PKA internal peripheral

Applicable for

STM32MP13x lines

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1. Article purpose

The purpose of this article is to:

• briefly introduce the PKA peripheral and its main features
• indicate the level of security supported by this hardware block
• explain how it can be allocated to the runtime contexts and linked to the corresponding software components
• explain, when necessary, how to configure the PKA peripheral.

2. Peripheral overview

The PKA (public key accelerator) is peripheral is used to ease computation of cryptographic public key primitives, specifically those related to RSA, Diffie-Hellmann or ECC (elliptic curve cryptography) over GF(p) (Galois fields).

2.1. Features

Refer to the STM32MP13 reference manuals for the complete list of features, and to the software components, introduced below, to see which features are implemented.

2.2. Security support

The PKA is a secure peripheral (under ETZPC control).

3. Peripheral usage and associated software

3.1. Boot time

PKA is a boot device, it is used for signature verification on secure boot processing.

3.2. Runtime

3.2.1. Overview

PKA instance is allocated to:

• the Arm^® Cortex^®-A7 secure core to be controlled in OP-TEE by the PKA OP-TEE driver through the ECC framework.

or

• the Arm^® Cortex^®-A7 non-secure core to be controlled in Linux^® with Linux Crypto framework.

Chapter Peripheral assignment describes which peripheral instance can be assigned to which context.

3.2.2. Software frameworks

Domain	Peripheral	Software components		Comment
		OP-TEE	Linux
Security	Peripheral (PKA internal peripheral)	OP-TEE PKA driver	Linux Crypto framework

3.2.3. Peripheral configuration

The configuration is applied by the firmware running in the context to which the peripheral is assigned. The configuration can be done alone via the STM32CubeMX tool for all internal peripherals, and then manually completed (particularly for external peripherals), according to the information given in the corresponding software framework article.

3.2.4. Peripheral assignment

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STM32MP13 internal peripherals

Check boxes illustrate the possible peripheral allocations supported by STM32 MPU Embedded Software:

• ☐ means that the peripheral can be assigned (☑) to the given runtime context.
• ⬚ means that the peripheral can be assigned to the given runtime context, but this configuration is not supported in STM32 MPU Embedded Software distribution.
• ✓ is used for system peripherals that cannot be unchecked because they are statically connected in the device.

Refer to How to assign an internal peripheral to a runtime context for more information on how to assign peripherals manually or via STM32CubeMX.
The present chapter describes STMicroelectronics recommendations or choice of implementation. Additional possiblities might be described in STM32MP13 reference manuals.

Domain	Peripheral	Runtime allocation			Comment
		Instance	Cortex-A7 secure (OP-TEE)	Cortex-A7 non-secure (Linux)
Security	PKA	PKA	☐	⬚	Assignment (single choice)