SSL_CTX_set_cert_verify_cb(3)SSL_CTX_set_cert_verify_cb(3)NAMESSL_CTX_set_cert_verify_cb - Set peer certificate verification proce‐
dure
SYNOPSIS
#include <openssl/ssl.h>
void SSL_CTX_set_cert_verify_cb(
SSL_CTX *ctx,
int (*cb)(),
char *arg ); int
*callback );
DESCRIPTION
The SSL_CTX_set_cert_verify_cb() sets the verification callback func‐
tion for ctx. SSL objects that are created from ctx inherit the setting
valid at the time SSL_new() is called. The arg is currently ignored.
NOTES
Whenever a certificate is verified during a SSL/TLS handshake, a veri‐
fication function is called. If the application does not explicitly
specify a verification callback function, the built-in verification
function is used. If a verification callback callback is specified via
SSL_CTX_set_cert_verify_callback(), the supplied callback function is
called instead.
By setting callback to NULL, the default behavior is restored. When the
verification must be performed, callback will be called with the argu‐
ment callback (X509_STORE_CTX *x509_store_ctx). The arguments that can
be specified when setting callback are currently ignored.
Callback should return 1 to indicate verification success and 0 to
indicate verification failure. If SSL_VERIFY_PEER is set and callback
returns 0, the handshake will fail. As the verification procedure may
allow to continue the connection in case of failure (by always return‐
ing 1) the verification result must be set in any case using the error
member of x509_store_ctx, so that the calling application will be
informed about the detailed result of the verification procedure.
Within x509_store_ctx, callback has access to the verify_callback func‐
tion set using SSL_CTX_set_verify()).
RESTRICTIONS
Do not mix the verification callback described in this function with
the verify_callback function called during the verification process.
The latter is set using the SSL_CTX_set_verify() family of functions.
Providing a complete verification procedure, including certificate
purpose settings, is a complex task. The built-in procedure is quite
powerful and in most cases it should be sufficient to modify its behav‐
ior using the verify_cb function.
It is possible to specify arguments to be passed to the verification
callback. However, they are currently ignored. The callback function
is not specified via a prototype, so that no type checking takes place.
RETURN VALUES
The SSL_CTX_set_cert_verify_cb() function does not provide diagnostic
information.
SEE ALSOSSL_CTX_set_verify(3), SSL_get_verify_result(3), SSL_CTX_load_ver‐
ify_locations(3)SSL_CTX_set_cert_verify_cb(3)
