In June 2015, Apple released its latest iOS security model. You can find the latest version of this guide at https://www.apple.com/business/docs/iOS_Security_Guide.pdf.
If we look at iOS security guide, iOS provides security right from the hardware level, as shown in the following figure:
Security architecture is layered as hardware level, OS level, and application level
Encryption right from hardware/firmware level
Data protection using encryption