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 100,
113 allowing for the peer certificate and additional 100 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; information about the certificate chain
173 is 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)>