SSL_CTX_SET_TLSEXT_STATUS_CB(3) | Library Functions Manual | SSL_CTX_SET_TLSEXT_STATUS_CB(3)

# NAME

`SSL_CTX_set_tlsext_status_cb`, `SSL_CTX_get_tlsext_status_cb`, `SSL_CTX_set_tlsext_status_arg`, `SSL_CTX_get_tlsext_status_arg`, `SSL_set_tlsext_status_type`, `SSL_get_tlsext_status_type`, `SSL_get_tlsext_status_ocsp_resp`, `SSL_set_tlsext_status_ocsp_resp` — OCSP Certificate Status Request functions

# SYNOPSIS

library “libssl” libcrypto
`#include <openssl/tls1.h>`

long
`SSL_CTX_set_tlsext_status_cb`(SSL_CTX *ctx, int (*callback)(SSL *, void *));

long
`SSL_CTX_get_tlsext_status_cb`(SSL_CTX *ctx, int (*callback)(SSL *, void *));

long
`SSL_CTX_set_tlsext_status_arg`(SSL_CTX *ctx, void *arg);

long
`SSL_CTX_get_tlsext_status_arg`(SSL_CTX *ctx, void **arg);

long
`SSL_set_tlsext_status_type`(SSL *s, int type);

long
`SSL_get_tlsext_status_type`(SSL *s);

long
`SSL_get_tlsext_status_ocsp_resp`(ssl, unsigned char **resp);

long
`SSL_set_tlsext_status_ocsp_resp`(ssl, unsigned char *resp, int len);

# DESCRIPTION

A client application may request that a server send back an OCSP status response (also known as OCSP stapling). To do so the client should call the `SSL_set_tlsext_status_type`() function on an individual SSL object prior to the start of the handshake. Currently the only supported type is `TLSEXT_STATUSTYPE_ocsp`. This value should be passed in the type argument.

The client should additionally provide a callback function to decide what to do with the returned OCSP response by calling `SSL_CTX_set_tlsext_status_cb`(). The callback function should determine whether the returned OCSP response is acceptable or not. The callback will be passed as an argument the value previously set via a call to `SSL_CTX_set_tlsext_status_arg`(). Note that the callback will not be called in the event of a handshake where session resumption occurs (because there are no Certificates exchanged in such a handshake).

The callback previously set via `SSL_CTX_set_tlsext_status_cb`() can be retrieved by calling `SSL_CTX_get_tlsext_status_cb`(), and the argument by calling `SSL_CTX_get_tlsext_status_arg`().

On the client side, `SSL_get_tlsext_status_type`() can be used to determine whether the client has previously called `SSL_set_tlsext_status_type`(). It will return `TLSEXT_STATUSTYPE_ocsp` if it has been called or -1 otherwise. On the server side, `SSL_get_tlsext_status_type`() can be used to determine whether the client requested OCSP stapling. If the client requested it, then this function will return `TLSEXT_STATUSTYPE_ocsp`, or -1 otherwise.

The response returned by the server can be obtained via a call to `SSL_get_tlsext_status_ocsp_resp`(). The value *resp will be updated to point to the OCSP response data and the return value will be the length of that data. If the server has not provided any response data, then *resp will be `NULL` and the return value from `SSL_get_tlsext_status_ocsp_resp`() will be -1.

A server application must also call the `SSL_CTX_set_tlsext_status_cb`() function if it wants to be able to provide clients with OCSP Certificate Status responses. Typically the server callback would obtain the server certificate that is being sent back to the client via a call to SSL_get_certificate(3), obtain the OCSP response to be sent back, and then set that response data by calling `SSL_set_tlsext_status_ocsp_resp`(). A pointer to the response data should be provided in the resp argument, and the length of that data should be in the len argument.

# RETURN VALUES

The callback when used on the client side should return a negative value on error, 0 if the response is not acceptable (in which case the handshake will fail), or a positive value if it is acceptable.

The callback when used on the server side should return with either `SSL_TLSEXT_ERR_OK` (meaning that the OCSP response that has been set should be returned), `SSL_TLSEXT_ERR_NOACK` (meaning that an OCSP response should not be returned), or `SSL_TLSEXT_ERR_ALERT_FATAL` (meaning that a fatal error has occurred).

`SSL_CTX_set_tlsext_status_cb`(), `SSL_CTX_get_tlsext_status_cb`(), `SSL_CTX_set_tlsext_status_arg`(), `SSL_CTX_get_tlsext_status_arg`(), `SSL_set_tlsext_status_type`(), and `SSL_set_tlsext_status_ocsp_resp`() always return 1, indicating success.

`SSL_get_tlsext_status_type`() returns `TLSEXT_STATUSTYPE_ocsp` on the client side if `SSL_set_tlsext_status_type`() was previously called, or on the server side if the client requested OCSP stapling. Otherwise -1 is returned.

`SSL_get_tlsext_status_ocsp_resp`() returns the length of the OCSP response data or -1 if there is no OCSP response data.

# SEE ALSO

ssl(3), SSL_CTX_callback_ctrl(3)

# HISTORY

`SSL_CTX_set_tlsext_status_cb`(), `SSL_CTX_set_tlsext_status_arg`(), `SSL_set_tlsext_status_type`(), `SSL_get_tlsext_status_ocsp_resp`(), and `SSL_set_tlsext_status_ocsp_resp`() first appeared in OpenSSL 0.9.8h and have been available since OpenBSD 4.5.

`SSL_CTX_get_tlsext_status_cb`() and `SSL_CTX_get_tlsext_status_arg`() first appeared in OpenSSL 1.1.0 and have been available since OpenBSD 6.3.

`SSL_get_tlsext_status_type`() first appeared in OpenSSL 1.1.0 and has been available since OpenBSD 7.0.

June 8, 2025 | Debian