CA Certificate Management

TL;DR

This guide explains how to manage CA (Certificate Authority) certificates throughout their lifecycle – from creation and renewal to revocation and replacement. It covers key concepts, tools, and best practices for keeping your systems secure.

1. Understanding the Certificate Lifecycle

A certificate’s life isn’t forever. Here’s what happens:

1. Creation: A CA issues a new certificate after verifying your identity and domain ownership.
2. Usage: The certificate is used to encrypt communications (e.g., HTTPS for websites).
3. Renewal: Certificates expire! You need to renew them before they do to avoid service disruptions.
4. Revocation: If a certificate’s private key is compromised, it must be revoked immediately.
5. Replacement: After revocation, a new certificate is issued.

2. Creating Certificates

You can get certificates in two main ways:

• Public CAs (e.g., Let’s Encrypt, DigiCert): These are trusted by most browsers and devices automatically. They require payment or meeting specific criteria for free options like Let’s Encrypt.
• Private CAs: You run your own CA infrastructure. This gives you more control but requires significant effort to maintain trust (e.g., distributing root certificates).

Using openssl is a common way to create Certificate Signing Requests (CSRs) which are then submitted to the CA:

openssl req -newkey rsa:2048 -nodes -keyout mydomain.key -out mydomain.csr

3. Automating Renewal

Manual renewal is error-prone. Automation is key.

• Certbot (Let’s Encrypt): A popular tool for automatically obtaining and renewing Let’s Encrypt certificates. It integrates with web servers like Apache and Nginx.
• ACME Protocol: Certbot uses the ACME protocol, which allows automated certificate management. Other tools also support it.
• Cron Jobs/Scheduled Tasks: Use these to run renewal scripts regularly (e.g., weekly).

Example certbot command for automatic renewal:

certbot renew --dry-run

(The --dry-run flag tests the renewal process without actually making changes.)

4. Revoking Compromised Certificates

If a private key is lost or stolen, revoke the certificate *immediately*.

• Public CAs: Follow their revocation procedures (usually through an online portal). They typically involve submitting the serial number of the certificate.
• Private CAs: Revoke the certificate in your CA database and publish a Certificate Revocation List (CRL) or use Online Certificate Status Protocol (OCSP).

A CRL is a list of revoked certificates. OCSP provides real-time revocation status checks.

5. Replacing Certificates

After revoking, get a new certificate:

1. Generate a new CSR: As in step 2.
2. Request a new certificate: From your CA.
3. Install the new certificate: Configure your web server or application to use it.

6. Monitoring and Alerts

Don’t wait for errors! Proactive monitoring is vital.

• Expiry Dates: Track certificate expiry dates using a spreadsheet, dedicated monitoring tool, or scripting.
• Automated Notifications: Set up alerts to notify you well in advance of expiration (e.g., 30, 60, 90 days).
• Regular Audits: Periodically review your certificate infrastructure and processes.

7. Best Practices for cyber security

• Secure Private Keys: Store private keys securely (e.g., using hardware security modules – HSMs). Limit access to them.
• Short Validity Periods: Use shorter certificate validity periods (e.g., 90 days) for increased security, especially with automated renewal.
• Strong Algorithms: Use strong cryptographic algorithms (e.g., RSA with at least 2048-bit keys or ECC).
• Regular Updates: Keep your CA software and related tools up to date.