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External OCSP Responders

Externalizing your OCSP service to a Validation Authority provides several benefits:

  • By separating the validation service from the CA, security is increased by allowing the CA to reside behind a firewall not allowing incoming connections, while the VA(s) reside in the DMZ. 
  • Externalization of the VA allows for greater degrees of availability. Separation allows for maintenance to be performed on even unclustered CAs without any downtime on OCSP services.  
  • Ensure the highest performance. Even though the OCSP responder is fast, it's not uncommon for loads on a VA infrastructure to be extremely high at times. Several VA nodes can set up to proxy for the same CA behind a load balancer, and VA nodes can be localized geographically to ensure minimal RTT. 

The following shows a rough schema of the architecture using external OCSP responders.


  • Implements RFC 2560RFC 6960 and RFC 5019.
  • Independent of CA software used (various degrees of integration possible and may be required).
  • One responder can respond for any number of CAs.
  • Status information stored in SQL database.
  • Not depending on CRLs. Status information can be updated in real-time.
  • Plug-in mechanism for custom OCSP extensions.
  • Highly configurable audit and transaction logging. Suitable for invoicing.
  • Supports PKCS#11 HSMs and soft keys.
  • Built-in health check used by load balancers and for monitoring.
  • Configurable for requiring signed requests, authorized signers, etc.
  • Can answer good or unknown to non-existing certificates, with different configuration based on request URI.
  • Linear scalability for performance and high availability by adding multiple nodes.
  • High performance, >500 requests per second on a single server.
  • On-line renewal of OCSP responder keys and certificates.
  • OCSP client in Java (Client ToolBox).
  • Support for Norwegian Unid FNR extension.
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