Together they have a lot of scratching power (aka mining power). With pools, the pool manager takes a stack of tickets and distributes it among a set of pool members in such a way that the winnings can only be deposited to the pool operator's address. To reduce this variance, people form pools. That's a long time to wait in between winning tickets. For instance, A $1500 mining card, available for preorder from Butterfly Labs, will need an expected time of over 6 years to mine a single block, if it were available today. But a lone miner working alone can be scratching for months before he finds a winning ticket. A miner scratches one ticket after another until he finds a winning ticket and publishes it to receive its rewards. The key insight behind this change is to make it difficult to delegate proofs of work, for as long as the proof of work can be delegated, huge pools can be built, leading to a winner-takes-all GHash-at-51% sort of scenario.īitcoin's puzzles are sometimes compared to scratch-off lottery tickets, with the miner's name at the top. In order to disincentivize large pools, we propose a small, backwards-compatible change to Bitcoin's Proof of Work (PoW) mechanism that retains both the current blockchain and miners' current investments in mining hardware. Mining pools over 25% are not good for Bitcoin. Such majority miners are toxic: not only can they engage in subtle attacks, but their mere presence, even when they are not engaging in any attacks at all, damages the Bitcoin value proposition, kills the critical features that make Bitcoin interesting and exciting, and therefore hinders Bitcoin adoption. When pools grow to be large, they pose a risk: Pools over 25% can cheat the system with selfish mining and earn more than their fair share, over 33% presents risk of unilaterally successful selfish mining, large pools risk double-spends with low confirmations, and over 50% is an unmitigated disaster.
Today, large pools are built out of independent entities that place their hashing power under the control of a pool manager that coordinates their efforts, collects rewards, and redistributes those rewards to the participants in proportion to their effort. Overall, it provides a gentle fix to the recent GHash fiasco and makes it highly unlikely that we'll find ourselves at the mercy of a single entity, without perturbing the existing economies and investments in place. Yet it enables the existing miners to continue to use their mining hardware in fact, it extends the lifetime of this hardware. It provides a seamless, smooth transition from the current PoW to the modified, large-miner-deterring 2P-PoW. The critical property of our solution that sets it apart from previous ideas is that it preserves the current investment in Bitcoin by both existing users and by existing miners. We first describe the problem, outline the requirements for a good solution, and then present the simplest solution that we know of that meets those requirements. In this post, we present a specific technical fix, called Two Phase Proof of Work (2P-PoW), to disincentivize large mining pools. Many people in the community, including us, have noted that etiquette or the good will of miners are not sufficient to keep monopolies at bay, and called for technical measures to disincentivize large mining pools. In turn, there has been considerable criticism and backlash. This collapsed the key value proposition of Bitcoin, namely, its decentralization. Recently, the GHash mining pool breached Bitcoin etiquette to become a 55% miner for Bitcoin.
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