Universally Composable (Non-Interactive) Two-Party Computation from Untrusted Reusable Hardware Tokens

Universally composable protocols provide security even in highly complex environments like the Internet. Without setup assumptions, however, UC-secure realizations of cryptographic tasks are impossible. To achieve efficient protocols, practical setup assumptions are needed. Tamper-proof hardware tokens, e.g. smart cards and USB tokens, can be used for this purpose. Apart from the fact that they are widely available, they are also cheap to manufacture and well understood. However, currently considered protocols based on tamper-proof hardware require a protocolspecific functionality of the hardware which cannot be reused for other protocols. For this to become possible, in addition to a versatile functionality, the hardware has to be modeled as a global setup. We propose the first formalization of tamper-proof hardware as an untrusted global setup assumption. Based on this setup, we construct protocols for both UC-secure two-party computation and UC-secure non-interactive secure computation. The token functionality that we choose is a simple signature functionality, i.e. our protocols can be realized with currently available signature cards.