To really understand it all, I highly recommend Apple’s iOS Security whitepaper. First released in May of 2012, with updates in October 2012, February 2014, and September 2014, the newest version (dated October 2014) includes changes to iOS 8. Also a great reference is “iPhone data protection in depth” by Jean-Baptiste Bédrune and Jean Sigwald of Sogeti, presented at HITB Amsterdam in 2011. Keep these open in other windows as I struggle to explain things. To truly understand what’s going on, those two references are your best bet.