We use cookies on our website to ensure we provide you with the best experience on our website. By using our website, you agree to the use of cookies for analytics and personalized content.This website uses cookies. More Information
It seems like your browser didn't download the required fonts. Please revise your security settings and try again.
Barracuda Web Application Firewall

Client Certificate Validation Using OCSP and CRLs

  • Last updated on

The Barracuda Web Application Firewall supports Online Certificate Status Protocol (OCSP) and Certificate Revocation Lists (CRLs) to determine the current status of client digital certificates. SSL connections from clients can be allowed or blocked based on the status of the client certificate presented to the Barracuda Web Application Firewall, which is maintained externally by a certificate management system.

OCSP ValidationCRL Validation
The Barracuda Web Application Firewall connects to the certificate management system to verify the current status of a client certificate.The certificate is verified using the downloaded CRL file.
OCSP provides current revocation status information for certificates.Certificate Revocation Lists (CRLs) provide periodically updated certificate status.

Client Certificate Validation Using OCSP

When a client attempts to access a server over an SSL connection that requires client certificate, an OCSP status request for the client certificate is sent to an OCSP responder. The OCSP responder determines whether the status request contains the information required to identify the certificate and then returns a signed response message indicating one of the following:

  • GOOD - a positive response indicating that the certificate has not been revoked.
  • REVOKED - a negative response indicating that the certificate has been revoked.
  • UNKNOWN - indication that the OCSP responder has no information about the requested certificate.

For any error or failure, the responder may return an unsigned message indicating a failed communication, logged under System Logs. Errors can occur because of a malformed request, an internal error, or an unauthorized request. To view system logs, navigate to the ADVANCED > System Logs page. If you want system events sent to the syslog servers, configure one or more (maximum of three) syslog servers using Add Syslog Server on the ADVANCED > Export Logs > Syslog section. For more information on configuring syslog, see How to Configure Syslog and Other Logs.

Enforce Client Certificate must be set to Yes for a service on the BASIC > Services page if you want to authenticate client certificates using OCSP.

Configuring OCSP Validation

To enable OCSP validation, do the following:

  1. Go to the ACCESS CONTROL > Client Certificates page.
  2. In the Client Certificate Validation - OCSP section, identify the service for which you want to enable client certificate validation using OCSP and click Edit next to that service. The Client Certificate Validation - OCSP window opens.
  3. Specify values for the following fields:
    • Enabled – Set to Yes to enable OCSP validation.
    • OCSP Responder URL Specify the OCSP responder URL. This is the URL issued by the trusted Certificate Authority (CA) where the Barracuda Web Application Firewall will send OCSP requests. Both HTTP and HTTPS (SSL/TLS) URLs can be specified. For example, http://ocsp.example.com
    • Certificate Select a certificate from the list to verify the signature on the OCSP response.
  4. Click Save.

Client Certificate Validation using CRLs

A CRL file contains a list of client certificates that are not expired, but are revoked by the Certificate Authority (CA) that issued the certificate. The certificate might be revoked for various reasons, such as the certificate was compromised by an unauthorized user, or the user no longer works for that company.

You can add multiple CRLs to a service. When a CRL is added, the CRL file is downloaded and stored locally on the Barracuda Web Application Firewall. This file remains in use unless automatic updates are configured. The CRL file can be updated periodically (daily, weekly, or monthly) by enabling the CRL Auto Update option. If CRL validation is enabled and a client attempts to access a server with a certificate, the Barracuda Web Application Firewall validates the certificate using the downloaded CRL file. If the certificate presented by the client matches a revoked client certificate in the CRL, the SSL connection from the client is dropped. Otherwise, the connection is established and the client is allowed to access the requested website. Also, if the CRL expires and there is no updated version available, the client authentication fails and the connection will be dropped.

If the certificate presented by the client contains the CRL path name in it, the Barracuda Web Application Firewall validates the CRL path name with the file name configured in the CRL URL parameter.

                     CRL-01.png

The Barracuda Web Application Firewall uses the default gateway or a static route to access the server hosting the CRL.

Configuring CRL Validation

To enable CRL validation, do the following:

  1. Go to the ACCESS CONTROL > Client Certificates page.
  2. In the Client Certificate Validation - CRL section, identify the service requiring client certificate validation using CRLs and click Add next to that service. The Add CRL window opens.
  3. Specify values for the following fields:
    • CRL Name Specify the name of the CRL file.
    • Enable CRL Select Yes to use this CRL file to validate the client certificates.
    • CRL URL Specify the location of the CRL file to download.
    • CRL Auto Update Select Yes if you wish to automatically update the CRL file (daily, weekly, or monthly).
    • Number of Retries Specify the maximum number of times the Barracuda Web Application Firewall can attempt to download the CRL file from the specified path before giving up.
  4. Click Save.
Last updated on