A method and an arrangement for providing keys for protecting communication between a terminal (300) and service points in a communication network. A basic key (Ik) is first established with a service control node (304) when the terminal has entered the network. An initial modified key (Ik1) is then created in both the service control node and the terminal, by applying a predetermined first function (f) to at least the basic key and an initial value of a key version parameter (v). The initial modified key is sent to a first service point (302), such that it can be used to protect communication between the terminal and the first service point. When the terminal switches to a second service point (306), the first service point and the terminal both create a second modified key (Ik2) by applying a predetermined second function (g) to the initial modified key, and the first service point sends the second modified key to the second service point.