如何在区块链和超级账本结构中检测到区块链或世界状态中的数据篡改（已添加块的数据）？

Question

I am a new learner of blockchain technology. I have a couple of question regarding the tamper proof mechanism of the blockchain.

1) My understanding: I understood that hash of [ hash the previous block + content of current block ] will go as a hash to the next block. if we tamper content of a block the hash will change and the link to the next block will be broken.

My Question: If a suspect changed the content of a block long after the block got added, will the calculation of hash and placing the hash in the next block happens automatically ?. Suppose if some one has already illegally changed the content and the link is broken, is there an automatic mechanism to trigger the event that the link has been broken ?. At what time the tampered copy of blockchain will be identified and invalidated ?

2) My understanding: In Hyperledger fabric I uderstood that ledger = blockchain + worldstate. The world state is calculated based on the blockchain. The application will depend on worldstate values, the applications will not traverse through blockchain to find a value.

My questions are: i) how frequetly the worldstate is recalculated ?

ii) will a broken chain(in case of a tamper) is detected while re-calculating the worldstate

iii) what if a suspect tampers the worldstate on a peer. how this situation is set right ? will the tampering be detected during the consensus or any other acticity ?

I read and understood that the blockchain is tamper proof, but really want to understand which processes safe guard the BC ?

Answer 1

Imagine a blockchain world where chain has 1000 blocks and 100 nodes .

Now node x temperas with block 950 and changes its hash . As a result all consecutive block's hash changes. So node x now has a version of chain that is different from other 99 nodes . As majority of the nodes still has same chain it will be decided that node x has faulty chain and node x 's decision will not be taken into account when creating a new block. This is how blockchain becomes tamper proof.

Now lets consider an edge case scenario. Out of 100 nodes 51 nodes temperas with block 950 and changes its hash . Now these 51 nodes has a faulty chain but same chain . As a result this chain will prevail and actual chain will be discarded. This is known as 51% attack .