In that case, you can refer to a set of standard APIs offered by GlobalPlatform (GP). This is supported on HiKey via OP-TEE, Linaro's Trusted OS running on 'top' of ARM Trusted Firmware (Trustzone Framework) and included by default in the HiKey releases.
- You'll want to look at TEE Client API Specification and TEE Internal Core API Specification
- Getting started with Trusted Apps
ARM Trusted Firmware
Please note that there are currently some caveats with using secure storage on HiKey OP-TEE due to hardware limitations. If you will eventually port your work to your own platform, you have to do a bit of extra work to allow it to operate fully securely. See here for details.