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Security & Cryptography Hardware

Secure Boot: How It Works

Secure boot ensures a device only runs software that's been cryptographically verified as authentic and unmodified – preventing attackers from replacing firmware with malicious code, even if they have physical access to the device.

VIDYUTT• July 22, 2026• 2 min read
Figure 1: A secure boot chain, where each stage cryptographically verifies the signature of the next before allowing it to run.
Figure 1: A secure boot chain, where each stage cryptographically verifies the signature of the next before allowing it to run.

What Secure Boot Involves

The process begins in immutable boot ROM, which cannot be altered after manufacturing. This ROM verifies the cryptographic signature of the next boot stage (typically a bootloader) before allowing it to execute. That bootloader in turn verifies the signature of the firmware or operating system it loads, and so on – forming an unbroken 'chain of trust' where each stage only runs code it has cryptographically confirmed comes from a trusted source.

Why It Matters

Without secure boot, an attacker with physical or remote access to a device could potentially replace its firmware with malicious software, compromising the device entirely. Secure boot closes this attack path by making unauthorized code modification cryptographically detectable and blocking it before it can execute.

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