## Cryptology ePrint Archive: Report 2017/1092

Universally Composable Secure Two and Multi-party Computation in the Corruptible Tamper-Proof Hardware Token Model

Nishanth Chandran and Wutichai Chongchitmate and Rafail Ostrovsky and Ivan Visconti

Abstract: In this work we introduce the corruptible token model. This model generalizes the stateless tamper-proof token model introduced by Katz (EUROCRYPT '07) and relaxes the trust assumption. Our improved model is motivated by the real-world practice of outsourcing hardware production to possibly untrusted manufacturers and allows tokens created by honest parties to be corrupted at the time of their creation.

Assuming one-way functions, we show how to UC-securely realize the tamper-proof token functionality of Katz in the corruptible token model with $n$ stateless tokens assuming that the adversary corrupts at most $n-1$ of them. We then apply this transformation to existing two and MPC protocols to achieve a UC-secure 2PC/MPC protocol in the corruptible token model assuming only the existence of one-way functions.

Finally, we further transform the above protocol to only use tokens of small size that take only short inputs. The technique in the last transformation can also be used to improve the assumption of UC-secure hardware obfuscation by Nayak et al. (NDSS '17) from collision-resistant hash functions to one-way functions, which can then be transformed into a protocol with $n$ corruptible tokens in our model.

Category / Keywords: cryptographic protocols / tamper-proof token, corruptible, setup assumption, UC security, MPC