Security analysis of the SIP Handover Extension

With the increased demand for mobility support in VoIP, a SIP Handover Extension has been proposed. This paper discusses and analyses the security threats to this extension. Different usage scenarios for the Handover Extension are identified. For each scenario we identify known threats, and discuss how to counter them using known security mechanisms. The Handover Extension is particularly vulnerable to wiretapping call-hijacking. Further we argue that all identified threats can be countered using known security mechanisms, and propose S/MIME as the best countermeasure, but with an added price of increased complexity.