esp-idf/components/bootloader/Kconfig.projbuild

menu "Bootloader config"

    config BOOTLOADER_OFFSET_IN_FLASH
        hex
        default 0x1000 if IDF_TARGET_ESP32 || IDF_TARGET_ESP32S2
        default 0x0
        help
            Offset address that 2nd bootloader will be flashed to.
            The value is determined by the ROM bootloader.
            It's not configurable in ESP-IDF.

    choice BOOTLOADER_COMPILER_OPTIMIZATION
        prompt "Bootloader optimization Level"
        default BOOTLOADER_COMPILER_OPTIMIZATION_SIZE
        help
            This option sets compiler optimization level (gcc -O argument)
            for the bootloader.

            - The default "Size" setting will add the -0s flag to CFLAGS.
            - The "Debug" setting will add the -Og flag to CFLAGS.
            - The "Performance" setting will add the -O2 flag to CFLAGS.
            - The "None" setting will add the -O0 flag to CFLAGS.

            Note that custom optimization levels may be unsupported.

        config BOOTLOADER_COMPILER_OPTIMIZATION_SIZE
            bool "Size (-Os)"
        config BOOTLOADER_COMPILER_OPTIMIZATION_DEBUG
            bool "Debug (-Og)"
        config BOOTLOADER_COMPILER_OPTIMIZATION_PERF
            bool "Optimize for performance (-O2)"
        config BOOTLOADER_COMPILER_OPTIMIZATION_NONE
            bool "Debug without optimization (-O0)"
    endchoice

    choice BOOTLOADER_LOG_LEVEL
        bool "Bootloader log verbosity"
        default BOOTLOADER_LOG_LEVEL_INFO
        help
            Specify how much output to see in bootloader logs.

        config BOOTLOADER_LOG_LEVEL_NONE
            bool "No output"
        config BOOTLOADER_LOG_LEVEL_ERROR
            bool "Error"
        config BOOTLOADER_LOG_LEVEL_WARN
            bool "Warning"
        config BOOTLOADER_LOG_LEVEL_INFO
            bool "Info"
        config BOOTLOADER_LOG_LEVEL_DEBUG
            bool "Debug"
        config BOOTLOADER_LOG_LEVEL_VERBOSE
            bool "Verbose"
    endchoice

    config BOOTLOADER_LOG_LEVEL
        int
        default 0 if BOOTLOADER_LOG_LEVEL_NONE
        default 1 if BOOTLOADER_LOG_LEVEL_ERROR
        default 2 if BOOTLOADER_LOG_LEVEL_WARN
        default 3 if BOOTLOADER_LOG_LEVEL_INFO
        default 4 if BOOTLOADER_LOG_LEVEL_DEBUG
        default 5 if BOOTLOADER_LOG_LEVEL_VERBOSE

    config BOOTLOADER_SPI_CUSTOM_WP_PIN
        bool "Use custom SPI Flash WP Pin when flash pins set in eFuse (read help)"
        depends on IDF_TARGET_ESP32 && (ESPTOOLPY_FLASHMODE_QIO || ESPTOOLPY_FLASHMODE_QOUT)
        default y if BOOTLOADER_SPI_WP_PIN != 7  # backwards compatibility, can remove in IDF 5
        default n
        help
            This setting is only used if the SPI flash pins have been overridden by setting the eFuses
            SPI_PAD_CONFIG_xxx, and the SPI flash mode is QIO or QOUT.

            When this is the case, the eFuse config only defines 3 of the 4 Quad I/O data pins. The WP pin (aka
            ESP32 pin "SD_DATA_3" or SPI flash pin "IO2") is not specified in eFuse. The same pin is also used
            for external SPIRAM if it is enabled.

            If this config item is set to N (default), the correct WP pin will be automatically used for any
            Espressif chip or module with integrated flash. If a custom setting is needed, set this config item to
            Y and specify the GPIO number connected to the WP.

    config BOOTLOADER_SPI_WP_PIN
        int "Custom SPI Flash WP Pin"
        range 0 33
        default 7
        depends on IDF_TARGET_ESP32 && (ESPTOOLPY_FLASHMODE_QIO || ESPTOOLPY_FLASHMODE_QOUT)
        #depends on BOOTLOADER_SPI_CUSTOM_WP_PIN  # backwards compatibility, can uncomment in IDF 5
        help
            The option "Use custom SPI Flash WP Pin" must be set or this value is ignored

            If burning a customized set of SPI flash pins in eFuse and using QIO or QOUT mode for flash, set this
            value to the GPIO number of the SPI flash WP pin.

    choice BOOTLOADER_VDDSDIO_BOOST
        bool "VDDSDIO LDO voltage"
        default BOOTLOADER_VDDSDIO_BOOST_1_9V
        help
            If this option is enabled, and VDDSDIO LDO is set to 1.8V (using eFuse
            or MTDI bootstrapping pin), bootloader will change LDO settings to
            output 1.9V instead. This helps prevent flash chip from browning out
            during flash programming operations.

            This option has no effect if VDDSDIO is set to 3.3V, or if the internal
            VDDSDIO regulator is disabled via eFuse.

        config BOOTLOADER_VDDSDIO_BOOST_1_8V
            bool "1.8V"
            depends on !ESPTOOLPY_FLASHFREQ_80M
        config BOOTLOADER_VDDSDIO_BOOST_1_9V
            bool "1.9V"
    endchoice

    config BOOTLOADER_FACTORY_RESET
        bool "GPIO triggers factory reset"
        default N
        help
            Allows to reset the device to factory settings:
            - clear one or more data partitions;
            - boot from "factory" partition.
            The factory reset will occur if there is a GPIO input pulled low while device starts up.
            See settings below.

    config BOOTLOADER_NUM_PIN_FACTORY_RESET
        int "Number of the GPIO input for factory reset"
        depends on BOOTLOADER_FACTORY_RESET
        range 0 39 if IDF_TARGET_ESP32
        range 0 44 if IDF_TARGET_ESP32S2
        default 4
        help
            The selected GPIO will be configured as an input with internal pull-up enabled.
            To trigger a factory reset, this GPIO must be pulled low on reset.
            Note that GPIO34-39 do not have an internal pullup and an external one must be provided.

    config BOOTLOADER_OTA_DATA_ERASE
        bool "Clear OTA data on factory reset (select factory partition)"
        depends on BOOTLOADER_FACTORY_RESET
        help
            The device will boot from "factory" partition (or OTA slot 0 if no factory partition is present) after a
            factory reset.

    config BOOTLOADER_DATA_FACTORY_RESET
        string "Comma-separated names of partitions to clear on factory reset"
        depends on BOOTLOADER_FACTORY_RESET
        default "nvs"
        help
            Allows customers to select which data partitions will be erased while factory reset.

            Specify the names of partitions as a comma-delimited with optional spaces for readability. (Like this:
            "nvs, phy_init, ...")
            Make sure that the name specified in the partition table and here are the same.
            Partitions of type "app" cannot be specified here.

    config BOOTLOADER_APP_TEST
        bool "GPIO triggers boot from test app partition"
        default N
        depends on !BOOTLOADER_APP_ANTI_ROLLBACK
        help
            Allows to run the test app from "TEST" partition.
            A boot from "test" partition will occur if there is a GPIO input pulled low while device starts up.
            See settings below.

    config BOOTLOADER_NUM_PIN_APP_TEST
        int "Number of the GPIO input to boot TEST partition"
        depends on BOOTLOADER_APP_TEST
        range 0 39
        default 18
        help
            The selected GPIO will be configured as an input with internal pull-up enabled.
            To trigger a test app, this GPIO must be pulled low on reset.
            After the GPIO input is deactivated and the device reboots, the old application will boot.
            (factory or OTA[x]).
            Note that GPIO34-39 do not have an internal pullup and an external one must be provided.

    config BOOTLOADER_HOLD_TIME_GPIO
        int "Hold time of GPIO for reset/test mode (seconds)"
        depends on BOOTLOADER_FACTORY_RESET || BOOTLOADER_APP_TEST
        default 5
        help
            The GPIO must be held low continuously for this period of time after reset
            before a factory reset or test partition boot (as applicable) is performed.

    config BOOTLOADER_WDT_ENABLE
        bool "Use RTC watchdog in start code"
        default y
        help
            Tracks the execution time of startup code.
            If the execution time is exceeded, the RTC_WDT will restart system.
            It is also useful to prevent a lock up in start code caused by an unstable power source.
            NOTE: Tracks the execution time starts from the bootloader code - re-set timeout, while selecting the
            source for slow_clk - and ends calling app_main.
            Re-set timeout is needed due to WDT uses a SLOW_CLK clock source. After changing a frequency slow_clk a
            time of WDT needs to re-set for new frequency.
            slow_clk depends on ESP32_RTC_CLK_SRC (INTERNAL_RC or EXTERNAL_CRYSTAL).

    config BOOTLOADER_WDT_DISABLE_IN_USER_CODE
        bool "Allows RTC watchdog disable in user code"
        depends on BOOTLOADER_WDT_ENABLE
        default n
        help
            If it is set, the client must itself reset or disable rtc_wdt in their code (app_main()).
            Otherwise rtc_wdt will be disabled before calling app_main function.
            Use function rtc_wdt_feed() for resetting counter of rtc_wdt.
            Use function rtc_wdt_disable() for disabling rtc_wdt.

    config BOOTLOADER_WDT_TIME_MS
        int "Timeout for RTC watchdog (ms)"
        depends on BOOTLOADER_WDT_ENABLE
        default 9000
        range 0 120000
        help
            Verify that this parameter is correct and more then the execution time.
            Pay attention to options such as reset to factory, trigger test partition and encryption on boot
            - these options can increase the execution time.
            Note: RTC_WDT will reset while encryption operations will be performed.

    config BOOTLOADER_APP_ROLLBACK_ENABLE
        bool "Enable app rollback support"
        default n
        help
            After updating the app, the bootloader runs a new app with the "ESP_OTA_IMG_PENDING_VERIFY" state set.
            This state prevents the re-run of this app. After the first boot of the new app in the user code, the
            function should be called to confirm the operability of the app or vice versa about its non-operability.
            If the app is working, then it is marked as valid. Otherwise, it is marked as not valid and rolls back to
            the previous working app. A reboot is performed, and the app is booted before the software update.
            Note: If during the first boot a new app the power goes out or the WDT works, then roll back will happen.
            Rollback is possible only between the apps with the same security versions.

    config BOOTLOADER_APP_ANTI_ROLLBACK
        bool "Enable app anti-rollback support"
        depends on BOOTLOADER_APP_ROLLBACK_ENABLE
        default n
        help
            This option prevents rollback to previous firmware/application image with lower security version.

    config BOOTLOADER_APP_SECURE_VERSION
        int "eFuse secure version of app"
        depends on BOOTLOADER_APP_ANTI_ROLLBACK
        default 0
        help
            The secure version is the sequence number stored in the header of each firmware.
            The security version is set in the bootloader, version is recorded in the eFuse field
            as the number of set ones. The allocated number of bits in the efuse field
            for storing the security version is limited (see BOOTLOADER_APP_SEC_VER_SIZE_EFUSE_FIELD option).

            Bootloader: When bootloader selects an app to boot, an app is selected that has
            a security version greater or equal that recorded in eFuse field.
            The app is booted with a higher (or equal) secure version.

            The security version is worth increasing if in previous versions there is
            a significant vulnerability and their use is not acceptable.

            Your partition table should has a scheme with ota_0 + ota_1 (without factory).

    config BOOTLOADER_APP_SEC_VER_SIZE_EFUSE_FIELD
        int "Size of the efuse secure version field"
        depends on BOOTLOADER_APP_ANTI_ROLLBACK
        range 1 32 if IDF_TARGET_ESP32
        default 32 if IDF_TARGET_ESP32
        range 1 16
        default 16
        help
            The size of the efuse secure version field.
            Its length is limited to 32 bits for ESP32 and 16 bits for ESP32-S2.
            This determines how many times the security version can be increased.

    config BOOTLOADER_EFUSE_SECURE_VERSION_EMULATE
        bool "Emulate operations with efuse secure version(only test)"
        default n
        depends on BOOTLOADER_APP_ANTI_ROLLBACK
        help
            This option allow emulate read/write operations with efuse secure version.
            It allow to test anti-rollback implemention without permanent write eFuse bits.
            In partition table should be exist this partition `emul_efuse, data, 5, , 0x2000`.

    config BOOTLOADER_SKIP_VALIDATE_IN_DEEP_SLEEP
        bool "Skip image validation when exiting deep sleep"
        depends on (SECURE_BOOT && SECURE_BOOT_INSECURE) || !SECURE_BOOT
        default n
        help
            This option disables the normal validation of an image coming out of
            deep sleep (checksums, SHA256, and signature). This is a trade-off
            between wakeup performance from deep sleep, and image integrity checks.

            Only enable this if you know what you are doing. It should not be used
            in conjunction with using deep_sleep() entry and changing the active OTA
            partition as this would skip the validation upon first load of the new
            OTA partition.

    config BOOTLOADER_RESERVE_RTC_SIZE
        hex
        default 0x10 if BOOTLOADER_SKIP_VALIDATE_IN_DEEP_SLEEP || BOOTLOADER_CUSTOM_RESERVE_RTC
        default 0
        help
            Reserve RTC FAST memory for Skip image validation. This option in bytes.
            This option reserves an area in the RTC FAST memory (access only PRO_CPU).
            Used to save the addresses of the selected application.
            When a wakeup occurs (from Deep sleep), the bootloader retrieves it and
            loads the application without validation.

    config BOOTLOADER_CUSTOM_RESERVE_RTC
        bool "Reserve RTC FAST memory for custom purposes"
        default n
        help
            This option allows the customer to place data in the RTC FAST memory,
            this area remains valid when rebooted, except for power loss.
            This memory is located at a fixed address and is available
            for both the bootloader and the application.
            (The application and bootoloader must be compiled with the same option).
            The RTC FAST memory has access only through PRO_CPU.

    config BOOTLOADER_CUSTOM_RESERVE_RTC_SIZE
        hex "Size in bytes for custom purposes"
        range 0 0x10
        default 0
        depends on BOOTLOADER_CUSTOM_RESERVE_RTC
        help
            This option reserves in RTC FAST memory the area for custom purposes.
            If you want to create your own bootloader and save more information
            in this area of memory, you can increase it. It must be a multiple of 4 bytes.
            This area (rtc_retain_mem_t) is reserved and has access from the bootloader and an application.

endmenu  # Bootloader


menu "Security features"

    # These three are the actual options to check in code,
    # selected by the displayed options
    config SECURE_SIGNED_ON_BOOT
        bool
        default y
        depends on SECURE_BOOT || SECURE_SIGNED_ON_BOOT_NO_SECURE_BOOT

    config SECURE_SIGNED_ON_UPDATE
        bool
        default y
        depends on SECURE_BOOT || SECURE_SIGNED_ON_UPDATE_NO_SECURE_BOOT

    config SECURE_SIGNED_APPS
        bool
        default y
        select MBEDTLS_ECP_DP_SECP256R1_ENABLED
        select MBEDTLS_ECP_C
        select MBEDTLS_ECDH_C
        select MBEDTLS_ECDSA_C
        depends on SECURE_SIGNED_ON_BOOT || SECURE_SIGNED_ON_UPDATE

    config SECURE_BOOT_SUPPORTS_RSA
        bool
        default y
        depends on ESP32_REV_MIN_3 || IDF_TARGET_ESP32S2 || IDF_TARGET_ESP32C3

    config SECURE_TARGET_HAS_SECURE_ROM_DL_MODE
        bool
        default y
        depends on IDF_TARGET_ESP32S2 || IDF_TARGET_ESP32C3


    config SECURE_SIGNED_APPS_NO_SECURE_BOOT
        bool "Require signed app images"
        depends on !SECURE_BOOT
        help
            Require apps to be signed to verify their integrity.

            This option uses the same app signature scheme as hardware secure boot, but unlike hardware secure boot it
            does not prevent the bootloader from being physically updated. This means that the device can be secured
            against remote network access, but not physical access. Compared to using hardware Secure Boot this option
            is much simpler to implement.

    choice SECURE_SIGNED_APPS_SCHEME
        bool "App Signing Scheme"
        depends on SECURE_BOOT || SECURE_SIGNED_APPS_NO_SECURE_BOOT
        default SECURE_SIGNED_APPS_ECDSA_SCHEME if SECURE_BOOT_V1_ENABLED
        default SECURE_SIGNED_APPS_RSA_SCHEME if SECURE_BOOT_V2_ENABLED
        help
            Select the Secure App signing scheme. Depends on the Chip Revision.
            There are two options:
            1. ECDSA based secure boot scheme. (Only choice for Secure Boot V1)
            Supported in ESP32 and ESP32-ECO3.
            2. The RSA based secure boot scheme. (Only choice for Secure Boot V2)
            Supported in ESP32-ECO3. (ESP32 Chip Revision 3 onwards)

        config SECURE_SIGNED_APPS_ECDSA_SCHEME
            bool "ECDSA"
            depends on IDF_TARGET_ESP32 && (SECURE_SIGNED_APPS_NO_SECURE_BOOT || SECURE_BOOT_V1_ENABLED)
            help
                Embeds the ECDSA public key in the bootloader and signs the application with an ECDSA key.

                Refer to the documentation before enabling.

        config SECURE_SIGNED_APPS_RSA_SCHEME
            bool "RSA"
            depends on SECURE_BOOT_SUPPORTS_RSA && SECURE_BOOT_V2_ENABLED
            help
                Appends the RSA-3072 based Signature block to the application.
                Refer to <Secure Boot Version 2 documentation link> before enabling.
    endchoice

    config SECURE_SIGNED_ON_BOOT_NO_SECURE_BOOT
        bool "Bootloader verifies app signatures"
        default n
        depends on SECURE_SIGNED_APPS_NO_SECURE_BOOT
        help
            If this option is set, the bootloader will be compiled with code to verify that an app is signed before
            booting it.

            If hardware secure boot is enabled, this option is always enabled and cannot be disabled.
            If hardware secure boot is not enabled, this option doesn't add significant security by itself so most
            users will want to leave it disabled.

    config SECURE_SIGNED_ON_UPDATE_NO_SECURE_BOOT
        bool "Verify app signature on update"
        default y
        depends on SECURE_SIGNED_APPS_NO_SECURE_BOOT
        help
            If this option is set, any OTA updated apps will have the signature verified before being considered valid.

            When enabled, the signature is automatically checked whenever the esp_ota_ops.h APIs are used for OTA
            updates, or esp_image_format.h APIs are used to verify apps.

            If hardware secure boot is enabled, this option is always enabled and cannot be disabled.
            If hardware secure boot is not enabled, this option still adds significant security against network-based
            attackers by preventing spoofing of OTA updates.

    config SECURE_BOOT
        bool "Enable hardware Secure Boot in bootloader (READ DOCS FIRST)"
        default n
        depends on !IDF_TARGET_ESP32C3 # IDF-2647
        help
            Build a bootloader which enables Secure Boot on first boot.

            Once enabled, Secure Boot will not boot a modified bootloader. The bootloader will only load a partition
            table or boot an app if the data has a verified digital signature. There are implications for reflashing
            updated apps once secure boot is enabled.

            When enabling secure boot, JTAG and ROM BASIC Interpreter are permanently disabled by default.

    choice SECURE_BOOT_VERSION
        bool "Select secure boot version"
        default SECURE_BOOT_V2_ENABLED if ESP32_REV_MIN_3
        depends on SECURE_BOOT
        help
            Select the Secure Boot Version. Depends on the Chip Revision.
            Secure Boot V2 is the new RSA based secure boot scheme.
            Supported in ESP32-ECO3. (ESP32 Chip Revision 3 onwards)
            Secure Boot V1 is the AES based secure boot scheme.
            Supported in ESP32 and ESP32-ECO3.

        config SECURE_BOOT_V1_ENABLED
            bool "Enable Secure Boot version 1"
            depends on IDF_TARGET_ESP32
            help
                Build a bootloader which enables secure boot version 1 on first boot.
                Refer to the Secure Boot section of the ESP-IDF Programmer's Guide for this version before enabling.

        config SECURE_BOOT_V2_ENABLED
            bool "Enable Secure Boot version 2"
            depends on SECURE_BOOT_SUPPORTS_RSA
            select SECURE_ENABLE_SECURE_ROM_DL_MODE if !IDF_TARGET_ESP32 && !SECURE_INSECURE_ALLOW_DL_MODE && !SECURE_DISABLE_ROM_DL_MODE # NOERROR
            select SECURE_DISABLE_ROM_DL_MODE if ESP32_REV_MIN_3 && !SECURE_INSECURE_ALLOW_DL_MODE
            help
                Build a bootloader which enables Secure Boot version 2 on first boot.
                Refer to Secure Boot V2 section of the ESP-IDF Programmer's Guide for this version before enabling.

    endchoice

    choice SECURE_BOOTLOADER_MODE
        bool "Secure bootloader mode"
        depends on SECURE_BOOT_V1_ENABLED
        default SECURE_BOOTLOADER_ONE_TIME_FLASH

        config SECURE_BOOTLOADER_ONE_TIME_FLASH
            bool "One-time flash"
            help
                On first boot, the bootloader will generate a key which is not readable externally or by software. A
                digest is generated from the bootloader image itself. This digest will be verified on each subsequent
                boot.

                Enabling this option means that the bootloader cannot be changed after the first time it is booted.

        config SECURE_BOOTLOADER_REFLASHABLE
            bool "Reflashable"
            help
                Generate a reusable secure bootloader key, derived (via SHA-256) from the secure boot signing key.

                This allows the secure bootloader to be re-flashed by anyone with access to the secure boot signing
                key.

                This option is less secure than one-time flash, because a leak of the digest key from one device
                allows reflashing of any device that uses it.

    endchoice

    config SECURE_BOOT_BUILD_SIGNED_BINARIES
        bool "Sign binaries during build"
        depends on SECURE_SIGNED_APPS
        default y
        help
            Once secure boot or signed app requirement is enabled, app images are required to be signed.

            If enabled (default), these binary files are signed as part of the build process. The file named in
            "Secure boot private signing key" will be used to sign the image.

            If disabled, unsigned app/partition data will be built. They must be signed manually using espsecure.py.
            Version 1 to enable ECDSA Based Secure Boot and Version 2 to enable RSA based Secure Boot.
            (for example, on a remote signing server.)

    config SECURE_BOOT_SIGNING_KEY
        string "Secure boot private signing key"
        depends on SECURE_BOOT_BUILD_SIGNED_BINARIES
        default "secure_boot_signing_key.pem"
        help
            Path to the key file used to sign app images.

            Key file is an ECDSA private key (NIST256p curve) in PEM format for Secure Boot V1.
            Key file is an RSA private key in PEM format for Secure Boot V2.

            Path is evaluated relative to the project directory.

            You can generate a new signing key by running the following command:
            espsecure.py generate_signing_key secure_boot_signing_key.pem

            See the Secure Boot section of the ESP-IDF Programmer's Guide for this version for details.

    config SECURE_BOOT_VERIFICATION_KEY
        string "Secure boot public signature verification key"
        depends on SECURE_SIGNED_APPS && !SECURE_BOOT_BUILD_SIGNED_BINARIES && !SECURE_SIGNED_APPS_RSA_SCHEME
        default "signature_verification_key.bin"
        help
            Path to a public key file used to verify signed images.
            Secure Boot V1: This ECDSA public key is compiled into the bootloader and/or
            app, to verify app images.
            Secure Boot V2: This RSA public key is compiled into the signature block at
            the end of the bootloader/app.

            Key file is in raw binary format, and can be extracted from a
            PEM formatted private key using the espsecure.py
            extract_public_key command.

            Refer to the Secure Boot section of the ESP-IDF Programmer's Guide for this version before enabling.

    choice SECURE_BOOTLOADER_KEY_ENCODING
        bool "Hardware Key Encoding"
        depends on SECURE_BOOTLOADER_REFLASHABLE
        default SECURE_BOOTLOADER_KEY_ENCODING_256BIT
        help

            In reflashable secure bootloader mode, a hardware key is derived from the signing key (with SHA-256) and
            can be written to eFuse with espefuse.py.

            Normally this is a 256-bit key, but if 3/4 Coding Scheme is used on the device then the eFuse key is
            truncated to 192 bits.

            This configuration item doesn't change any firmware code, it only changes the size of key binary which is
            generated at build time.

        config SECURE_BOOTLOADER_KEY_ENCODING_256BIT
            bool "No encoding (256 bit key)"

        config SECURE_BOOTLOADER_KEY_ENCODING_192BIT
            bool "3/4 encoding (192 bit key)"

    endchoice

    config SECURE_BOOT_INSECURE
        bool "Allow potentially insecure options"
        depends on SECURE_BOOT
        default N
        help
            You can disable some of the default protections offered by secure boot, in order to enable testing or a
            custom combination of security features.

            Only enable these options if you are very sure.

            Refer to the Secure Boot section of the ESP-IDF Programmer's Guide for this version before enabling.

    config SECURE_FLASH_ENC_ENABLED
        bool "Enable flash encryption on boot (READ DOCS FIRST)"
        default N
        select SPI_FLASH_ENABLE_ENCRYPTED_READ_WRITE
        help
            If this option is set, flash contents will be encrypted by the bootloader on first boot.

            Note: After first boot, the system will be permanently encrypted. Re-flashing an encrypted
            system is complicated and not always possible.

            Read https://docs.espressif.com/projects/esp-idf/en/latest/security/flash-encryption.html
            before enabling.

    choice SECURE_FLASH_ENCRYPTION_KEYSIZE
        bool "Size of generated AES-XTS key"
        default SECURE_FLASH_ENCRYPTION_AES128
        depends on IDF_TARGET_ESP32S2 && SECURE_FLASH_ENC_ENABLED
        help
            Size of generated AES-XTS key.

            AES-128 uses a 256-bit key (32 bytes) which occupies one Efuse key block.
            AES-256 uses a 512-bit key (64 bytes) which occupies two Efuse key blocks.

            This setting is ignored if either type of key is already burned to Efuse before the first boot.
            In this case, the pre-burned key is used and no new key is generated.

        config SECURE_FLASH_ENCRYPTION_AES128
            bool "AES-128 (256-bit key)"

        config SECURE_FLASH_ENCRYPTION_AES256
            bool "AES-256 (512-bit key)"
    endchoice

    choice SECURE_FLASH_ENCRYPTION_MODE
        bool "Enable usage mode"
        depends on SECURE_FLASH_ENC_ENABLED
        default SECURE_FLASH_ENCRYPTION_MODE_DEVELOPMENT
        help
            By default Development mode is enabled which allows UART bootloader to perform flash encryption operations

            Select Release mode only for production or manufacturing. Once enabled you can not reflash using UART
            bootloader

            Refer to the Secure Boot section of the ESP-IDF Programmer's Guide for this version and
            https://docs.espressif.com/projects/esp-idf/en/latest/security/flash-encryption.html for details.

        config SECURE_FLASH_ENCRYPTION_MODE_DEVELOPMENT
            bool "Development(NOT SECURE)"
            select SECURE_FLASH_UART_BOOTLOADER_ALLOW_ENC

        config SECURE_FLASH_ENCRYPTION_MODE_RELEASE
            bool "Release"
            select SECURE_ENABLE_SECURE_ROM_DL_MODE if SECURE_TARGET_HAS_SECURE_ROM_DL_MODE && !SECURE_DISABLE_ROM_DL_MODE # NOERROR

    endchoice

    menu "Potentially insecure options"
        visible if SECURE_FLASH_ENCRYPTION_MODE_DEVELOPMENT || SECURE_BOOT_INSECURE

        # NOTE: Options in this menu NEED to have SECURE_BOOT_INSECURE
        # and/or SECURE_FLASH_ENCRYPTION_MODE_DEVELOPMENT in "depends on", as the menu
        # itself doesn't enable/disable its children (if it's not set,
        # it's possible for the insecure menu to be disabled but the insecure option
        # to remain on which is very bad.)

        config SECURE_BOOT_ALLOW_ROM_BASIC
            bool "Leave ROM BASIC Interpreter available on reset"
            depends on (SECURE_BOOT_INSECURE || SECURE_FLASH_ENCRYPTION_MODE_DEVELOPMENT) && IDF_TARGET_ESP32
            default N
            help
                By default, the BASIC ROM Console starts on reset if no valid bootloader is
                read from the flash.

                When either flash encryption or secure boot are enabled, the default is to
                disable this BASIC fallback mode permanently via eFuse.

                If this option is set, this eFuse is not burned and the BASIC ROM Console may
                remain accessible.  Only set this option in testing environments.

        config SECURE_BOOT_ALLOW_JTAG
            bool "Allow JTAG Debugging"
            depends on SECURE_BOOT_INSECURE || SECURE_FLASH_ENCRYPTION_MODE_DEVELOPMENT
            default N
            help
                If not set (default), the bootloader will permanently disable JTAG (across entire chip) on first boot
                when either secure boot or flash encryption is enabled.

                Setting this option leaves JTAG on for debugging, which negates all protections of flash encryption
                and some of the protections of secure boot.

                Only set this option in testing environments.

        config SECURE_BOOT_ALLOW_SHORT_APP_PARTITION
            bool "Allow app partition length not 64KB aligned"
            depends on SECURE_BOOT_INSECURE
            help
                If not set (default), app partition size must be a multiple of 64KB. App images are padded to 64KB
                length, and the bootloader checks any trailing bytes after the signature (before the next 64KB
                boundary) have not been written. This is because flash cache maps entire 64KB pages into the address
                space. This prevents an attacker from appending unverified data after the app image in the flash,
                causing it to be mapped into the address space.

                Setting this option allows the app partition length to be unaligned, and disables padding of the app
                image to this length. It is generally not recommended to set this option, unless you have a legacy
                partitioning scheme which doesn't support 64KB aligned partition lengths.

        config SECURE_BOOT_V2_ALLOW_EFUSE_RD_DIS
            bool "Allow additional read protecting of efuses"
            depends on SECURE_BOOT_INSECURE && SECURE_BOOT_V2_ENABLED
            help
                If not set (default, recommended), on first boot the bootloader will burn the WR_DIS_RD_DIS
                efuse when Secure Boot is enabled. This prevents any more efuses from being read protected.

                If this option is set, it will remain possible to write the EFUSE_RD_DIS efuse field after Secure
                Boot is enabled. This may allow an attacker to read-protect the BLK2 efuse holding the public
                key digest, causing an immediate denial of service and possibly allowing an additional fault
                injection attack to bypass the signature protection.

        config SECURE_BOOT_ALLOW_UNUSED_DIGEST_SLOTS
            bool "Leave unused digest slots available (not revoke)"
            depends on SECURE_BOOT_INSECURE && !IDF_TARGET_ESP32
            default N
            help
                If not set (default), during startup in the app all unused digest slots will be revoked.
                To revoke unused slot will be called esp_efuse_set_digest_revoke(num_digest) for each digest.
                Revoking unused digest slots makes ensures that no trusted keys can be added later by an attacker.
                If set, it means that you have a plan to use unused digests slots later.

        config SECURE_INSECURE_ALLOW_DL_MODE
            bool "Don't automatically restrict UART download mode"
            depends on SECURE_BOOT_INSECURE && SECURE_BOOT_V2_ENABLED
            default N
            help
                By default, enabling either flash encryption in release mode or secure boot will automatically
                disable UART download mode on ESP32 ECO3, or enable secure download mode on newer chips.
                This is recommended to reduce the attack surface of the chip.

                To allow the full UART download mode to stay enabled, enable this option and ensure
                the options SECURE_DISABLE_ROM_DL_MODE and SECURE_ENABLE_SECURE_ROM_DL_MODE are disabled as applicable.
                This is not recommended.

        config SECURE_FLASH_UART_BOOTLOADER_ALLOW_ENC
            bool "Leave UART bootloader encryption enabled"
            depends on SECURE_FLASH_ENCRYPTION_MODE_DEVELOPMENT
            default N
            help
                If not set (default), the bootloader will permanently disable UART bootloader encryption access on
                first boot. If set, the UART bootloader will still be able to access hardware encryption.

                It is recommended to only set this option in testing environments.

        config SECURE_FLASH_UART_BOOTLOADER_ALLOW_DEC
            bool "Leave UART bootloader decryption enabled"
            depends on SECURE_FLASH_ENCRYPTION_MODE_DEVELOPMENT && IDF_TARGET_ESP32
            default N
            help
                If not set (default), the bootloader will permanently disable UART bootloader decryption access on
                first boot. If set, the UART bootloader will still be able to access hardware decryption.

                Only set this option in testing environments. Setting this option allows complete bypass of flash
                encryption.

        config SECURE_FLASH_UART_BOOTLOADER_ALLOW_CACHE
            bool "Leave UART bootloader flash cache enabled"
            depends on SECURE_FLASH_ENCRYPTION_MODE_DEVELOPMENT
            default N
            help
                If not set (default), the bootloader will permanently disable UART bootloader flash cache access on
                first boot. If set, the UART bootloader will still be able to access the flash cache.

                Only set this option in testing environments.

        config SECURE_FLASH_REQUIRE_ALREADY_ENABLED
            bool "Require flash encryption to be already enabled"
            depends on SECURE_FLASH_ENCRYPTION_MODE_DEVELOPMENT
            default N
            help
                If not set (default), and flash encryption is not yet enabled in eFuses, the 2nd stage bootloader
                will enable flash encryption: generate the flash encryption key and program eFuses.
                If this option is set, and flash encryption is not yet enabled, the bootloader will error out and
                reboot.
                If flash encryption is enabled in eFuses, this option does not change the bootloader behavior.

                Only use this option in testing environments, to avoid accidentally enabling flash encryption on
                the wrong device. The device needs to have flash encryption already enabled using espefuse.py.

    endmenu  # Potentially Insecure

    config SECURE_DISABLE_ROM_DL_MODE
        bool "Permanently disable ROM Download Mode"
        depends on !IDF_TARGET_ESP32 || ESP32_REV_MIN_3
        default n
        help
            If set, during startup the app will burn an eFuse bit to permanently disable the UART ROM
            Download Mode. This prevents any future use of esptool.py, espefuse.py and similar tools.

            Once disabled, if the SoC is booted with strapping pins set for ROM Download Mode
            then an error is printed instead.

            It is recommended to enable this option in any production application where Flash
            Encryption and/or Secure Boot is enabled and access to Download Mode is not required.

            It is also possible to permanently disable Download Mode by calling
            esp_efuse_disable_rom_download_mode() at runtime.

    config SECURE_ENABLE_SECURE_ROM_DL_MODE
        bool "Permanently switch to ROM UART Secure Download mode"
        depends on SECURE_TARGET_HAS_SECURE_ROM_DL_MODE && !SECURE_DISABLE_ROM_DL_MODE
        select ESPTOOLPY_NO_STUB
        help
            If set, during startup the app will burn an eFuse bit to permanently switch the UART ROM
            Download Mode into a separate Secure Download mode. This option can only work if
            Download Mode is not already disabled by eFuse.

            Secure Download mode limits the use of Download Mode functions to simple flash read,
            write and erase operations, plus a command to return a summary of currently enabled
            security features.

            Secure Download mode is not compatible with the esptool.py flasher stub feature,
            espefuse.py, read/writing memory or registers, encrypted download, or any other
            features that interact with unsupported Download Mode commands.

            Secure Download mode should be enabled in any application where Flash Encryption
            and/or Secure Boot is enabled. Disabling this option does not immediately cancel
            the benefits of the security features, but it increases the potential "attack
            surface" for an attacker to try and bypass them with a successful physical attack.

            It is also possible to enable secure download mode at runtime by calling
            esp_efuse_enable_rom_secure_download_mode()

    config SECURE_FLASH_CHECK_ENC_EN_IN_APP
        bool "Check Flash Encryption enabled on app startup"
        depends on SECURE_FLASH_ENC_ENABLED
        default y
        help
            If set (default), in an app during startup code,
            there is a check of the flash encryption eFuse bit is on
            (as the bootloader should already have set it).
            The app requires this bit is on to continue work otherwise abort.

            If not set, the app does not care if the flash encryption eFuse bit is set or not.

endmenu  # Security features