Keys are the cornerstone of the security architecture; as such their protection is of paramount importance, and keys are never supposed to be transported through an insecure channel. A momentary exception to this rule occurs during the initial phase of the addition to the network of a previously unconfigured device. The Zigbee network model must take particular care of security considerations, as ad hoc networks may be physically accessible to external devices. Also the state of the working environment cannot be predicted.