Instantaneous Decentralized Poker

We present efficient protocols for amortized secure multiparty computation with penalties and secure cash distribution, of which poker is a prime example. Our protocols have an initial phase where the parties interact with a cryptocurrency network, that then enables them to interact only among themselves over the course of playing many poker games in which money changes hands. The high efficiency of our protocols is achieved by harnessing the power of stateful contracts. Compared to the limited expressive power of Bitcoin scripts, stateful contracts enable richer forms of interaction between standard secure computation and a cryptocurrency. We formalize the stateful contract model and the security notions that our protocols accomplish, and provide proofs using the simulation paradigm. Moreover, we provide a reference implementation in Ethereum/Solidity for the stateful contracts that our protocols are based on. We also adopt our off-chain cash distribution protocols to the special case of stateful duplex micropayment channels, which are of independent interest. In comparison to Bitcoin based payment channels, our duplex channel implementation is more efficient and has additional features

Novel Contract Signature based on Key Exchange

A contract signature is a particular form of digital multi-signature that only involves two signers. Contract signing plays a critical role in any business transaction, particularly in situations where the involved parties do not trust each other. One of the most significant concerns in exchange signatures is the fraudulent and unfair exchange, which occurs when one party gets the signature of another party without giving his own signature. In the view of these security concerns, this thesis presents a secure and fair contract signature scheme based on key exchange protocol. The security and protection of the proposed scheme is based on solving hard computational assumptions such as discrete logarithm problem (DLP). The proposed protocol is abuse-free. The proposed scheme targets to have lesser computational overhead and high-security features than existing scheme[1]. The proposed scheme has wide application in real life scenarios, such as in electronic cash system

Formal Analysis of Fairness for Optimistic Multiparty Contract Signing Protocol

Optimistic multiparty contract signing (OMPCS) protocols are proposed for exchanging multiparty digital signatures in a contract. Compared with general two-party exchanging protocols, such protocols are more complicated, because the number of protocol messages and states increases considerably when signatories increase. Moreover, fairness property in such protocols requires protection from each signatory rather than from an external hostile agent. It thus presents a challenge for formal verification. In our analysis, we employ and combine the strength of extended modeling language CSP# and linear temporal logic (LTL) to verify the fairness of OMPCS protocols. Furthermore, for solving or mitigating the state space explosion problem, we set a state reduction algorithm which can decrease the redundant states properly and reduce the time and space complexity greatly. Finally, this paper illustrates the feasibility of our approach by analyzing the GM and CKS protocols, and several fairness flaws have been found in certain computation times