One known cataclysm that could make the whole interruption of all the telecommunications but also every electricity network is a Major big Solar storm that hits the earth!
According to Google, cable on sea are mostly safe from big solar storm[1].
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.
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.
So what of a code would be part of Bitcoin protocol and that would depend on that the network is running that could sign blindly the blocks.. (Putting like a seal on them), include in the blocks a cryptographic signature that works like authentication signature ?
Authentication signature? There's no such thing on Bitcoin protocol.
[1]
https://cloud.google.com/blog/products/infrastructure/are-internet-subsea-cables-susceptible-to-solar-storms[2]
https://bitcoin.stackexchange.com/a/662