SSL_CTX_SET_CERT_VERIFY_CALLBOSSL_CTX_SET_CERT_VERIFY_CALLBACK(3)NAMESSL_CTX_set_cert_verify_callback - set peer certificate
verification procedure
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 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 appli-
cation 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 connec-
tion in case of failure (by always returning 1) the verifi-
cation 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 pro-
cedure!
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 func-
tion 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 certi-
ficate purpose settings etc is a complex task. The built-in
procedure is quite powerful and in most cases it should be
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SSL_CTX_SET_CERT_VERIFY_CALLBOSSL_CTX_SET_CERT_VERIFY_CALLBACK(3)
sufficient to modify its behaviour using the verify_callback
function.
BUGSRETURN VALUESSSL_CTX_set_cert_verify_callback() does not provide diagnos-
tic information.
SEE ALSOssl(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 writ-
ten for previous versions of OpenSSL, a dummy argument will
have to be added to callback.
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