Mobile phone incorporating security firmware

In accordance with the disclosed method and arrangement, for purpose of client authentication, private keys for digital certificates, or in general, any private or secret information that is necessary for client authentication can be stored in a personal SIM-card/smartcard and used in combination with the mobile telephone as a security gateway upon establishment of a IPsec tunnel. An employee staying away from his ordinary office may, by means of a personal independent access unit functioning as a security gateway, communicate with the protected Intranet of his employer. Such a scenario enables the employee to borrow any remote host in order to access the Intranet by means of a mobile communication network or a fix network, e.g. PSTN. The solution is to move the security function to the mobile telephone or the independent access unit, preferably a wireless independent access unit, where a lightweight security gateway or firewall is implemented.