Working with the Python Cryptographic Library

Question

I'm attempting to add the JWT_PUBLIC and JWT_PRIVATE key functionality to djangorestframework-jwt . This is the section in the documentation which gives details as to how to use it:

To start, I have the following:

from cryptography.hazmat.primitives.asymmetric.rsa import RSAPublicKey, RSAPrivateKey

JWT_SECRET_KEY = 'supercrazysecretjwtstringwowamazing'

JWT_PUBLIC_KEY = RSAPublicKey().encrypt(JWT_SECRET_KEY)

JWT_PRIVAT_KEY = RSAPrivateKey().encrypt(JWT_SECRET_KEY)

However, I am receiving the following error:

TypeError: Can't instantiate abstract class RSAPublicKey with abstract methods encrypt, key_size, public_bytes, public_numbers, verifier, verify

Having looked through the documentation, I am none the wiser as to what the is specifically asking me to do/change.

So, my question/(s) is/are:

1.) How do we use the JWT_PUBLIC_KEY and JWT_PRIVATE_KEY functionality of this package?

2.) What does the " Can't instantiate abstract class X with abstract methods " actually mean in a Python context?

Answer 1

asymmetric crypto (ie having public and private keys) is different from symmetric crypto (ie just having a single secret key). you can't (generally) derive an asymmetric (public/private) key pair from a passphrase, you have to generate them with something like openssl

those docs also look incorrect, the code just passes the private and public keys to PyJWT which in turn expects strings

to solve your problem:

1. start by generating the keypair , and extracting the public part into a separate file
2. change your config to something like:

JWT_ALGORITHM = 'RS256'
JWT_PUBLIC_KEY = open('public.pem').read()
JWT_PRIVATE_KEY = open('private.pem').read()

and things will hopefully work!

looks like I misread the code, you can load keys with something like:

def load_rsa_private_key(path):
    from cryptography.hazmat.backends import default_backend
    from cryptography.hazmat.primitives import serialization

    with open(path, 'rb') as priv:
        private_key = serialization.load_pem_private_key(
            priv.read(), password=None, backend=default_backend())

    return private_key

JWT_PRIVATE_KEY = load_rsa_private_key('keypair.pem')
JWT_PUBLIC_KEY = JWT_PRIVATE_KEY.public_key()

I'm doing it in a function so that it doesn't pollute your config namespace too much