Abstract. For ubiquitous communication self-organising adhoc networks become more and more important. We consider mobile phones as appropriate secure gateways to provide access to the Internet for external machines with low communication needs. A message-based approach is best in such a scenario with moving mobile phones and machines. In this paper we propose a security model for access control to the communication infrastructure, which is also message oriented. To meet the requirements of ubiquitously communicating machines, all algorithms on the sender’s side are based on symmetric cryptography resulting in low computation requirements. Our sophisticated symmetric key infrastructure for access control is based on unique combinations of keys and is completed with an effective key management. This results in a carrier grade security level although many parties share the same keys. Adopting the Subscriber Identity Module as a secure storage and computing module achieves the trustwort...