TL;DR
Generally, you cannot directly overwrite fields from a Certificate Signing Request (CSR) after the certificate has been issued. The certificate authority (CA) uses the CSR to create the certificate, and once signed, those values are cryptographically bound. However, there are ways to achieve similar results through re-issuance or extensions.
Solution Guide
- Understand the CSR Process: A CSR is a request containing information like your domain name, organisation details, and public key. You submit this to a CA who verifies it and issues a certificate based on that data.
- Why Overwriting Isn’t Direct: Certificates are digitally signed by the CA. Changing any of the core fields after signing invalidates the signature, making the certificate untrusted. Think of it like a tamper-proof seal.
- Common Scenarios & Solutions:
- Incorrect Domain Name: The most common issue. You’ll need to revoke the existing certificate (if possible) and create a new CSR with the correct domain name, then request a re-issue from your CA.
- Typo in Organisation Name: Similar to above – revocation and re-issuance are required. Some CAs may offer free or discounted re-issues for minor typos.
- Adding Subject Alternative Names (SANs): You can’t add SANs after issuance. Revoke the old certificate, update your CSR with the additional domains/subdomains, and request a new one.
- Changing Certificate Policies: Requires re-issuance as these are fundamental to the certificate’s trust model.
- Revoking a Certificate: The process varies by CA.
- Online Revocation (OCSP): A real-time check of a certificate’s status. Useful for immediate validation.
- Certificate Revocation List (CRL): A periodically updated list of revoked certificates. Clients download this list to verify trust.
- CA Portal: Most CAs provide a web portal where you can initiate the revocation process. You’ll typically need your certificate details and possibly a reason for revocation.
- Re-issuing a Certificate:
- Generate New CSR: Create a new CSR with the correct information using tools like OpenSSL or your web server’s interface.
openssl req -new -key private.key -out csr.csr - Submit to CA: Follow your CA’s instructions for submitting a re-issue request, usually through their portal. They will likely require you to verify ownership again.
- Install New Certificate: Once issued, download the new certificate and install it on your server.
- Generate New CSR: Create a new CSR with the correct information using tools like OpenSSL or your web server’s interface.
- Extensions (Limited Cases): Some CAs allow adding certain extensions *after* issuance through a process called certificate chaining or using OCSP stapling. This is not field overwriting but can address specific issues.
- OCSP Stapling: Your server presents the CA’s signed revocation status alongside your certificate, improving performance and security.
- Important Considerations:
- Downtime: Revocation and re-issuance will cause a brief period of downtime while the new certificate propagates. Plan accordingly.
- CA Policies: Each CA has its own policies regarding revocation, re-issuance fees, and acceptable reasons for changes. Check their documentation.
- Intermediate Certificates: Ensure you install any required intermediate certificates along with your main certificate to establish a complete chain of trust.