How are X.509 certificates issued?

The X.509 certificate generation procedure consists of several stages:

1. The applicant (future certificate owner) generates the certificate’s private and public keys.
2. The applicant generates a Certificate Signing Request (CSR). The CSR contains the subject, the public key of the future certificate, the X509v3 extensions requested by the applicant, and the CSR signature. The CSR is signed by the certificate’s private key.
3. The applicant sends the CSR to a CA for signing.
4. The CA checks the applicant’s identity.
5. The CA makes a certificate based on information from the CSR. The CA also adds other information to the certificate, such as the issuer, validity fields, and X509v3 extensions. Finally, the CA signs the certificate.
6. The CA sends the certificate back to the applicant, who then becomes the certificate owner or holder.

Note that no one exposes the private key to another party in the process.

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