Zenith seminar : 27/05/2019, 15h
Campus Saint Priest, BAT5-01.124
Bounce Blockchain: a secure, energy-efficient permissionless blockchain
Dennis Shasha
New York University & Inria International Chair in the Zenith team at LIRMM
Performing proof-of-work for the Bitcoin blockchain currently requires as much electricity as consumed by the country of Denmark. This enormous energy expenditure translates into higher costs for users (on the order of $US 6.00 or more per transaction) and is frankly ecologically irresponsible. As of this writing, it can be subverted (i.e. the blockchain can be forked) by a collusion attack of just a handful of data centers. This paper proposes the design of a cheap (less than $US 0.01 per transaction), essentially energy-free public blockchain called a Bounce Blockchain which cannot be forked in any reasonable failure scenario, even most Byzantine failure scenarios.
The basic idea is to send one or more cubesats into orbit, each equipped with a hardware security module. Users would send their transaction to the cubesats which would collect them into blocks, sign them, and send (bounce) them back to earth (and to one another). Bounce Blockchain provides scalability through sharding (transactions will be partitioned over cubesats).
Because modern hardware security modules are tamper-resistant (become inoperable if tampered with) or tamper-responsive (erase their keys if tampered with), take their keys from physical processes, and have been validated, socio-technical protocols can ensure that it is infeasible to forge the identity of a hardware security module in a cubesat with another cubesat. If, however, some cubesats are destroyed, the blockchain will continue to execute correctly though some transactions will be lost. New cubesats can be sent up in short order as they are quite cheap to launch. If, in spite of these assurances, some cubesats fail traitorously, the blockchain can survive through algorithms similar to Practical Byzantine Fault Tolerance techniques.
Biography
Dennis Shasha is a Julius Silver Professor of computer science at the Courant Institute of New York University and an Associate Director of NYU Wireless. He works on meta-algorithms for machine learning to achieve guaranteed correctness rates, with biologists on pattern discovery for network inference; with physicists and financial people on algorithms for time series; on computational reproducibility; and on energy-efficient blockchains. Other areas of interest include database tuning as well as tree and graph matching. Because he likes to type, he has written six books of puzzles about a mathematical detective named Dr. Ecco, a biography about great computer scientists, and a book about the future of computing. He has also written five technical books about database tuning, biological pattern recognition, time series, DNA computing, resampling statistics, and causal inference in molecular networks. He has written the puzzle column for various publications including Scientific American, Dr. Dobb’s Journal, and currently the Communications of the ACM. He is a fellow of the ACM and an Inria International Chair in the Zenith team at LIRMM.
