What is code signing?

Code signing is the process of attaching a cryptographic signature to an app that proves who built it and confirms the code has not been altered since it was signed. On iOS, code signing is mandatory: every app must be signed with a valid Apple developer certificate before it can run on a device, go through TestFlight, or ship to the App Store.

How code signing works

Code signing uses public-key cryptography. Apple issues a signing certificate tied to your developer account, which contains a private key only you hold. When you build the app, the toolchain uses that private key to generate a signature over the app's contents. The device and Apple's systems can then check the signature against the matching public certificate. If the app has been modified after signing, even slightly, the signature no longer matches and the system refuses to run it. This guarantees two things at once: the app comes from a verified developer, and it is exactly the code that developer signed.

What code signing requires

Signing an iOS app pulls together several pieces that all have to agree. You need an Apple Developer account, a signing certificate, an App ID and a bundle identifier that uniquely names the app, and a provisioning profile that ties the certificate, the App ID, and the allowed devices or distribution method together. If any of these do not match, the build fails to sign. This is why signing errors are one of the most common frustrations in iOS development: it is less a single switch than a set of credentials that must line up.

Why it matters

Code signing is a foundation of Apple's security model. It is how iOS ensures that apps cannot be silently tampered with and that users can trust an app's origin. It is not optional and cannot be skipped, which is why it sits on the critical path between writing an app and shipping it.

Code signing in AppFlight

Because signing is mechanical but error-prone, automating it removes a major source of friction. AppFlight handles code signing as part of its path from prompt to the App Store, alongside building native Swift, uploading to TestFlight, and submitting for review, so you do not have to assemble certificates and profiles by hand. The app still passes through Apple's checks, so signing gets the app accepted for distribution, not automatically approved.