Quote from: KlondikeBear on July 26, 2015, 10:02:43 AM

PoS is derived from Sunny King's code and advanced checkpoints were there since the beginning.
Any coin which has implemented advanced checkpoints is not completely decentralized, checkpoints control can be hacked, or misused by devs.
With staking you get additional coins if you keep your wallet online. It helps network, but in the same time if you are just an investor, or don't keep your wallet online and unlocked because of any reason, you are out of game.
Some PoS coins are accused to be unfair with big staking percent at the beginning.

Please argue if you dont't agree.

This discussion is interesting:

Quote from: cynicSOB on June 26, 2015, 02:50:10 AM

Quote from: markm on June 26, 2015, 12:00:28 AM

There are two problems with POS that I'd care about, and I think both have been called "nothing at stake" at least once, but they are different issues:
- One is that in POW finding a block or not depends on the (hash of the) transactions of the new block. But in POS, once you find a block you can create another one (at the same height) with different tx's for free.
- The other one is a history rewrite: in POW, if I own in the present 51% of the hashrate of some point in the past, I can do nothing with that. For example you can buy some ASIC that has more hashrate than all the network combined had in some moment of 2011. But that's useless. However in POS if I have control in the present of the private keys to a stake larger than 51% in some past then I can use that to rewrite the blockchain from that time until the present (overriding the tx's in which that 51% changed hands).

Many coins take measures to mitigate -with different levels of success- the consecuences of these two problems. However it's hard to deny that they are security weaknesses inherent to POS.

Quote from: Nxtblg on June 26, 2015, 01:51:54 PM

Quote from: markm on June 26, 2015, 09:04:11 AM

Oh wow that keys to the past trick is killer!

It certainly explains why checkpoints were introduced! Nxt et. al. improved checkpoints by making transactions irreversible after 720 blocks. In fact, cynicSOB was invited to try attacking Nxt after he managed to double-spend a minor PoS alt.

Thanks to you both for your informative replies.

So NXT solution successfully solved problem #2 assuming that noone controls 51% of coins as of yesterday.
What can be done with weakness #1 ? How can it be exploited with less than 51% stake ?