Security OTA Sketch

[Anduril]

ohh sorry, I was not completely clear: I will use RFM96 with DualOptiboot bootloader. I can upload the SecurityPersonalizer followed by the correct sketch. But it takes some effort, as I need to connect ISP/FTDI. Therefore I thought about compiling a hex file with DualOptibootloader, Personalizer sketch with running MySensors (not only core) and #define MY_OTA_FIRMWARE_FEATURE

[Anticimex]

@Anduril that should be doable.

[Anduril]

well I did a first test, without result. Maybe someone can help:
I did run the Personalizer with #define GENERATE_KEYS_ATSHA204A and generated some keys. I added those to the #define MY_XXX_KEY and got a confirmation. But it seems to not start up the radio, there is no output in the node or the gateway.

sketch:

/*
 * The MySensors Arduino library handles the wireless radio link and protocol
 * between your home built sensors/actuators and HA controller of choice.
 * The sensors forms a self healing radio network with optional repeaters. Each
 * repeater and gateway builds a routing tables in EEPROM which keeps track of the
 * network topology allowing messages to be routed to nodes.
 *
 * Created by Henrik Ekblad <henrik.ekblad@mysensors.org>
 * Copyright (C) 2013-2019 Sensnology AB
 * Full contributor list: https://github.com/mysensors/MySensors/graphs/contributors
 *
 * Documentation: http://www.mysensors.org
 * Support Forum: http://forum.mysensors.org
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * version 2 as published by the Free Software Foundation.
 *
 */
/**
 * @ingroup MySigninggrp
 * @{
 * @file SecurityPersonalizer.ino
 * @brief Security personalization sketch
 *
 * REVISION HISTORY
 *  - See git log (git log libraries/MySensors/examples/SecurityPersonalizer/SecurityPersonalizer.ino)
 */

/**
 * @example SecurityPersonalizer.ino
 * This sketch will personalize either none-volatile memory or ATSHA204A for security functions
 * available in the MySensors library.<br>
 * Details on personalization procedure is given in @ref personalization.<br>
 * This sketch will when executed without modifications also print a guided workflow on the UART.
 */

#include "sha204_library.h"
#include "sha204_lib_return_codes.h"
/** @brief Make use of the MySensors framework without invoking the entire system */
//#define MY_CORE_ONLY
#define MY_RADIO_RFM69
#define MY_OTA_FIRMWARE_FEATURE
#define MY_BAUD_RATE      38400
#include <MySensors.h>

/************************************ User defined key data ***************************************/

/** @brief The user-defined HMAC key to use unless @ref GENERATE_HMAC_KEY is set */
#define MY_HMAC_KEY 0x01,0x02,0x03,0x04,0x05,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00

/** @brief The user-defined AES key to store in EEPROM unless @ref GENERATE_AES_KEY is set */
#define MY_AES_KEY 0x06,0x07,0x08,0x09,0x10,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00

/** @brief The user-defined soft serial to use for soft signing unless @ref GENERATE_SOFT_SERIAL is set */
#define MY_SOFT_SERIAL 0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF

/***************************** Flags for guided personalization flow ******************************/

/**
 * @def GENERATE_KEYS_ATSHA204A
 * @brief Default settings for generating keys using ATSHA204A
 *
 * @note The generated keys displayed in the serial log with this setting needs to be written down
 *       and transferred to all nodes this gateway will communicate with. This is mandatory for ALL
 *       nodes for encryption (AES key). For signing (HMAC key) it is only required for nodes that
 *       use signing. Typically you set the values for @ref MY_HMAC_KEY and @ref MY_AES_KEY.
 */
//#define GENERATE_KEYS_ATSHA204A

/**
 * @def GENERATE_KEYS_SOFT
 * @brief Default settings for generating keys using software
 *
 * @b Important<br>
 * You will need to ensure @ref MY_SIGNING_SOFT_RANDOMSEED_PIN is set to an unconnected analog pin
 * in order to provide entropy to the software RNG if your hardware has no HWRNG.
 *
 * @note The generated keys displayed in the serial log with this setting needs to be written down
 *       and transferred to all nodes this gateway will communicate with. This is mandatory for ALL
 *       nodes for encryption (AES key). For signing (HMAC key) it is only required for nodes that
 *       use signing. Typically you set the values for @ref MY_HMAC_KEY and @ref MY_AES_KEY.
 */
//#define GENERATE_KEYS_SOFT

/**
 * @def PERSONALIZE_ATSHA204A
 * @brief Default settings for personalizing an ATSHA204A
 *
 * It is assumed that you have updated @ref MY_HMAC_KEY and @ref MY_AES_KEY with the keys displayed
 * when executing this sketch with @ref GENERATE_KEYS_ATSHA204A or @ref GENERATE_KEYS_SOFT defined.
 */
#define PERSONALIZE_ATSHA204A

/**
 * @def PERSONALIZE_SOFT
 * @brief Default settings for personalizing EEPROM for software signing
 *
 * It is assumed that you have updated @ref MY_HMAC_KEY and @ref MY_AES_KEY with the keys displayed
 * when executing this sketch with @ref GENERATE_KEYS_ATSHA204A or @ref GENERATE_KEYS_SOFT defined.
 */
//#define PERSONALIZE_SOFT

/**
 * @def PERSONALIZE_SOFT_RANDOM_SERIAL
 * @brief This is an alternative to @ref PERSONALIZE_SOFT which will also store a randomly generated
 * serial to EEPROM in addition to the actions performed by @ref PERSONALIZE_SOFT. Take note of the
 * generated soft serial as it will be needed if you plan to use whitelisting. It should be
 * unique for each node.
 *
 * @note This is only needed for targets that lack unique device IDs. The sketch will inform you if
 *       there is a need for generating a random serial or not. Check the "Hardware security
 *       peripherals" listing. If a target has a unique device ID and a serial in EEPROM, the serial
 *       in EEPROM will be used. If erased (replaced with FF:es) the unique device ID will be used
 *       instead.
 */
//#define PERSONALIZE_SOFT_RANDOM_SERIAL

/*************************** The settings below are for advanced users ****************************/
/**
 * @def USE_SOFT_SIGNING
 * @brief Uncomment this to generate keys by software and store them to EEPROM instead of ATSHA204A
 */
//#define USE_SOFT_SIGNING

/**
 * @def LOCK_ATSHA204A_CONFIGURATION
 * @brief Uncomment this to enable locking the ATSHA204A configuration zone
 *
 * It is still possible to change the key, and this also enable random key generation.
 * @warning BE AWARE THAT THIS PREVENTS ANY FUTURE CONFIGURATION CHANGE TO THE CHIP
 */
//#define LOCK_ATSHA204A_CONFIGURATION

/**
 * @def SKIP_UART_CONFIRMATION
 * @brief Uncomment this for boards that lack UART
 *
 * This will disable additional confirmation for actions that are non-reversible.
 *
 * @b Important<br> For ATSHA204A, no confirmation will be required for locking any zones with this
 * configuration! Also, if you generate keys on a board without UART, you have no way of determining
 * what the key is unless it is stored in EEPROM.
 */
//#define SKIP_UART_CONFIRMATION

/**
 * @def GENERATE_HMAC_KEY
 * @brief Uncomment this to generate a random HMAC key using ATSHA204A or software depending on
 *        @ref USE_SOFT_SIGNING
 * @note If not enabled, key defined by @ref MY_HMAC_KEY will be used instead.
 */
//#define GENERATE_HMAC_KEY

/**
 * @def STORE_HMAC_KEY
 * @brief Uncomment this to store HMAC key to ATSHA204A or EEPROM depending on @ref USE_SOFT_SIGNING
 */
//#define STORE_HMAC_KEY

/**
 * @def GENERATE_AES_KEY
 * @brief Uncomment this to generate a random AES key using ATSHA204A or software depending on
 * @ref USE_SOFT_SIGNING
 * @note If not enabled, key defined by @ref MY_AES_KEY will be used instead.
 */
//#define GENERATE_AES_KEY

/**
 * @def STORE_AES_KEY
 * @brief Uncomment this to store AES key to EEPROM
 */
//#define STORE_AES_KEY

/**
 * @def GENERATE_SOFT_SERIAL
 * @brief Uncomment this to generate a random serial number for software signing
 * @note If not enabled, serial defined by @ref MY_SOFT_SERIAL will be used instead.
 */
//#define GENERATE_SOFT_SERIAL

/**
 * @def STORE_SOFT_SERIAL
 * @brief Uncomment this to store the serial number to EEPROM
 */
//#define STORE_SOFT_SERIAL

/**
 * @def PRINT_DETAILED_ATSHA204A_CONFIG
 * @brief Uncomment to print the detailed ATSHA204A configuration
 */
#define PRINT_DETAILED_ATSHA204A_CONFIG

/**
 * @def RESET_EEPROM_PERSONALIZATION
 * @brief Uncomment to reset the personalization data in EEPROM to 0xFF:es
 */
//#define RESET_EEPROM_PERSONALIZATION

/********************* Guided mode flag configurations (don't change these) ***********************/
#ifdef GENERATE_KEYS_ATSHA204A
#define LOCK_ATSHA204A_CONFIGURATION // We have to lock configuration to enable random number generation
#define GENERATE_HMAC_KEY // Generate random HMAC key
#define GENERATE_AES_KEY // Generate random AES key
#define SKIP_UART_CONFIRMATION // This is an automated mode
#endif

#ifdef GENERATE_KEYS_SOFT
#define USE_SOFT_SIGNING // Use software backend
#define GENERATE_HMAC_KEY // Generate random HMAC key
#define GENERATE_AES_KEY // Generate random AES key
#define SKIP_UART_CONFIRMATION // This is an automated mode
#endif

#ifdef PERSONALIZE_ATSHA204A
#define LOCK_ATSHA204A_CONFIGURATION // We have to lock configuration to enable random number generation
#define STORE_HMAC_KEY // Store the HMAC key
#define STORE_AES_KEY // Store the AES key
#define SKIP_UART_CONFIRMATION // This is an automated mode
#endif

#ifdef PERSONALIZE_SOFT_RANDOM_SERIAL
#define GENERATE_SOFT_SERIAL // Generate a soft serial number
#define PERSONALIZE_SOFT // Do the rest as PERSONALIZE_SOFT
#endif

#ifdef PERSONALIZE_SOFT
#define USE_SOFT_SIGNING // Use software backend
#define STORE_HMAC_KEY // Store the HMAC key
#define STORE_AES_KEY // Store the AES key
#define STORE_SOFT_SERIAL // Store the soft serial number
#define SKIP_UART_CONFIRMATION // This is an automated mode
#endif

#if defined(GENERATE_HMAC_KEY) || defined(GENERATE_AES_KEY) || defined(GENERATE_SOFT_SERIAL)
#define GENERATE_SOMETHING
#endif

#if defined(MY_LOCK_MCU)
#undefine MY_LOCK_MCU  // The Sketch after SecurityPersonaliter should lock the MCU
#endif

/********************************** Preprocessor sanitychecks *************************************/
#if defined(GENERATE_SOFT_SERIAL) && !defined(USE_SOFT_SIGNING)
#error Cannot generate soft serial using ATSHA204A, use USE_SOFT_SINGING for this
#endif
#if defined(STORE_SOFT_SERIAL) && !defined(USE_SOFT_SIGNING)
#error Cannot store soft serial to ATSHA204A, use USE_SOFT_SINGING for this
#endif
#if defined(PRINT_DETAILED_ATSHA204A_CONFIG) && defined(USE_SOFT_SIGNING)
#error Cannot print ATSHA204A config using software signing flag, disable USE_SOFT_SINGING for this
#endif
#if defined(LOCK_ATSHA204A_CONFIGURATION) && defined(USE_SOFT_SIGNING)
#error Cannot lock ATSHA204A config using software signing flag, disable USE_SOFT_SINGING for this
#endif
#ifdef GENERATE_KEYS_ATSHA204A
#ifdef USE_SOFT_SIGNING
#error You cannot select soft signing if you want to generate keys using ATSHA204A
#endif
#ifdef STORE_HMAC_KEY
#error Disable STORE_SOFT_KEY, you should not store keys in this mode
#endif
#ifdef STORE_SOFT_SERIAL
#error Disable STORE_SOFT_SERIAL, you should not store serial in this mode
#endif
#ifdef STORE_AES_KEY
#error Disable STORE_AES_KEY, you should not store keys in this mode
#endif
#if defined(GENERATE_KEYS_SOFT) ||\
		defined (PERSONALIZE_ATSHA204A) ||\
		defined (PERSONALIZE_SOFT) ||\
		defined (PERSONALIZE_SOFT_RANDOM_SERIAL)
#error You can not enable GENERATE_KEYS_ATSHA204A together with other guided modes
#endif
#endif // GENERATE_KEYS_ATSHA204A
#ifdef GENERATE_KEYS_SOFT
#ifdef STORE_HMAC_KEY
#error Disable STORE_SOFT_KEY, you should not store keys in this mode
#endif
#ifdef STORE_SOFT_SERIAL
#error Disable STORE_SOFT_SERIAL, you should not store serial in this mode
#endif
#ifdef STORE_AES_KEY
#error Disable STORE_AES_KEY, you should not store keys in this mode
#endif
#ifndef MY_SIGNING_SOFT_RANDOMSEED_PIN
#error You have to set MY_SIGNING_SOFT_RANDOMSEED_PIN to a suitable value in this mode
#endif
#if defined(GENERATE_KEYS_ATSHA204A) ||\
		defined (PERSONALIZE_ATSHA204A) ||\
		defined (PERSONALIZE_SOFT) ||\
		defined (PERSONALIZE_SOFT_RANDOM_SERIAL)
#error You can not enable GENERATE_KEYS_SOFT together with other guided modes
#endif
#endif // GENERATE_KEYS_SOFT
#ifdef PERSONALIZE_ATSHA204A
#ifdef USE_SOFT_SIGNING
#error You cannot select soft signing if you want to personalize an ATSHA204A
#endif
#if defined(GENERATE_KEYS_ATSHA204A) ||\
		defined (GENERATE_KEYS_SOFT) ||\
		defined (PERSONALIZE_SOFT) ||\
		defined (PERSONALIZE_SOFT_RANDOM_SERIAL)
#error You can not enable PERSONALIZE_ATSHA204A together with other guided modes
#endif
#ifdef RESET_EEPROM_PERSONALIZATION
#error You cannot reset EEPROM personalization when personalizing a device
#endif
#endif // PERSONALIZE_ATSHA204A
#ifdef PERSONALIZE_SOFT
#if defined(GENERATE_KEYS_ATSHA204A) ||\
		defined (GENERATE_KEYS_SOFT) ||\
		defined (PERSONALIZE_ATSHA204A)
#error You can not enable PERSONALIZE_SOFT together with other guided modes
#endif
#ifdef RESET_EEPROM_PERSONALIZATION
#error You cannot reset EEPROM personalization when personalizing a device
#endif
#endif // PERSONALIZE_SOFT
#ifdef PERSONALIZE_SOFT_RANDOM_SERIAL
#if defined(GENERATE_KEYS_SOFT) ||\
		defined (PERSONALIZE_ATSHA204A) ||\
		defined (GENERATE_KEYS_ATSHA204A)
#error You can only enable one of the guided modes at a time
#endif
#ifdef RESET_EEPROM_PERSONALIZATION
#error You cannot reset EEPROM personalization when personalizing a device
#endif
#endif // PERSONALIZE_SOFT_RANDOM_SERIAL

#if !defined(GENERATE_KEYS_ATSHA204A) &&\
		!defined(GENERATE_KEYS_SOFT) &&\
		!defined(PERSONALIZE_ATSHA204A) &&\
		!defined(PERSONALIZE_SOFT) &&\
		!defined(PERSONALIZE_SOFT_RANDOM_SERIAL) &&\
		!defined(USE_SOFT_SIGNING) &&\
		!defined(LOCK_ATSHA204A_CONFIGURATION) &&\
		!defined(SKIP_UART_CONFIRMATION) &&\
		!defined(GENERATE_HMAC_KEY) &&\
		!defined(STORE_HMAC_KEY) &&\
		!defined(GENERATE_SOFT_SERIAL) &&\
		!defined(STORE_SOFT_SERIAL) &&\
		!defined(GENERATE_AES_KEY) &&\
		!defined(STORE_AES_KEY) &&\
		!defined(PRINT_DETAILED_ATSHA204A_CONFIG) &&\
		!defined(RESET_EEPROM_PERSONALIZATION)
/** @brief Set when there are no config flags defined */
#define NO_SETTINGS_DEFINED
#endif

#if defined(GENERATE_KEYS_ATSHA204A) ||\
		defined(GENERATE_KEYS_SOFT) ||\
		defined(PERSONALIZE_ATSHA204A) ||\
		defined(PERSONALIZE_SOFT) ||\
		defined(PERSONALIZE_SOFT_RANDOM_SERIAL)
/** @brief Set when there is a guided mode flag defined */
#define GUIDED_MODE
#endif

/************************************* Function declarations ***************************************/
static void halt(bool success);
#ifdef GENERATE_SOMETHING
static bool generate_random_data(uint8_t* data, size_t sz);
#endif
static void generate_keys(void);
static void store_keys(void);
static void print_hex_buffer(uint8_t* data, size_t sz);
static void print_c_friendly_hex_buffer(uint8_t* data, size_t sz);
#ifdef STORE_HMAC_KEY
static bool store_hmac_key_data(uint8_t* data, size_t sz);
#endif
#ifdef STORE_AES_KEY
static bool store_aes_key_data(uint8_t* data, size_t sz);
#endif
#ifdef STORE_SOFT_SERIAL
static bool store_soft_serial_data(uint8_t* data, size_t sz);
#endif
#ifndef USE_SOFT_SIGNING
static void init_atsha204a_state(void);
#ifdef LOCK_ATSHA204A_CONFIGURATION
static void	lock_atsha204a_config(void);
static uint16_t write_atsha204a_config_and_get_crc(void);
#endif
static bool get_atsha204a_serial(uint8_t* data);
#ifdef STORE_HMAC_KEY
static bool write_atsha204a_key(uint8_t* key);
#endif
#endif // not USE_SOFT_SIGNING
static void print_greeting(void);
static void print_ending(void);
static void	probe_and_print_peripherals(void);
static void print_eeprom_data(void);
static void print_whitelisting_entry(void);
#ifdef PRINT_DETAILED_ATSHA204A_CONFIG
static void dump_detailed_atsha204a_configuration(void);
#endif
#ifdef RESET_EEPROM_PERSONALIZATION
static void reset_eeprom(void);
#endif
static void write_eeprom_checksum(void);

/**************************************** File local data *****************************************/
#if defined(GENERATE_HMAC_KEY) || defined(STORE_HMAC_KEY)
/** @brief The data to store as HAMC key in ATSHA204A or EEPROM */
static uint8_t user_hmac_key[32] = {MY_HMAC_KEY};
#endif

#if defined(GENERATE_SOFT_SERIAL) || defined(STORE_SOFT_SERIAL)
/** @brief The data to store as soft serial in EEPROM */
static uint8_t user_soft_serial[9] = {MY_SOFT_SERIAL};
#endif

#if defined(GENERATE_AES_KEY) || defined(STORE_AES_KEY)
/* @brief The data to store as AES key in EEPROM */
static uint8_t user_aes_key[16] = {MY_AES_KEY};
#endif

#ifndef USE_SOFT_SIGNING
const int sha204Pin = MY_SIGNING_ATSHA204_PIN; //!< The IO pin to use for ATSHA204A
atsha204Class sha204(sha204Pin);
static uint8_t tx_buffer[SHA204_CMD_SIZE_MAX];
static uint8_t rx_buffer[SHA204_RSP_SIZE_MAX];
static uint8_t ret_code;
static uint8_t lockConfig = 0;
static uint8_t lockValue = 0;
#endif
static bool has_device_unique_id = false;
static const uint8_t reset_buffer[32] = {
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF
};

/******************************************* Functions ********************************************/

void presentation() {
  sendSketchInfo("Secure Startup","1.0");
}

/** @brief Sketch setup code (all personalization is done here as it is a run-once sketch) */
void setup()
{
	// Delay startup a bit for serial consoles to catch up
	uint32_t enter = hwMillis();
	while (hwMillis() - enter < (uint32_t)500);
#ifdef USE_SOFT_SIGNING
	// initialize pseudo-RNG
	hwRandomNumberInit();
#endif

	while(!Serial); // For USB enabled devices, wait for USB enumeration before continuing

	print_greeting();

#ifndef USE_SOFT_SIGNING
	init_atsha204a_state();
	// Lock configuration now if requested to enable RNG in ATSHA
#ifdef LOCK_ATSHA204A_CONFIGURATION
	lock_atsha204a_config();
#endif
#endif
	// Generate the requested keys (if any)
	generate_keys();

#ifdef RESET_EEPROM_PERSONALIZATION
	// If requested, reset EEPROM before storing keys
	reset_eeprom();
#endif

	// Store the keys (if configured to do so)
	store_keys();

	// Write a checksum on the EEPROM data
	write_eeprom_checksum();

	// Print current EEPROM
	print_eeprom_data();
	print_whitelisting_entry();
	Serial.println();

	print_ending();
	halt(true);
}

/** @brief Sketch execution code (unused) */
void loop()
{
  
}

[had to make it shorter, but I didn't change anything below here]

node serial monitor:

+------------------------------------------------------------------------------------+
|                                  WHAT TO DO NEXT?                                  |
+------------------------------------------------------------------------------------+
| This device has now been personalized. Run this sketch with its current settings   |
| on all the devices in your network that have security enabled.                     |
+------------------------------------------------------------------------------------+

+------------------------------------------------------------------------------------+
|                                  Execution result                                  |
+------------------------------------------------------------------------------------+
| SUCCESS                                                                            |
+------------------------------------------------------------------------------------+

[Anticimex]

@Anduril There should not be anytning preventing radio startup when you have personalized a device. Have you looked at the debug output of the node/gateway, and tried with security disabled? Also, remember that the personalization has to be done on all devices that use secure communication, and if you use encryption, all devices in the entire network.

[Anduril]

I have not yet enabled signing or encryption on the node that was running the personalizer with radio activated. Therefor I would expect it to give serial output mysensors started, find parent and so on. Nothing on the output after that security Execution result SUCCESS
The gateway also has no security activated for now, as this node was the first one to test the personalizer with radio and OTA

[Anticimex]

@Anduril I believe the setup() function is hijacked by the personalizer so radio is not initialized properly, nor is the library.

[Anduril]

that might be true... so it's kind of impossible I think to merge those.
So I have to first upload the personalizer and directly after that the sketch with security enabled and OTA. Is the personalizer sketch the only way to find out its serial for whitelisting? Maybe I need this feature down the road so it's good to know how to get it later

[Anticimex]

@Anduril well, you can always rewrite the personalizer to not use a setup() function.

[Anduril]

I think that's a little beyond my skills :-)

[Anduril]

@Anticimex still the question: is there a way to find out a nodes whitelist serial later?

[Anticimex]

@Anduril that depend on your backend. For software signing the serial is stored in eeprom. For atsha204a it is only readable from the device itself.

[Anduril]

that's sad.
Maybe it would be possible to write a sketch to read out the atsha serial and transmit it via mysensors... I will be looking into this further when in need of whitelisting. Until then I will just leave it as it is and only use signing and maybe encryption.

[Anticimex]

@Anduril I'd prefer not as the serial is also considered a semi-secret to maintain the integrity of the security infrastructure. It should not be thrown around the network unprotected.

[Anduril]

I understand that. Two questions:
what about updating via OTA with whitelisting enabled? Everyone could sniff the new hexfile and read the serial of the whitelisted node, correct?
what about activating encryption? Would that prevent both of these cases? No one could read the hexfile or the send serial without knowing the AES key before.

[Anticimex]

@Anduril if encrypted the data "cannot" be decoded. The serial is not stored in any firmware. The only exception being a personalizer sketch that will personalize for software signing.
For atsha204a based signing, serial is never stored in sketch, only in runtime.

[Anduril]

Just in the rare case I want to use it later (and I have encryption enabled in the whole mysensors network) I could theoretically write a sketch inspired by the personalizer to read the serial and send this as a payload to the gateway without anyone out there able to read.

[Anticimex]

@Anduril Well, its all opensource, so you are free to do whatever you want. Just remember that if you are starting to alter the behaviour and use of the security infrastructure, you could potentially compromise it for yourself and those that use your code.