Extract a public key from certificate

Question

I’m trying to extract a public key from my certificate but i keep getting this error: ValueError: RSA key format is not supported.. Below is my code:

from Crypto.PublicKey import RSA

bob_crt = 'bob.crt'

public_key = RSA.import_key(bob_crt)
if isinstance(public_key, RSA.RsaKey):
    print("RSA public key")
else:
    print("Other key")

This is the certififcate, its a x.509. Do i convert it to a PEM? I’m really confused. Any help would be great. I’m using Python.

Error is below:

Traceback (most recent call last):
  File "C:UsersDocumentstestencryptionencrypt.py", line 91, in <module>
    public_key = RSA.import_key(bob_crt)
  File "C:Usersvenvlibsite-packagesCryptoPublicKeyRSA.py", line 791, in import_key
    raise ValueError("RSA key format is not supported")
ValueError: RSA key format is not supported

Process finished with exit code 1

Thanks

Asked By: coder

||

Source

Answer 1

RSA.import_key expects the content, not the filename. If you read the content first, your script works.

from Crypto.PublicKey import RSA

with open("bob.crt") as f:
    bob_crt = f.read()

public_key = RSA.import_key(bob_crt)
if isinstance(public_key, RSA.RsaKey):
    print(public_key.export_key())
else:
    print("Other key")

Answered By: kosciej16

Extract a public key from certificate

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