A security protocol for use in a multi-site authentication system. After authenticating a user, an authentication server generates a ticket including information associated with the user. The authentication server encrypts content of the ticket using a symmetric key shared with an affiliate server. The affiliate server has a public key that the authentication server uses to encrypt the shared key. The authentication server has private key for creating a signature on the ticket. The affiliate server decrypts the shared key with its private key and then decrypts the content of the ticket using the decrypted shared key. The affiliate server validates the signature with the authentication server's public key.