By introducing a hierarchical encryption scheme and the use of asymmetric cryptography, the critical information in message exchanges is concealed from unauthorized entities. This helps greatly in preventing man-in-the-middle attacks faced by inter-working. In addition, access control is conducted by introducing a network structure having a rule interpreter that is capable of mapping general rules to WLAN specific commands. It obviates the needs for mobile user's home network to understand information about every WLAN it is inter-worked with. A common interface independent of WLAN technologies could be used by the home network for all the WLANs. The above conception provides a solution to the problems of the protection of user identification information and access control in the inter-working of WLAN.