Is it possible to encrypt message between client and server in Vaadin client?

Hi Team,

There are two enquiries about data encryption from chinese forum. Due to some conditions ,they can’t use HTTPS for encrypted communication.
In RestApi or some technologies based Spring MVC,there we can use Message Converter to process the data encryption task, because we can control the two ends of a communication.
In Vaadin client, the communication is through long poll or websocket, i didn’t find the way to intercept the message.
Please suggestion.