Check key algorithm with Python

Question

Supposing that I have an X509 Certificate as follows:

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

Is there a way to check which algorithm was used in order to generate the key starting from the value (string) above in Python?

Answer 1

You can use the pyOpenSSL library (https://github.com/pyca/pyopenssl).

from OpenSSL import crypto
cert = crypto.load_certificate(crypto.FILETYPE_PEM, cert_string)
cert.get_signature_algorithm()

For more documentation on X509 objects see https://pyopenssl.readthedocs.org/en/latest/api/crypto.html#OpenSSL.crypto.X509