arXiv:1709.08750 Date: submitted by
2017-10-19 Author(s): George Bissias
, Brian Neil Levine
Blockchain systems are designed to produce blocks at a constant average rate. The most popular systems currently employ a Proof of Work (PoW) algorithm as a means of creating these blocks. Bitcoin produces, on average, one block every 10 minutes. An unfortunate limitation of all deployed PoW blockchain systems is that the time between blocks has high variance. For example, 5% of the time, Bitcoin's inter-block time is at least 40 minutes. This variance impedes the consistent flow of validated transactions through the system. We propose an alternative process for PoW-based block discovery that results in an inter-block time with significantly lower variance. Our algorithm, called Bobtail, generalizes the current algorithm by comparing the mean of the k lowest order statistics to a target. We show that the variance of inter-block times decreases as k increases. If our approach were applied to Bitcoin, about 80% of blocks would be found within 7 to 12 minutes, and nearly every block would be found within 5 to 18 minutes; the average inter-block time would remain at 10 minutes. Further, we show that low-variance mining significantly thwarts doublespend and selfish mining attacks. For Bitcoin and Ethereum currently (k=1), an attacker with 40% of the mining power will succeed with 30% probability when the merchant sets up an embargo of 8 blocks; however, when k>=20, the probability of success falls to less than 1%. Similarly, for Bitcoin and Ethereum currently, a selfish miner with 40% of the mining power will claim about 66% of blocks; however, when k>=5, the same miner will find that selfish mining is less successful than honest mining. The cost of our approach is a larger block header.
 Bitcoin cash. https://www.bitcoincash.org/
 Litecoin. https://litecoin.org/
 Ethash. https://github.com/ethereum/wiki/wiki/Ethash
, Aug 3 2017.
 Martin Abadi, Mike Burrows, Mark Manasse, and Ted Wobber. Moderately hard, memory-bound functions. ACM Trans. Internet Technol., 5(2):299–327, May 2005.
 Tuomas Aura, Pekka Nikander, and Jussipekka Leiwo. Dos-resistant authentication with client puzzles. In Revised Papers from the 8th International Workshop on Security Protocols, pages 170–177, 2001.
 Adam Back. Hashcash - Amortizable Publicly Auditable CostFunctions, 2002.
 Iddo Bentov, Ariel Gabizon, and Alex Mizrahi. Cryptocurrencies without proof of work. In International Conference on Financial Cryptography and Data Security, pages 142–157. Springer, 2016.
 Iddo Bentov, Charles Lee, Alex Mizrahi, and Meni Rosenfeld. Proof of Activity: Extending Bitcoin’s Proof of Work via Proof of Stake [Extended Abstract] y. ACM SIGMETRICS Performance Evaluation Review, 42(3):34–37, 2014.
 Bobtails. https://en.wikipedia.org/wiki/Natural_bobtail
 Xavier Boyen, Christopher Carr, and Thomas Haines. BlockchainFree Cryptocurrencies: A Framework for Truly Decentralised Fast Transactions. Cryptology ePrint Archive, Report 2016/871, Sept 2016. http://eprint.iacr.org/2016/871
 George Casella and Roger L. Berger. Statistical inference. Brooks Cole, Pacific Grove, CA, 2002.
 Liqun Chen and Wenbo Mao. An auditable metering scheme for web advertisement applications. Information Security, pages 475–485, 2001.
 F. Coelho. An (Almost) Constant-Effort Solution- Verification Proofof-Work Protocol Based on Merkle Trees. In Progress in Cryptology – AFRICACRYPT, pages 80–93, June 2008.
 Drew Dean and Adam Stubblefield. Using client puzzles to protect tls. In Proceedings of the 10th Conference on USENIX Security Symposium - Volume 10, SSYM’01, Berkeley, CA, USA, 2001. USENIX Association.
 J. Douceur. The Sybil Attack. In Proc. Intl Wkshp on Peer-to-Peer Systems (IPTPS), March 2002.
 Cynthia Dwork and Moni Naor. Pricing via processing or combatting junk mail. In In 12th Annual International Cryptology Conference, pages 139–147, 1992.
 Ethereum Homestead Documentation. http://ethdocs.org/en/latest/
 Ittay Eyal, Adem Efe Gencer, Emin Gun Sirer, and Robbert Van Renesse. Bitcoin-ng: A scalable blockchain protocol. In 13th USENIX Symposium on Networked Systems Design and Implementation (NSDI 16), pages 45–59, Santa Clara, CA, 2016. USENIX Association.
 Ittay Eyal and Emin Gün Sirer. Majority is not enough: Bitcoin mining is vulnerable. In International conference on financial cryptography and data security, pages 436–454. Springer, 2014.
 M. Franklin and D. Malkhi. Auditable metering with ligthweigth security. In Proc. Financial Cryptography, pages 151–160, 1997.
 Arthur Gervais, Ghassan O. Karame, Karl Wust, Vasileios Glykantzis, Hubert Ritzdorf, and Srdjan Capkun. On the Security and Performance of Proof of Work Blockchains. https://eprint.iacr.org/2016/555
 Bogdan Groza and Bogdan Warinschi. Cryptographic puzzles and dos resilience, revisited. Des. Codes Cryptography, 73(1):177–207, October 2014.
 Markus Jakobsson and Ari Juels. Proofs of Work and Bread Pudding Protocols. In Proc. Conference on Secure Information Networks: Communications and Multimedia Security, pages 258–272, 1999.
 A. Juels and J. Brainard. Client puzzles: A cryptographic countermeasure against connection depletion attacks. In Proc. Networks and Distributed Security Systems, pages 151–165, 1999.
 Ben Laurie and Richard Clayton. “Proof-of-work" proves not to work; version 0.2. In Proc. Workshop on Economics and Information Security, 2004.
 Andrew Miller, Ari Juels, Elaine Shi, Bryan Parno, and Jonathan Katz. Permacoin: Repurposing bitcoin work for data preservation. In Proc. IEEE Security and Privacy, pages 475–490, 2014.
 Satoshi Nakamoto. Bitcoin: A Peer-to-Peer Electronic Cash System, May 2009.
 A. Pinar Ozisik and Brian Neil Levine. An Explanation of Nakamoto’s Analysis of Double-spend Attacks. Technical Report arXiv:1701.03977, University of Massachusetts, Amherst, MA, January 2017.
 Ayelet Sapirshtein, Yonatan Sompolinsky, and Aviv Zohar. Optimal Selfish Mining Strategies in Bitcoin. https://arxiv.org/pdf/1507.06183.pdf
, July 2015.
 XiaoFeng Wang and Michael K. Reiter. Defending against denial-ofservice attacks with puzzle auctions. In Proceedings of the 2003 IEEE Symposium on Security and Privacy, SP ’03, pages 78–, Washington, DC, USA, 2003. IEEE Computer Society
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