Ivan Kristin earlier this month gave a talk at Black Hat around the security of iOS. He covered the three main concerns,
"HomeKit, Auto Unlock and iCloud Keychain are three Apple technologies that handle exceptionally sensitive user data - controlling devices (including locks) in the user's home, the ability to unlock a user's Mac from an Apple Watch, and the user's passwords and credit card information, respectively. We will discuss the cryptographic design and implementation of our novel secure synchronization fabric which moves confidential data between devices without exposing it to Apple, while affording the user the ability to recover data in case of device loss.
Data Protection is the cryptographic system protecting user data on all iOS devices. We will discuss the Secure Enclave Processor present in iPhone 5S and later devices and explain how it enabled a new approach to Data Protection key derivation and brute force rate limiting within a small TCB, making no intermediate or derived keys available to the normal Application Processor.
Traditional browser-based vulnerabilities are becoming harder to exploit due to increasingly sophisticated mitigation techniques. We will discuss a unique JIT hardening mechanism in iOS 10 that makes the iOS Safari JIT a more difficult target."
The full video is available here.