Data integrity refers to the accuracy, consistency, and reliability of data throughout its lifecycle. Blockchain technology ensures data integrity through several key mechanisms:

1. Immutable Ledger

Once data is recorded on a blockchain, it cannot be altered or deleted without consensus from the network participants. This immutability is achieved through cryptographic hashing.

Each block in a blockchain contains a hash of the previous block, creating a chain of blocks. If any data in a block is changed, its hash will change, breaking the chain and alerting the network to the tampering.

2. Cryptographic Hashing

Blockchain uses cryptographic hash functions (like SHA-256) to create a unique digital fingerprint of data. This hash serves as a secure representation of the data, ensuring that even a minor change in the input data results in a completely different hash output.

Example: If a block contains the transaction data "Alice pays Bob 10 BTC", its hash would be unique. If someone alters this data to "Alice pays Bob 15 BTC", the hash will change entirely.

3. Consensus Mechanisms

Blockchain networks use consensus mechanisms (like Proof of Work, Proof of Stake, etc.) to agree on the validity of transactions. This ensures that only valid transactions are added to the blockchain, maintaining the integrity of the data.

Consensus prevents malicious actors from adding fraudulent data to the blockchain, as they would need to control a majority of the network to do so.

4. Decentralization

In a decentralized network, multiple copies of the blockchain exist across various nodes. Each node maintains a copy of the entire blockchain, making it difficult for any single entity to manipulate the data without detection. Any attempt to alter the data would need to be replicated across all copies, which is practically impossible.

5. Transparency and Auditability

Blockchain provides a transparent and auditable record of all transactions. Participants can verify the integrity of data at any time by reviewing the transaction history. This transparency fosters trust among users and helps identify any discrepancies.

Sample Code: Demonstrating Data Integrity with Hashing

Below is a simple example in JavaScript that demonstrates how hashing can be used to ensure data integrity:

const crypto = require('crypto');

// Function to create a SHA-256 hash
function createHash(data) {
    return crypto.createHash('sha256').update(data).digest('hex');
}

// Example data
const originalData = "Alice pays Bob 10 BTC";
const originalHash = createHash(originalData);

console.log("Original Data:", originalData);
console.log("Original Hash:", originalHash);

// Simulating data alteration
const alteredData = "Alice pays Bob 15 BTC";
const alteredHash = createHash(alteredData);

console.log("Altered Data:", alteredData);
console.log("Altered Hash:", alteredHash);

// Check for data integrity
if (originalHash === alteredHash) {
    console.log("Data integrity is intact.");
} else {
    console.log("Data integrity has been compromised!");
}
    

Conclusion

Blockchain technology provides robust mechanisms to ensure data integrity, including immutability, cryptographic hashing, consensus mechanisms, decentralization, and transparency. These features make blockchain a reliable solution for various applications, from cryptocurrencies to supply chain management.