Deserializing public key with python's cryptography module

Question

I am writing a python script that involves sending a public key over a network. I am using <https://cryptography.io/en/latest/hazmat/primitives/asymmetric/serialization/.>

public_key = self.node.public_key
pem = public_key.public_bytes(
    encoding=serialization.Encoding.PEM,
    format=serialization.PublicFormat.SubjectPublicKeyInfo
)

deserialized_key = load_pem_public_key(pem)

I get the error:

TypeError: load_pem_public_key() missing 1 required positional argument: 'backend'

I am therefore unable to deserialize the key - I am confused because according to the documentation, load_pem_public_key() takes 1 required argument (data) and 1 optional argument (backend).

You should be sending the entire certificate, not just the public key. — user207421
– user207421, Commented Sep 4, 2020 at 9:51
cryptography < 3.1 requires backend arguments. You can get a default backend with from cryptography.hazmat.backends import default_backend and pass default_backend() (note that you must invoke it as a method!) as the argument. You can also upgrade to 3.1+. — Paul Kehrer
– Paul Kehrer, Commented Sep 4, 2020 at 15:58

Anton Perepelitcyn · Accepted Answer · 2020-09-04 09:28:05Z

12

Looks like you use cryptography==3.0 or lower where backend argument is required https://github.com/pyca/cryptography/blob/3.0/src/cryptography/hazmat/primitives/serialization/base.py#L19

Bump to cryptography==3.1 or put something to backend arg

answered Sep 4, 2020 at 9:28

Anton Perepelitcyn

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JBSnorro · Accepted Answer · 2021-01-12 18:11:31Z

0

Even with cryptography==3.1 I still had the problem.

I can't provide the backend arg either because it was triggered in a library (python-jose==3.1). Upgrading to python-jose==3.2 (=current latest) didn't help either.

Installing python-jose-cryptodome==1.3.2 did help.

Relevant section of the python-jose documentation:

Th[e naive python] backend is always installed but any other backend will take precedence if one is installed.

answered Jan 12, 2021 at 18:11

JBSnorro

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