code: def _load_rsa_private_key(pem):
      
      # ADB uses private RSA keys in pkcs#8 format. 'rsa' library doesn't support
      # them natively. Do some ASN unwrapping to extract naked RSA key
      # (in der-encoded form). See https://www.ietf.org/rfc/rfc2313.txt.
      # Also http://superuser.com/a/606266.
      try:
          der = rsa.pem.load_pem(pem, 'PRIVATE KEY')
          keyinfo, _ = decoder.decode(der)
          if keyinfo[1][0] != univ.ObjectIdentifier(
                  '1.2.840.113549.1.1.1'):  # pragma: no cover
              raise ValueError('Not a DER-encoded OpenSSL private RSA key')
          private_key_der = keyinfo[2].asOctets()
      except IndexError:  # pragma: no cover
          raise ValueError('Not a DER-encoded OpenSSL private RSA key')
      return rsa.PrivateKey.load_pkcs1(private_key_der, format='DER')
docs: PEM encoded PKCS#8 private key -> rsa.PrivateKey.