code: def sign(self, data, b64=True):
          
          padder = padding.PKCS1v15()
          signer = self.private_key.signer(padder, None)
          if not isinstance(data, six.binary_type):
              data = data.encode('utf_8')
          signer.update(data)
          signed = signer.finalize()
          if b64:
              signed = base64.b64encode(signed)
          return signed
docs: Sign data with the private key and return the signed data.
  
          The signed data will be Base64 encoded if b64 is True.