Mutual restricted identification*

Abstract

We extend the idea of Restricted Identification deployed in the personal identity documents in Germany. Our protocol, Mutual Restricted Authentication (MRI for short), is designed for direct anonymous authentication between users who belong to the same domain (called also a sector). MRI requires only one private key per user. Still there are no limitations to which domain a user may belong and the domains are not fixed in advance. This enables an implementation of MRI when a strictly limited secure memory is available (like for smart cards). MRI guarantees that a user has exactly one identity within a domain, while the identities from different domains of the same user are not linkable. The main difference between RI and MRI is that for MRI the privacy of both participants are protected, while in case of RI the terminal is fully exposed. The protocol is efficient, extremely simple (in particular, it outperforms RI) and well suited for an implementation on resource limited devices such as smart cards.