OTP Code Generation with CryptoKit: A Swift Approach
Tags: swiftcryptokittotp
Published: 2024-02-27 16:05:22

---
title: OTP Code Generation with CryptoKit: A Swift Approach
published: true
date: 2024-02-15 10:10:04 UTC
tags: SwiftCryptoKitTOTP
canonical_url: https://wesleydegroot.nl/blog/post/CryptoKit-TOTP
---

<h2><strong>Introduction</strong></h2> <p>In the realm of secure authentication, <strong>One-Time Passwords (OTPs)</strong> play a crucial role. Whether it's two-factor authentication (2FA) or protecting sensitive transactions, OTPs provide an additional layer of security. In this article, we'll explore how to generate OTPs using <strong>CryptoKit</strong>, Apple's powerful cryptographic framework.</p> <h2><strong>What Is an OTP?</strong></h2> <p>An OTP is a temporary password that is valid for a single use or a short period. It ensures that even if an attacker intercepts the password, they won't be able to reuse it. OTPs are commonly used in scenarios like logging into online accounts, confirming transactions, or accessing secure systems.</p> <h2><strong>Understanding TOTP (Time-Based OTP)</strong></h2> <ul> <li><strong>TOTP</strong> is a type of OTP that changes over time. It's based on a shared secret key and the current time.</li> <li>The secret key is known only to the user and the server.</li> <li>The server and the user's device both calculate the same OTP based on the secret key and the current time.</li> <li>The OTP is typically a 6 or 8-digit numeric code.</li> </ul> <h2><strong>Generating TOTP with CryptoKit</strong></h2> <p>Let's dive into the Swift code for generating a TOTP using <strong>CryptoKit</strong>. We'll assume you already have a shared secret key (usually provided during user registration).</p> <pre><code class="language-swift">import CryptoKit import CommonCrypto import Foundation func cryptoKitTOTP(secret: String) -&gt; String { let period = TimeInterval(30) let digits = 6 let secret = base32Decode(value: secret)! var counter = UInt64(Date().timeIntervalSince1970 / period).bigEndian // Generate the key based on the counter. let key = SymmetricKey(data: Data(bytes: &amp;counter, count: MemoryLayout.size(ofValue: counter))) let hash = HMAC&lt;Insecure.SHA1&gt;.authenticationCode(for: secret, using: key) var truncatedHash = hash.withUnsafeBytes { ptr -&gt; UInt32 in let offset = ptr[hash.byteCount - 1] &amp; 0x0f let truncatedHashPtr = ptr.baseAddress! + Int(offset) return truncatedHashPtr.bindMemory(to: UInt32.self, capacity: 1).pointee } truncatedHash = UInt32(bigEndian: truncatedHash) truncatedHash = truncatedHash &amp; 0x7FFF\_FFFF truncatedHash = truncatedHash % UInt32(pow(10, Float(digits))) return String(format: "%0\*u", digits, truncatedHash) } print(cryptoKitTOTP(secret: "5FAA5JZ7WHO5WDNN"))</code></pre> <h2><strong>Conclusion</strong></h2> <p>By leveraging <strong>CryptoKit</strong>, you can easily implement TOTP generation in your iOS apps. Remember to securely store and manage the shared secret key. OTPs enhance security and protect your users' accounts from unauthorized access.</p> <p>For more details, refer to the <a href="https://developer.apple.com/documentation/cryptokit">official Apple CryptoKit documentation</a>.</p>