Bitcoin Q&A: Miners, Pools, and Consensus

How many miners and/or pools are there? Can the distribution of miners be determined? Would mining pools be incentivised to merge? Is miner collusion through 51% attacks a present threat? Could they double-spend their coins? How are they impacted by replace-by-fee (RBF)?

Chapters
0:00 How many miners are out there? How many have successfully mined blocks so far? Where can I find this information? Are most miners traceable to IP addresses, or are they anonymized?
4:15 How can the distribution of hash power amongst miners in the Bitcoin network be identified? For example, by looking at statistics on sites like blockchain.info/pools? How reliable is this information?
6:15 If mining is for preventing miners from double-spending their own transactions, why not simply flag their transactions and check them regularly?
7:05 Bitcoin solves the Byzantine Generals' Problem so long as at least 50% of the hashing power consists of honest, non-collaborating miners. How do I know that at least 50% of miners are honest and not traitors?
7:41 During a 51% attack, can the miner spend his or her bitcoins twice? What does it mean that a 51% attacker can produce a longer chain than the other miners or reverse past transactions?
12:42 This question refers to Cornell University's selfish mining model, quoted on page 30 of the course material. It's about the threshold of honest, non-nefariously colluding miners, at which point Bitcoin solves the Byzantine Generals' Problem and creates the guarantee for system integrity. Is it 51% or 66% of the hashing power? "What countermeasures might work against dishonest miners?
16:31 How is dishonesty meaning trying to move the same bitcoin to two different addresses -- weeded out?
20:29 Roy posted a tweet from June 2013 that says, "ghash.io is now at 52% hash rate," and this can cause issues. The question from Roy is, "Did someone find a way to prevent this from happening?"
23:35 If the top three Bitcoin mining pools were to merge, they would control 54% of the hash power. Why hasn't it happened?

These questions are from the MOOC sessions 7.2, 8.2, and 9.2 covering the Byzantine Generals' Problem, which took place on February 26th 2017, September 15th 2017, and February 23rd 2018 respectively. Andreas is a teaching fellow with the University of Nicosia. The first course in their Master of Science in Digital Currency degree, DFIN-511: Introduction to Digital Currencies, is offered for free as an open enrollment MOOC course to anyone interested in learning about the fundamental principles.

If you want early-access to talks and a chance to participate in the monthly live Q&As with Andreas, become a patron:   / aantonop  

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Andreas M. Antonopoulos is a technologist and serial entrepreneur who has become one of the most well-known and respected figures in bitcoin.

Follow on Twitter: @aantonop   / aantonop  
Website: https://antonopoulos.com/

He is the author of two books: “Mastering Bitcoin,” published by O’Reilly Media and considered the best technical guide to bitcoin; “The Internet of Money,” a book about why bitcoin matters.

THE INTERNET OF MONEY, v1: https://www.amazon.co.uk/Internet-Mon...

[NEW] THE INTERNET OF MONEY, v2: https://www.amazon.com/Internet-Money...

MASTERING BITCOIN: https://www.amazon.co.uk/Mastering-Bi...

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