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Boot ROM

As explained in Real-World Cryptography

A boot ROM is immutable memory containing the initial code executed when a device powers on.

A boot ROM is immutable memory containing the first code executed when a device powers on. It anchors secure boot as a root of trust. section 13.2.4

A boot ROM typically performs three small, high-trust steps:

  • Prepares protected memory and loads the next boot loader. section 13.2.4
  • Hashes the loaded program and verifies its signature against a hardcoded public key. section 13.2.4
  • Executes the verified program, continuing a chain until a boot loader starts the operating system. section 13.2.4

Apple device startup

When a recent Apple device powers up, its Secure Enclave ROM executes the boot ROM first. Each later boot loader repeats verification, preventing unsigned operating-system updates from being installed. section 13.2.4

How Real-World Cryptography covers it

How deep it goes
Explains immutable storage, protected loading, signature verification, and chained boot loaders, but not implementation-level ROM details.
Examples
Uses Apple Secure Enclave ROM startup and chained verification to explain why unsigned operating-system updates are rejected.
What it assumes
Assumes only a basic understanding of powering on a device, while introducing boot stages, signatures, and hardware roots of trust.
What you can do after
Evaluate how a device establishes trusted startup code and rejects modified boot components.
How it connects
Connects secure boot with TPMs, secure elements, roots of trust, boot loaders, signature verification, and operating systems.
Cover of Real-World Cryptography
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This explainer was generated by Manning's knowledge graph from the text of Real-World Cryptography. The section links point to the parts of the book it draws on.