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

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• Changyu Dong, School of Computing, Newcastle University
• Tuesday 17 October 2017, 14:00-15:00
• LT2, Computer Laboratory, William Gates Building.

If you have a question about this talk, please contact Alexander Vetterl.

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 https://arxiv.org/abs/1708.01171.

This talk is part of the Computer Laboratory Security Seminar series.

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