Implementing Resettable UC-Functionalities with Untrusted Tamper-Proof Hardware-Tokens

Resettable hardware tokens, usually in the form of smart cards, are used for a variety of security-critical tasks in open environments. Many of these tasks require trusted hardware tokens. With the complexity of hardware, however, it is not feasible to check if the hardware contains an internal state or gives away information over side channels. This inspires the question of the cryptographic strength of untrusted resettable hardware tokens in the universal composability framework. In this work, we consider the problem of realizing general UC-functionalities from untrusted resettable hardware-tokens, with the goal of minimizing both the amount of interaction and the number of tokens employed. Our main result consists of two protocols, realizing functionalities that are sufficient to UC-realize any resettable two-party functionality. The first protocol requires two rounds of interaction in an initialization phase and only a single hardware-token. The second protocol is fully noninteractive and requires two tokens. One of these relaxations, allowing either communication with the issuer of the token or issuing two tokens, is necessary. We show that even a simple functionality cannot be realized non-interactively using a single token.