Building a Simple Blockchain in Swift: A Beginner’s Guide

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Blockchain technology has revolutionized industries by introducing secure, decentralized systems. But have you ever wondered how a blockchain works under the hood? In this blog post, I’ll build a simple blockchain using Swift, step-by-step, to understand its core principles.

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What is a Blockchain?

A blockchain is a chain of blocks, where each block contains data, a timestamp, and a hash that links it to the previous block. The hash ensures data integrity—if a block is tampered with, the hash changes, breaking the chain.

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Setting Up the Project

Let’s dive into creating a simple blockchain in Swift.

1. Create a New Swift Project

• Open Xcode.
• Create a new macOS or iOS project.
• Choose a Command Line Tool template for simplicity.
• Name the project Blockchain.

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Writing the Code

Step 1: Define the Block

Each block in the blockchain contains:

1. Index
2. Timestamp
3. Data
4. Previous Hash
5. Current Hash

Here’s the code for a block:

import Foundation
import CryptoKit // For hashing

struct Block {
    let index: Int
    let timestamp: Date
    let data: String
    let previousHash: String
    var hash: String {
        let content = "\(index)\(timestamp)\(data)\(previousHash)"
        return SHA256.hash(data: content.data(using: .utf8)!)
            .map { String(format: "%02x", $0) }
            .joined()
    }
}

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Step 2: Define the Blockchain

The blockchain manages the list of blocks and ensures their integrity.

class Blockchain {
    private(set) var chain: [Block] = []

    init() {
        // Create the genesis block
        addBlock(data: "Genesis Block")
    }

    func addBlock(data: String) {
        let previousHash = chain.last?.hash ?? "0000"
        let newBlock = Block(
            index: chain.count,
            timestamp: Date(),
            data: data,
            previousHash: previousHash
        )
        chain.append(newBlock)
    }

    func isValid() -> Bool {
        for i in 1..<chain.count {
            let previousBlock = chain[i - 1]
            let currentBlock = chain[i]

            if currentBlock.previousHash != previousBlock.hash {
                return false
            }

            if currentBlock.hash != currentBlock.hash {
                return false
            }
        }
        return true
    }
}

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Step 3: Test the Blockchain

Now, let’s create and test the blockchain.

let blockchain = Blockchain()
blockchain.addBlock(data: "Block 1 Data")
blockchain.addBlock(data: "Block 2 Data")

print("Blockchain:")
for block in blockchain.chain {
    print("""
    --------------------
    Index: \(block.index)
    Timestamp: \(block.timestamp)
    Data: \(block.data)
    Previous Hash: \(block.previousHash)
    Hash: \(block.hash)
    """)
}

print("\nBlockchain Validity: \(blockchain.isValid() ? "Valid" : "Invalid")")

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Output Example

When you run the code, you’ll see an output like this:

Blockchain:
--------------------
Index: 0
Timestamp: 2024-11-22 06:52:46 +0000
Data: Genesis Block
Previous Hash: 0000
Hash: 3333794d35a5edf9165c562cea2c883e8c94d46e93dcb6817a0d09e8b86706fe
--------------------
Index: 1
Timestamp: 2024-11-22 06:52:46 +0000
Data: Block 1 Data
Previous Hash: 3333794d35a5edf9165c562cea2c883e8c94d46e93dcb6817a0d09e8b86706fe
Hash: 20962ef4d47b5f09b39c576a8b658a90318c3761c8dae7b8f227947475043ad6
--------------------
Index: 2
Timestamp: 2024-11-22 06:52:46 +0000
Data: Block 2 Data
Previous Hash: 20962ef4d47b5f09b39c576a8b658a90318c3761c8dae7b8f227947475043ad6
Hash: f118ae5c5a0679b513790847d015cd1b1a9c47599101c99bd983adaa0365d92a

Blockchain Validity: Valid

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What’s Next?

Now that you’ve built a simple blockchain, you can explore advanced features like:

1. Proof of Work: Introduce mining and difficulty levels.
2. Decentralization: Simulate a peer-to-peer network.
3. Transactions: Add transaction structures for practical use cases.

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Conclusion

Building a blockchain in Swift is an excellent way to understand how this technology works. While my example is basic, it lays the foundation for creating more complex systems. Try it out, and let me know your thoughts in the comments below! Also, I have added the complete project for your reference.

https://github.com/fareethjohn/SwiftBlockchain

Happy coding! 🚀