How can I remove keychain data from iOS?

Question

I have a phone and the only explanation I can arrive at is the app is re-identifying my device via keychain data, even after reinstalling the application.

Is there a way how I can remove the keychain data from my phone to test if the Keychain is leaking identity? I am not talking about passwords only, the app saves some data and I need to remove it.

I am okay removing all keychain data from my phone. All answers I see on the internet are for Mac. I am looking for something that works on iOS.

I want to make sure ALL data is removed and that an app does not have knowledge of a previous session.

Answer 1

Yes, I too was surprised to find an app where, despite the warning when deleting the app that all data would be deleted too, a reinstall retains all account information and data. The app I encountered does not use iCloud at all. I’m guessing it stores an identifying token in the device keychain and uses that token to retrieve data from a server.

According to Apple Developer Technical Support person ‘Quinn “The Eskimo!”’ on the Apple Developer Forums,

• This is currently expected behaviour despite being ‘an obvious privacy concern’
• Apple tried to fix this around 2017 but enough app developers complained that they decided to keep it
• However, Apple could theoretically fix this in the future without warning

For now, it seems that completely wiping your device before re-installing apps is the only practical way to go. And don’t restore from a backup after wiping either, as the backup could contain the old keychain data.

To quote some of the details Quinn ‘The Eskimo’ gave:

First, a timeline:

• All versions of iOS prior to 10.3 beta preserve keychain items when an app is deleted.

IMPORTANT This was most definitely an implementation detail of the original iOS keychain. Our keychain documentation has never specified what would happen in this case.

• 10.3 beta included a change that deleted such items.

• That caused compatibility problems (apps were relying on the existing behaviour, even though it wasn’t documented), so it was rolled back before 10.3 GM.

• iOS 11 introduced the DeviceCheck framework, which provides a forward path for one of the most common legitimate use cases of this behaviour. For more info on this, see WWDC 2017 Session 702 Privacy and Your Apps.

Second, preserving keychain items on delete is an obvious privacy concern. As far as I know Apple has not made any specific announcements as to how we intend to resolve this issue (1). However, I don’t think it would surprise anyone if the 10.3 behaviour returned at some point in the future. I would hope that we’d be more proactive about announcing such a change -- for example, talking about it at WWDC -- but, as always, I can’t make any promises about The Future™.

Answer 2

iOS used to retain keychain content even when you delete the whole app (I know for sure because an app I maintained relied on it). But this has changed in recent years and now it's deleted as well. Depending on your iOS version, you might see the old behavior.

But it's more likely the data is stored in your iCloud keychain. If you have a Mac, then you can use the macOS /Applications/Utilities/Keychain Access.app and select iCloud on the left to see the content. Search for the app name or company name. Once you have found the item and are absolutely sure it's the right one, simply delete it.

If you can't find an entry or you're not sure which item to delete, contact the developer. It's probably the best option anyway as there might be a supported way in the app to remove/reset the data.

Answer 3

Keychain data is stored (assuming you are signed into your Apple Account on the phone) in iCloud and synced to all your devices signed into iCloud.

On your iPhone you can turn off iCloud Keychain in:

Settings > [Account name] > iCloud > Keychain

Just turn off iCloud Keychain and (assuming that App does indeed use iCloud keychain) will all be gone from your phone.