Starting from an initial trust anchor, each stage verifies a cryptographic signature or other approved integrity evidence for the next component before transferring control, forming a chain of verification toward the operating environment.
Implementations differ across device classes. Unified Extensible Firmware Interface (UEFI) Secure Boot, for example, uses enrolled keys and signature databases to authorize or forbid UEFI drivers and boot applications. Key enrollment, update, revocation, recovery, and physical or administrative controls are therefore part of the security design.
Key points
Authorization policyDefine who may authorize boot components, protect trust anchors and signing keys, manage authorization and revocation data, and record controlled changes to policy.
Verification and failureAuthenticate each covered component before execution and enter a defined refusal, recovery, or restricted path when verification fails rather than silently bypassing enforcement.
Lifecycle operationSupport secure updates, compromised-key or vulnerable-component revocation, ownership transfer, recovery media, and tested procedures that preserve availability.
Important limitationSecure boot establishes that covered components are authorized under the current policy; it does not prove they are vulnerability-free, correctly configured, or trustworthy at runtime. Weak keys, permissive policy, rollback, uncovered components, or later compromise can defeat the intended outcome.