Hashrate and 50% attack

Dear zcash miners,

I would suggest that people mining on flypool, target their GPU/CPUs to another pool. The network safety is in danger, since flypool could in principle do a 50% attack (https://en.bitcoin.it/wiki/Majority_attack). The move of a large chunk of miners to other pools will bring more security to the ZCash network.

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Please provide evidence for this claim.

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adjusted post regarding prices falldown.

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Think before you post. Just stop with the stupid conspiracies. This is not specific to ZEC.

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Although it may only be a source of panic on the market and maybe not even the main reason, the claim that flypool holds about 50% of mining power is still very much true. Please consider moving miners to other pools to increase network security.

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I have no reason to move my miners anywhere. You've provided absolutely nothing to substantiate anything you're claiming.

Moving miners would only lower the difficulty and may increase price. May. It has nothing to do with network security I think

50% attacks are a real concern for some coins. I'm unsure to what extent this vector is a threat to Zcash. I don't see how moving miners would lower network difficulty or increase price?

It would decrease the difficulty because it would take longer for a pool to find a block. Flypool has 100+ mh/s. It can find a block quickly that's why the difficulty is high. When flypool was around 50mh/s the difficulty was roughly half. Not a direct correlation but to find a block with lower hash in 2.5 minutes you'd need a lower difficulty than having higher hash. I hope that made sense :joy:


flypool: h/s: 110000000 diff: 6000000
coinmine: h/s: 1867930 diff: 5423820
nanopool: h/s: 20 ks/s fiff: 5.5mil


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I don't get your argument. Say the network hashrate is 100 MSols/s. Flypool constitutes 50 MSols/s of that total and Suprnova 20 MSols/s. Now, 20% of Flypool's miners move to Suprnova, leaving Flypool with 40 MSol/s and Suprnova with 30. The total network hashrate is still 100 MSol/s and difficulty remains the same.


Okay maybe I am thinking about this wrong but for example scenario 1: if everyone was solo mining and the total network hashrate is 100 MSol/s, would the difficulty be the same as if scenario 2: Fly was 70 MSol/s, Suprnova was 20 MSol/s and Coinotron was 10MSol/s?

Yes, the network difficulty would be exactly the same. Pools have their own mechanisms for divvying up what is mined (sometimes using a "pool difficulty" factor) and what you as a miner earn may differ across pools.

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Flypool is the first pool I've tried that isn't obviously skimming from everyone. Tried Nanopool, another popular one, and would stop getting deposits for 8-10 hours at a time when I normally get them less than 2 hours apart.

This is usually a function of the pool hashrate relative to the network hashrate. Over the long run, the smaller pools will generate rewards one would expect them to when calculating average rewards for the pool's hashrate. However, in the short run, pool rewards will vary significantly from the average, with many hours passing without any.

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The network difficulty would be exactly the same if miners would switch over to other pools. If we would consider a situation where a large portion of the miners switch to another pool and the total hashrate would be the same (that is: no increase or decrease of miners to zcash) THEN the expected payout per miner would also be identical. HOWEVER there is a larger fluctuation on this expected payout per miner depending on the pool's relative hashrate compared to the global hashrate.

The problem with this 50%+ hashrate of flypool may be a reason why poloniex and other exchanges stopped their deposit and withdrawal of zcash. These exchanges still need to make an official statement however, so I have no proof that this is the case. Due to this centralisation of mining power, exchanges can no longer be confident that deposits are actually valid. Increasing the number of confirmations for exchanges is not a solution when flypool has more than 50% of the mining hashrate, see https://en.bitcoin.it/wiki/Majority_attack. The probability for flypool to double spend would in the case of a 50%+ global hashrate share be a 100% success. If they would abuse this power and double spend, it could seriously damage all running operations of exchanges that accepts any transaction from the zcash network.

There is nothing wrong with zcash and its implementation, however due to flypool nobody can now be sure that the transactions in the network are actually valid. There is no way for users to see a double spend in the zcash network, since protected transactions can have their input from void. Eventhough users can check if the total amount of transparent ZEC does not surpass the total mined ZEC, it would still give attackers the possibility to double spend the total amount of protected ZEC in the whole network (at this moment about 63489ZEC). Nodes however would identify a false zero-knowledge proof, but cannot act on it because the blockchain that is the longest is the valid chain in their eyes. In this case the blockchain would be operated by the attackers.

Nothing to worry however, when miners decide to eventually switch their hashpower to other pools the probability of a successful double spend would decrease and the network goes back to normal operating mode. Even in the case where flypool cheated, there would be a chain correction and the chain in which a double spend occurred would be declared invalid. But this may be very inconvenient for zcash users as their passed transactions may be declared invalid.

The fact that flypool has the possibility to inflict damage by having the possibility to do a double spend makes zcash not trustworthy at the moment and therefore I strongly encourage miners on flypool to reconsider and move towards other pools.

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This is not correct. Each full node defines its "best chain" as the chain with the most work among chains that are valid according to its own implementation of the consensus rules. A chain with any invalid zk proofs will never be seen as the best chain by full nodes that are correctly implementing the specification.

The above argument does not apply to SPV nodes; those are more vulnerable to 51% attacks.

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I do, however, encourage miners to distribute their hash power more evenly between pools. The attack @ampy described is not possible, but other attacks (which also apply to Bitcoin and other PoW-based cryptocurrencies) are.


Thanks Daira for the precision.
Anyway i think understand that for little miner it seems more "secure" to stay in big pool, ensuring regular and stable ernings. Those of us who have big hashrate are more flexible in this regards i think.

I'm more sure why having a small hash power would require you to choose a larger pool. You need to choose a pool that provides a variance in mining rewards that is acceptable to you, but there's no evidence that you need a pool as large as Flypool's current size in order to achieve that, unless you need exceptionally low variance for some reason.