Hi Taco! Glad to hear from you! Okey no problem, just keep them coming!  Another bug to add for the fix... Sometimes, if you stop a miner that was runing at 20 intensity, and change it to less intensity (ex: 13, 14, 15), and then stop. And save and restart the miner again at 20 intensity, the GUIMiner will cause the driver to crash. Even after the recovery, the miner will not recover, giving very slow performance and cannot start at full speed at any intensity setting. Maybe there is a way to recover the miner... my "fix" is to stop everything and reboot the machine... Best Regards, LPC This is a known bug and is an issue with cgminer I'm pretty sure. I'm not sure what to do about it. Usually if you do to "Device Manager" and disable and then re-enable the video card you can also use it again. |
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what would be a good TC value? how would one determine an optimal TC??
for 7xxx or 2xx cards with GPU threads = 1 it's usually ~12-13 * number_of_shaders with GPU threads = 2 it's usually ~4 * number_of_shaders |
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Well it be ASIC resistant?
Depends on what the demand is for that at launch. |
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Is there a projected release date or is it totally experimental?
Hopefully testnet within 2-5 months or so, then mainchain launch after the testnet seems stable. |
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rat4 wrote you that for those atacks BC POS is not valuable how many times he need wrote the same ?
Writing that you don't think attack vectors exist does not mean that attack vectors do not actually exist. Replies of "that will not happen" are denials of the rich conceptual history and well noted theoretical problems of proof-of-stake systems. |
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Umm you were here 9 months ago saying PPCoin is doomed, it's flawed etc. Made lots of noise about it. Nothing happened. Nothing needs to happen as long as PoW is chugging along -- but then it's just another PoW coin. The PoS system it is eventually supposed to become as reward goes to 0 is deeply flawed. I would anticipate BlackCoin to demonstrate this, and eventually leave rat4 scrambling to apply patch after patch as the system breaks in new and exciting ways. |
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Hence my 'Purely from a PoW/Pos Hybrid perspective'.
I understand there are some PoS issues which clearly you have a greater understanding of than 99.9% of the people on this thread, myself included. I hope these can be addressed appropriately, and as an onlooker and potential investor of any coin am keeping my eye on it. Can't devs/code gurus get together and whittle down the actual issues together? Isn't that what open source is all about? Well, yes, but the issue is a severe one and not easily fixed. Greg Maxwell (the bitcoin core dev whose IQ is probably above 180) couldn't figure it out after spending months trying, Vitalik Buterin (an Honour's student in maths who dropped out of the University of Waterloo to work on Ethereum) is also now struggling very hard with how to solve the issue with his Slasher algorithm, etc... Pure PoS is a *very* hard problem to solve effectively, and the only reasonable solutions for pure PoS are coming in a soon to be published scientific paper I'm not really at liberty to talk about. The first author of that paper is even a little wary about what he's proposed, though. |
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Hi Tacotime, thanks for the information! I notice you have an ad in your signature that describes a PoS/PoW hybrid.
Have you been able to resolve the issue with that coin?
It's a very different system; basically PoS miners vote on every PoW block to verify the contents, and PoW blocks are validated one block at a time. PoS miners are given complete control over the contents of PoW blocks and whether or not the PoW miner gets rewards. This is a *really* experimental incentives system and it might do crazy things yet. The Bitcoin core devs I've talked to are wary of it doing things I haven't predicted. Additionally, it relies heavily on PoW (which I think is a good and reasonably fair distribution system). But it does not have the "nothing at stake" forking issue. It's more comparable to a blockchain with "two factor authentication" for every PoW block, to ensure that miners aren't putting weird transactions into the network or are simply not including transactions. |
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so Tacotime,
for a newbie which coin Mintcoin/Blackcoin is more vulnerable to attack, with Blackcoin being Pure POS and Mintcoin being a POW/POS hybrid?
They both are vulnerable. PeerCoin is what is (sort of) functional. |
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What if everyone else IS NOT mining both?
As soon as someone doublespends successfully on the network using the current PoS protocol, any node that is even modestly intelligent is going to switch to a more belligerent protocol that better defends the value of their coins. Then you run into this problem. OK, but can they doublespend if some miners are already only doing PoW mining for a hybrid PoS coin? No, so long as the PoW difficulty is high enough to actually secure the network. This requires subsidy (block reward) to be high enough to justify lots of people mining the chain. Hence why PeerCoin works. |
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What if everyone else IS NOT mining both?
As soon as someone doublespends successfully on the network using the current PoS protocol, any node that is even modestly intelligent is going to switch to a more belligerent protocol that better defends the value of their coins. Then you run into this problem. |
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Thanks a lot, this is very interesting. To problem #1: What exactly is meant with consensus failure and how does it affect network security? So if I have a faked time stamp that is t seconds in the future, how much less coins do I need to perform a 51% attack? This is the means to generating hashes for PoS for PPC (paraphrased a little): int64 nTimeWeight = min((int64)nTimeTx - txPrev.nTime, (int64)STAKE_MAX_AGE) - nStakeMinAge);
CBigNum bnCoinDayWeight = CBigNum(nValueIn) * nTimeWeight / COIN / (24 * 60 * 60);
if (!GetKernelStakeModifier(blockFrom.GetHash(), nStakeModifier, nStakeModifierHeight, nStakeModifierTime, fPrintProofOfStake))
return false;
ss << nStakeModifier;
ss << nTimeBlockFrom << nTxPrevOffset << txPrev.nTime << prevout.n << nTimeTx;
hashProofOfStake = Hash(ss.begin(), ss.end());
if (CBigNum(hashProofOfStake) > bnCoinDayWeight * bnTargetPerCoinDay){
return hashProofOfStake; } // Golden "nonce" found, we have a block!
else {return false;} You can game this in a bunch of ways. If you're building your own chain of blocks, you can manipulate the timestamp; BlackCoin uses 10 minute intervals, so there's another 600 chances right there (+ 10 min). If you want to build lots of blocks, you need coinstake distributed in lots of places (nTimeBlockFrom << nTxPrevOffset << txPrev.nTime << prevout.n). Now you can bruteforce a chain of length whatever privately so long as you have a bunch of coinstake at different addresses, and then doublespend using that. Unless everyone is trying to do this, you don't need 51% stake to do this -- just the hoarding of a bunch of stake and some bruteforcing at an exacting time and you can doublespend. This is why PoS in PPC and friends defaults to PoW; you're just manipulating a bunch of different factors in search of golden "nonces" (manipulations of non-nonce parameters) in a chain of blocks instead of simply increasing the nonce. Using PoW blocks to make stake modifiers can also help prevent you from being able to game this a bit from the "if (!GetKernelStakeModifier(blockFrom.GetHash(), nStakeModifier, nStakeModifierHeight, nStakeModifierTime, fPrintProofOfStake)) return false;" portion, but I don't think it completely eliminates the risk. Sunny King at some point mentioned changing confirmation rules from number of blocks that have passed to the amount of coinage that has been included in blocks since a transaction has taken place ("trust score"). But this still doesn't solve the "nothing at stake" forking problem, and you can still likely doublespend in that case with <51% stake. |
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So basically the claim is that because of this vulnerability it is possible to complete a 51% attack.
Is that or is that not also a possibility with pure PoS coins?
I'm not seeing how the security status of blackcoin is any different than the security status of mintcoin, as both are supposedly vulnerable to this attack. Which from what i gather is quite expensive to launch successfully and therefore highly unlikely in the first place.
In the event of a fork, whether the fork is accidental or a malicious attempt to rewrite history and reverse a transaction, the optimal strategy for any miner is to mine on every chain, so that the miner gets their reward no matter which fork wins. Thus, assuming a large number of economically interested miners, an attacker may be able to send a transaction in exchange for some digital good (usually another cryptocurrency), receive the good, then start a fork of the blockchain from one block behind the transaction and send the money to themselves instead, and even with 1% of the total stake the attacker's fork would win because everyone else is mining on both. |
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Zero difficulty PoW is open door and cannot be trusted. One of possible fixes is to disable PoW.
Or you can have PoW with a reasonable subsidy and use it to secure the network, but then you just have PeerCoin. Unsurprisingly, Peercoin works because of this and not in spite of this. Now you've simply opened yourself to all the catastrophic bugs in PeerCoin's PoS system that you refuse to acknowledge. There are easy applied fixes for hybrid PoW/PoS with low subsidy that involve adjusting the trust of the timestamping of PoW blocks and content of PoW blocks in general -- but again, there are the same PoS bugs which already exist in PeerCoin, which are non-trivial. |
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If they're taking notes from RealSolid, perhaps they should also start begging for donations.
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