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Certificate Authority

An organisation that issues digital certificates after verifying the requester controls the domain or identity in the certificate, trusted by browsers and operating systems.

A Certificate Authority (CA) is an organisation that issues TLS/SSL certificates after validating the requester's control of the domain (DV), organisation (OV), or extended-vetted identity (EV). Browsers and operating systems ship with a root store listing CAs they trust; a certificate is trusted only if it chains up to one of those roots. Public CAs like Let's Encrypt, DigiCert, Sectigo, and Google Trust Services dominate the public web. Internal CAs issue private certificates for intranets and service-mesh mTLS. CA mis-issuance is rare but high-impact, which is why Certificate Transparency exists.

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