APCKeychainStore.stringForKey randomly returning empty values

[brendenwest]

I'm seeing unpredictable behavior with APCKeychain, where APCKeychainStore.stringForKey incorrectly returns an empty value about 1/3 of the time. Where APCKeychainStore incorrectly returns empty values, I can force-close the app and see the correct values returned on subsequent queries.

I'm getting and setting keychain values via Swift, like this:

var email : String {
    get {
        if let value = APCKeychainStore.stringForKey(kEmailPropertyName) {
            return value
        }
        return ""
    }
    set {
        APCKeychainStore.setString(newValue, forKey: kEmailPropertyName)
    }
}

var password : String {
    get {
        if let value = APCKeychainStore.stringForKey(kPasswordPropertyName) {
            return value
        }
        return ""
    }
    set {
        APCKeychainStore.setString(newValue, forKey: kPasswordPropertyName)
    }
}

[rsanchezsaez]

Could this be related to the infamous -34018 (errSecMissingEntitlement) keychain bug?

[brendenwest]

I get no errors on compile or at run time.

Also, I haven't enabled the Keychain sharing entitlement, since I don't expect to share the keychain data with other apps.

[rsanchezsaez]

Are you sure you don't see any keychain-related message logged onto the console at runtime when you get nil from the stringForKey() method? (AppCore should be compiled in Debug for you to see them)

The bug I was mentioning would manifest by APCKeychainStore running this code path, which would print a debug log message on the console and return nil.

There's more info about this issue here. It has been a longstanding keychain issue on iOS, and unfortunately it's quite random.

[brendenwest]

I see this error when I haven't yet set a passcode:

APC_DEBUG in +[APCKeychainStore dataForKey:service:accessGroup:] at APCKeychainStore.m:105 => SecItemCopyMatching query failed with error code: 4294941996i

But an error is expected there. I haven't recently repro'd the issue of unexpected missing values.