code: def verify_signature(self, signature, nonce, timestamp, signed_id):
          
          message = "%s%s%s%s" % (self.api_key, nonce, timestamp, signed_id)
  
          if self._pub_key is None:
              warnings.warn("Skipping RSA signature verification. Please pass public key on class initialization to ensure highest level of security!")
              return True
  
          try:
              rsa.verify(message.encode('utf-8'), signature, self._pub_key)
          except rsa.VerificationError:
              return False
  
          return True
docs: Verify the server response signature. 
          
          :param signature: 
          :param nonce: 
          :param timestamp: 
          :param signed_id: either transactionid, documentid or marketplacemerchantid
          :return: true of false