5 SSL_get_ex_data_X509_STORE_CTX_idx,
6 SSL_CTX_set_verify, SSL_set_verify,
7 SSL_CTX_set_verify_depth, SSL_set_verify_depth,
9 - set peer certificate verification parameters
13 #include <openssl/ssl.h>
15 typedef int (*SSL_verify_cb)(int preverify_ok, X509_STORE_CTX *x509_ctx);
17 void SSL_CTX_set_verify(SSL_CTX *ctx, int mode, SSL_verify_cb verify_callback);
18 void SSL_set_verify(SSL *s, int mode, SSL_verify_cb verify_callback);
19 SSL_get_ex_data_X509_STORE_CTX_idx(void);
21 void SSL_CTX_set_verify_depth(SSL_CTX *ctx, int depth);
22 void SSL_set_verify_depth(SSL *s, int depth);
26 SSL_CTX_set_verify() sets the verification flags for B<ctx> 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>.
30 SSL_set_verify() sets the verification flags for B<ssl> to be B<mode> and
31 specifies the B<verify_callback> function to be used. If no callback function
32 shall be specified, the NULL pointer can be used for B<verify_callback>. In
33 this case last B<verify_callback> set specifically for this B<ssl> remains. If
34 no special B<callback> was set before, the default callback for the underlying
35 B<ctx> is used, that was valid at the time B<ssl> was created with
36 L<SSL_new(3)>. Within the callback function,
37 B<SSL_get_ex_data_X509_STORE_CTX_idx> can be called to get the data index
38 of the current SSL object that is doing the verification.
40 SSL_CTX_set_verify_depth() sets the maximum B<depth> for the certificate chain
41 verification that shall be allowed for B<ctx>.
43 SSL_set_verify_depth() sets the maximum B<depth> for the certificate chain
44 verification that shall be allowed for B<ssl>.
48 The verification of certificates can be controlled by a set of logically
55 B<Server mode:> the server will not send a client certificate request to the
56 client, so the client will not send a certificate.
58 B<Client mode:> if not using an anonymous cipher (by default disabled), the
59 server will send a certificate which will be checked. The result of the
60 certificate verification process can be checked after the TLS/SSL handshake
61 using the L<SSL_get_verify_result(3)> function.
62 The handshake will be continued regardless of the verification result.
66 B<Server mode:> the server sends a client certificate request to the client.
67 The certificate returned (if any) is checked. If the verification process
68 fails, the TLS/SSL handshake is
69 immediately terminated with an alert message containing the reason for
70 the verification failure.
71 The behaviour can be controlled by the additional
72 SSL_VERIFY_FAIL_IF_NO_PEER_CERT and SSL_VERIFY_CLIENT_ONCE flags.
74 B<Client mode:> the server certificate is verified. If the verification process
75 fails, the TLS/SSL handshake is
76 immediately terminated with an alert message containing the reason for
77 the verification failure. If no server certificate is sent, because an
78 anonymous cipher is used, SSL_VERIFY_PEER is ignored.
80 =item SSL_VERIFY_FAIL_IF_NO_PEER_CERT
82 B<Server mode:> if the client did not return a certificate, the TLS/SSL
83 handshake is immediately terminated with a "handshake failure" alert.
84 This flag must be used together with SSL_VERIFY_PEER.
86 B<Client mode:> ignored
88 =item SSL_VERIFY_CLIENT_ONCE
90 B<Server mode:> only request a client certificate on the initial TLS/SSL
91 handshake. Do not ask for a client certificate again in case of a
92 renegotiation. This flag must be used together with SSL_VERIFY_PEER.
94 B<Client mode:> ignored
98 If the B<mode> is SSL_VERIFY_NONE none of the other flags may be set.
100 The actual verification procedure is performed either using the built-in
101 verification procedure or using another application provided verification
103 L<SSL_CTX_set_cert_verify_callback(3)>.
104 The following descriptions apply in the case of the built-in procedure. An
105 application provided procedure also has access to the verify depth information
106 and the verify_callback() function, but the way this information is used
109 SSL_CTX_set_verify_depth() and SSL_set_verify_depth() set a limit on the
110 number of certificates between the end-entity and trust-anchor certificates.
112 end-entity nor the trust-anchor certificates count against B<depth>. If the
113 certificate chain needed to reach a trusted issuer is longer than B<depth+2>,
114 X509_V_ERR_CERT_CHAIN_TOO_LONG will be issued.
115 The depth count is "level 0:peer certificate", "level 1: CA certificate",
116 "level 2: higher level CA certificate", and so on. Setting the maximum
117 depth to 2 allows the levels 0, 1, 2 and 3 (0 being the end-entity and 3 the
119 The default depth limit is 100,
120 allowing for the peer certificate, at most 100 intermediate CA certificates and
121 a final trust anchor certificate.
123 The B<verify_callback> function is used to control the behaviour when the
124 SSL_VERIFY_PEER flag is set. It must be supplied by the application and
125 receives two arguments: B<preverify_ok> indicates, whether the verification of
126 the certificate in question was passed (preverify_ok=1) or not
127 (preverify_ok=0). B<x509_ctx> is a pointer to the complete context used
128 for the certificate chain verification.
130 The certificate chain is checked starting with the deepest nesting level
131 (the root CA certificate) and worked upward to the peer's certificate.
132 At each level signatures and issuer attributes are checked. Whenever
133 a verification error is found, the error number is stored in B<x509_ctx>
134 and B<verify_callback> is called with B<preverify_ok>=0. By applying
135 X509_CTX_store_* functions B<verify_callback> can locate the certificate
136 in question and perform additional steps (see EXAMPLES). If no error is
137 found for a certificate, B<verify_callback> is called with B<preverify_ok>=1
138 before advancing to the next level.
140 The return value of B<verify_callback> controls the strategy of the further
141 verification process. If B<verify_callback> returns 0, the verification
142 process is immediately stopped with "verification failed" state. If
143 SSL_VERIFY_PEER is set, a verification failure alert is sent to the peer and
144 the TLS/SSL handshake is terminated. If B<verify_callback> returns 1,
145 the verification process is continued. If B<verify_callback> always returns
146 1, the TLS/SSL handshake will not be terminated with respect to verification
147 failures and the connection will be established. The calling process can
148 however retrieve the error code of the last verification error using
149 L<SSL_get_verify_result(3)> or by maintaining its
150 own error storage managed by B<verify_callback>.
152 If no B<verify_callback> is specified, the default callback will be used.
153 Its return value is identical to B<preverify_ok>, so that any verification
154 failure will lead to a termination of the TLS/SSL handshake with an
155 alert message, if SSL_VERIFY_PEER is set.
159 In client mode, it is not checked whether the SSL_VERIFY_PEER flag
160 is set, but whether any flags are set. This can lead to
161 unexpected behaviour if SSL_VERIFY_PEER and other flags are not used as
166 The SSL*_set_verify*() functions do not provide diagnostic information.
170 The following code sequence realizes an example B<verify_callback> function
171 that will always continue the TLS/SSL handshake regardless of verification
172 failure, if wished. The callback realizes a verification depth limit with
173 more informational output.
175 All verification errors are printed; information about the certificate chain
176 is printed on request.
177 The example is realized for a server that does allow but not require client
180 The example makes use of the ex_data technique to store application data
181 into/retrieve application data from the SSL structure
182 (see L<CRYPTO_get_ex_new_index(3)>,
183 L<SSL_get_ex_data_X509_STORE_CTX_idx(3)>).
194 static int verify_callback(int preverify_ok, X509_STORE_CTX *ctx)
202 err_cert = X509_STORE_CTX_get_current_cert(ctx);
203 err = X509_STORE_CTX_get_error(ctx);
204 depth = X509_STORE_CTX_get_error_depth(ctx);
207 * Retrieve the pointer to the SSL of the connection currently treated
208 * and the application specific data stored into the SSL object.
210 ssl = X509_STORE_CTX_get_ex_data(ctx, SSL_get_ex_data_X509_STORE_CTX_idx());
211 mydata = SSL_get_ex_data(ssl, mydata_index);
213 X509_NAME_oneline(X509_get_subject_name(err_cert), buf, 256);
216 * Catch a too long certificate chain. The depth limit set using
217 * SSL_CTX_set_verify_depth() is by purpose set to "limit+1" so
218 * that whenever the "depth>verify_depth" condition is met, we
219 * have violated the limit and want to log this error condition.
220 * We must do it here, because the CHAIN_TOO_LONG error would not
221 * be found explicitly; only errors introduced by cutting off the
222 * additional certificates would be logged.
224 if (depth > mydata->verify_depth) {
226 err = X509_V_ERR_CERT_CHAIN_TOO_LONG;
227 X509_STORE_CTX_set_error(ctx, err);
230 printf("verify error:num=%d:%s:depth=%d:%s\n", err,
231 X509_verify_cert_error_string(err), depth, buf);
232 } else if (mydata->verbose_mode) {
233 printf("depth=%d:%s\n", depth, buf);
237 * At this point, err contains the last verification error. We can use
238 * it for something special
240 if (!preverify_ok && (err == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT)) {
241 X509_NAME_oneline(X509_get_issuer_name(err_cert), buf, 256);
242 printf("issuer= %s\n", buf);
245 if (mydata->always_continue)
255 mydata_index = SSL_get_ex_new_index(0, "mydata index", NULL, NULL, NULL);
258 SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER | SSL_VERIFY_CLIENT_ONCE,
262 * Let the verify_callback catch the verify_depth error so that we get
263 * an appropriate error in the logfile.
265 SSL_CTX_set_verify_depth(verify_depth + 1);
268 * Set up the SSL specific data into "mydata" and store it into th SSL
271 mydata.verify_depth = verify_depth; ...
272 SSL_set_ex_data(ssl, mydata_index, &mydata);
275 SSL_accept(ssl); /* check of success left out for clarity */
276 if (peer = SSL_get_peer_certificate(ssl)) {
277 if (SSL_get_verify_result(ssl) == X509_V_OK) {
278 /* The client sent a certificate which verified OK */
284 L<ssl(7)>, L<SSL_new(3)>,
285 L<SSL_CTX_get_verify_mode(3)>,
286 L<SSL_get_verify_result(3)>,
287 L<SSL_CTX_load_verify_locations(3)>,
288 L<SSL_get_peer_certificate(3)>,
289 L<SSL_CTX_set_cert_verify_callback(3)>,
290 L<SSL_get_ex_data_X509_STORE_CTX_idx(3)>,
291 L<CRYPTO_get_ex_new_index(3)>
295 Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
297 Licensed under the OpenSSL license (the "License"). You may not use
298 this file except in compliance with the License. You can obtain a copy
299 in the file LICENSE in the source distribution or at
300 L<https://www.openssl.org/source/license.html>.