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Security Fundamentals & Crypto · Advanced

Cross-Certification

Establishing trust between separate PKI hierarchies by having CAs sign each other's certificates.

Definition

Cross-certification lets users in one PKI trust certificates from another without adding a new root. A bridge CA can act as a hub connecting many PKIs, as in the US Federal PKI. Cross-signing is also used by new public CAs to gain trust in older devices.

Example

Let's Encrypt's early certificates were cross-signed by IdenTrust so older clients would trust them.

Exam tip

Bridge CAs and cross-certification connect separate trust domains.

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