19.Immutability: Hashing and Chaining with Proof of Work
Channel: Rafiq Bouhsen
Date: 04/06/2021

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Source:
EDX
LinuxFoundationX LFS170x
Blockchain: Understanding Its Uses and Implications
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A) Specific Immutability Mechanisms:
Now, let’s look at how different blockchains implement immutability.

In Ethereum and Hyperledger, the immutability mechanism is the one that we’ve described previously. Each transaction and block is digitally signed and are linked using cryptographic hashes.

Corda, on the other hand, relies on its notary service for immutability. Each Corda network has one or more notary services that verify transactions. Each transaction is considered separately and, if approved, is signed by the notary service. Transactions signed by a notary are finalized and cannot be modified after the fact.

B) Hashing and Chaining:
It is important to understand the value of locking in the previous block by including its hash in the next block.

Creating a ledger of transactions with blocks that refer to previous blocks is a much better idea than numbering the blocks sequentially.
In a book with pages, 1, 2, 3, etc., it would be easy to tear out page 25 and replace it with another page.
The integrity of the book has been manipulated and altered. However, there is nothing about the new page number that ties it (chains it) to the content of the previous page.
Instead, in a blockchain, blocks are referenced by their hash and each block explicitly specifies which block (hash) it is building on.

C) Lab: Blocks
Next, let's engage with an interactive lab. This lab will give you the chance to examine blocks on the blockchain. Enjoy!
LINK: https://blockchaintrainingalliance.com/pages/lab-blocks