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I use latest version of Vaadin. How to implement a data encryption, for example, of Text Field in the area from server side to client side? Use of channel encryption with SSL/TLS is not allowed by project requirements.
My first thought is that you're going to need to make your own version of the framework for that, as one of the main points of the framework is automatizing the client-server communication. Generally rolling your own crypto systems is heavily discouraged, as it's easy to make mistakes that leave you vulnerable and widely used systems have had more time for people to find out those holes. If you have decided that you want to do that, start by looking into the com.vaadin.client.communication and com.vaadin.server.communication packages in the sources.