Step-by-Step Guide: Resigning IPA Files for Distribution

You have a perfectly good IPA file, but it's refusing to install. Maybe the certificate expired, or maybe you forgot to add a new tester's UDID.

Instead of rebuilding the entire project from Xcode (which might take hours or require source code you don't have handy), you can just resign the IPA. This guide walks you through the process of swapping out the signature and provisioning profile of an existing iOS app.

Prerequisites

• A macOS computer (required for standard tools).
• The .ipa file you want to resign.
• A valid Distribution Certificate (installed in Keychain).
• A matching Provisioning Profile (.mobileprovision).

Method 1: Using Fastlane (Recommended)

If you have fastlane installed (and you should), this is the easiest CLI method.

fastlane sigh resign ./path/to/app.ipa \ --signing_identity "Apple Distribution: Your Company (ID)" \ --provisioning_profile ./path/to/profile.mobileprovision

Fastlane automatically handles expanding the IPA, replacing the profile, resigning the binary, and zipping it back up.

Method 2: iOS App Signer (GUI)

If you prefer a visual interface, "iOS App Signer" is an excellent open-source tool.

1. Download iOS App Signer from GitHub.
2. Open the app.
3. Input File: Browse and select your IPA.
4. Signing Certificate: Select your valid certificate from the dropdown.
5. Provisioning Profile: Select your new profile (or choose "Re-Sign Only" if just updating cert).
6. Click Start.
7. Save your new IPA.

Method 3: Terminal (The Hard Way)

For those who want to understand exactly what's happening under the hood:

1. Unzip the IPA: unzip App.ipa
2. Remove old signature: rm -rf Payload/App.app/_CodeSignature
3. Replace profile: cp new.mobileprovision Payload/App.app/embedded.mobileprovision
4. Resign: codesign -f -s "Certificate Name" Payload/App.app
5. Zip it back: zip -qr Resigned.ipa Payload

Common Pitfalls

Entitlement Mismatches

The most common error. If your original app was built with "Push Notifications" entitlement but your new mobileprovision doesn't have it, the resign will technically succeed, but the app will crash on launch.

Keychain Issues

Ensure the specific private key for your signing certificate is present in your Keychain. having the public certificate is not enough.

Summary

Resigning is a vital skill for iOS release managers. It allows you to fix expiration issues and add testers without touching the source code.