Anonymous Roaming Authentication Protocol with ID-Based Signatures

We propose an off-line roaming authentication protocol which not only the server in a foreign network authenticates any roaming user without the involvement of the home network, but also the anonymity of the user is preserved. That is, the user can prove his/her roaming legality without letting the server know his/her real identity. We employ the ID-based signature technique and secret sharing technique to provide the user anonymity and nonrepudiation of roaming service during the mutual authentication process. The proposed scheme only requires two messages exchanged between the roaming user and the server, and a polynomial function is designed to revoke the roaming service of an illegal user.