5
SSL_CTX_set_verify, SSL_set_verify, SSL_CTX_set_verify_depth, SSL_set_verify_depth - set peer certificate verification parameters
9
#include <openssl/ssl.h>
11
void SSL_CTX_set_verify(SSL_CTX *ctx, int mode,
12
int (*verify_callback)(int, X509_STORE_CTX *));
13
void SSL_set_verify(SSL *s, int mode,
14
int (*verify_callback)(int, X509_STORE_CTX *));
15
void SSL_CTX_set_verify_depth(SSL_CTX *ctx,int depth);
16
void SSL_set_verify_depth(SSL *s, int depth);
18
int verify_callback(int preverify_ok, X509_STORE_CTX *x509_ctx);
22
SSL_CTX_set_verify() sets the verification flags for B<ctx> to be B<mode> and
23
specifies the B<verify_callback> function to be used. If no callback function
24
shall be specified, the NULL pointer can be used for B<verify_callback>.
26
SSL_set_verify() sets the verification flags for B<ssl> to be B<mode> and
27
specifies the B<verify_callback> function to be used. If no callback function
28
shall be specified, the NULL pointer can be used for B<verify_callback>. In
29
this case last B<verify_callback> set specifically for this B<ssl> remains. If
30
no special B<callback> was set before, the default callback for the underlying
31
B<ctx> is used, that was valid at the time B<ssl> was created with
32
L<SSL_new(3)|SSL_new(3)>.
34
SSL_CTX_set_verify_depth() sets the maximum B<depth> for the certificate chain
35
verification that shall be allowed for B<ctx>. (See the BUGS section.)
37
SSL_set_verify_depth() sets the maximum B<depth> for the certificate chain
38
verification that shall be allowed for B<ssl>. (See the BUGS section.)
42
The verification of certificates can be controlled by a set of logically
49
B<Server mode:> the server will not send a client certificate request to the
50
client, so the client will not send a certificate.
52
B<Client mode:> if not using an anonymous cipher (by default disabled), the
53
server will send a certificate which will be checked. The result of the
54
certificate verification process can be checked after the TLS/SSL handshake
55
using the L<SSL_get_verify_result(3)|SSL_get_verify_result(3)> function.
56
The handshake will be continued regardless of the verification result.
60
B<Server mode:> the server sends a client certificate request to the client.
61
The certificate returned (if any) is checked. If the verification process
62
fails, the TLS/SSL handshake is
63
immediately terminated with an alert message containing the reason for
64
the verification failure.
65
The behaviour can be controlled by the additional
66
SSL_VERIFY_FAIL_IF_NO_PEER_CERT and SSL_VERIFY_CLIENT_ONCE flags.
68
B<Client mode:> the server certificate is verified. If the verification process
69
fails, the TLS/SSL handshake is
70
immediately terminated with an alert message containing the reason for
71
the verification failure. If no server certificate is sent, because an
72
anonymous cipher is used, SSL_VERIFY_PEER is ignored.
74
=item SSL_VERIFY_FAIL_IF_NO_PEER_CERT
76
B<Server mode:> if the client did not return a certificate, the TLS/SSL
77
handshake is immediately terminated with a "handshake failure" alert.
78
This flag must be used together with SSL_VERIFY_PEER.
80
B<Client mode:> ignored
82
=item SSL_VERIFY_CLIENT_ONCE
84
B<Server mode:> only request a client certificate on the initial TLS/SSL
85
handshake. Do not ask for a client certificate again in case of a
86
renegotiation. This flag must be used together with SSL_VERIFY_PEER.
88
B<Client mode:> ignored
92
Exactly one of the B<mode> flags SSL_VERIFY_NONE and SSL_VERIFY_PEER must be
95
The actual verification procedure is performed either using the built-in
96
verification procedure or using another application provided verification
98
L<SSL_CTX_set_cert_verify_callback(3)|SSL_CTX_set_cert_verify_callback(3)>.
99
The following descriptions apply in the case of the built-in procedure. An
100
application provided procedure also has access to the verify depth information
101
and the verify_callback() function, but the way this information is used
104
SSL_CTX_set_verify_depth() and SSL_set_verify_depth() set the limit up
105
to which depth certificates in a chain are used during the verification
106
procedure. If the certificate chain is longer than allowed, the certificates
107
above the limit are ignored. Error messages are generated as if these
108
certificates would not be present, most likely a
109
X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY will be issued.
110
The depth count is "level 0:peer certificate", "level 1: CA certificate",
111
"level 2: higher level CA certificate", and so on. Setting the maximum
112
depth to 2 allows the levels 0, 1, and 2. The default depth limit is 9,
113
allowing for the peer certificate and additional 9 CA certificates.
115
The B<verify_callback> function is used to control the behaviour when the
116
SSL_VERIFY_PEER flag is set. It must be supplied by the application and
117
receives two arguments: B<preverify_ok> indicates, whether the verification of
118
the certificate in question was passed (preverify_ok=1) or not
119
(preverify_ok=0). B<x509_ctx> is a pointer to the complete context used
120
for the certificate chain verification.
122
The certificate chain is checked starting with the deepest nesting level
123
(the root CA certificate) and worked upward to the peer's certificate.
124
At each level signatures and issuer attributes are checked. Whenever
125
a verification error is found, the error number is stored in B<x509_ctx>
126
and B<verify_callback> is called with B<preverify_ok>=0. By applying
127
X509_CTX_store_* functions B<verify_callback> can locate the certificate
128
in question and perform additional steps (see EXAMPLES). If no error is
129
found for a certificate, B<verify_callback> is called with B<preverify_ok>=1
130
before advancing to the next level.
132
The return value of B<verify_callback> controls the strategy of the further
133
verification process. If B<verify_callback> returns 0, the verification
134
process is immediately stopped with "verification failed" state. If
135
SSL_VERIFY_PEER is set, a verification failure alert is sent to the peer and
136
the TLS/SSL handshake is terminated. If B<verify_callback> returns 1,
137
the verification process is continued. If B<verify_callback> always returns
138
1, the TLS/SSL handshake will not be terminated with respect to verification
139
failures and the connection will be established. The calling process can
140
however retrieve the error code of the last verification error using
141
L<SSL_get_verify_result(3)|SSL_get_verify_result(3)> or by maintaining its
142
own error storage managed by B<verify_callback>.
144
If no B<verify_callback> is specified, the default callback will be used.
145
Its return value is identical to B<preverify_ok>, so that any verification
146
failure will lead to a termination of the TLS/SSL handshake with an
147
alert message, if SSL_VERIFY_PEER is set.
151
In client mode, it is not checked whether the SSL_VERIFY_PEER flag
152
is set, but whether SSL_VERIFY_NONE is not set. This can lead to
153
unexpected behaviour, if the SSL_VERIFY_PEER and SSL_VERIFY_NONE are not
154
used as required (exactly one must be set at any time).
156
The certificate verification depth set with SSL[_CTX]_verify_depth()
157
stops the verification at a certain depth. The error message produced
158
will be that of an incomplete certificate chain and not
159
X509_V_ERR_CERT_CHAIN_TOO_LONG as may be expected.
163
The SSL*_set_verify*() functions do not provide diagnostic information.
167
The following code sequence realizes an example B<verify_callback> function
168
that will always continue the TLS/SSL handshake regardless of verification
169
failure, if wished. The callback realizes a verification depth limit with
170
more informational output.
172
All verification errors are printed, informations about the certificate chain
173
are printed on request.
174
The example is realized for a server that does allow but not require client
177
The example makes use of the ex_data technique to store application data
178
into/retrieve application data from the SSL structure
179
(see L<SSL_get_ex_new_index(3)|SSL_get_ex_new_index(3)>,
180
L<SSL_get_ex_data_X509_STORE_CTX_idx(3)|SSL_get_ex_data_X509_STORE_CTX_idx(3)>).
190
static int verify_callback(int preverify_ok, X509_STORE_CTX *ctx)
198
err_cert = X509_STORE_CTX_get_current_cert(ctx);
199
err = X509_STORE_CTX_get_error(ctx);
200
depth = X509_STORE_CTX_get_error_depth(ctx);
203
* Retrieve the pointer to the SSL of the connection currently treated
204
* and the application specific data stored into the SSL object.
206
ssl = X509_STORE_CTX_get_ex_data(ctx, SSL_get_ex_data_X509_STORE_CTX_idx());
207
mydata = SSL_get_ex_data(ssl, mydata_index);
209
X509_NAME_oneline(X509_get_subject_name(err_cert), buf, 256);
212
* Catch a too long certificate chain. The depth limit set using
213
* SSL_CTX_set_verify_depth() is by purpose set to "limit+1" so
214
* that whenever the "depth>verify_depth" condition is met, we
215
* have violated the limit and want to log this error condition.
216
* We must do it here, because the CHAIN_TOO_LONG error would not
217
* be found explicitly; only errors introduced by cutting off the
218
* additional certificates would be logged.
220
if (depth > mydata->verify_depth) {
222
err = X509_V_ERR_CERT_CHAIN_TOO_LONG;
223
X509_STORE_CTX_set_error(ctx, err);
226
printf("verify error:num=%d:%s:depth=%d:%s\n", err,
227
X509_verify_cert_error_string(err), depth, buf);
229
else if (mydata->verbose_mode)
231
printf("depth=%d:%s\n", depth, buf);
235
* At this point, err contains the last verification error. We can use
236
* it for something special
238
if (!preverify_ok && (err == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT))
240
X509_NAME_oneline(X509_get_issuer_name(ctx->current_cert), buf, 256);
241
printf("issuer= %s\n", buf);
244
if (mydata->always_continue)
254
mydata_index = SSL_get_ex_new_index(0, "mydata index", NULL, NULL, NULL);
257
SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER|SSL_VERIFY_CLIENT_ONCE,
261
* Let the verify_callback catch the verify_depth error so that we get
262
* an appropriate error in the logfile.
264
SSL_CTX_set_verify_depth(verify_depth + 1);
267
* Set up the SSL specific data into "mydata" and store it into th SSL
270
mydata.verify_depth = verify_depth; ...
271
SSL_set_ex_data(ssl, mydata_index, &mydata);
274
SSL_accept(ssl); /* check of success left out for clarity */
275
if (peer = SSL_get_peer_certificate(ssl))
277
if (SSL_get_verify_result(ssl) == X509_V_OK)
279
/* The client sent a certificate which verified OK */
285
L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>,
286
L<SSL_CTX_get_verify_mode(3)|SSL_CTX_get_verify_mode(3)>,
287
L<SSL_get_verify_result(3)|SSL_get_verify_result(3)>,
288
L<SSL_CTX_load_verify_locations(3)|SSL_CTX_load_verify_locations(3)>,
289
L<SSL_get_peer_certificate(3)|SSL_get_peer_certificate(3)>,
290
L<SSL_CTX_set_cert_verify_callback(3)|SSL_CTX_set_cert_verify_callback(3)>,
291
L<SSL_get_ex_data_X509_STORE_CTX_idx(3)|SSL_get_ex_data_X509_STORE_CTX_idx(3)>,
292
L<SSL_get_ex_new_index(3)|SSL_get_ex_new_index(3)>