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Security Fundamentals & Crypto · Foundational

Chain of Trust

Sequence of certificates from an end-entity certificate through intermediates to a trusted root CA.

Definition

Each certificate in the chain is signed by the next one up, and validation succeeds only if every signature, validity period, constraint, and revocation status checks out up to a trusted root. Path building and validation rules are defined in RFC 5280. The term is also used for boot processes where each stage verifies the next.

Example

A browser validates example.com's certificate, then the R11 intermediate, then the ISRG Root X1 in its trust store.

Exam tip

A broken or incomplete chain causes trust errors even if the leaf certificate is valid.

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