Revoke SHA1 Self-Signed Certificates

TL;DR

Yes, you should revoke any identity self-signed certificates using SHA1 immediately. SHA1 is considered cryptographically broken and poses a significant security risk. Replace them with certificates signed using SHA256 or higher.

Why Revoke SHA1 Certificates?

SHA1 (Secure Hash Algorithm 1) was once widely used for digital signatures, including those in self-signed certificates. However, vulnerabilities have been discovered that allow attackers to create collisions – forging valid signatures. This means someone could potentially impersonate your identity.

• Security Risk: Collisions can be exploited to bypass security checks and compromise trust.
• Browser Support: Major browsers (Chrome, Firefox, Safari) have already removed support for SHA1 certificates. Users will see errors or warnings when encountering them.
• Industry Standards: Modern cybersecurity best practices mandate the use of stronger hashing algorithms like SHA256 or higher.

Step-by-Step Revocation and Replacement

1. Identify SHA1 Certificates: You need to find all self-signed certificates using SHA1 within your systems.
   • OpenSSL: Use OpenSSL to inspect the certificate.

   openssl x509 -in your_certificate.pem -text -noout | grep 'SHA1'

   • Certificate Stores: Check your operating system’s certificate store (e.g., Windows Certificate Manager, macOS Keychain Access).
2. Revoke the Old Certificates: Revocation depends on how the certificates are used.
   • If used in applications: Remove the old certificate from the application’s trust store. Update configuration files accordingly.
   • If used for code signing: If you have a Certificate Revocation List (CRL), add the serial number of the SHA1 certificate to it. Publish the updated CRL.
   • Self-Signed Web Server Certificates: Stop using the old certificate in your web server configuration.
3. Generate a New Certificate with SHA256 or Higher: Create a new self-signed certificate using a stronger hashing algorithm.
   • OpenSSL Example (SHA256): This creates a 30-day valid certificate. Adjust the validity period as needed.

     openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 30 -sha256

   • Important: Ensure you provide accurate information during certificate generation (Common Name, Organization, etc.).
4. Install the New Certificate: Replace the old SHA1 certificate with the new one in all relevant systems and applications.
   • Web Servers: Configure your web server to use the new certificate. Restart the server after making changes.
   • Applications: Add the new certificate to the application’s trust store.
5. Test Thoroughly: Verify that the new certificate is working correctly.
   • Web Browsers: Access your website using different browsers to confirm there are no errors or warnings.
   • Applications: Test all functionality that relies on the certificate.

Additional Considerations

• Automated Certificate Management: Consider using automated certificate management tools (e.g., Let’s Encrypt) to simplify certificate renewal and reduce the risk of outdated certificates.
• cyber security Audits: Regularly audit your systems for weak or expired certificates as part of a comprehensive cybersecurity program.