Q:

Any example on how to implement the new VerificationController and the KNOWN_TRANSACTIONS_KEY constant?

I've been looking at implementing the new VerificationController to verify in-App-Purchases:
http://developer.apple.com/library/ios/#releasenotes/StoreKit/IAP_ReceiptValidation/_index.html
And I wonder if there is some example anywhere en how to validate a transaction, since it seems that the - (BOOL)verifyPurchase:(SKPaymentTransaction *)transaction; is not enough and it has to be implemented internally to verify the purchase when the data form the server is received.  
Another question is if anyone has a clue on what the KNOWN_TRANSACTIONS_KEY is and how to fill it, is it just the product id of the purchase? 

A:

In the file "VerificationController.m", check this function:
- (void)saveTransactionId:(NSString *)transactionId

we can see, KNOWN_TRANSACTIONS_KEY is a key to be wrote to NSUserDefaults. So we don't need to touch it.
login iTunes Connect > Manage Your Apps > (click your app) > Manage In-App Purchases > click the link View or generate a shared secret (at bottom-left of the page)
it'll show us:

A shared secret is a unique code that you should use when you make the
  call to our servers for your In-App Purchase receipts.

Just click Generate.

A:

You can find a complete implementation over here: https://github.com/evands/iap_validation

A:

RayWenderlich.com Tutorial
This article, In-App Purchases in iOS 6 Tutorial: Consumables and Receipt Validation on the RayWenderlich.com site, offers a download of Apple's code but fleshed-out (including Base64 methods) and tweaked.

