1. What is a Cryptocurrency?

A cryptocurrency is a digital form of money that uses blockchain technology to ensure security, transparency, and decentralization. The main features of a cryptocurrency are:

• Decentralization – there is no central authority controlling the currency.

• Security – each transaction is cryptographically secured.

• Immutability – once recorded in the blockchain, data cannot be altered.

2. Basic Components of Cryptocurrency

In creating a cryptocurrency, there are three key elements to implement:

• Blockchain – a structure that stores transaction history in blocks.

• Transactions – records of transferring value between users.

• Tokens – representations of value within the system (e.g., cryptocurrency units).

3. How to Create a Simple Blockchain in Swift

A blockchain is a chain of blocks that stores transaction data. You can define a simple structure in Swift:

Block Structure

import Foundation
import CryptoKit

struct Block {
    let index: Int
    let previousHash: String
    let timestamp: Date
    let data: String
    let hash: String
    
    init(index: Int, previousHash: String, data: String) {
        self.index = index
        self.previousHash = previousHash
        self.timestamp = Date()
        self.data = data
        self.hash = Block.calculateHash(index: index, previousHash: previousHash, timestamp: self.timestamp, data: data)
    }
    
    static func calculateHash(index: Int, previousHash: String, timestamp: Date, data: String) -> String {
        let input = "\(index)\(previousHash)\(timestamp)\(data)"
        let hash = SHA256.hash(data: input.data(using: .utf8)!)
        return hash.compactMap { String(format: "%02x", $0) }.joined()
    }
}

Blockchain

Now you can create a blockchain structure that stores these blocks:

struct Blockchain {
    var blocks: [Block]
    
    init() {
        self.blocks = [Block(index: 0, previousHash: "0", data: "Genesis Block")]
    }
    
    mutating func addBlock(data: String) {
        let previousBlock = blocks.last!
        let newBlock = Block(index: previousBlock.index + 1, previousHash: previousBlock.hash, data: data)
        blocks.append(newBlock)
    }
}

4. Adding Transaction Functionality

Every cryptocurrency is based on a transaction system. We can define a simple transaction structure:

struct Transaction {
    let sender: String
    let recipient: String
    let amount: Double
}

Transactions will be added to blocks to ensure they are consistent with the blockchain.

5. Using Cryptography for Signatures

To secure transactions, we need to add digital signatures. We will use CryptoKit to generate signatures for transactions:

import CryptoKit

func signTransaction(transaction: Transaction, privateKey: P256.Signing.PrivateKey) -> String {
    let transactionData = "\(transaction.sender)\(transaction.recipient)\(transaction.amount)"
    let signature = try! privateKey.signature(for: Data(transactionData.utf8))
    return signature.compactMap { String(format: "%02x", $0) }.joined()
}

func verifyTransaction(transaction: Transaction, signature: String, publicKey: P256.Signing.PublicKey) -> Bool {
    let transactionData = "\(transaction.sender)\(transaction.recipient)\(transaction.amount)"
    let signatureData = Data(hex: signature)
    return publicKey.isValidSignature(signatureData, for: Data(transactionData.utf8))
}

6. What's Next?

This example gives you the basics of creating a cryptocurrency. In a full system, you would need to implement:

• Consensus mechanism (e.g., Proof of Work or Proof of Stake),

• Wallet management and user balances,

• Network communication between blockchain nodes,

• Protection against attacks (e.g., Double Spend).

Summary

Creating a cryptocurrency in Swift is an ambitious yet educational project. Thanks to CryptoKit and modern tools like Blockchain in Swift, you can create your own simple cryptocurrency. While this is just the beginning, it provides a solid foundation for further development into a full-fledged cryptocurrency system.