Cryptography in Swift (iOS/macOS): Encryption and Hashing

Cryptography in Swift (iOS/macOS): Encryption and Hashing

In modern iOS and macOS development, data security is a critical aspect. Swift provides powerful built-in tools for cryptography, ranging from the low-level CommonCrypto (C-API) to the modern framework CryptoKit (iOS 13+/macOS 10.15+). In this article, we will cover the main encryption and hashing methods available to a Swift developer.

1. Hashing

Hashing is a one-way transformation of data into a fixed-length string. It is used for data integrity verification and password storage (with salt).

Example with CryptoKit (SHA-256)

import CryptoKit

func hashSHA256(_ input: String) -> String {    let inputData = Data(input.utf8)    let hashed = SHA256.hash(data: inputData)    return hashed.compactMap { String(format: "%02x", $0) }.joined()}

// Usagelet hash = hashSHA256("Hello, Swift!")print("SHA-256: \\(hash)")// Output: 8e3a... (64 characters)

Example with CommonCrypto (MD5, deprecated)

Note: MD5 is not recommended for security but can be used for integrity checks.

import CommonCrypto

func md5Hash(_ input: String) -> String {    let data = Data(input.utf8)    var digest = [UInt8](repeating: 0, count: Int(CC_MD5_DIGEST_LENGTH))    data.withUnsafeBytes { bytes in        _ = CC_MD5(bytes.baseAddress, CC_LONG(data.count), &digest)    }    return digest.map { String(format: "%02x", $0) }.joined()}

2. Symmetric Encryption (AES-GCM)

Symmetric encryption uses a single key for both encryption and decryption. CryptoKit provides a secure implementation of AES-GCM (Galois/Counter Mode).

Example of encryption and decryption with CryptoKit

import CryptoKit

func encryptAESGCM(plaintext: String, key: SymmetricKey) throws -> Data {    let plaintextData = Data(plaintext.utf8)    let sealedBox = try AES.GCM.seal(plaintextData, using: key)    return sealedBox.combined! // combined = nonce + ciphertext + tag}

func decryptAESGCM(ciphertext: Data, key: SymmetricKey) throws -> String {    let sealedBox = try AES.GCM.SealedBox(combined: ciphertext)    let decryptedData = try AES.GCM.open(sealedBox, using: key)    return String(data: decryptedData, encoding: .utf8)!}

// Usagelet key = SymmetricKey(size: .bits256) // 256-bit keylet encrypted = try encryptAESGCM(plaintext: "Secret message", key: key)let decrypted = try decryptAESGCM(ciphertext: encrypted, key: key)print("Decrypted: \\(decrypted)")

3. Asymmetric Encryption (RSA)

Asymmetric encryption uses a key pair: a public key (for encryption) and a private key (for decryption). In iOS/macOS, Security.framework and SecKey are used for working with RSA.

Example of RSA key generation and encryption

import Security

func generateRSAKeyPair() -> (privateKey: SecKey, publicKey: SecKey)? {    let attributes: [String: Any] = [        kSecAttrKeyType as String: kSecAttrKeyTypeRSA,        kSecAttrKeySizeInBits as String: 2048,        kSecPrivateKeyAttrs as String: [kSecAttrIsPermanent as String: false],        kSecPublicKeyAttrs as String: [kSecAttrIsPermanent as String: false]    ]    guard let privateKey = SecKeyCreateRandomKey(attributes as CFDictionary, nil) else {        return nil    }    let publicKey = SecKeyCopyPublicKey(privateKey)!    return (privateKey, publicKey)}

func encryptRSA(plaintext: String, publicKey: SecKey) -> Data? {    let plaintextData = Data(plaintext.utf8)    var error: Unmanaged<CFError>?    guard let ciphertext = SecKeyCreateEncryptedData(        publicKey,        .rsaEncryptionPKCS1,        plaintextData as CFData,