Systems and techniques are disclosed to protect a user equipment's international mobile subscriber identity by providing a privacy mobile subscriber identity instead. In an attach attempt to a serving network, the UE provides the PMSI instead of IMSI, protecting the IMSI from exposure. The PMSI is determined between a home network server and the UE so that intermediate node elements in the serving network do not have knowledge of the relationship between the PMSI and the IMSI. Upon receipt of the PMSI in the attach request, the server generates a next PMSI to be used in a subsequent attach request and sends the next PMSI to the UE for confirmation. The UE confirms the next PMSI to synchronize between the UE and server and sends an acknowledgment token to the server. The UE and the server then each update local copies of the current and next PMSI values.