Patent ID: 8555345

Claim:
A method of authenticating a client to two or more servers coupled together via a communications network, wherein the client and a first server possess a shared secret, the method comprising: sending an authentication request from the client to said first server via a second server; upon receipt of said request at the first server, generating a first authentication challenge using said shared secret, and sending the challenge to the second server; generating a second authentication challenge at the second server, and sending the first and second challenges together from the second server to the client; upon receipt of the challenges at the client, generating a first challenge response to the first challenge, and a session key, using the shared secret, and generating a second challenge response to the second challenge using the session key; sending said challenge responses together to said second server, and forwarding the first challenge response to the first server; authenticating the client at the first server using the first challenge response and said shared secret, and, in the event that the client is authenticated, generating said session key at the first server and sending this to the second server; and authenticating the client at the second server using the second challenge response and said session key.