espressif/esp-idf
1
0
Fork 1
mirror of https://github.com/espressif/esp-idf.git synced 2025-10-04 02:50:58 +02:00
Code Issues Packages Projects Releases Wiki Activity

bootloader/esp32c3: Adds secure boot (not yet supported)

Browse Source
This commit is contained in:
KonstantinKondrashov
2020-12-28 21:53:02 +08:00
parent f45c881f82
commit 98f726fa4b
14 changed files with 446 additions and 127 deletions
Download Patch File Download Diff File Expand all files Collapse all files

23
docs/en/security/secure-boot-v2.rst
View File

@@ -25,11 +25,15 @@ Advantages
- The RSA public key is stored on the device. The corresponding RSA private key is kept secret on a server and is never accessed by the device.
- Up to three public keys can be generated and stored in ESP32-S2 during manufacturing. (ESP32 ECO3: only one key)
.. only:: esp32
- ESP32-S2 provides the facility to permanently revoke individual public keys. This can be configured conservatively or aggressively.
- Only one public key can be generated and stored in ESP32 ECO3 during manufacturing.
.. only:: esp32s2
- Up to three public keys can be generated and stored in the chip during manufacturing.
- {IDF_TARGET_NAME} provides the facility to permanently revoke individual public keys. This can be configured conservatively or aggressively.
- Conservatively - The old key is revoked after the bootloader and application have successfully migrated to a new key. Aggressively - The key is revoked as soon as verification with this key fails.
@@ -96,7 +100,15 @@ The remainder of the signature sector is erased flash (0xFF) which allows writin
Verifying the signature Block
-----------------------------
A signature block is “valid” if the first byte is 0xe7 and a valid CRC32 is stored at offset 1196. Upto 3 signature blocks can be appended to the bootloader or application image in ESP32-S2. (ESP32 ECO3: only one key)
A signature block is “valid” if the first byte is 0xe7 and a valid CRC32 is stored at offset 1196.
.. only:: esp32
Only one signature block can be appended to the bootloader or application image in ESP32 ECO3.
.. only:: esp32s2
Upto 3 signature blocks can be appended to the bootloader or application image in {IDF_TARGET_NAME}.
An image is “verified” if the public key stored in any signature block is valid for this device, and if the stored signature is valid for the image data read from flash.
@@ -153,7 +165,7 @@ eFuse usage
- SECURE_BOOT_EN - Enables secure boot protection on boot.
- KEY_PURPOSE_X - Set the purpose of the key block on ESP32-S2 by programming SECURE_BOOT_DIGESTX (X = 0, 1, 2) into KEY_PURPOSE_X (X = 0, 1, 2, 3, 4). Example: If KEY_PURPOSE_2 is set to SECURE_BOOT_DIGEST1, then BLOCK_KEY2 will have the Secure Boot V2 public key digest.
- KEY_PURPOSE_X - Set the purpose of the key block on {IDF_TARGET_NAME} by programming SECURE_BOOT_DIGESTX (X = 0, 1, 2) into KEY_PURPOSE_X (X = 0, 1, 2, 3, 4). Example: If KEY_PURPOSE_2 is set to SECURE_BOOT_DIGEST1, then BLOCK_KEY2 will have the Secure Boot V2 public key digest.
- BLOCK_KEYX - The block contains the data corresponding to its purpose programmed in KEY_PURPOSE_X. Stores the SHA-256 digest of the public key. SHA-256 hash of public key modulus, exponent, precalculated R & M’ values (represented as 776 bytes – offsets 36 to 812 - as per the :ref:`signature-block-format`) is written to an eFuse key block.
@@ -288,6 +300,7 @@ Secure Boot Best Practices
* The bootloader can be signed with multiple keys from the factory.
Assuming a trusted private key (N-1) has been compromised, to update to new keypair (N).
1. Server sends an OTA update with an application signed with the new private key (#N).
2. The new OTA update is written to an unused OTA app partition.
3. The new application's signature block is validated. The public keys are checked against the digests programmed in the eFuse & the application is verified using the verified public key.