Podcast Swift

AppForce1: Special 2

Donny is a curious, passionate iOS Developer from the Netherlands who loves learning, sharing knowledge and programming in general. He has experience with several technologies like Python, SQL, PHP, Javascript but iOS has been his passion for a while now.

00:14 Donny Wals

01:07 How Donny and Jeroen met

01:46 The Do iOS birdie

02:32 Beamer specs, check the DO iOS video

09:54 Disney Streaming Services

13:28 I’m in App

13:50 The A10 ring)

14:20 Company went bankrupt, now what?

15:47 Packt publishing

17:26 Donny’ blog

18:24 Practical Combine book

18:43 Why switch from SDK to topical books?

21:22 Jeroen on the costs of organizing a conference

22:40 A little recap on what’s discussed

23:55 What’s your target audience for your books?

25:48 Recommendations by Donny

26:19 Book: Algorithms to Live By

29:18 Swift Concurrency Roadmap

32:56 Favorite Swift Language change

34:48 Does everything you do pay the bills?

36:14 Motivation to do “the work”

38:05 How to start? Tips by Donny.

41:27 Workflow when writing blog posts.

42:51 Who helped you?

44:48 Parting words, follow your heart.

Additional notes:

WikiPedia artikel over The Mythical Man-Month

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Podcast Swift

AppForce1: Episode 3

Welcome to my 3rd episode.

The focus of this episode will be a bit more on basic Swift related items. I will also mention a great online event next month you should check out. CocoaHeadsNL has released the video from their October meetup with Donny Wals. I have some great news about upcoming interviews I will be releasing in the coming weeks.

Please rate me on Apple Podcasts.
Sponsor me on
Send me feedback on SpeakPipe
Or contact me through twitter.

00:00 Intro

01:01 Welcome

01:13 @AppForce1

01:16 SpeakPipe

01:23 Results 1st interview

01:59 Monday morning tweet

03:45 Mobile Optimized 2020

03:56 CocoaHeadsNL: Video Donny Wals

04:07 CocoaHeadsNL: RSVP

04:14 Under the Radar: Marco Arment on Overcast and SwiftUI

04:36 Obscure APIs

04:59 Progress Expectations

05:33 Porting iPhone app to iPad

06:02 Presenting Popovers from SwiftUI

06:48 How to Create App Clips

07:13 JSON Parsing in Swift

07:41 Formatting numbers in Swift

08:16 Getting the number of days between two dates in Swift

08:45 Swift Concurrency Roadmap

Podcast Swift

AppForce1: Episode 2

Welcome to my 2nd episode.

The focus of this episode will be a bit more on SwiftUI related items. I will also mention a great online event next month you should check out. CocoaHeadsNL has announced their november and december planning.
Please rate me on Apple Podcasts.
Sponsor me on
Send me feedback on SpeakPipe
Or contact me through twitter.

00:00 Intro

00:46 Special: Antoine van der Lee

00:58 Feedback: Speakpipe

01:07 Home Screen Quick Actions — SwiftUI 2.0

01:27 Getting started with the Combine framework in Swift

01:49 The magic of redacted modifier in SwiftUI

02:15 Updating your apps with silent push notifications

02:32 Connecting and merging Combine publishers in Swift

02:56 Evolution of the programming languages from iPhone OS 1.0 to iOS 14

03:12 How Swift API Availability Works Internally

03:48 Nova is here

04:14 How to pass data between views using Coordinator pattern in Swift

04:37 Donny’s monday morning

06:08 CocoaHeadsNL meetups

06:16 Sponsor CocoaHeadsNL

06:20 SwiftAlps

06:42 Outro

06:52 Sponsor me

06:56 Feedback?

07:05 Remember the special

Random thoughts Swift

At the Dutch CocoaHeads meetup in september I presented about Tuist.

Our path to micro frameworks using

In this video I show how we at Achmea changed the architecture of our app to use µ frameworks with I demonstrates how to create a sample app and shows the new structure of the ‘Even Appen’ app.

Random thoughts Swift

Github Actions and MacOS based Actions charged at 10x

Something I forgot to mention on my previous post on GitHub Actions.

GitHub charges 10 build minutes for each MacOS build minute. Be aware of this when working with GitHub Actions for your Mac based builds. It is probably worth it to try and off load as much work as possible to a Linux based image.

SwiftLint and other code analysis is a perfect example of examples of work to be offloaded to a Linux image.

Security Swift

Store data, encrypted

Today I want to share a helper class I worked on a while back. The requirement was that some (large) piece of data needed to be stored on the device, it should be stored encrypted. File protection complete was deemed not enough.

The idea was that a piece of data needed to be stored on disk, with a key stored in the keychain, in the secure enclave if available.

Just a few lines, but there’s actually a lot going on. The code created was inspired by various bits and pieces online and it took a bit of trial and error to get right.

First things first. We need to determine if a Secure Enclave is available and functional.

import Foundation
import os.log

enum CryptoError: Error {
    case keyCreationFailed
class Crypto {
    static var shared: Crypto {
        return self.sharedInstance
    private static let sharedInstance = Crypto()
    private let keyName = "disk_storage_key"
    private let hasSecurityEnclave: Bool
    private let algorithm: SecKeyAlgorithm
    private let keySize: Int
    private let keyType: CFString
    init() {
        var attributes = [String: Any]()
        attributes[kSecAttrKeyType as String] = kSecAttrKeyTypeEC
        attributes[kSecAttrKeySizeInBits as String] = 256
        attributes[kSecAttrTokenID as String] = kSecAttrTokenIDSecureEnclave
        var error: Unmanaged<CFError>?
        let randomKey = SecKeyCreateRandomKey(attributes as CFDictionary, &error)
        if randomKey != nil {
            self.hasSecurityEnclave = true
            self.keySize = 256
            self.keyType = kSecAttrKeyTypeEC
            self.algorithm = .eciesEncryptionCofactorVariableIVX963SHA256AESGCM
        } else {
            self.hasSecurityEnclave = false
            self.keySize = 4096
            self.keyType = kSecAttrKeyTypeRSA
            self.algorithm = .rsaEncryptionOAEPSHA512AESGCM

That actually quite a lot of code already isn’t it. But if you follow along in the above code, it’s not that complicated. We just try to create a random key that requires the Secure Enclave. To my knowledge this generates a key pair, but does not store anything in the keychain or the Secure Enclave. Based on the result, a couple properties are stored on the Crypto class.

Generating a new key pair

Next up is generating a key pair and actually hanging on to it.

private func makeAndStoreKey(name: String) throws -> SecKey {
        guard let access =
                self.hasSecurityEnclave ? SecAccessControlCreateFlags.privateKeyUsage : [],
                nil) else {
                    throw CryptoError.keyCreationFailed
        var attributes = [String: Any]()
        attributes[kSecAttrKeyType as String] = self.keyType
        attributes[kSecAttrKeySizeInBits as String] = self.keySize
        #if targetEnvironment(simulator)
        print("SIMULATOR does not support secure enclave.")
        if self.hasSecurityEnclave {
            attributes[kSecAttrTokenID as String] = kSecAttrTokenIDSecureEnclave

        let tag = name
        attributes[kSecPrivateKeyAttrs as String] = [
            kSecAttrIsPermanent as String: true,
            kSecAttrApplicationTag as String: tag,
            kSecAttrAccessControl as String: access

        var error: Unmanaged<CFError>?
        let privateKey = SecKeyCreateRandomKey(attributes as CFDictionary, &error)

        if let error = error {
            throw error.takeRetainedValue() as Error

        guard let unwrappedPrivateKey = privateKey else {
            throw CryptoError.keyCreationFailed

        return unwrappedPrivateKey

Why is using these keychain functions so verbose? A lot of stuff going on. But if you read through it carefully you will see that, again, a key pair is generated, but now we actually hang on to it. See that kSecAttrIsPermanent being give a value of true?

Also notice that there is some code to deal with a simulator not having a Secure Enclave.

Loading a key

We did most of the hard work already now. We also need some code to load a key. We’ll get to choosing between loading and generating in a bit. Key take away in the next bit is that the resulting SecKey is optional. We just might try and load a key and if it fails, we create one…

    private func loadKey(name: String) -> SecKey? {
        let tag = name
        let query: [String: Any] = [
            kSecClass as String: kSecClassKey,
            kSecAttrApplicationTag as String: tag,
            kSecAttrKeyType as String: self.keyType,
            kSecAttrKeyClass as String: kSecAttrKeyClassPrivate,
            kSecReturnRef as String: true

        var item: CFTypeRef?
        let status = SecItemCopyMatching(query as CFDictionary, &item)
        guard status == errSecSuccess else {
            return nil
        return (item as! SecKey) // swiftlint:disable:this force_cast

Let’s encrypt

Now we are getting to the good part. Let’s encrypt (pun intended).

func encrypt(data clearTextData: Data) throws -> Data? {
        let key = try loadKey(name: keyName) ?? makeAndStoreKey(name: keyName)

        guard let publicKey = SecKeyCopyPublicKey(key) else {
            // Can't get public key
            return nil
        let algorithm: SecKeyAlgorithm = self.algorithm
        guard SecKeyIsAlgorithmSupported(publicKey, .encrypt, algorithm) else {
            os_log("Can't encrypt. Algorithm not supported.", log: Log.crypto, type: .error)
            return nil
        var error: Unmanaged<CFError>?
        let cipherTextData = SecKeyCreateEncryptedData(publicKey, algorithm,
                                                       clearTextData as CFData,
                                                       &error) as Data?
        if let error = error {
            os_log("Can't encrypt. %{public}@", log: Log.crypto, type: .error, (error.takeRetainedValue() as Error).localizedDescription)
            return nil
        guard cipherTextData != nil else {
            os_log("Can't encrypt. No resulting cipherTextData", log: Log.crypto, type: .error)
            return nil

        os_log("Encrypted data.", log: Log.crypto, type: .info)
        return cipherTextData

Did you notice the optional chaining on the loadKey call?

Let’s decrypt

Having encrypted data is fun and all, but we do need some way to decrypt it again. Notice that in the next bit, being unable to load a key is a failure. When decrypting we do expect that a key is already present.

func decrypt(data cipherTextData: Data) -> Data? {
        guard let key = loadKey(name: keyName) else { return nil }

        let algorithm: SecKeyAlgorithm = self.algorithm
        guard SecKeyIsAlgorithmSupported(key, .decrypt, algorithm) else {
            os_log("Can't decrypt. Algorithm not supported.", log: Log.crypto, type: .error)
            return nil

        var error: Unmanaged<CFError>?
        let clearTextData = SecKeyCreateDecryptedData(key,
                                                      cipherTextData as CFData,
                                                      &error) as Data?
        if let error = error {
            os_log("Can't decrypt. %{public}@", log: Log.crypto, type: .error, (error.takeRetainedValue() as Error).localizedDescription)
            return nil
        guard clearTextData != nil else {
            os_log("Can't decrypt. No resulting cleartextData.", log: Log.crypto, type: .error)
            return nil
        os_log("Decrypted data.", log: Log.crypto, type: .info)
        return clearTextData


A couple things to notice in all of the above.

Security Swift

Client certificate with URLSession in Swift

Recently we I needed to implement an API in an app requiring a TLS client certificate.

It proved to be pretty simple, but I did need connect various bits and pieces together to get to a working solution. In this post I’ll show what worked for me.

To learn more about client certificate:

Basically it involves a few things.

  • A client certificate, in my case packaged as a p12 file.
  • A password for the p12 files.
  • A cocoa pod called ASN1Decoder, to allow interpretation of ASN.1 formatted data.
  • An URLSessionDelegate
  • Once successfully obtaining the client certificate identity, we can create an URLCredential to respond to the challenge.

So here is the lowdown extracted from the session delegate I created:

public class MyURLSessionDelegate: NSObject, URLSessionDelegate {
    public func urlSession(_ session: URLSession, didReceive challenge: URLAuthenticationChallenge, completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void) {
        // `NSURLAuthenticationMethodClientCertificate`
        // indicates the server requested a client certificate.
        if challenge.protectionSpace.authenticationMethod
             != NSURLAuthenticationMethodClientCertificate {
                completionHandler(.performDefaultHandling, nil)

        guard let file = Bundle(for: HTTPAccessURLSessionDelegate.self).url(forResource: p12Filename, withExtension: "p12"),
              let p12Data = try? Data(contentsOf: file) else {
            // Loading of the p12 file's data failed.
            completionHandler(.performDefaultHandling, nil)

        // Interpret the data in the P12 data blob with
        // a little helper class called `PKCS12`.
        let password = "MyP12Password" // Obviously this should be stored or entered more securely.
        let p12Contents = PKCS12(pkcs12Data: p12Data, password: password)
        guard let identity = p12Contents.identity else {
            // Creating a PKCS12 never fails, but interpretting th contained data can. So again, no identity? We fall back to default.
            completionHandler(.performDefaultHandling, nil)

        // In my case, and as Apple recommends,
        // we do not pass the certificate chain into
        // the URLCredential used to respond to the challenge.
        let credential = URLCredential(identity: identity,
                                   certificates: nil,
                                    persistence: .none)
        challenge.sender?.use(credential, for: challenge)
        completionHandler(.useCredential, credential)

As you can see, there is a lot of “if it fails we go to default” going on. This is security related code, so if things don’t work, we do not try any recovery, default handling just implies that no client certificate will be used and thus the connect should fail.

Here is the PKCS12 implementation. It is actually based on It is basically some helper code to bridge Core Foundation types into the memory safety of Swift.

private class PKCS12 {
    let label: String?
    let keyID: NSData?
    let trust: SecTrust?
    let certChain: [SecTrust]?
    let identity: SecIdentity?

    /// Creates a PKCS12 instance from a piece of data.
    /// - Parameters:
    ///   - pkcs12Data:
              the actual data we want to parse.
    ///   - password:
              The password required to unlock the PKCS12 data.
    public init(pkcs12Data: Data, password: String) {
        let importPasswordOption: NSDictionary
          = [kSecImportExportPassphrase as NSString: password]
        var items: CFArray?
        let secError: OSStatus
          = SecPKCS12Import(pkcs12Data as NSData,
                            importPasswordOption, &items)
        guard secError == errSecSuccess else {
            if secError == errSecAuthFailed {
                NSLog("Incorrect password?")

            fatalError("Error trying to import PKCS12 data")
        guard let theItemsCFArray = items else { fatalError() }
        let theItemsNSArray: NSArray = theItemsCFArray as NSArray
        guard let dictArray
          = theItemsNSArray as? [[String: AnyObject]] else {
        func f<T>(key: CFString) -> T? {
            for dict in dictArray {
                if let value = dict[key as String] as? T {
                    return value
            return nil
        self.label = f(key: kSecImportItemLabel)
        self.keyID = f(key: kSecImportItemKeyID) = f(key: kSecImportItemTrust)
        self.certChain = f(key: kSecImportItemCertChain)
        self.identity = f(key: kSecImportItemIdentity)


Any question? I’ll gladly answer any questions you might have.