the identity of the identity module and if the same device mobile telephone is used to transmit the authentication to the client in this case the pin code need not be re sent over the local wireless link merely for refreshing the authenticator and the authenticator can be refreshed automatically without user interaction the above described process of obtaining an identity from a subscriber identity module and of further accessing the sim for further generation of responses and keys may be referred to as beaming the sim capability may be beamed to the client 110 for an authentication purpose the mobile station 120 carrying the sim need not be switched off moreover the mobile station 120 may be configured such that it can perform the beaming even while being used e g for voice transmission or reception while the preferred embodiment as described was based on comparing the secrets provided by the auc and by the sim the subscriber identity module access may be combined with other subscriber identity module based authentication procedures and protocols for example the a sres may be replaced with one way hashed codes as alternative secrets the different embodiments of the invention may be scaleable to any particular subscriber identity module based authentication of a client to a communication system separate from the telecommunication network to which that module actually belongs the subscriber identity module may be such a device that it can produce a response and a key corresponding to a challenge in a manner such that unauthorised.