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OCSP stapling lets a TLS server attach a certificate authority’s signed certificate-status response to the handshake, so a client that requests status information can check a cached response without contacting the CA’s responder for that connection. The server transports the response; it does not create or vouch for the CA’s assertion. Whether a client checks it, and what happens if the response is missing, depends on the client, certificate, and validation policy.
What OCSP stapling does
Online Certificate Status Protocol (OCSP) provides a way to ask whether a particular certificate has been revoked. In the usual client-driven arrangement, a client contacts an OCSP responder identified for the certificate. With stapling, the server obtains a signed OCSP response from the responder, caches it, and supplies it during a TLS handshake when the client asks for status information.
The response is the CA’s or an authorized responder’s signed statement, not a live query made on behalf of that particular client. The client still has to validate the certificate chain and the response. Stapling changes who fetches and distributes the status response; it does not make the server the authority on whether a certificate is valid.
What the status values mean
RFC 6960 defines three basic OCSP certificate-status values: good, revoked, and unknown. Good means, at minimum, that the responder has no record that a certificate with the requested serial number is revoked during its validity period. It does not necessarily prove that the certificate was ever issued. A client should not treat a status value in isolation as proof that every aspect of a certificate or connection is legitimate. RFC 6960
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How the handshake works
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The client can request status information. During the TLS handshake, it may indicate that it wants certificate-status information using the
status_requestextension. Clients do not all behave alike, and not every TLS connection necessarily performs a revocation check. -
The server provides an available staple. If it has a suitable response, the server sends it as part of the handshake. In TLS 1.2 and earlier, the response is carried in a
CertificateStatusmessage. In TLS 1.3, OCSP information is carried in an extension associated with the certificate’sCertificateEntry. The TLS 1.3 specification also deprecates the olderstatus_request_v2extension for TLS 1.3. RFC 9846 -
The client validates the response. It checks that the response identifies the certificate in question, has a valid signature from an authorized signer, and is current under its validation rules. A server’s staple is not accepted just because it arrived in the handshake. RFC 6960
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The server refreshes its cached response. The server or its TLS termination layer must obtain new responses in time to serve clients that request them. The staple represents status information current at the times stated in the response, not a real-time check at the moment each client connects.
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How clients assess response freshness
OCSP responses include timestamps that help a client assess how current the information is. The fields have distinct meanings:
thisUpdate: when the responder knew the stated status to be correct.nextUpdate: the time by which newer status information is expected to be available.producedAt: when the response was signed.
A response with a valid signature can still be unsuitable if it is stale, identifies another certificate, or was signed by an unauthorized party. Under the high-volume OCSP profile in RFC 9919, clients must check that the current time falls between thisUpdate and nextUpdate; they must reject a response if nextUpdate is missing or expired. That is a profile-level rule, not a description of every legacy client’s behavior. RFC 9919
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In practice, a server needs a refresh strategy that keeps staples usable under the policies of the clients it serves. An expired response should not be described as equivalent to a fresh good response; what a client does with an absent or unusable staple depends on its implementation and configuration.
Stapling compared with client-driven OCSP and CRLs
| Approach | Who fetches status information | Privacy and network effects | Freshness and operational considerations |
|---|---|---|---|
| Client-driven OCSP | Each client may contact the certificate’s OCSP responder. | The responder may learn which site the client is checking and the requester’s IP address. The client’s connection can also depend on reaching the responder, subject to its software’s policy. | The client receives a response from the responder, which it must validate for identity, signature, authorization, and freshness. |
| OCSP stapling | The server fetches and caches the CA’s response, then supplies it to clients that request status information. | It avoids a direct status query from each client to the CA for that connection and lets the server reuse a response for multiple clients. | The server must keep a usable response available and refresh it. The response is time-bounded, and client behavior varies. |
| Certificate revocation lists (CRLs) | Clients obtain a list of revoked certificates from a distribution point, where their policy requires or supports it. | Revocation information is distributed as a list rather than one responder’s answer to an individual certificate query. | Clients need a current list and must apply their own validation policy. CRLs and OCSP are different mechanisms; neither alone establishes one universally best approach. |
Stapling can reduce per-client responder traffic and the privacy exposure associated with clients making individual OCSP requests. The Internet Architecture Board described stapling as avoiding the latency of a browser fetching revocation status information; that refers to the direct responder-fetch component, not all latency in a TLS connection. IAB Statement on OCSP Stapling
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What happens if a staple is missing or invalid?
There is no universal answer that every browser rejects a connection when a staple is missing. Client policy, runtime configuration, certificate extensions such as Must-Staple, and the issuing CA’s support affect the outcome. A client might not request a staple, might use another configured revocation method, or might fail validation under a stricter policy.
For example, Oracle’s Java Secure Socket Extension (JSSE) documentation treats OCSP revocation checking and acceptance of stapled status information as configuration-dependent behavior. In its Java configuration, OCSP revocation checking must be enabled to use OCSP for validation, while use of a staple also depends on client status-request settings. That is Java-specific guidance, not a rule for all browsers or TLS libraries. Oracle JSSE documentation
Must-Staple is a certificate extension that signals that a staple is required by clients that honor it. If the server cannot provide the required staple, such a client may reject the connection. Do not infer from that extension that every TLS client enforces the same behavior.
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What operators should check before deploying stapling
- Issuer support: confirm that the certificate’s issuer provides OCSP responses and that the certificate and its chain have the relevant responder information. A particular CA’s policy does not establish what all other CAs offer.
- Server or TLS terminator support: check the documentation for the web server, load balancer, CDN, or other component that actually terminates TLS. Stapling is configured at that layer, and implementations differ.
- Response refresh and failure behavior: determine how the component obtains, validates, caches, and refreshes responses, and what it serves when it cannot fetch a fresh response. Do not assume the cache lifetime or fallback behavior without checking that implementation’s documentation.
- Client requirements: consider the client libraries and applications that connect to the service. Their policies may differ from those of browsers, especially where revocation checking is explicitly enabled.
- Monitoring: verify that the served response matches the active certificate and remains within the required time window. A configured feature is not evidence that a usable staple is being sent.
Current CA context: Let’s Encrypt no longer offers OCSP
Let’s Encrypt turned off its OCSP service on August 6, 2025, and says it now publishes revocation information exclusively through CRLs. It had already stopped including OCSP URLs in its certificates more than 90 days earlier. The change applies to Let’s Encrypt certificates and services; it is not evidence that every certificate authority has discontinued OCSP. Let’s Encrypt’s August 2025 announcement
In its December 2024 notice, Let’s Encrypt advised operators of non-browser software that relies on OCSP to verify what happens when certificates no longer contain an OCSP URL, and said it was removing its support for OCSP Must-Staple. Operators using certificates from other issuers should check those issuers’ current documentation rather than generalize from Let’s Encrypt’s transition. Let’s Encrypt’s December 2024 notice
When to use each mechanism
- Consider stapling when the issuer supplies suitable OCSP responses, the TLS termination software supports refreshing and serving them, and the clients you care about can use the staple. It can avoid direct per-client OCSP lookups.
- Check client-driven OCSP dependencies when non-browser applications explicitly enable revocation checking. Confirm that their issuer URLs and fallback behavior will continue to work.
- Follow issuer and client policy for CRLs where CRLs are the distribution method available or required. Plan for how clients obtain current lists and handle them.
There is no universal revocation-checking guarantee from enabling stapling: client support and policy determine whether a status check occurs and how its result affects the connection.
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Frequently Asked Questions
Does OCSP stapling prove that a website is safe?
No. A status response concerns certificate revocation; it is not a general safety verdict about the site or connection.
Is OCSP stapling still used after Let’s Encrypt ended OCSP?
Let’s Encrypt ended its own OCSP service in 2025. That change does not establish the status of other certificate authorities; check the issuer for the certificate in question.
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