Sign Secure Boot V2 images with Esptool from Espressif using PKCS11 library
Esptool is a Python-based, open-source, platform-independent utility to communicate with the ROM bootloader in Espressif chips. Integrate Esptool with DigiCert® Software Trust Manager’s PKCS11 library to sign image files.
Anmerkung
Espressif only supports:
RSA 3072 bit keys.
ECDSA 192 and 256 bit keys.
Prerequisites
Esptool (version 4.5 or higher).
DigiCert® Software Trust Manager PKCS11 library
Software Trust Manager keypair
Install Esptool
To install Esptool, run the following command from command line:
pip install esptool[hsm]
Anmerkung
For additional context, refer to Installation and dependancies.
Download and configure PKCS11 library
A HSM configuration file is required for Esptool to use DigiCert® Software Trust Manager PKCS11 library. This file is required in sign commands.
Download PKCS11 library
To download the Software Trust Manager PKCS11 library:
Sign in to DigiCert ONE.
Navigate to Software Trust Manager > Resources > Client tool repository.
Select your operating system.
Click the download icon next to Software Trust Manager PKCS#11 Library.
Create configuration file
To create the HSM configuration file:
Open a text editor or IDE.
Copy and paste the content below:
[hsm_config] pkcs11_lib =<path to the Software Trust Manager PKCS11 library> credentials =NONE slot =0 label =<keypair-alias>
Input the necessary values.
Example:
[hsm_config] pkcs11_lib =C:\Tools\smpkcs11.dll credentials =NONE slot =0 label =keypair-1
Save the file as hsm-config.ini
Sign
To sign, use:
espsecure.py sign_data --version 2 --hsm --hsm-config <hsm-config-ini> --output <signed-output-filename> <input-image-file>
Command example:
espsecure.py sign_data --version 2 --hsm --hsm-config hsm-config.ini --output v2-rsa-pss-hello_world.bin hello_world.bin espsecure.py v4.5-dev
Command output:
Trying to establish a session with the HSM. Session creation successful with HSM slot 0. Trying to extract public key from the HSM. Config option 'label_pubkey' not found, using config option 'label' for public key. Got public key with label keypair-1. Connection closed successfully Trying to establish a session with the HSM. Session creation successful with HSM slot 0. Got private key metadata with label keypair-1. Signing payload using the HSM. Signature generation successful. Connection closed successfully Pre-calculated signatures found 1 signing key(s) found. Signed 196608 bytes of data from hello_world.bin. Signature sector now has 1 signature blocks.
Verify signature
Download the public key of the keypair used in signing. The downloaded public key is required in the command to verify a signed image file.
Anmerkung
If you download the public key from the UI, you must remove the EC/RSA keyword in the header and footer of the PEM file.
The beginning and end of the ECDSA/RSA PEM public key, should read as follows:
-----BEGIN PUBLIC KEY----- . . . -----END PUBLIC KEY-----
To verify, use:
espsecure.py verify_signature --version 2 --keyfile <public-key-file-of-keypair> <image-file-to-verify>
Command example:
espsecure.py verify_signature --version 2 --keyfile keypair-1.pem v2-rsa-pss-hello_world.bin
Command output:
espsecure.py v4.5-dev Signature block 0 is valid (RSA). Signature block 0 verification successful using the supplied key (RSA). Signature block 1 invalid. Skipping. Signature block 2 invalid. Skipping.