SSL_CTX_SET_CERT_VERI... BSD Library Functions Manual SSL_CTX_SET_CERT_VERI...NAMESSL_CTX_set_cert_verify_callback — set peer certificate verification pro‐
cedure
SYNOPSIS
#include <openssl/ssl.h>
void
SSL_CTX_set_cert_verify_callback(SSL_CTX *ctx,
int (*callback)(X509_STORE_CTX *, void *), void *arg);
DESCRIPTIONSSL_CTX_set_cert_verify_callback() sets the verification callback func‐
tion for ctx. SSL objects that are created from ctx inherit the setting
valid at the time when SSL_new(3) is called.
NOTES
Whenever a certificate is verified during a SSL/TLS handshake, a verifi‐
cation function is called. If the application does not explicitly spec‐
ify 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 behaviour is
restored.
When the verification must be performed, callback will be called with the
arguments callback(X509_STORE_CTX *x509_store_ctx, void *arg). The argu‐
ment arg is specified by the application when setting callback.
callback should return 1 to indicate verification success and 0 to indi‐
cate verification failure. If SSL_VERIFY_PEER is set and callback
returns 0, the handshake will fail. As the verification procedure may
allow the connection to continue in case of failure (by always returning
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(3).
WARNINGS
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(3) family of functions.
Providing a complete verification procedure including certificate purpose
settings, etc., is a complex task. The built-in procedure is quite pow‐
erful and in most cases it should be sufficient to modify its behaviour
using the verify_callback function.
RETURN VALUESSSL_CTX_set_cert_verify_callback() does not provide diagnostic informa‐
tion.
SEE ALSOssl(3), SSL_CTX_load_verify_locations(3), SSL_CTX_set_verify(3),
SSL_get_verify_result(3)HISTORY
Previous to OpenSSL 0.9.7, the arg argument to
SSL_CTX_set_cert_verify_callback() was ignored, and callback was called
simply as int (*callback)(X509_STORE_CTX *). To compile software written
for previous versions of OpenSSL, a dummy argument will have to be added
to callback.
BSD April 28, 2024 BSD
