext,
            padding.OAEP(
                mgf=padding.MGF1(algorithm=hashes.SHA1()),
                algorithm=hashes.SHA1(),
                label=None
            )
        )

    return decrypt


decrypt = create_decryptor("privkey", "server/pubkey.txt")