security in in-app-purchase iphone

I used in-app-purchase in my application. i am purchasing books from in-app-purchase. after successfully payment i am downloading books from my server. but i am thinking about the security. 开发者_开发知识库because if any user track the url of my server and download book and used without any payment. so can any one suggest how i enable security for this.

plz suggest thx

The in-app purchase transaction contains a receipt from Apple. Apple also has a service that will verify that receipt. So your iPhone app should pass the receipt to your server when requesting the download. The server can then verify the receipt before sending the content.

See http://developer.apple.com/library/ios/#documentation/NetworkingInternet/Conceptual/StoreKitGuide/VerifyingStoreReceipts/VerifyingStoreReceipts.html#//apple_ref/doc/uid/TP40008267-CH104-SW1