NAME
SSL_CTX_set_cert_verify_callback - set peer certificate verification procedure
LIBRARY
libcrypto, -lcrypto
SYNOPSIS
#include <openssl/ssl.h>
void SSL_CTX_set_cert_verify_callback(SSL_CTX *ctx, int (*callback)(X509_STORE_CTX *,void *), void *arg);
DESCRIPTION
SSL_CTX_set_cert_verify_callback() sets the verification callback
function 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 verification
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 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 argument
arg is specified by the application when setting
callback.
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 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 function 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 powerful and
in most cases it should be sufficient to modify its behaviour using the
verify_callback function.
BUGS
RETURN VALUES
SSL_CTX_set_cert_verify_callback() does not provide diagnostic
information.
SEE ALSO
ssl(3),
SSL_CTX_set_verify(3),
SSL_get_verify_result(3),
SSL_CTX_load_verify_locations(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.