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Intermediate CA

A certificate authority that sits between the trusted root CA and end-entity certificates in a chain of trust. Roots sign intermediates, which sign certificates, so the root's key can stay offline and protected.

In public key infrastructure, an intermediate CA is signed by the root CA and in turn issues end-entity (such as server) certificates, forming a chain of trust from the root through the intermediate to the certificate. This layering lets the highly sensitive root key stay offline while intermediates do day-to-day issuance, and it allows revoking or rotating an intermediate without replacing the root. Understanding intermediates is key to how certificate validation and trust chains work.

Introduced in: Cryptography Essentials

Examples

  • A root CA signing an intermediate that then issues server certificates.
  • Keeping the root key offline while an intermediate handles issuance.
  • Validating a certificate by following the chain through the intermediate to the root.