1. Article purpose[edit | edit source]
The purpose of this article is to:
- briefly introduce the SAES peripheral and its main features,
- indicate the peripheral instances assignment at boot time and their assignment at runtime (including whether instances can be allocated to secure contexts),
- list the software frameworks and drivers managing the peripheral,
- explain how to configure the peripheral.
2. Peripheral overview[edit | edit source]
The SAES peripheral provides hardware acceleration to encrypt or decrypt data using the AES[1] algorithms. It supports two key sizes (128 bits and 256 bits) and different chaining modes. It incorporates protections against differential power analysis (DPA) and the related side-channel attacks.
Refer to the STM32MP13 reference manuals for the complete list of features, and to the software frameworks and drivers, introduced below, to see which features are implemented.
3. Peripheral usage[edit | edit source]
This chapter is applicable in the scope of the OpenSTLinux BSP running on the Arm® Cortex®-A processor(s), and the STM32CubeMPU Package running on the Arm® Cortex®-M processor.
3.1. Boot time assignment[edit | edit source]
3.1.1. On STM32MP13x lines 
[edit | edit source]
The SAES instance is used to decrypt the firmware.
Click on the right to expand the legend...
| Domain | Peripheral | Boot time allocation | Comment | |||
|---|---|---|---|---|---|---|
| Instance | Cortex-A7 secure (ROM code) |
Cortex-A7 secure (TF-A BL2) |
Cortex-A7 non-secure (U-Boot) | |||
| Security | SAES | SAES | ☐ | ☑ | Boot ROM allocation is managed with the bit 7 in OTP 9 | |
3.2. Runtime assignment[edit | edit source]
3.2.1. On STM32MP13x lines [edit | edit source]
Click on the right to expand the legend...
| Domain | Peripheral | Runtime allocation | Comment | ||
|---|---|---|---|---|---|
| Instance | Cortex-A7 secure (OP-TEE) |
Cortex-A7 non-secure (Linux) | |||
| Security | SAES | SAES | ☑ | ⬚ | Assignment (single choice) |
4. Software frameworks and drivers[edit | edit source]
Below are listed the software frameworks and drivers managing the SAES peripheral for the embedded software components listed in the above tables.
- Linux®: crypto framework
- OP-TEE: SAES driver and Cryptographic Provider API (CP API)
- TF-A BL2: SAES driver
5. How to assign and configure the peripheral[edit | edit source]
The peripheral assignment can be done via the STM32CubeMX graphical tool (and manually completed if needed).
This tool also helps to configure the peripheral:
- partial device trees (pin control and clock tree) generation for the OpenSTLinux software components,
- HAL initialization code generation for the STM32CubeMPU Package.
The configuration is applied by the firmware running in the context in which the peripheral is assigned.
6. References[edit | edit source]
Arm® is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere. 
Arm® is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere.