Use rsa sha256 public key to verify signed text in Python

rsa_sha256_signed_verify.py

# packages required but not limited to:
# asn1crypto==0.24.0
# cryptography==2.2.2
# pyOpenSSL==17.5.0
import crypto

# Use the public key file: 'pub_key_filename' to verify
# if 'signed' is a valid one from 'plain_text'
# if it's valid return True, otherwise return False
def verify_signed_text(pub_key_filename, plain_text, signed):
  rsa_public_key = None
  with open(pub_key_filename, 'r') as pub_key_file:
      rsa_public_key = pub_key_file.read()

  pkey = crypto.load_publickey(crypto.FILETYPE_PEM, rsa_public_key)
  x509 = crypto.X509()
  x509.set_pubkey(pkey)

  signed = base64.b64decode(signed) # Skip this if signed text is not encoded

  try:
    crypto.verify(x509, signed,
                  plain_text.encode('utf-8'), 'sha256')
    return True
  except crypto.Error as err:
    return False
  except BaseException as exp:
    return False