Abstract: The invention relates to a method for communicating between a server and a client. The server and the client access at least one session extension key and/or a key associated with the session extension key, as an associated key. The server authorizes to extend an open communication session with the client until an expiration time only if the client sends to the server authentication data allowing the server to authenticate at least the client on a basis of the session extension key. The expiration time is a time at which the communication session is open completed by a predetermined extension time period. The invention also relates to corresponding client, server and system.