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Thoughts on Keccak as a mining puzzle - HackMD
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<div id="doc" class="markdown-body container-fluid comment-inner comment-enabled" data-hard-breaks="true"><h1 id="Thoughts-on-Keccak-as-a-mining-puzzle" data-id="Thoughts-on-Keccak-as-a-mining-puzzle"><a class="anchor hidden-xs" href="#Thoughts-on-Keccak-as-a-mining-puzzle" title="Thoughts-on-Keccak-as-a-mining-puzzle"><span class="octicon octicon-link"></span></a><span>Thoughts on Keccak as a mining puzzle</span></h1><p><span>If we assume that it is not worth the while to pursue ASIC-resistance and simply accept that, given economic instentive, any algorithm can be optimised in hardware, then here are the thoughts:</span></p><p><span>It is desirable that any individual PoW blockchain had its own, sufficiently distinct mining algorithm (tweaking the algorithm slightly does not create sufficiently distinct one, because a lot of tweaks can be easily generalised in hardware and turned into switches or configuration). This is because if the algorithm is shared between two blockchains (like SHA256 is shared between BTC and BCH, EtHash is shared between ETH and ETC), then ASICs employed on one chain could be used to mess with another. Non-ASICed algoritms (like EtHash now and before) are even worse, because GPUs can be relatively easily switched from mining one blockchain to the other.</span></p><p><span>What does it mean to ETC? We saw Linzhi presenting their new EtHash chip, which looks impressive. Though they are still testing it, etc., it is much closer to manufacturing than before. So, lets assume that they start shipping this year. Depending on the cost of their devices, and power consumption, they may or may not be able to scale it quick enough to saturate the market within this year. If nothing changes with ETH and ETC (in terms of mining algorithm), Linzhi’s ASICs will eventually replace all GPUs. The situation won’t be worse than now, because now extra GPUs can be brought from other activities in someone wants to mess with ETC mining. If all ETH and ETC mining are done by ASICs, there will be no spare ASICs liyng around to potentially jump on and cause problems.</span></p><p><span>Now lets assume that ETH rolls out ProgPOW. That would make EtHash ASICs useless for ETH, but still useful for ETC. This is a good outcome in general, but timing is going to be crucial for what happens.</span><br>
<span>If the ProgPOW is activated at the time when most of ETH and ETC are mined by ASICs, all ASICs employed on ETH will be swithced to mine ETC, which will cause the spike in hash rate, then difficulty. If the price of ETC stays relatively stable during this, the profitability of mining on ETC will fall. It may fall to either the level where miners with existing ASICs can still pay for electricity and make tiny pay-off towards the CapEx. Or it may fall below that level, and a lot of devices will have to be turned off.</span><br>
<span>If, however, ProgPOW activation happens before ASICs are dominating ETH and ETC mining, there will be small amount of ASICs that will move over from ETH to ETC, and similar effect described below, will happen, though less severely.</span></p><p><span>Switching mining from EtHash to Keccak256 (SHA3) has some benefits in its own right. But lets see how it will change the events in the cases when ETH does not switch to ProgPOW (or switches after migration to Keccak/SHA3), and when ETH does switch to ProgPOW before the migration to Keccak256/SHA3.</span></p><p><span>In the first case, ETH does not switch to ProgPOW, or switches later than ETC switches to Keccak/SHA3. Here we will see ETC getting mined either by GPUs, and then rapidly replaced by SHA3 ASICs, or, if the change is pre-announced and committed to some time in advance, some ASICs will already exist by the time of the switch. In any case, it will decouple mining of ETH and ETC forever (unless ETH decides to switch to Keccak256/SHA3 too, which seems unlikely at this point), and the switchover should not be very painful for the ETC network.</span></p><p><span>In the second case, ETH does switch to ProgPOW, before ETC switches to Keccak256/SHA3. The losers of this situations will obviously be people who bought EtHash ASICs and the manufacturers of such ASICs. SHA3 ASICs can come to the market very quickly, because they are very easy to design and produce. Perhaps, in such case, there is less of the motivation to switch to Keccak256/SHA3, because the goal of having a unique ASIC-ed mining algorithm would have been achieved. And it will only be due to other potential benefits of SHA3 mining puzzle, ETC may decide to switch.</span></p><h3 id="Benefits-of-SHA3-mining-puzzle" data-id="Benefits-of-SHA3-mining-puzzle"><a class="anchor hidden-xs" href="#Benefits-of-SHA3-mining-puzzle" title="Benefits-of-SHA3-mining-puzzle"><span class="octicon octicon-link"></span></a><span>Benefits of SHA3 mining puzzle.</span></h3><p><span>The most obvious one is the ease of verification. One of the biggest trouble with EtHash (and even more so ProgPOW) for mobile devices is that it is very hard to verify, and such verification drains batteries.</span><br>
<span>Second, less obvious one, is the potential to generate the compact proof of header chain ansestry. It would allow to not download the entire chain of headers and verify PoW on every single header, but instead use proof systems like SNARK or STARK to have a compact proof that a certain header is correct in the sense that it has ansestry all the way to the genesis block (or some other “checkpoint” block), with all PoW correct along the way. Circuit sizes for such proofs would be much smaller for simpler puzzles like SHA3, than for EtHash (and ProgPOW will probably make this task almost impossible).</span><br>
<span>Thirdly, it would be easier implementation of side-chains? I am not yet sure how to take advantage of this, but general idea is that currently there is no EtHash verification precompile in EVM. But there is SHA3 opcode that can be used to verify PoW based on Keccak256/SHA3. Not done thoughou analysis on that, but this can potentially be used to experiment with the new upgrades on the side chains (with real Ether) before applying them to the mainnet.</span></p></div>
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