This is another entry in Andrew's series of tutorials on receipt validation. If you are considering how to make it harder to pirate your apps, you should take a look at this but also do some research on if the time you spend is worth it. Is the perceived lost revenue worth the extra hours and stress of implementing receipt validation?
Though many of the tutorials in this series are older, they have been updated for Swift 3. Andrew is on top of things. :)
Finalizing Receipt Validation in Swift – Computing a GUID Hash by Andrew Bancroft
In case you missed it, raywenderlich.com has released their iOS 11 tutorial book and four of the chapters are available for free. As always, top-notch tutorials with great explanations.
The four chapters include Drag & Drop, Natural Language Processing, Intro to ARKit, & PDFKit.
iOS 11 by Tutorials: First 4 Chapters Now Available! by Chris Belanger