Post by human » Sat Sep 08, am. Post by GeorgeFlorian1 » Tue Apr 02, pm. Post by human » Fri Apr 05, am. Users browsing this forum: Bing [Bot] and 16 guests. Espressif Systems is a fabless semiconductor company providing cutting-edge low power WiFi SoCs and wireless solutions for wireless communications and Internet of Things applications. Skip to content. However, during manufacturing or production stages, Firmware Download mode should not be allowed to access flash contents for security reasons.
Hence, two different flash encryption configurations were created: for development and for production. For details on these configurations, see Section Flash Encryption Configuration. Release Mode - recommended for manufacturing and production to prevent physical readout of encrypted flash contents. This section provides information on the mentioned flash encryption modes and step by step instructions on how to use them.
During development, you can encrypt flash using either an ESPS2 generated key or external host-generated key. In Project Configuration Menu , do the following:. Enable flash encryption on boot. Select encryption mode Development mode by default. Select the appropriate bootloader log verbosity. Enabling flash encryption will increase the size of bootloader, which might require updating partition table offset. See Bootloader Size. This command does not include any user files which should be written to the partitions on the flash memory.
Please write them manually before running this command otherwise the files should be encrypted separately before writing. This command will write to flash memory unencrypted images: the firmware bootloader, the partition table and applications. Once the flashing is complete, ESPS2 will reset. On the next boot, the firmware bootloader encrypts: the firmware bootloader, application partitions and partitions marked as encrypted then resets.
After that, the application is decrypted at runtime and executed. A sample output of subsequent ESPS2 boots just mentions that flash encryption is already enabled:.
At this stage, if you need to update and re-flash binaries, see Re-flashing Updated Partitions. It is possible to pre-generate a flash encryption key on the host computer and burn it into the eFuse.
This allows you to pre-encrypt data on the host and flash already encrypted data without needing a plaintext flash update. This feature can be used in both Development Mode and Release Mode. Without a pre-generated key, data is flashed in plaintext and then ESPS2 encrypts the data in-place. This option is not recommended for production, unless a separate key is generated for each individual device. This action can be done only once. When this is used espefuse. If the key is not burned and the device is started after enabling flash encryption, the ESPS2 will generate a random key that software cannot access or modify.
If using Development Mode, then the easiest way to update and re-flash binaries is Re-flashing Updated Partitions. If using Release Mode, then it is possible to pre-encrypt the binaries on the host and then flash them as ciphertext. See Manually Encrypting Files. If you update your application code done in plaintext and want to re-flash it, you will need to encrypt it before flashing. To encrypt the application and flash it in one step, run:.
New plaintext images can ONLY be downloaded using the over-the-air OTA scheme which will encrypt the plaintext image before writing to flash. This is the default option, and is recommended. For subsequent plaintext field updates, use OTA scheme. Do not reuse the same flash encryption key between multiple devices. This means that an attacker who copies encrypted data from one device cannot transfer it to a second device.
Secure Download Mode permanently limits the available commands to basic flash read and write only. The default behaviour is to set Secure Download Mode on first boot in Release mode.
Enable Secure Boot as an extra layer of protection, and to prevent an attacker from selectively corrupting any part of the flash before boot. It means that all the partitions marked with the encryption flag are expected to contain encrypted ciphertext.
Below are the three typical failure cases if the ESPS2 is erroneously loaded with plaintext data:. If the bootloader partition is re-flashed with a plaintext firmware bootloader image , the ROM bootloader will fail to load the firmware bootloader resulting in the following failure:. If the firmware bootloader is encrypted, but the partition table is re-flashed with a plaintext partition table image , the bootloader will fail to read the partition table resulting in the following failure:.
If the bootloader and partition table are encrypted, but the application is re-flashed with a plaintext application image , the bootloader will fail to load the application resulting in the following failure:. It includes:. The MMU flash cache unconditionally decrypts all existing data. This function will only decrypt data when it is read from an encrypted partition.
Data read from unencrypted partitions will not be decrypted. In this way, software can access encrypted and non-encrypted flash in the same way. It is up to the library to provide encryption feature if required. Refer to NVS Encryption for more details. This function will only encrypt data when it is written to an encrypted partition. NVS Encryption deals with this and is suitable for many uses. Flash encryption alone may not prevent an attacker from modifying the firmware of the device.
To prevent unauthorised firmware from running on the device, use flash encryption in combination with Secure Boot.
It is recommended to use flash encryption in combination with Secure Boot. However, if Secure Boot is enabled, additional restrictions apply to device re-flashing:. OTA Updates are not restricted, provided that the new app is signed correctly with the Secure Boot signing key. In such configuration, idf. When following the plaintext serial re-flashing steps it is necessary to re-flash this file before flashing other plaintext data.
Re-flashing via Pregenerated Flash Encryption Key is still possible, provided the bootloader is not re-flashed. Re-flashing the bootloader requires the same Re-flashable option to be enabled in the Secure Boot config. Some partitions are encrypted by default. As a result, data in these marked partitions will be treated as encrypted in the same manner as an app partition.
For details on partition table description, see partition table. With flash encryption enabled, the app partition is always treated as encrypted and does not require marking.
The nvs partition cannot be encrypted, because the NVS library is not directly compatible with flash encryption. However, before the first boot you can choose to keep any of these features enabled by burning only selected eFuses and write-protect the rest of eFuses with unset value 0.
For example:. An attacker with physical access to the chip can use UART bootloader mode with custom stub code to read out the flash contents. For details, see Flash Encryption Algorithm. On the first boot of the firmware bootloader, this value is set to the maximum 0xF. It is possible to burn this eFuse manually and write protect it before the first boot in order to select different tweak values. However, this is not recommended. Otherwise, its value will remain zero permanently, and no bits in the flash encryption key will be tweaked.
The bootloader does this on first boot, at the same time it enables flash encryption. Manually encrypting or decrypting files requires the flash encryption key to be pre-burned in eFuse see Using Host Generated Key and a copy to be kept on the host. The key file should be a single raw binary file example: key. Run espsecure. The file my-app-ciphertext. To see all of the command line options recommended for esptool.
If the flashed ciphertext file is not recognized by the ESP32 when it boots, check that the keys match and that the command line arguments match exactly, including the correct offset. This will not happen if the device configured flash encryption by itself, but may happen if burning eFuses manually to enable flash encryption.
The command espsecure. The following sections provide some reference information about the operation of flash encryption. AES operates on byte blocks of data. The flash encryption engine encrypts and decrypts data in byte blocks - two AES blocks in series. This is for performance reasons and does not alter the effeciency of the algorithm. Each byte block two adjacent byte AES blocks is encrypted with a unique key.
This is a 4-bit eFuse where each bit enables XORing of a particular range of the key bits:. The high 19 bits of the block offset bit 5 to bit 23 are XORed with the main flash encryption key. This range is chosen for two reasons: the maximum flash size is 16MB 24 bits , and each block is 32 bytes so the least significant 5 bits are always zero.
There is a particular mapping from each of the 19 block offset bits to the bits of the flash encryption key to determine which bit is XORed with which. Provide feedback about this document. Choose version Secure Boot bootloader digest if Secure Boot is enabled see below.
Important Enabling flash encryption limits the options for further updates of ESP The default value of these bits is 0 afer manufacturing. To test flash encryption process, take the following steps: Ensure that you have an ESP32 device with default flash encryption eFuse settings as shown in Relevant eFuses.
Select the appropriate bootloader log verbosity Save the configuration and exit. Note This command does not include any user files which should be written to the partitions on the flash memory. Note This option is not recommended for production, unless a separate key is generated for each individual device.
Enable flash encryption on boot Select encryption mode Development mode by default Select the appropriate bootloader log verbosity Save the configuration and exit. To encrypt the application and flash it in one step, run: idf.
To use this mode, take the following steps: Ensure that you have an ESP32 device with default flash encryption eFuse settings as shown in Relevant eFuses. Note This error also appears if the flash contents are erased or corrupted. Find the serial port name under which your ESP32 device is connected, replace PORT with your port name in the following command, and run it: espefuse. Once flash encryption is enabled, be more careful with accessing flash contents from code.
All read-only data stored in flash DROM. The firmware bootloader image when it is read by the ROM bootloader. Important The MMU flash cache unconditionally decrypts all existing data. It can only be done three times per chip by taking the following steps: In Project Configuration Menu , disable Enable flash encryption on boot , then save and exit.
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