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SSL_CTX_SET_TLSEXT_STATUS_CB(3) Library Functions Manual SSL_CTX_SET_TLSEXT_STATUS_CB(3)

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

#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);

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 () 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 (). 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 (). 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 () can be retrieved by calling (), and the argument by calling ().

On the client side, () 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 (). 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 () 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 (). 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.

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.

ssl(3), SSL_CTX_callback_ctrl(3)

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.

September 11, 2021 OpenBSD-7.0