Blockchain technology has revolutionized data storage and transmission in our imagination. A blockchain, in its most basic sense, is a decentralized, immutable ledger that keeps transactions on many computers. But how does data in a block of a blockchain get secured and locked? This article explores the mechanisms that ensure the integrity and immutability of blockchain data.

The Design of a Blockchain

To understand how data is secured, first learn the basic design of a blockchain. A blockchain has a chain of "blocks," each block having:

Data: This can be transactions (in cryptocurrencies), contracts, or any other type of data.

Hash of the Previous Block: A unique reference to the preceding block in the chain.

• Nonce: A random value utilized throughout the mining process.

• Timestamp: A ledger of when the block was created.

• Merkle Root: A hash of every transaction within the block, in order to verify data integrity.

Cryptographic Hashing: The Foundation of Immutability

Embedded within blockchain security is cryptography, most notably cryptographic hashing. A hash function works by taking an input (data of any size) and producing a fixed-length character string, the "hash." This hash has a number of significant properties:

• Deterministic: The same input always produces the same hash.

• One-way: It is computationally infeasible to take the hash and produce the original input.

• Collision-resistant: It is extremely difficult to find two different inputs that have the same hash.

• In a blockchain, information of every block is passed through a hash function and produces a unique fingerprint. The hash is added to the header of the

• subsequent block. This process creates a chain of blocks with every block connected to the previous block by its hash.

The Role of the Previous Block's Hash

The inclusion of the hash of the previous block in the present block is the very basic component of blockchain security. It makes the blocks interdependent, meaning if the data of any previous block is altered, its hash will be altered. This alteration will again have an effect on the next block's hash and so on, throughout the entire chain.

This makes it virtually impossible to manipulate data on a blockchain. For an attacker to change one block, they would not only need to change the block's data but also need to recalculate its hash, as well as the hashes of all the subsequent blocks. This requires an unimaginable amount of computational power, making such an attack practically impossible for any blockchain of reasonable size.

Consensus Mechanisms: Reaching Agreement

While cryptographic hashing provides data integrity, consensus algorithms ensure that all members of the network agree on the state of the blockchain. Different blockchains use different consensus algorithms, but they are all for the same fundamental purpose: to validate new blocks and append them to the chain securely and in a decentralized manner.

Proof of Work (PoW)

In Proof of Work (PoW), miners compete to solve a complex mathematical puzzle. The winning miner gets to propose the next block. It requires a great amount of computation power, and hence it is expensive to alter the blockchain.

The solution to the problem is included in the block as the "nonce." Miners continually try different nonce values over and over again until they find one which, when added to the data in the block and hashed, produces a hash meeting certain criteria (e.g., it has a certain number of leading zeros).

As soon as a miner finds a valid nonce, other nodes within the network verify the solution. The block is added to the blockchain when the solution is correct, and the miner receives cryptocurrency reward.

Proof of Stake (PoS)

In Proof of Stake (PoS), validators are chosen to create new blocks depending on how much cryptocurrency they "stake" or own. Validators do not need to solve complex mathematical problems, but they have to risk their own funds. When they try to cheat the blockchain, they lose their stake.

PoS has various advantages over PoW, such as lower energy consumption and faster transaction processing. However, it also has some challenges of its own, such as the "nothing at stake" problem, which must be designed against cautiously.

Other Consensus Mechanisms

Other than PoW and PoS, there are several other consensus mechanisms such as Delegated Proof of Stake (DPoS), Practical Byzantine Fault Tolerance (PBFT), and hybrid models. Each of these mechanisms has its strengths and weaknesses, and the mechanism to be employed is based on the specific requirements of the blockchain.

Merkle Trees: Efficient Data Verification

As additional evidence to guarantee data integrity and efficiency, Merkle trees are often used on blockchains. A Merkle tree is an upside-down tree where the leaf nodes all hold the hash of a dataset, and an internal node will hold the hash of its children. The root of the tree, or the Merkle root, holds the hash of all datasets in the block.

Merkle trees allow us to confirm data in a very efficient way. Instead of downloading the entire block to confirm if one transaction is valid or not, a node only needs to download the Merkle path, a small number of hashes that prove the existence of that specific transaction in the Merkle tree.

The Immutability of Blockchain Data

Cryptographic hashing, in addition to the hash of the previous block, and robust consensus algorithms together serve to make blockchain data effectively unalterable. Once a block is linked to the chain, it is very difficult to alter its data without invalidating the entire chain

The immutability is an inherent property of blockchain technology and has wide-reaching implications for many applications including:

• Cryptocurrencies: Ensuring integrity of transaction records and preventing double-spending.

• Supply chain management: Tracking the source of products and preventing counterfeiting.

• Voting systems: Creating open and auditable voting systems.

• Digital identity: Providing secure and verifiable identities.

Conclusion

In a blockchain, how does a block of data on a blockchain get locked? It's through a combination of cryptographic hashing, the chaining of blocks via previous block hashes, and the consensus mechanism that validates and adds new blocks to the chain. This multi-layered approach ensures that blockchain data is not only secure but also immutable and tamper-proof. The resulting integrity and reliability of blockchain data are fundamental to its potential to revolutionize various industries and applications.