And what if some entities wanted to fool the word creating completely artificial blocks and adding them to the blockchain ? How to trust a copy of the blockchain then ? Do all late copies should not-trusted/canceled ??
That entity still have to produce valid block. It means attack they could do is limited[2] (e.g. creating empty block), while requiring lots of ASIC due to high difficulty.
I remembre around 2014 or so a website offering to buy empty used (addresses/wallets) .. If they do it in a limited network, they will be not in need of very high ressources/hardwares ! (or no?)
Sorry, but i fail to see correlation between high mining difficulty and old empty used address. Difficulty isn't affected by what address you use to receive mining reward. Can you elaborate further?
How to trust a copy of the blockchain then ? Do all late copies should not-trusted/canceled ??
Trust? Full node software automatically verify whether the block is valid or not. And as stated by other member, node eventually will choose chain with most work after telecommunication problem is solved.
And if they are the only actors of the/that network ??
They still need to create valid block, otherwise current full node on that network would reject it.
Authentication signature? There's no such thing on Bitcoin protocol.
I didn't say there is, It will need to be added !
It looks like i misunderstood your earlier statement. But such addition will add debate such as,
1. It may introduce some centralization.
2. Risk of the private key (used to create authentication signature) got leaked.