What is OCSP (Online Certificate Status Protocol)? Advantages and disadvantages of OCSP

 If you are using CRL but encounter some problems such as frequent periodic downloads or CRL is consuming too much bandwidth, you can switch to using OCSP. OCSP is an alternative solution to CRL. Let's explore with  TipsMake  what OCSP is and the advantages and disadvantages of this protocol in the following article.

What is OCSP (Online Certificate Status Protocol)?

OCSP (Online Certificate Status Protocol) is an Internet protocol (IP) used to determine the revocation status of X.509 digital certificates. The protocol is described in RFC 6960 and was developed as an alternative to certificate revocation lists (CRLs), to overcome the problems associated with the use of CRLs in public key infrastructure (PKI).

What is OCSP (Online Certificate Status Protocol)?

How does OCSP work?

OCSP allows servers or browsers to send online requests to an OCSP server to check whether a certificate is still valid or has been revoked. This process follows a client-server model:

1. Client sends request to OCSP server
2. The server will respond with information about the certificate status. This response can be "good", "revoked", or "unknown".

The OCSP process works specifically as follows:

1. When a client wants to connect to a server, it sends an OCSP request with the certificate serial number.
2. The OCSP server receives the request and verifies the certificate status from the certificate authority (CA) database.
3. The OCSP responder retrieves the certificate serial number from the request.
4. Verify revocation status from CA database.
5. Returns a successfully signed response to the client if the certificate is valid.
6. The client uses the CA's public key to verify the digitally signed response.
7. The customer completes the transaction with the server.

The Role of OCSP

The primary role of OCSP is to check the current status of an SSL/TLS certificate to ensure that it is still valid at the time of the check. OCSP checks the validity of the certificate by sending a request to an OCSP server.

Additionally, OCSP was created as a replacement for the Certificate Revocation List (CRL) to address certain issues associated with the use of CRLs in public key infrastructure (PKI).

Advantages and disadvantages of OCSP

Advantages of OCSP Stapling

1. Check certificate status faster than using traditional certificate revocation lists (CRLs) that are responded to directly by the OCSP server.
2. Provides a communication security mechanism between the requesting server and the OCSP server, ensuring that information is not tampered with.
3. Save bandwidth, reduce the amount of data to download, because there is no need to download the entire CRL list, but only need to send requests for each specific certificate.
4. Easily integrates into certificate validation workflows, adapting to a variety of security environments.

Disadvantages of OCSP Stapling

1. Maintaining an OCSP server and providing certificate status information over time can increase costs for certification authorities (CAs).
2. Depending on the performance of the OCSP server, this can cause problems if the server crashes or becomes unavailable.
3. Checking the certificate status every time a user wants to connect to a website can slow down browsing speed, as it has to wait for a response from the OCSP server.

Conclude

With the information that TipsMake above, surely readers have understood what OCSP is. Compared to CRL, OCSP has outstanding advantages but still has limitations, so you need to learn and base on actual needs to decide which protocol to use. 

David Pac

Update 26 February 2025