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Merge branch 'doc/security_features_small_fixes_v3.2' into 'release/v3.2'

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doc: Small secure boot & flash encryption corrections (v3.2)

See merge request idf/esp-idf!3888
This commit is contained in:
Ivan Grokhotkov 2018-12-05 11:07:41 +08:00
commit 3b4d51bbfa
2 changed files with 6 additions and 4 deletions
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4
docs/en/security/flash-encryption.rst
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@ -3,7 +3,7 @@ Flash Encryption
Flash Encryption is a feature for encrypting the contents of the ESP32's attached SPI flash. When flash encryption is enabled, physical readout of the SPI flash is not sufficient to recover most flash contents.
Flash Encryption is separate from the :doc:`Secure Boot <secure-boot>` feature, and you can use flash encryption without enabling secure boot. However we recommend using both features together for a secure environment. In absence of secure boot, additional configuration needs to be performed to ensure effectiveness of flash encryption. See :ref:`flash-encryption-without-secure-boot` for more details.
Flash Encryption is separate from the :doc:`Secure Boot <secure-boot>` feature, and you can use flash encryption without enabling secure boot. However, for a secure environment both should be used simultaneously. In absence of secure boot, additional configuration needs to be performed to ensure effectiveness of flash encryption. See :ref:`flash-encryption-without-secure-boot` for more details.
.. important::
Enabling flash encryption limits your options for further updates of your ESP32. Make sure to read this document (including :ref:`flash-encryption-limitations`) and understand the implications of enabling flash encryption.
@ -146,7 +146,7 @@ Limited Updates
Only 4 plaintext serial update cycles of this kind are possible, including the initial encrypted flash.
After the fourth time encryption is disabled, :ref:`FLASH_CRYPT_CNT` has the maximum value `0xFF` and encryption is permanently disabled.
After the fourth time encryption is enabled, :ref:`FLASH_CRYPT_CNT` has the maximum value ``0x7F`` (7 bits set) and encryption is permanently enabled. Flashing :ref:`FLASH_CRYPT_CNT` to ``0xFF`` (8 bits set) does not re-disable encryption, the eighth bit is ignored.
Using :ref:`updating-encrypted-flash-ota` or :ref:`pregenerated-flash-encryption-key` allows you to exceed this limit.

6
docs/en/security/secure-boot.rst
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@ -3,7 +3,7 @@ Secure Boot
Secure Boot is a feature for ensuring only your code can run on the chip. Data loaded from flash is verified on each reset.
Secure Boot is separate from the :doc:`Flash Encryption <flash-encryption>` feature, and you can use secure boot without encrypting the flash contents. However we recommend using both features together for a secure environment. See :ref:`secure-boot-and-flash-encr` for more details.
Secure Boot is separate from the :doc:`Flash Encryption <flash-encryption>` feature, and you can use secure boot without encrypting the flash contents. However, for a secure environment both should be used simultaneously. See :ref:`secure-boot-and-flash-encr` for more details.
.. important::
@ -258,7 +258,9 @@ To generate a bootloader digest::
espsecure.py digest_secure_bootloader --keyfile ./securebootkey.bin --output ./bootloader-digest.bin build/bootloader/bootloader.bin
Keyfile is the 32 byte raw secure boot key for the device. To flash this digest onto the device::
Keyfile is the 32 byte raw secure boot key for the device.
The output of the ``espsecure.py digest_secure_bootloader`` command is a single file which contains both the digest and the bootloader appended to it. To flash the combined digest plus bootloader to the device::
esptool.py write_flash 0x0 bootloader-digest.bin