"ValueError: Fernet key must be 32 url-safe base64-encoded bytes." When converting str to fernet key

I’m trying to convert a raw string password into a fernet key. This code doesn’t work:

# Convert the string to bytes
key_bytes = self.PrintPassword.encode()

# Base64 encode the bytes
base64_encoded_key = base64.urlsafe_b64encode(key_bytes)

# Create a Fernet key using the encoded bytes
fernet_key = base64.urlsafe_b64decode(base64_encoded_key)

self. Fern = Fernet(fernet_key)

>Solution :

Your string should be 32 bytes long.
to ensure this size, you can hash it and then pass it to your function like this:

from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC
from cryptography.fernet import Fernet
import os
import base64

class YourClass:
    def __init__(self, password):
        self.password = password

    def generate_fernet_key(self):
        # Convert the password to bytes if it's not already
        password_bytes = self.password.encode()

        # Generate a salt
        salt = os.urandom(16)

        # Use PBKDF2HMAC to derive a secure key from the password
        kdf = PBKDF2HMAC(
            algorithm=hashes.SHA256(),
            length=32,  # Fernet keys are 32 bytes
            salt=salt,
            iterations=100000,
            backend=default_backend()
        )
        key = base64.urlsafe_b64encode(kdf.derive(password_bytes))
        self.fern = Fernet(key)

        # Optionally, return the key and salt for storage
        return key, salt

# Example usage
your_class_instance = YourClass("your_password_here")
fernet_key, salt = your_class_instance.generate_fernet_key()

Now you can use your_class_instance.fern for encryption/decryption

This is how you can encrypt/decrypt data:

encrypted = your_class_instance.fern.encrypt(b"my secret data123")
decrypted = your_class_instance.fern.decrypt(encrypted)