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What are VDPOS and HIPOS ?
They are probably two things of Proof-of-Stake(PoS) but I have not heard of VDPoS before and sorry, I still have not understood what exactly is 'HiPoS'.
if they are good strategy why bitcoin developers didn't apply them on BTC ?
Bitcoin is Proof-of-Work(PoW) and will always be PoW unless if "PoS is better" is provable.
That page is pretty embarrassing. There is absolutely no mention of the fundamental flaw in PoS consensus which none of your proposals have addressed: As of yet none of the proof of stake proposals are workable because there is nothing at stake! If someone is PoS mining it is in their best interest to attempt to concurrently build an honest chain as well as all possible attack forks just in case one of them happens to win. Under most schemes this is the profit maximizing move, in all I've seen so far its at least neutral. Mining an attack under PoW actually involves _spending_ something and taking the risk other miners will extend it. PoW works because your work is at stake so even a very small amount of honest miners make mercenary rational miners behave honestly too.
Moreover, I don't see why you argue here that it better aligns incentives. Parties can't mine PoW without having a validating node (or face the extreme risk other miners will toss them off on forks). All it does is redistribute control, which might be useful— if not for the fact that it makes attacking more attractive for selfish participants. I was hopeful of these techniques but as of yet I don't see how any can be workable.
This is a problem at any stake. Random coalitions to alter the past can be formed at no cost to those colluding.
Checkpointing is not an alternative to decentralized consensus but central override of it.
The same works for Bitcoin, too.
You misunderstand. The risk isn't that someone could attack the network, it is that they could attack the network with
no cost.
Imagine bitcoin worked using a PoS. An early adopter had acquired 1M BTC at one time in the past but over time he lost/sold/spent/transferred them. Today he has no bitcoins but the blockchain contains a history of a time when he did have 1M BTC. If the amount of the stake being used is <1M BTC he could rewrite history not by using coins he has today (a real cost), not by buying millions of mining rigs (a real cost) but by using the history of the coins he once had (no cost). He has absolutely nothing at risk and nothing to lose. If he and potentially others decided to attack the network they would rewrite the blockchain starting from when they had a larger stake, creating a parallel history where they didn't lose/sell/spend/transfer the coins.
They can attack the network based on what they had (but no longer do) in the past. There is nothing at risk and no cost to the attack. THAT is the PoS problem.
If bitcoin miners collude, they could alter the past.
Sure they can, however there is a cost to that attack and there is something at risk which they lose if they fail. With PoS you can attack the network for "free" using something you had but no longer do. It is very hard to secure against an attack where the attacker can do so at any time without any cost and without any risk.
