Check whether in-app payment item has been purchased

I now spent about 24 hours implementing Apple's StoreKit IAP system. After 3 hours I got "purchasing" itself working but the last 21 hours I wasted on implementing all the receipt communication. Now I am struggling to get openSSL working (some bitcode compiler error) and I reached the point of giving up.

I don't care about people cracking my apps or things like this, so is there a simple way of just asking the App Store servers whether an in-app purchase has been made? Without any encryptions, keys, certificates or likewise?

The flow would be like this:

set a NSUserDefault to "true" after purchasing
on every app launch, if there is an internet connection, check again
unless the device is connected to the internet, the NSUserDefault stays on "true"
if a user tempered with the NSUserDefault, it will be overwritten as soon as the app connects to the internet again
If the user finds his way around it, he deserves to keep the item, no user on the world can pay me enough to spend one more hour on that

So if you know a simple way of achieving this, please let me know. I noticed that after buying a (non-consumable) product with the test account, the popup tells you that you've already bought this item before. Maybe this can be used for this purpose?

I am sorry for the rather informal way of posting right now, but this is the first ever time where I think Google did a better job with Android than Apple did with iOS. There are cracks for literally every app anyway, Google's system is far from being bulletproof but in the end of the day, what difference does it make if a cracker takes 10 minutes or 2 hours to manipulate the app?

It took me like 1 hour to get in app payments working in my Android apps but what Apple requires here is ridiculous. Their "instructions" aren't helping at all, it's like they want to make it a secret how to implement all that and you gotta take a guess.

Solution

If you don't want to check receipts, you only need to implement the SKPaymentTransactionObserver protocol and add whatever object you implemented it in as an observer using SKPaymentQueue's addTransactionObserver. Ideally, you want this done early in your App Delegate to ensure you receive any transactions sent to your app on launch (this is most important for subscriptions).

In the paymentQueue:updatedTransactions: method, check the transactionState of each transaction. If it's SKPaymentTransactionStatePurchased or SKPaymentTransactionStateRestored, then the purchase is (supposed to be) valid. You can then store the status in NSUserDefaults or a database.

Don't forget to implement restoring purchases.

This works quite well, but anyone who has jailbroken their device and installed whatever software it is that bypasses IAPs will get IAPs for free: it does not need to be specific to your app, they just return "purchased" for any IAP.