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As far as I understand iOS Security, Oct. 12, an encrypted backup via iTunes also backs up the keychain of the device. While I recognize that some elements might not be restorable onto a different device (non-migatory), I was wondering if anything substantial is actually missing in an encrypted backup.

I am asking this because I heard that after wiping an iPhone, the private key of the app Threema is lost and cannot be restored via backup, even on the same device.

  • I've rolled back your edit because this site works better if answers are posted as such and not included into the answer. Can you please post an answer instead? – nohillside Dec 20 '13 at 14:15
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Got answer from Threema support. The keys actually are included in an encrypt iTunes backup but can only be restored to the same device. That is why they advise a separate backup.

Hello,

Yes, encrypted iOS backups include the iOS keychain and therefore also the Threema private key; however as it is stored with kSecAttrAccessibleWhenUnlockedThisDeviceOnly, it will additionally be encrypted with the device-specific UID key. Therefore, it will only be usable if restored to the same device that the backup was created on.

Best Regards,

Threema Support

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I would post this question to the support guys at Threema.

However from my understanding the only way to get your private key off the iPhone is to jailbreak your device.

Having said that there may be a way to get it off the backup.

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From Apple Developer:

The iOS gives an application access to only its own keychain items.

In iOS, an application always has access to its own keychain items and does not have access to any other application’s items. The system generates its own password for the keychain, and stores the key on the device in such a way that it is not accessible to any application. When a user backs up iPhone data, the keychain data is backed up but the secrets in the keychain remain encrypted in the backup. The keychain password is not included in the backup. Therefore, passwords and other secrets stored in the keychain on the iPhone cannot be used by someone who gains access to an iPhone backup. For this reason, it is important to use the keychain on iPhone to store passwords and other data (such as cookies) that can be used to log into secure web sites.

However it is still up to the application developer to allow the keychain to be backed up.

  • I think it is the other way around. The developer has to explicitly exclude files from an encrypted iTunes backup. See [developer.apple.com/library/ios/qa/qa1719/_index.html] – Norbert Fabritius Dec 20 '13 at 12:37
  • According to that documentation: iCloud and iTunes do not back up the contents of the following directories: <Application_Home>/AppName.app <Application_Home>/Library/Caches <Application_Home>/tmp – james_fuller Dec 30 '13 at 21:46

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