294 lines
11 KiB
Text
294 lines
11 KiB
Text
=pod
|
|
|
|
=head1 NAME
|
|
|
|
SSL_CTX_set_verify, SSL_set_verify, SSL_CTX_set_verify_depth, SSL_set_verify_depth - set peer certificate verification parameters
|
|
|
|
=head1 SYNOPSIS
|
|
|
|
#include <openssl/ssl.h>
|
|
|
|
void SSL_CTX_set_verify(SSL_CTX *ctx, int mode,
|
|
int (*verify_callback)(int, X509_STORE_CTX *));
|
|
void SSL_set_verify(SSL *s, int mode,
|
|
int (*verify_callback)(int, X509_STORE_CTX *));
|
|
void SSL_CTX_set_verify_depth(SSL_CTX *ctx,int depth);
|
|
void SSL_set_verify_depth(SSL *s, int depth);
|
|
|
|
int verify_callback(int preverify_ok, X509_STORE_CTX *x509_ctx);
|
|
|
|
=head1 DESCRIPTION
|
|
|
|
SSL_CTX_set_verify() sets the verification flags for B<ctx> to be B<mode> and
|
|
specifies the B<verify_callback> function to be used. If no callback function
|
|
shall be specified, the NULL pointer can be used for B<verify_callback>.
|
|
|
|
SSL_set_verify() sets the verification flags for B<ssl> to be B<mode> and
|
|
specifies the B<verify_callback> function to be used. If no callback function
|
|
shall be specified, the NULL pointer can be used for B<verify_callback>. In
|
|
this case last B<verify_callback> set specifically for this B<ssl> remains. If
|
|
no special B<callback> was set before, the default callback for the underlying
|
|
B<ctx> is used, that was valid at the time B<ssl> was created with
|
|
L<SSL_new(3)|SSL_new(3)>.
|
|
|
|
SSL_CTX_set_verify_depth() sets the maximum B<depth> for the certificate chain
|
|
verification that shall be allowed for B<ctx>. (See the BUGS section.)
|
|
|
|
SSL_set_verify_depth() sets the maximum B<depth> for the certificate chain
|
|
verification that shall be allowed for B<ssl>. (See the BUGS section.)
|
|
|
|
=head1 NOTES
|
|
|
|
The verification of certificates can be controlled by a set of logically
|
|
or'ed B<mode> flags:
|
|
|
|
=over 4
|
|
|
|
=item SSL_VERIFY_NONE
|
|
|
|
B<Server mode:> the server will not send a client certificate request to the
|
|
client, so the client will not send a certificate.
|
|
|
|
B<Client mode:> if not using an anonymous cipher (by default disabled), the
|
|
server will send a certificate which will be checked. The result of the
|
|
certificate verification process can be checked after the TLS/SSL handshake
|
|
using the L<SSL_get_verify_result(3)|SSL_get_verify_result(3)> function.
|
|
The handshake will be continued regardless of the verification result.
|
|
|
|
=item SSL_VERIFY_PEER
|
|
|
|
B<Server mode:> the server sends a client certificate request to the client.
|
|
The certificate returned (if any) is checked. If the verification process
|
|
fails, the TLS/SSL handshake is
|
|
immediately terminated with an alert message containing the reason for
|
|
the verification failure.
|
|
The behaviour can be controlled by the additional
|
|
SSL_VERIFY_FAIL_IF_NO_PEER_CERT and SSL_VERIFY_CLIENT_ONCE flags.
|
|
|
|
B<Client mode:> the server certificate is verified. If the verification process
|
|
fails, the TLS/SSL handshake is
|
|
immediately terminated with an alert message containing the reason for
|
|
the verification failure. If no server certificate is sent, because an
|
|
anonymous cipher is used, SSL_VERIFY_PEER is ignored.
|
|
|
|
=item SSL_VERIFY_FAIL_IF_NO_PEER_CERT
|
|
|
|
B<Server mode:> if the client did not return a certificate, the TLS/SSL
|
|
handshake is immediately terminated with a "handshake failure" alert.
|
|
This flag must be used together with SSL_VERIFY_PEER.
|
|
|
|
B<Client mode:> ignored
|
|
|
|
=item SSL_VERIFY_CLIENT_ONCE
|
|
|
|
B<Server mode:> only request a client certificate on the initial TLS/SSL
|
|
handshake. Do not ask for a client certificate again in case of a
|
|
renegotiation. This flag must be used together with SSL_VERIFY_PEER.
|
|
|
|
B<Client mode:> ignored
|
|
|
|
=back
|
|
|
|
Exactly one of the B<mode> flags SSL_VERIFY_NONE and SSL_VERIFY_PEER must be
|
|
set at any time.
|
|
|
|
The actual verification procedure is performed either using the built-in
|
|
verification procedure or using another application provided verification
|
|
function set with
|
|
L<SSL_CTX_set_cert_verify_callback(3)|SSL_CTX_set_cert_verify_callback(3)>.
|
|
The following descriptions apply in the case of the built-in procedure. An
|
|
application provided procedure also has access to the verify depth information
|
|
and the verify_callback() function, but the way this information is used
|
|
may be different.
|
|
|
|
SSL_CTX_set_verify_depth() and SSL_set_verify_depth() set the limit up
|
|
to which depth certificates in a chain are used during the verification
|
|
procedure. If the certificate chain is longer than allowed, the certificates
|
|
above the limit are ignored. Error messages are generated as if these
|
|
certificates would not be present, most likely a
|
|
X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY will be issued.
|
|
The depth count is "level 0:peer certificate", "level 1: CA certificate",
|
|
"level 2: higher level CA certificate", and so on. Setting the maximum
|
|
depth to 2 allows the levels 0, 1, and 2. The default depth limit is 9,
|
|
allowing for the peer certificate and additional 9 CA certificates.
|
|
|
|
The B<verify_callback> function is used to control the behaviour when the
|
|
SSL_VERIFY_PEER flag is set. It must be supplied by the application and
|
|
receives two arguments: B<preverify_ok> indicates, whether the verification of
|
|
the certificate in question was passed (preverify_ok=1) or not
|
|
(preverify_ok=0). B<x509_ctx> is a pointer to the complete context used
|
|
for the certificate chain verification.
|
|
|
|
The certificate chain is checked starting with the deepest nesting level
|
|
(the root CA certificate) and worked upward to the peer's certificate.
|
|
At each level signatures and issuer attributes are checked. Whenever
|
|
a verification error is found, the error number is stored in B<x509_ctx>
|
|
and B<verify_callback> is called with B<preverify_ok>=0. By applying
|
|
X509_CTX_store_* functions B<verify_callback> can locate the certificate
|
|
in question and perform additional steps (see EXAMPLES). If no error is
|
|
found for a certificate, B<verify_callback> is called with B<preverify_ok>=1
|
|
before advancing to the next level.
|
|
|
|
The return value of B<verify_callback> controls the strategy of the further
|
|
verification process. If B<verify_callback> returns 0, the verification
|
|
process is immediately stopped with "verification failed" state. If
|
|
SSL_VERIFY_PEER is set, a verification failure alert is sent to the peer and
|
|
the TLS/SSL handshake is terminated. If B<verify_callback> returns 1,
|
|
the verification process is continued. If B<verify_callback> always returns
|
|
1, the TLS/SSL handshake will not be terminated with respect to verification
|
|
failures and the connection will be established. The calling process can
|
|
however retrieve the error code of the last verification error using
|
|
L<SSL_get_verify_result(3)|SSL_get_verify_result(3)> or by maintaining its
|
|
own error storage managed by B<verify_callback>.
|
|
|
|
If no B<verify_callback> is specified, the default callback will be used.
|
|
Its return value is identical to B<preverify_ok>, so that any verification
|
|
failure will lead to a termination of the TLS/SSL handshake with an
|
|
alert message, if SSL_VERIFY_PEER is set.
|
|
|
|
=head1 BUGS
|
|
|
|
In client mode, it is not checked whether the SSL_VERIFY_PEER flag
|
|
is set, but whether SSL_VERIFY_NONE is not set. This can lead to
|
|
unexpected behaviour, if the SSL_VERIFY_PEER and SSL_VERIFY_NONE are not
|
|
used as required (exactly one must be set at any time).
|
|
|
|
The certificate verification depth set with SSL[_CTX]_verify_depth()
|
|
stops the verification at a certain depth. The error message produced
|
|
will be that of an incomplete certificate chain and not
|
|
X509_V_ERR_CERT_CHAIN_TOO_LONG as may be expected.
|
|
|
|
=head1 RETURN VALUES
|
|
|
|
The SSL*_set_verify*() functions do not provide diagnostic information.
|
|
|
|
=head1 EXAMPLES
|
|
|
|
The following code sequence realizes an example B<verify_callback> function
|
|
that will always continue the TLS/SSL handshake regardless of verification
|
|
failure, if wished. The callback realizes a verification depth limit with
|
|
more informational output.
|
|
|
|
All verification errors are printed; information about the certificate chain
|
|
is printed on request.
|
|
The example is realized for a server that does allow but not require client
|
|
certificates.
|
|
|
|
The example makes use of the ex_data technique to store application data
|
|
into/retrieve application data from the SSL structure
|
|
(see L<SSL_get_ex_new_index(3)|SSL_get_ex_new_index(3)>,
|
|
L<SSL_get_ex_data_X509_STORE_CTX_idx(3)|SSL_get_ex_data_X509_STORE_CTX_idx(3)>).
|
|
|
|
...
|
|
typedef struct {
|
|
int verbose_mode;
|
|
int verify_depth;
|
|
int always_continue;
|
|
} mydata_t;
|
|
int mydata_index;
|
|
...
|
|
static int verify_callback(int preverify_ok, X509_STORE_CTX *ctx)
|
|
{
|
|
char buf[256];
|
|
X509 *err_cert;
|
|
int err, depth;
|
|
SSL *ssl;
|
|
mydata_t *mydata;
|
|
|
|
err_cert = X509_STORE_CTX_get_current_cert(ctx);
|
|
err = X509_STORE_CTX_get_error(ctx);
|
|
depth = X509_STORE_CTX_get_error_depth(ctx);
|
|
|
|
/*
|
|
* Retrieve the pointer to the SSL of the connection currently treated
|
|
* and the application specific data stored into the SSL object.
|
|
*/
|
|
ssl = X509_STORE_CTX_get_ex_data(ctx, SSL_get_ex_data_X509_STORE_CTX_idx());
|
|
mydata = SSL_get_ex_data(ssl, mydata_index);
|
|
|
|
X509_NAME_oneline(X509_get_subject_name(err_cert), buf, 256);
|
|
|
|
/*
|
|
* Catch a too long certificate chain. The depth limit set using
|
|
* SSL_CTX_set_verify_depth() is by purpose set to "limit+1" so
|
|
* that whenever the "depth>verify_depth" condition is met, we
|
|
* have violated the limit and want to log this error condition.
|
|
* We must do it here, because the CHAIN_TOO_LONG error would not
|
|
* be found explicitly; only errors introduced by cutting off the
|
|
* additional certificates would be logged.
|
|
*/
|
|
if (depth > mydata->verify_depth) {
|
|
preverify_ok = 0;
|
|
err = X509_V_ERR_CERT_CHAIN_TOO_LONG;
|
|
X509_STORE_CTX_set_error(ctx, err);
|
|
}
|
|
if (!preverify_ok) {
|
|
printf("verify error:num=%d:%s:depth=%d:%s\n", err,
|
|
X509_verify_cert_error_string(err), depth, buf);
|
|
}
|
|
else if (mydata->verbose_mode)
|
|
{
|
|
printf("depth=%d:%s\n", depth, buf);
|
|
}
|
|
|
|
/*
|
|
* At this point, err contains the last verification error. We can use
|
|
* it for something special
|
|
*/
|
|
if (!preverify_ok && (err == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT))
|
|
{
|
|
X509_NAME_oneline(X509_get_issuer_name(ctx->current_cert), buf, 256);
|
|
printf("issuer= %s\n", buf);
|
|
}
|
|
|
|
if (mydata->always_continue)
|
|
return 1;
|
|
else
|
|
return preverify_ok;
|
|
}
|
|
...
|
|
|
|
mydata_t mydata;
|
|
|
|
...
|
|
mydata_index = SSL_get_ex_new_index(0, "mydata index", NULL, NULL, NULL);
|
|
|
|
...
|
|
SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER|SSL_VERIFY_CLIENT_ONCE,
|
|
verify_callback);
|
|
|
|
/*
|
|
* Let the verify_callback catch the verify_depth error so that we get
|
|
* an appropriate error in the logfile.
|
|
*/
|
|
SSL_CTX_set_verify_depth(verify_depth + 1);
|
|
|
|
/*
|
|
* Set up the SSL specific data into "mydata" and store it into th SSL
|
|
* structure.
|
|
*/
|
|
mydata.verify_depth = verify_depth; ...
|
|
SSL_set_ex_data(ssl, mydata_index, &mydata);
|
|
|
|
...
|
|
SSL_accept(ssl); /* check of success left out for clarity */
|
|
if (peer = SSL_get_peer_certificate(ssl))
|
|
{
|
|
if (SSL_get_verify_result(ssl) == X509_V_OK)
|
|
{
|
|
/* The client sent a certificate which verified OK */
|
|
}
|
|
}
|
|
|
|
=head1 SEE ALSO
|
|
|
|
L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>,
|
|
L<SSL_CTX_get_verify_mode(3)|SSL_CTX_get_verify_mode(3)>,
|
|
L<SSL_get_verify_result(3)|SSL_get_verify_result(3)>,
|
|
L<SSL_CTX_load_verify_locations(3)|SSL_CTX_load_verify_locations(3)>,
|
|
L<SSL_get_peer_certificate(3)|SSL_get_peer_certificate(3)>,
|
|
L<SSL_CTX_set_cert_verify_callback(3)|SSL_CTX_set_cert_verify_callback(3)>,
|
|
L<SSL_get_ex_data_X509_STORE_CTX_idx(3)|SSL_get_ex_data_X509_STORE_CTX_idx(3)>,
|
|
L<SSL_get_ex_new_index(3)|SSL_get_ex_new_index(3)>
|
|
|
|
=cut
|