What Are Enterprise Blockchains?

Updated on: May 13th, 2020
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One property of the Blockchain is, that it’s “append only”, i.e. only new blocks can be added and old blocks cannot be changed.

According to the course – CE101 Introduction To CryptoEconomics – this immutability is achieved through the use of cryptographic hash functions to create a unique hash-value for each block in the blockchain. This block hash is produced based on two things:

The block hash of the previous block in the blockchain.
The hash value of the information contained within the current block.

Therefor, if someone modify the content of a block (e.g. change some of the transactions), then the hash of all transactions within the block will change. Since the hash of the next block is calculated based on the previous hash, the hash of that block will change as well.

This will produce a domino effect in which all the block hashes in all the blocks followed the tampered block will change. Therefor all other nodes in the network can detect discrepancies to the main chain and would reject the tampered block.

Imagine a blockchain of length more than 4 blocks. In case a hacker attacks block 3 and tries to change the data, then the hash value of block 3 will change. And since the hash of block 4 is based on the block hash of previous block (block 3), it will change as well. The domino effect will change all block hashes in all blocks following the tampered block.

OF allphn
OF allphn

According your image(simplified bitcoin block chain),it seems block 3’s hash is not saved in block2.

OF allphn
OF allphn

From your post :”Imagine this for a second, a hacker attacks block 3 and tries to change the data. Because of the properties of hash functions, a slight change in data will change the hash drastically. This means that any slight changes made in block 3, will change the hash which is stored in block 2, now that in turn will change the data and the hash of block 2 which will result in changes in block 1 and so on and so forth. This will completely change the chain, which is impossible. This is exactly how blockchains attain immutability.”

I’m confused,why block 2 hash will changed after hacker changed block 3’s data? Could you explain more details?

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