ACE Seminar: Betrayal, Distrust, and Rationality: Smart Counter-Collusion Contracts for Verifiable Cloud Computing

Speaker: Changyu Dong

Date/Time: 19-Oct-2017, 16:00 UTC

Venue: Roberts 508



Cloud computing has become an irreversible trend. There is a pressing need for verifiability: the cloud providers are external parties whose interests may not fully align with those of its clients, therefore they cannot be fully trusted. To exercise due diligence and gain greater confidence in computation outsourced to the cloud, clients need to be able to verify the correctness of the results returned. However, existing verifiable computation techniques all have a high overhead, thus if being deployed in the clouds, would render cloud computing more expensive than the on-premises counterpart, and would diminish the motivation for using the clouds.

In this talk, I will present our recent attempt to achieve verifiability at a reasonable cost, by leveraging game theory and smart contracts, which is a newly developed paradigm on top of the blockchain technology. In a nutshell, a client lets two clouds compute the same task, and uses smart contracts to stimulate tension, betrayal and distrust between the clouds, so that rational clouds will not collude and cheat. In the absence of collusion, verification of correctness can be done easily by crosschecking the results from the two clouds. We provide a formal analysis of the games induced by the contracts, and prove that the contracts will be effective under certain reasonable assumptions. By resorting to game theory and smart contracts, we are able to avoid heavy cryptographic protocols. The client only needs to pay two clouds to compute in the clear, and a small transaction fee to use the smart contracts. We also conducted a feasibility study that involves implementing the contracts in Solidity and running them on the official Ethereum network.  

The talk is based on a recent paper in CCS 2017, the full version of the paper can be accessed through


Changyu Dong is a senior lecturer in security at Newcastle University, UK. He obtained his PhD from the Department of Computing at Imperial College London in 2009. His research interests fall under the broad heading of cyber security, including applied cryptography, game theory, trust management, data privacy and security policies. He has published more than 30 research papers in major journals and international conferences, including the most prestigious venues in security such as ACM CCS, ESORICS and Journal of Computer Security (JCS), IEEE Transactions on Dependable and Secure Computing (TDSC) and IEEE Transactions on Information Forensics and Security (TIFS). Three of his papers were selected as best paper at international conferences. He has served on and chaired program committees for many conferences and workshops, and is a regular invited reviewer for top international journals. Currently, he leads an EPSRC project “Practical Data-intensive Secure Computation: a Data Structural Approach”.

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