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Secure Boot Chain Fundamentals for Embedded Systems

Updated: Jan 12, 2023

Introduction

Secure Boot is a system that is used to ensure the integrity and authenticity of the code that is executing on a given embedded system. It serves to protect the system’s environment and its data by only allowing applications and services that are digitally signed and verified by an authorized source. This blog post is a comprehensive description of the fundamentals of secure boot, concentrating on the various components of the secure boot chain and how they interact with each other.


What is Secure Boot?

Secure boot is a trusted boot process that verifies the authenticity of a device's firmware, BIOS, operating system, and other critical components during the boot-up process. It ensures that all the firmware and software components loaded during the boot process originated from a trusted source and have not been tampered with or altered. Secure boot makes sure the code running on a device is the same code that the device’s vendor supplied, and can provide protection from buffer overflow attacks and rootkits.


Secure Boot Chain

The secure boot chain consists of a digital signature from the manufacturer, an encrypted messaging platform, and a trusted processor. First, the manufacturer generates a digital signature, which is used as an authentication token for the secure boot process. This digital signature contains information about the type of code and its authentication status. The encrypted messaging platform communicates the authentication status between the device’s processor and the manufacturer’s servers, ensuring that the code being loaded onto the device is the same code that was originally supplied by the manufacturer. Finally, the trusted processor verifies the digital signature and code. If the authentication is successful, then the code is allowed to be loaded onto the device. If any changes have been made to the code, such as malicious code, then the secure boot process will block the code from being loaded onto the device.


Steps for Implementing Secure Boot

1. The manufacturer will first generate a digital signature for the code and hash it using a secure cryptosystem.


2. The manufacturer then adds the digital signature to the code and publishes it to their servers.


3. The end user then downloads the code to the device. The code is then checked against the digital signature to make sure it hasn’t been tampered with.


4. The code is then authenticated by the device’s trusted processor.


5. If the authentication is successful, then the code is allowed to be loaded onto the device. If any changes have been made to the code, then the secure boot process will block the code from being loaded onto the device.


Conclusion

Secure boot is a security feature designed to protect embedded systems from malicious code and attackers. It works by requiring that only digitally signed and verified code be allowed to be loaded onto a device. Secure boot helps ensure the integrity and authenticity of code running on a device and is an essential component for the secure operation of any embedded system.



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