SEC_ERROR_INADEQUATE_KEY_USAGE

• Cert issued without digitalSignature/keyEncipherment
• Extended Key Usage lacks TLS Web Server Authentication
• CA compromise forced narrow key-usage restriction
• Reused client cert as server (wrong EKU)
• Code-signing cert pressed into HTTPS duty (wrong EKU)

1. Reissue via Let's Encrypt — EKU + Key Usage correct by default
2. Check: openssl x509 -in cert.pem -text | grep -A2 "Key Usage"
3. Required bits: Digital Signature + Key Encipherment for RSA
4. Required EKU: TLS Web Server Authentication
5. Enterno SSL Checker — highlights missing KU

Check SSL Certificate →

• ERR_SSL_PROTOCOL_ERROR
• NET::ERR_CERT_AUTHORITY_INVALID
• SSL Handshake Failed
• All SSL errors

To fix the SEC_ERROR_INADEQUATE_KEY_USAGE error in Firefox, ensure your SSL certificate is configured correctly to meet key usage requirements. Specifically, the certificate must include the 'Digital Signature' and 'Key Encipherment' usages. You can verify this using the OpenSSL command line tool with openssl x509 -in your_certificate.crt -text -noout to check the key usage extensions.

The SEC_ERROR_INADEQUATE_KEY_USAGE error in Firefox occurs when a server's SSL/TLS certificate lacks the appropriate key usage attributes. This error typically arises in environments where strict compliance with security standards is enforced, such as in the EU's GDPR framework. Key usage attributes define the purposes for which a certificate's public key can be used, and if these are misconfigured, clients like Firefox will reject the connection.

Key usage attributes are defined in the X.509 standard, which is widely used for SSL/TLS certificates. The main usages relevant for web servers include:

• Digital Signature: Required for verifying the authenticity of the certificate.
• Key Encipherment: Necessary for encrypting data exchanged between the client and server.
• Key Agreement: Used for establishing shared secrets.

When any of these usages are improperly set or missing, users may encounter the SEC_ERROR_INADEQUATE_KEY_USAGE error when trying to access secured websites.

To resolve the SEC_ERROR_INADEQUATE_KEY_USAGE error, follow these steps to ensure your SSL certificate is properly configured:

1. Check Your SSL Certificate: Use the OpenSSL command to inspect your certificate and verify the key usage settings. Run the following command:

openssl x509 -in your_certificate.crt -text -noout

1. Review Key Usage Extensions: Look for the Key Usage and Extended Key Usage fields in the output. Ensure they include Digital Signature and Key Encipherment. Example output:

Key Usage: critical, Digital Signature, Key Encipherment

1. Update Certificate if Necessary: If the required usages are missing, you will need to either generate a new certificate or modify the existing one. Depending on your certificate authority (CA), you may have options to reissue or renew the certificate with the correct settings.
2. Test Your Configuration: After updating your certificate, restart your web server to apply changes. You can test your SSL configuration using online tools like SSL Labs' SSL Test to ensure that the certificate is set up correctly and is compliant with current standards.
3. Verify in Firefox: Finally, revisit the website in Firefox. If the configuration is correct, the SEC_ERROR_INADEQUATE_KEY_USAGE error should no longer appear, allowing secure connections to be established.

By following these steps, you can effectively address the SEC_ERROR_INADEQUATE_KEY_USAGE error and improve the security posture of your web applications.