Patent ID: 7243370

Claim:
A method for mutual authentication between a Session Initiation Protocol (“SIP”) client and a SIP proxy in connection with initiating a session through the SIP proxy, the method comprising: sending from the SIP client to the SIP proxy a first invite request; in response to the SIP proxy receiving the first invite request, sending to the SIP client a challenge that includes a SIP proxy security context; in response to the SIP client receiving the challenge, obtaining from a domain controller of the SIP client a session key of the SIP proxy and a server ticket, the session key encrypted with a key of the SIP client, the server ticket encrypted with a long-term key of the SIP proxy and including authentication data of the SIP client; decrypting the session key based the key of the SIP client; and sending to the SIP proxy a second invite request signed by the session key and that includes the server ticket and the SIP proxy security context; in response to receiving at the SIP proxy the second invite request, decrypting the server ticket based on the long-term key of the SIP proxy; when the authentication data of the SIP client in the server ticket indicates that the SIP client is authentic, the security context included in the second invite request matches the SIP proxy security context, and the second invite request is signed by the session key, sending to an intended server an invite request based on the second invite request; upon receiving from the intended server a response to the invite request, signing the response with the session key; and forwarding the signed response to the SIP client so that SIP client authenticates the SIP proxy.