1. Context

By way of introduction and definition, the use of client-server applications on the Internet often takes the form of a two-stage process. In the first stage, the customer retrieves public information on the services offered by the server, such as its product catalog, in order to prepare an order: in more everyday terms, he "fills his basket". Secondly, he formalizes the transaction – online purchase – which is the objective and conclusion of his connection to the server.

All the added value is in this one-off transaction, which is drowned in a stream of purely informative data, containing nothing crucial in itself. It is this initial observation that guides the whole process of providing the reliability and security that cannot be ignored. In fact, it's clearly in our interest to focus anything that might be considered critical on an ephemeral, detached, characterized...