Abstract Recent work has demonstrated significant anonymity vulnerabilities in Bitcoin's networking stack. In particular, the current mechanism for broadcasting Bitcoin transactions allows third-party observers to link transactions to the IP addresses that originated them. This lays the groundwork for low-cost, large-scale deanonymization attacks. In this work, we present Dandelion++, a first-principles defense against large-scale deanonymization attacks with near-optimal information-theoretic guarantees. Dandelion++ builds upon a recent proposal called Dandelion that exhibited similar goals. However, in this paper, we highlight simplifying assumptions made in Dandelion, and show how they can lead to serious deanonymization attacks when violated. In contrast, Dandelion++ defends against stronger adversaries that are allowed to disobey protocol. Dandelion++ is lightweight, scalable, and completely interoperable with the existing Bitcoin network. 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Viswanath. 2015. Spy vs. Spy: Rumor Source Obfuscation. In SIGMETRICS Perform. Eval. Rev., Vol. 43. 271–284. Issue 1.  Giulia Fanti and Pramod Viswanath. 2017. Anonymity Properties of the Bitcoin P2P Network. arXiv preprint arXiv:1703.08761 (2017).  M.J. Freedman and R. Morris. 2002. Tarzan: A peer-to-peer anonymizing network layer. In Proc. CCS. ACM.  Sam Frizell. 2015. Bitcoins Are Easier To Track Than You Think. Time (January 2015).  Adam Efe Gencer and Emin Gün Sirer. 2017. State of the Bitcoin Network. Hacking Distributed, http://hackingdistributed.com/2017/02/15/state-of-the-bitcoin-network/. (February 2017).  S. Goel, M. Robson, M. Polte, and E. Sirer. 2003. Herbivore: A scalable and efficient protocol for anonymous communication. Technical Report.  P. Golle and A. Juels. 2004. Dining cryptographers revisited. In Advances in Cryptology-Eurocrypt 2004.  Ethan Heilman, Leen Alshenibr, Foteini Baldimtsi, Alessandra Scafuro, and Sharon Goldberg. 2016. 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Abstract 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. References  Bitcoin cash. https://www.bitcoincash.org/.  Litecoin. https://litecoin.org/.  Ethash. https://github.com/ethereum/wiki/wiki/Ethash, Aug 3 2017.  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A new report by crypto research company Bitooda claims that China accounts for only 50% of global Bitcoin mining capacity, and the U.S. 14%. The data is in sharp contrast with earlier findings Upon the release of Bitcoin (client) v.01, the early responders in January 2009 were: Ben Laurie Bill Frantz Bill Stewart dan at geer.org Hal Finney Jerry Leichter Ben Laurie, a respected web security expert and cryptographer, makes a compelling case that Bitcoin won’t work because it accrues such a huge advantage to people who can bring the most computing As well, let’s toss in some blog posts on Bitcoin by the cryptographer Ben Laurie and Victor Grischchenko; Laurie particularly criticizes 23 the hash-contest which guarantees heavy resource consumption: “Bitcoin” “Bitcoin 2” “Bitcoin is Slow Motion” Peercoin (or PPC, PPCoin) is a peer-to-peer cryptocurrency utilizing both proof-of-stake and proof-of-work systems.. Peercoin is based on an August 2012 paper which listed the authors as Scott Nadal and Sunny King. Sunny King, who also created Primecoin, is a pseudonym.Nadal's involvement had diminished by November 2013, leaving King as Peercoin's sole core developer.
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