Secure Boot: A Key to Digital Security

23/04/2024 by Johann Philipp Thiers

The Foundation of System Security

In the realm of digital security, safeguarding the booting process is paramount. Secure boot is a critical feature for maintaining the integrity and confidentiality of data and code stored across various devices, including SSDs, USB drives, and SD cards. This security mechanism is pivotal in establishing a trustworthy environment by ensuring that only authenticated and unaltered firmware or software is executed during device startup, thereby preventing unauthorized access and control by attackers.

The Mechanics of Secure Boot

At its core, secure boot aims to thwart arbitrary code execution by validating the digital signature of a device's firmware during the boot process. This involves a secret cryptographic key used to sign the firmware image, with the corresponding public key securely stored on the device to verify this signature. If the firmware has been tampered with, its signature won't match, stopping the boot process and preventing potential security breaches.

Figure 1: The process of secure boot. Measured boot in contrast does not enforce a secure system state but reports the systems state to verifiers. It is often implemented in conjunction with secure boot.

Building a Chain of Trust

Secure boot is instrumental in forming a Chain of Trust (CoT), beginning with the Root of Trust (RoT) - a set of immutable hardware components within the NAND flash controller, which are inherently trusted.  The process of secure booting extends this trust across the system's software components, by ensuring the trustworthiness of each component before executing it. This chain not only bolsters security against malware but also prevents prolonged access in case a system was successfully attacked.

Figure 2: A Chain of Trust (CoT) verifies trustworthiness starting with a Root of Trust (RoT).

The Significance of Secure Boot

Secure boot is essential for maintaining ecosystem integrity and meeting compliance requirements across various industries, by ensuring that devices boot with authorized software. It acts as an important line of defense in a multi-layered security strategy, protecting sensitive data and systems from unauthorized access and tampering.

Implementing Secure Boot in NAND Flash Storage

A secure boot method implemented in Swissbit NAND flash devices with their Hyperstone controller technology protects the controller’s firmware as well as application-specific firmware extensions. This approach ensures that industrial-grade storage devices come with built-in secure boot capabilities, providing robust security without compromising on space or cost.       

Extending the Chain of Trust

The trust established in the working state of the storage device can now be even extended to the host device by verifying the trustworthiness of its software. This could help with achieving upcoming EU CRA requirements, without extending the bill of material. For example, our PS-45u DP micro-SD card “Raspberry Edition” verifies the bootloader of a Raspberry Pi.


Secure boot is a fundamental feature for ensuring the security of digital devices, offering a reliable method to protect against unauthorized access and ensure compliance with industry standards. Its role in establishing a Chain of Trust and the various implementation levels highlight its importance in today's digital security landscape.