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by KirinDave 3179 days ago
No. It'd require only slightly more work than the cost of generating a block at that time, to generate a new plausible block altered arbitrarily.

The power of the "head" of the blockchain is the human consensus around it. It is otherwise unprivileged.
1 comments
DennisP 3179 days ago
As with any transaction on a proof of work chain, the more work there is layered on top of the item in question, the more confidence you can have. Even if you don't know that someone's presenting you with a truncated chain, you can still see that their credential is at the end of it, and know that they could have cheaply faked it.

Proof of stake would require more human consensus but proof of work is measurably expensive to produce.

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KirinDave 3179 days ago
> As with any transaction on a proof of work chain,

Only active proof of work chains. Discontinued chains have no active, competitive consensus and may be arbitrarily rewritten by attackers since there is no competition at any historical point in the chain for a quick mining operation and there is no consensus about the head of the chain.

If there are additional credentials and signatures embedded in the chain (there need not be) then THESE are the trust tokens that have value after the chain is discontinued.

Blockchains only offer one thing: human consensus when humans are not necessarily inclined to reach it. That is what a PoW or PoS blockchain algorithm for cryptocurrency is trying to guarantee.

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DennisP 3178 days ago
You can still measure the total amount of hashpower applied. Someone could add arbitrarily many blocks but you can calculate how much it cost for them to do it.
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KirinDave 3178 days ago
So? Without competition for time it's pretty easy to make quite long blockchains.

It's the competition for time that makes the mining reliable right now.

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psyc 3178 days ago
I'm struggling to pinpoint where you two are talking past each other. "Length" in the context of a blockchain refers quite specifically to the amount of actual work. So "easy" to make "long" chain, seems like a straightforward contradiction.
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KirinDave 3178 days ago
The amount of calculation necessary to add a block to the chain is not undoable by someone with modest resources.

What's difficult is doing it as quickly as Bitcoin miners with specialized hardware and big energy footprints.

You can make a new blockchain add got Bitcoin today on EC2 without overwhelming expense. Even 30 of them. No problem! It'd take too long to be practical for mining, but that's not the senario we are discussing

Would you beat other miners in? Absolutely not. But the scenario being discussed here is the historical value of blockchains once there is no mining pool racing on them.

And the answer both the article and I propose is: "It is almost none" compared to the other cryptographic tokens. Especially if the chain isn't receiving constant, small commits.

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DennisP 3178 days ago
The competition works by increasing the difficulty. At any given time there's a maximum numerical value of the block hash; the lower it is, the more hashes you have to make before you find a valid one.

The difficulty can be checked after the fact, by simply checking the numerical values of hashes. If a hash is one in a trillion, you know it took about a trillion attempts on average to make it, and you can figure out the economic cost of doing that.

It would be easy to make a chain with lots of blocks of low difficulty. It would also be easy for anyone to see that it didn't cost much to make it.

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