Backing up the blockchain to improve security

[Imnotbenbernanke]

I was reading Satoshi's white paper and it said:

The
system   is   secure   as   long   as   honest   nodes   collectively   control   more   CPU   power   than   any
cooperating group of attacker nodes.

...

If   a   greedy   attacker   is   able   to
assemble more CPU power than all the honest nodes, he would have to choose between using it
to defraud people by stealing back his payments, or using it to generate new coins.  He ought to
find it more profitable to play by the rules, such rules that favour him with more new coins than
everyone else combined, than to undermine the system and the validity of his own wealth

Because then they could falsely sign transactions and double-spend without getting caught. If a trusted central authority, for example a website controlled by a commity, would make a backup of the blockchain every day and then check it every 24 hours for suspicious activity increase security? In theory they could also restore transactions since the last backup. Bitcoin has alot of CPU power, so the risk for someone having enough CPU power for this is lower but alot of cryptocurrencies don't have alot of CPU power. Is it a good solution for those cryptocurrencies to increase security? Since the risk for this to happen is greater if you have less CPU power.

p.s. I'm new to this forum but intrigued by the technology, I hope to learn more so sorry if I ask a stupid question.
p.p.s. I'm not Janet Yellen either ^^

[watashi-kokoto]

This already happens.

In fact thousands of people's computers all over the world download the chain every 10 minutes and automatically verify what you've said.
So suspicious activity like reorganizations are spotted instantly.

What you read is the 51% attack. There used to be doublespends attacks back in the good old days of huge pools, against a dice roll gambling site. You can look it up, the site has a bug , that enabled the attack.

But currently there is no evidence that there's doublespends going on today, (except against 0-confirmation sites) so feel free to report or mention any suspicion that you may have.

0-conf sites don't really count as an attacks because everyone knows that accepting 0-conf transactions is unsafe.

EDIT: you see the problem with 51% isn't that it won't be spotted (it will), but what can be done about it.
Making Bitcoin centralized would "solve" the problem users have:

• payments do not confirm
• The attacker makes received funds return back to senders for fun
• coins value drops to $0.01 ... actually the price will start tanking much sooner when rumors that 51% attack is about to happen

But miners can't mine anymore. Logical solution is to "upgrade" hash algorithm to Keccak. This would mean that attacker's mining devices become worthless instantly. But so will honest miner's devices. The huge problem is Bitcoin rules need to be changed, and the difficulty will drop. There is no consensus how to solve this issue, but it definitely can be done once Bitcoin is really 51% attacked.

Because then they could falsely sign transactions and double-spend without getting caught.

This is false. Even with 51% attack (or 99% attack or 100% attack) The real owner still controls their funds. But the attacker can return the funds back in time to previous owners or create fake histories. But the attacker cannot steal for example coinbase transactions, so users in principe could "put" their funds to miner's wallet to save the funds from going back to whoever sent them.


Another possible solution

The honest users can all go to factories and make more mining devices. In this way, the honest users could regain control of the network and "save" Bitcoin.

But don't worry. Dogecoin will work correctly.