Quote from: vjudeu on Today at 09:59:40 AM

You can start from the Genesis Block, or from the current block. In both cases, changing the rule from the heaviest chain to the longest chain is a hard-fork change. That means, the starting point is not that important, because it is hard-fork anyway. Also, "drop the difficulty to 1" without going through difficulty adjustments is again a hard-fork. When it comes to this rule, you can even see it in action by looking at testnet3: it is much longer, but it also has much lower chainwork.

Hard-fork is a strawman argument. EVERY time this argument is used, it's used as an example of "If Bitcoin WAS designed that way, then this is what could happen." My point is no, that couldn't happen. Even if Bitcoin was designed that way. There absolutely are problems with using longest chain instead of most work, and I would never suggest that we should use longest chain. I'm just saying that the argument that I see over and over. that "someone could start at block 1 and build a longer chain in minutes (or days, or weeks, or even a few months)" under that scenario is dishonest and misleading.

Quote from: vjudeu on Today at 09:59:40 AM

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Secondly, after you've churned out 2016 blocks, in order to create valid blocks, you'd need to immediately increase your difficulty by a factor of 4, then again after the next 2016 blocks, and again after the next 2,016 blocks.

Not really, because you don't have to put the correct timestamp in your blocks.

This is the piece I wasn't thinking about. I'll have to think about that a bit. You might be right. That might be enough to make it possible.

Quote from: vjudeu on Today at 09:59:40 AM

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Pretty quickly, you'd encounter a situation where your particular equipment can't mine blocks any faster than an average of one block every 10 minutes. You could shut your equipment off for a few weeks to get the difficulty to come back down, but you'd burn a lot of time waiting, and then once you've spent a few days mining another 2016 blocks, the difficulty would shoot right back up again.

There is no need to wait. You can mine blocks with future timestamps here and now

Yes. This is the part I wasn't thinking about. You're probably right. I'll think about it a bit.

Quote from: o_e_l_e_o on Today at 10:17:38 AM

If we did use the longest chain, then what would be possible would be a miner mining in secret while manipulating the time stamps on their blocks to artificially drop the difficulty.

Maybe. I'm not 100% convinced yet, but I'm coming around.

It seems like in order to adjust timestamps enough to keep the difficulty low, you'd have to have timestamps that average to at least 10 minutes per block (otherwise at the end of 2016 blocks, the difficulty would increase). Meanwhile, the current blockchain has an average over it's lifespan that is significantly less than 10 minutes (which is WHY the difficulty almost always increases). Therefore, if you started your block 1 with a timestamp of January 1, 2009, then it seems like you'd still have less blocks in your blockchain than the current blockchain has by the time you had advanced your timestamps all the way to now.

I'm beginning to suspect that, with some careful planning, it can MAYBE be accomplished, but it certainly isn't as simple as "set difficulty to 1, start at block 1, mine more blocks than the current blockchain in a few minutes."