Immutability is a property in a system that makes it difficult to change. A system is considered immutable if it cannot be altered, replaced or manipulated after its creation or deployment.
This is a significant property and the fundamental advantage of blockchain technology. Bitcoin – the largest cryptocurrency by market capitalization – leverages blockchain technology to verify and store transactions and they are largely immutable once chained to the previous blocks.
Ethereum smart contracts, which are self-executing programs that run on the ethereum blockchain, are also immutable objects once deployed on the network.
What Is Blockchain Immutability, and how is it achieved?
Blockchain is a distributed ledger technology used to store information in chunks referred to as blocks. It is a type of database used to hold information in a secure and immutable manner. Each block has a unique hash value generated from the previous block’s hash using the SHA-256 hashing algorithm. A hashing algorithm is such that no two input data can produce the same outcome, and altering even a tiny portion of the input data produces an entirely different output.
Each block consists of the data to be stored, the hash of the previous block and that of the current block. Hence, altering the data in one block changes the hash value entirely, which renders it inconsistent with the previous block. Therefore, a malicious hacker would need to alter all the hashes of the previous blocks to cover their tracks.
Furthermore, each copy of the blockchain ledger is replicated and distributed across a decentralized network of computer nodes. This means that besides altering the hashes of each block, the hacker would need to access all the other computer nodes on the network to keep the information consistent.
Not to say all of this is impossible; however, it is improbable that any hackers will go through the stress, and this is how blockchain maintains its immutability and ensures the complete integrity of information.