iOS Keychain writing value results in error code -34018

Seems like this is a bug in Keychain, which only appears when you launch your app from xcode. See here: https://github.com/soffes/sskeychain/issues/52

We debugged it a lot and it seems an issue accessing the keychain when the app is launched from the background. This is only happening with the debugger (i.e. when launched from Xcode). We think the issue might be related in our case to the debugger keeping alive the app even if it should be killed by the OS. We tried in fact to run the app and then put it in background and launch many other app to occupy RAM. With the debugger the bug came up when resuming the app from the background, while without the debugger it didn't (we did run at least 10 tests each).

If someone will come here back with this error and XCode8 with iOS10, probably you have to enable KeyChain Share in the tab Capabilities:

As others have mentioned, this is a Keychain bug, one that Apple is aware of and has been aware of since at least mid-2015.

As of March 22, 2016, however, Apple has said:

We believe these problems were resolved in iOS 9.3.

iOS 9.3 was released on March 21, 2016.

See the thread: https://forums.developer.apple.com/thread/4743

To quote the response by an Apple employee:

Mar 22, 2016 3:28 AM

OK, here’s the latest. This is a complex problem with multiple possible causes:

• Some instances of the problem are caused by incorrect app signing. You can easily distinguish this case because the problem is 100% reproducible.

• Some instances of the problem are caused by a bug in how iOS supports app development (r. 23,991,853). Debugging this was complicated by the fact that another bug in the OS (r. 23,770,418) masked its effect, meaning the problem only cropped up when the device was under memory pressure.

  We believe these problems were resolved in iOS 9.3.

• We suspect that there may be yet more causes of this problem.

So, if you see this problem on a user device (one that hasn’t been talked to by Xcode) that’s running iOS 9.3 or later, please do file a bug report about it. Try to include the device system log in your bug report (I realise that can be tricky when dealing with customer devices; one option is to ask the customer to install Apple Configurator, which lets them view the system log). And if you do file a bug, please post your bug number, just for the record.

On behalf of Apple I’d like to thank everyone for their efforts in helping to track down this rather horrid issue.

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