Secure boot and firmware updates (OTA) in IOT Protocols - Step-by-Step Execution

Process Flow - Secure boot and firmware updates (OTA)

Power On Device

↓

Start Secure Boot

↓

Verify Bootloader Signature

Yes↓

Load Firmware

↓

Verify Firmware Signature

Yes↓

Run Firmware

↓

Check for OTA Update

Yes↓

Download Update

↓

Verify Update Signature

Yes↓

Install Update

↓

Reboot Device

↩Back to Start Secure Boot

The device powers on, verifies bootloader and firmware signatures to ensure integrity, runs firmware, checks for OTA updates, verifies and installs updates securely, then reboots to apply changes.

Execution Sample

IOT Protocols

power_on()
if verify_signature(bootloader):
  load_firmware()
  if verify_signature(firmware):
    run_firmware()
    if check_ota_update():
      download_update()
      if verify_signature(update):
        install_update()
        reboot()

This code simulates secure boot by verifying signatures and performs OTA update if available and verified.

Process Table

Step	Action	Condition/Check	Result	Next Step
1	Power on device	N/A	Device powered on	Verify bootloader signature
2	Verify bootloader signature	Is bootloader signature valid?	Yes	Load firmware
3	Load firmware	N/A	Firmware loaded into memory	Verify firmware signature
4	Verify firmware signature	Is firmware signature valid?	Yes	Run firmware
5	Run firmware	N/A	Firmware running	Check for OTA update
6	Check for OTA update	Is OTA update available?	Yes	Download update
7	Download update	N/A	Update downloaded	Verify update signature
8	Verify update signature	Is update signature valid?	Yes	Install update
9	Install update	N/A	Update installed	Reboot device
10	Reboot device	N/A	Device rebooting	Start secure boot again
11	Verify bootloader signature	Is bootloader signature valid?	Yes	Load firmware
12	Verify firmware signature	Is firmware signature valid?	Yes	Run firmware
13	Check for OTA update	Is OTA update available?	No	Continue running firmware
14	Continue running firmware	N/A	Device running updated firmware	End
15	End	N/A	Secure boot and OTA update complete	Stop

💡 No OTA update available after reboot, device runs updated firmware securely.

Status Tracker

Variable	Start	After Step 6	After Step 9	After Step 13	Final
bootloader_signature_valid	Unknown	Yes	Yes	Yes	Yes
firmware_signature_valid	Unknown	Yes	Yes	Yes	Yes
ota_update_available	Unknown	Yes	Yes	No	No
update_signature_valid	Unknown	N/A	Yes	N/A	N/A
firmware_running	No	No	No	Yes	Yes

Key Moments - 3 Insights

Why do we verify the bootloader signature before loading firmware?

Verifying the bootloader signature ensures the device starts from trusted code. As shown in execution_table step 2, if this check fails, the device will not proceed, preventing untrusted code from running.

What happens if the OTA update signature is invalid?

If the update signature is invalid (step 8), the device will reject the update and not install it, protecting from malicious updates. This is critical for security.

Why does the device reboot after installing the update?

Rebooting (step 10) restarts the secure boot process to load the new firmware safely, ensuring the update is applied correctly and verified again before running.

Visual Quiz - 3 Questions

Look at the execution_table at step 6. What is the value of 'ota_update_available'?

A Yes

B No

C Unknown

D Invalid

💡 Hint

Check the 'Condition/Check' column at step 6 and variable_tracker for 'ota_update_available' after step 6.

At which step does the device install the update?

A Step 7

B Step 8

C Step 9

D Step 10

💡 Hint

Look at the 'Action' column in execution_table for the step labeled 'Install update'.

If the firmware signature was invalid at step 4, what would happen next?

A Device would run firmware anyway

B Device would stop booting

C Device would download OTA update

D Device would reboot immediately

💡 Hint

Refer to step 4's 'Condition/Check' and 'Result' columns in execution_table to understand the flow on signature failure.

Concept Snapshot

Secure Boot and OTA Updates:
- Device powers on and verifies bootloader signature.
- Loads and verifies firmware signature before running.
- Checks for OTA updates, downloads and verifies update signature.
- Installs update and reboots to apply securely.
- Ensures only trusted code runs, protecting device integrity.

Full Transcript

When the device powers on, it starts the secure boot process by verifying the bootloader's signature to ensure it is trusted. If valid, it loads the firmware and verifies its signature. Only if the firmware is verified does the device run it. The running firmware checks if an OTA update is available. If yes, it downloads the update and verifies the update's signature. If the update is valid, it installs the update and reboots the device. After reboot, the secure boot process repeats to verify and run the updated firmware. If no OTA update is available, the device continues running the current firmware. This process ensures the device runs only trusted software and safely applies updates.