ESP Secure Certificate Manager

The esp_secure_cert_mgr provides a simplified interface to access the PKI credentials of a device pre-provisioned with the Espressif Provisioning Service. It provides the set of APIs that are required to access the contents of the esp_secure_cert partition. A demo example has also been provided with the esp_secure_cert_mgr, more details can be found out in the example README

Usage Guidelines

1) Include esp_secure_cert_mgr in your project

There are two ways to include esp_secure_cert_mgr in your project:

i) Add esp_secure_cert_mgr to your project with help of IDF component manager:

• The component is hosted at https://components.espressif.com/component/espressif/esp_secure_cert_mgr. Please use the same link to obtain the latest available version of the component along with the instructions on how to add it to your project.
• Additional details about using a component through IDF component manager can be found here

ii) Add esp_secure_cert_mgr as an extra component in your project.

• Download esp_secure_cert_mgr with:

    git clone https://github.com/espressif/esp_secure_cert_mgr.git

• Include esp_secure_cert_mgr in ESP-IDF with setting EXTRA_COMPONENT_DIRS in CMakeLists.txt/Makefile of your project.For reference see Optional Project Variables

2) Use the public API provided by esp_secure_cert_mgr in your project

• The file esp_secure_cert_read.h contains the public APIs provided by the esp_secure_cert_mgr. Please include the file in your project to make use of the available APIs. The file also contains more details about the available APIs.

What is Pre-Provisioning?

With the Espressif Pre-Provisioning Service, the ESP modules are pre-provisioned with an encrypted RSA private key and respective X509 public certificate before they are shipped out to you. The PKI credentials can then be registered with the cloud service to establish a secure TLS channel for communication. With the pre-provisioning taking place in the factory, it provides a hassle-free PKI infrastructure to the Makers. You may use this repository to set up your test modules to validate that your firmware works with the pre-provisioned modules that you ordered through Espressif's pre-provisioning service.

ESP Secure Cert Partition

When a device is pre-provisioned that means the PKI credentials are generated for the device. The PKI credentials are then stored in a partition named esp_secure_cert.

The esp_secure_cert partition can be generated on host with help of configure_esp_secure_cert.py utility, more details about the utility can be found in the tools/README.

For esp devices that support DS peripheral, the pre-provisioning is done by leveraging the security benefit of the DS peripheral. In that case, all of the data which is present in the esp_secure_cert partition is completely secure.

When the device is pre-provisioned with help of the DS peripheral then by default the partition primarily contains the following data:

1. Device certificate: It is the public key/ certificate for the device's private key. It is used in TLS authentication.
2. CA certificate: This is the certificate of the CA which is used to sign the device cert.
3. Ciphertext: This is the encrypted private key of the device. The ciphertext is encrypted using the DS peripheral, thus it is completely safe to store on the flash.

As listed above, the data only contains the public certificates and the encrypted private key and hence it is completely secure in itself. There is no need to further encrypt this data with any additional security algorithm.

Partition Format

The esp_secure_cert partition uses TLV format by default. Please take a look at the format document for more details.

This file contains the list of changes across different versions

v2.3.1

• Make esp_secure_cert_get_key_type API available for DS peripheral case as well.

v2.3.0

• Added support to obtain the priv key type
• Added support for getting the efuse key id for priv key

v2.2.0

• tools: Support DER encoded private keys when creating secure cert partition on host

Breaking changes in v2.2.0

• Updated the order of arguments for esp_pbkdf2_hmac_sha256 API to match it with corresponding mbedTLS API

v2.1.0

• Added support for HMAC based ECDSA key derivation with PBKDF2-HMAC-SHA256
• Fixed build failure when example is setup through component manager

v2.0.8

• Fix for supporting IDF v4.3

v2.0.7

• Updated documentation regarding TLV format
• Fixed priv_key free API when HMAC based encryption scheme is enabled.

v2.0.6

• Added HMAC based encryption scheme to protect private key data
• Added support for private key validation in the esp_secure_cert_app
• Added support of configurable esp_secure_cert partition offset in for configure_esp_secure_cert.py utility

v2.0.5

• Fixed targets in Kconfig to reflect DS Peripheral compatibility

v2.0.4

• Add implementation of esp_secure_cert_free_* APIs for TLV configuration.

v2.0.3

• Added C linkage so that C++ code can find the definitions for secure cert APIs.
• Minor documentation fixes.

v2.0.2

• Updated reference to the new esp_partition component (IDFv5.0)

v2.0.1

• Added fixes for build failures with -Wstrict-prototypes CFLAG.
• Added fix for build failure with toolchain change in IDFv4.x and IDFv5.x

v2.0.0

• Added esp-secure-cert-tool to PyPi.
• Restructure esp-secure-cert-tool

Breaking changes in v2.0.0

• Added the support for TLV format for storing data in esp_secure_cert partition.
• Make the TLV cust_flash_tlv as the default flash format.
• Marked all the supported flash formats before TLV as legacy: cust_flash, nvs.
• esp_secure_cert_app: Updated the partition table for the example

v1.0.3

• esp_secure_cert API now Dynamically identify the type of partitionand access the data accordingly
• esp_secure_cert_app: Enable support for target esp32
• Added tests based on qemu
• Added priv_key functionality to the configure_esp_secure_cert.py script.

Breaking changes in v1.0.3

• Removed all the configuration options related to selecting the type of esp_secure_cert partition
• Remove esp_secure_cert_get_*_addr API, the contents can now be obtained through esp_secure_cert_get_* API.
• Remove APIs to obain the contents of the DS contexts e.g. efuse key id, ciphertext, iv etc. The contents can be accesed from inside the DS context which can be obtained through respective API.
• Breaking change in the esp_secure_cert_get_* API: The API now accepts char **buffer instead of char *buffer. It will allocate the required memory dynamically and directly if necessary and provide the respective pointer.