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Flash Encryption

The example checks if the flash encryption feature is enabled/disabled and if enabled prints the flash encryption mode (DEVELOPMENT / RELEASE) and FLASH_CRYPT_CNT eFuse value.

The example also demonstrates writing and reading encrypted partitions in flash.

How to use example

Hardware Required

Configure the project

idf.py menuconfig

Set serial port under Serial Flasher Options.
Enable the flash encryption mode (Development or Release) under Security Features. Default usage mode is Development (recommended during test and development phase).
Ensure Bootloader log verbosity is Info under Bootloader config.
Select Single factory app, no OTA under Partition Table options. Change the partition table offset to 0x9000 from 0x8000 since after enabling flash encryption the size of bootloader is increased.

Build and Flash

When building the project and flashing it to the board FOR THE FIRST TIME after enabling flash encryption feature in menuconfig, run following command to program ESP32 and monitor the output:

idf.py -p PORT flash monitor

(To exit the serial monitor, type Ctrl-].)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

When reprogramming the device subsequently use following command for encrypted write of new plaintext application:

idf.py -p PORT encrypted-app-flash monitor

Please note above command programs only the app partition. In order to reprogram all partitions (bootloader, partition table and application) in encrypted form use:

idf.py -p PORT encrypted-flash monitor

Example Output

When running the example without enabling flash encryption, the output would be as follows:

Example to check Flash Encryption status
This is ESP32 chip with 2 CPU cores, WiFi/BT/BLE, silicon revision 0, 2MB external flash
FLASH_CRYPT_CNT eFuse value is 0
Flash encryption feature is disabled
Erasing partition "storage" (0x1000 bytes)
Writing data with esp_partition_write:
I (378) example: 0x3ffb4dc0   00 01 02 03 04 05 06 07  08 09 0a 0b 0c 0d 0e 0f  |................|
I (378) example: 0x3ffb4dd0   10 11 12 13 14 15 16 17  18 19 1a 1b 1c 1d 1e 1f  |................|
Reading with esp_partition_read:
I (388) example: 0x3ffb4da0   00 01 02 03 04 05 06 07  08 09 0a 0b 0c 0d 0e 0f  |................|
I (398) example: 0x3ffb4db0   10 11 12 13 14 15 16 17  18 19 1a 1b 1c 1d 1e 1f  |................|
Reading with spi_flash_read:
I (408) example: 0x3ffb4da0   00 01 02 03 04 05 06 07  08 09 0a 0b 0c 0d 0e 0f  |................|
I (418) example: 0x3ffb4db0   10 11 12 13 14 15 16 17  18 19 1a 1b 1c 1d 1e 1f  |................|

After enabling flash encryption in Development mode, the output shows the process of enabling the flash encryption:

I (168) boot: Checking flash encryption...
I (168) flash_encrypt: Generating new flash encryption key...
I (187) flash_encrypt: Read & write protecting new key...
I (187) flash_encrypt: Setting CRYPT_CONFIG efuse to 0xF
W (188) flash_encrypt: Not disabling UART bootloader encryption
I (195) flash_encrypt: Disable UART bootloader decryption...
I (201) flash_encrypt: Disable UART bootloader MMU cache...
I (208) flash_encrypt: Disable JTAG...
I (212) flash_encrypt: Disable ROM BASIC interpreter fallback...
....
....
....
I (13229) flash_encrypt: Flash encryption completed
I (13229) boot: Resetting with flash encryption enabled...

Once the flash encryption is enabled the device will reset itself. At this stage the flash contents are in encrypted form. The output would be similar to:

Example to check Flash Encryption status
This is ESP32 chip with 2 CPU cores, WiFi/BT/BLE, silicon revision 0, 4MB external flash
FLASH_CRYPT_CNT eFuse value is 1
Flash encryption feature is enabled in DEVELOPMENT mode
Erasing partition "storage" (0x1000 bytes)
Writing data with esp_partition_write:
I (451) example: 0x3ffb4dc0   00 01 02 03 04 05 06 07  08 09 0a 0b 0c 0d 0e 0f  |................|
I (451) example: 0x3ffb4dd0   10 11 12 13 14 15 16 17  18 19 1a 1b 1c 1d 1e 1f  |................|
Reading with esp_partition_read:
I (461) example: 0x3ffb4da0   00 01 02 03 04 05 06 07  08 09 0a 0b 0c 0d 0e 0f  |................|
I (471) example: 0x3ffb4db0   10 11 12 13 14 15 16 17  18 19 1a 1b 1c 1d 1e 1f  |................|
Reading with spi_flash_read:
I (491) example: 0x3ffb4da0   29 68 2e 13 88 a0 5b 7f  cc 6b 39 f9 d7 7b 32 2f  |)h....[..k9..{2/|
I (491) example: 0x3ffb4db0   9f e6 55 37 4b 91 b0 83  cd a6 e9 4e cd fa b4 c7  |..U7K......N....|

Troubleshooting

It is also possible to use esptool.py utility to read the eFuse values and check if flash encryption is enabled or not

python $IDF_PATH/components/esptool_py/esptool/espefuse.py --port PORT summary

If FLASH_CRYPT_CNT eFuse value is non-zero flash encryption is enabled

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