A communication device of a communication network receives, via a network, a challenge, generates a first Diffie Hellman, DH, parameter, a first verification code for the first DH parameter, forwards the challenge or a derivative thereof to an identity module, receives at least one result parameter as response from the identity module, determines, based on the result parameter, whether the first DH parameter is authentic, and if the first DH parameter is authentic, generates and sends a second DH parameter to the network device for session key generation based on the first DH parameter and the second DH parameter.