Transaction-based authentication and key agreement protocol for inter-domain VoIP

We present an authentication and key agreement protocol to secure Voice over IP call establishment between interconnection proxies of different domains. The protocol operates on a transaction basis. Each transaction is defined as the set of operations and data required to send an authenticated message from a sender to a responder. A transaction allows a sender to either transmit a cryptographically protected stand-alone message; or a key-agreement message required to establish a secure session. The protocol handles transaction synchronisation loss and guarantees the use of a single transaction window in the general (inter-domain) context with multiple originating servers.