X509_STORE_CTX_set_verify_cb(3)
X509_STORE_CTX_set_verify_cb(3OpenSSX509_STORE_CTX_set_verify_cb(3)
NAME
X509_STORE_CTX_set_verify_cb - set verification callback
SYNOPSIS
#include <openssl/x509_vfy.h>
void X509_STORE_CTX_set_verify_cb(X509_STORE_CTX *ctx,
int (*verify_cb)(int ok, X509_STORE_CTX *ctx));
DESCRIPTION
X509_STORE_CTX_set_verify_cb() sets the verification
callback of ctx to verify_cb overwriting any existing
callback.
The verification callback can be used to customise the
operation of certificate verification, either by overriding
error conditions or logging errors for debugging purposes.
However a verification callback is not essential and the
default operation is often sufficient.
The ok parameter to the callback indicates the value the
callback should return to retain the default behaviour. If
it is zero then and error condition is indicated. If it is 1
then no error occurred. If the flag
X509_V_FLAG_NOTIFY_POLICY is set then ok is set to 2 to
indicate the policy checking is complete.
The ctx parameter to the callback is the X509_STORE_CTX
structure that is performing the verification operation. A
callback can examine this structure and receive additional
information about the error, for example by calling
X509_STORE_CTX_get_current_cert(). Additional application
data can be passed to the callback via the ex_data
mechanism.
WARNING
In general a verification callback should NOT
unconditionally return 1 in all circumstances because this
will allow verification to succeed no matter what the error.
This effectively removes all security from the application
because any certificate (including untrusted generated ones)
will be accepted.
NOTES
The verification callback can be set and inherited from the
parent structure performing the operation. In some cases
(such as S/MIME verification) the X509_STORE_CTX structure
is created and destroyed internally and the only way to set
a custom verification callback is by inheriting it from the
associated X509_STORE.
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X509_STORE_CTX_set_verify_cb(3OpenSSX509_STORE_CTX_set_verify_cb(3)
RETURN VALUES
X509_STORE_CTX_set_verify_cb() does not return a value.
EXAMPLES
Default callback operation:
int verify_callback(int ok, X509_STORE_CTX *ctx)
{
return ok;
}
Simple example, suppose a certificate in the chain is
expired and we wish to continue after this error:
int verify_callback(int ok, X509_STORE_CTX *ctx)
{
/* Tolerate certificate expiration */
if (X509_STORE_CTX_get_error(ctx) == X509_V_ERR_CERT_HAS_EXPIRED)
return 1;
/* Otherwise don't override */
return ok;
}
More complex example, we don't wish to continue after any
certificate has expired just one specific case:
int verify_callback(int ok, X509_STORE_CTX *ctx)
{
int err = X509_STORE_CTX_get_error(ctx);
X509 *err_cert = X509_STORE_CTX_get_current_cert(ctx);
if (err == X509_V_ERR_CERT_HAS_EXPIRED)
{
if (check_is_acceptable_expired_cert(err_cert)
return 1;
}
return ok;
}
Full featured logging callback. In this case the bio_err is
assumed to be a global logging BIO, an alternative would to
store a BIO in ctx using ex_data.
int verify_callback(int ok, X509_STORE_CTX *ctx)
{
X509 *err_cert;
int err,depth;
err_cert = X509_STORE_CTX_get_current_cert(ctx);
err = X509_STORE_CTX_get_error(ctx);
depth = X509_STORE_CTX_get_error_depth(ctx);
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X509_STORE_CTX_set_verify_cb(3OpenSSX509_STORE_CTX_set_verify_cb(3)
BIO_printf(bio_err,"depth=%d ",depth);
if (err_cert)
{
X509_NAME_print_ex(bio_err, X509_get_subject_name(err_cert),
0, XN_FLAG_ONELINE);
BIO_puts(bio_err, "\n");
}
else
BIO_puts(bio_err, "<no cert>\n");
if (!ok)
BIO_printf(bio_err,"verify error:num=%d:%s\n",err,
X509_verify_cert_error_string(err));
switch (err)
{
case X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT:
BIO_puts(bio_err,"issuer= ");
X509_NAME_print_ex(bio_err, X509_get_issuer_name(err_cert),
0, XN_FLAG_ONELINE);
BIO_puts(bio_err, "\n");
break;
case X509_V_ERR_CERT_NOT_YET_VALID:
case X509_V_ERR_ERROR_IN_CERT_NOT_BEFORE_FIELD:
BIO_printf(bio_err,"notBefore=");
ASN1_TIME_print(bio_err,X509_get_notBefore(err_cert));
BIO_printf(bio_err,"\n");
break;
case X509_V_ERR_CERT_HAS_EXPIRED:
case X509_V_ERR_ERROR_IN_CERT_NOT_AFTER_FIELD:
BIO_printf(bio_err,"notAfter=");
ASN1_TIME_print(bio_err,X509_get_notAfter(err_cert));
BIO_printf(bio_err,"\n");
break;
case X509_V_ERR_NO_EXPLICIT_POLICY:
policies_print(bio_err, ctx);
break;
}
if (err == X509_V_OK && ok == 2)
/* print out policies */
BIO_printf(bio_err,"verify return:%d\n",ok);
return(ok);
}
SEE ALSO
X509_STORE_CTX_get_error(3) X509_STORE_set_verify_cb_func(3)
X509_STORE_CTX_get_ex_new_index(3)
HISTORY
X509_STORE_CTX_set_verify_cb() is available in all versions
of SSLeay and OpenSSL.
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