Immutability

immutability means that once data is written to the blockchain, it cannot be altered, deleted, or tampered with. This is a foundational characteristic that ensures the integrity and security of the data stored on the blockchain.

The blockchain’s structure, where each block is linked to the previous one, creates a chronological chain of blocks. Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data.

Altering a block would require changing all subsequent blocks, which is computationally infeasible in a secure blockchain. The hash function creates a unique identifier for each block based on its content, and if any data in the block is altered, the hash will change, making it evident that the block has been tampered with.

Blockchain networks use consensus mechanisms like Proof of Work (PoW) or Proof of Stake (PoS) to agree on the validity of transactions and the state of the blockchain. This decentralised agreement process ensures that no single entity can unilaterally alter the blockchain.

On platforms like Ethereum, immutability also applies to smart contracts. Once deployed, the code of a smart contract cannot be changed, ensuring that the contract will execute exactly as written.