1SSL_CTX_SET_VERIFY(3) OpenSSL SSL_CTX_SET_VERIFY(3)
2
6 SSL_get_ex_data_X509_STORE_CTX_idx, SSL_CTX_set_verify, SSL_set_verify,
7 SSL_CTX_set_verify_depth, SSL_set_verify_depth, SSL_verify_cb,
8 SSL_verify_client_post_handshake, SSL_set_post_handshake_auth,
9 SSL_CTX_set_post_handshake_auth - set peer certificate verification
10 parameters
11
13 #include <openssl/ssl.h>
14 typedef int (*SSL_verify_cb)(int preverify_ok, X509_STORE_CTX *x509_ctx);
16 void SSL_CTX_set_verify(SSL_CTX *ctx, int mode, SSL_verify_cb verify_callback);
18 void SSL_set_verify(SSL *ssl, int mode, SSL_verify_cb verify_callback);
19 SSL_get_ex_data_X509_STORE_CTX_idx(void);
20 void SSL_CTX_set_verify_depth(SSL_CTX *ctx, int depth);
22 void SSL_set_verify_depth(SSL *ssl, int depth);
23 int SSL_verify_client_post_handshake(SSL *ssl);
25 void SSL_CTX_set_post_handshake_auth(SSL_CTX *ctx, int val);
26 void SSL_set_post_handshake_auth(SSL *ssl, int val);
27
29 SSL_CTX_set_verify() sets the verification flags for ctx to be mode and
30 specifies the verify_callback function to be used. If no callback
31 function shall be specified, the NULL pointer can be used for
32 verify_callback.
33 SSL_set_verify() sets the verification flags for ssl to be mode and
35 specifies the verify_callback function to be used. If no callback
36 function shall be specified, the NULL pointer can be used for
37 verify_callback. In this case last verify_callback set specifically for
38 this ssl remains. If no special callback was set before, the default
39 callback for the underlying ctx is used, that was valid at the time ssl
40 was created with SSL_new(3). Within the callback function,
41 SSL_get_ex_data_X509_STORE_CTX_idx can be called to get the data index
42 of the current SSL object that is doing the verification.
43 SSL_CTX_set_verify_depth() sets the maximum depth for the certificate
45 chain verification that shall be allowed for ctx.
46 SSL_set_verify_depth() sets the maximum depth for the certificate chain
48 verification that shall be allowed for ssl.
49 SSL_CTX_set_post_handshake_auth() and SSL_set_post_handshake_auth()
51 enable the Post-Handshake Authentication extension to be added to the
52 ClientHello such that post-handshake authentication can be requested by
53 the server. If val is 0 then the extension is not sent, otherwise it
54 is. By default the extension is not sent. A certificate callback will
55 need to be set via SSL_CTX_set_client_cert_cb() if no certificate is
56 provided at initialization.
57 SSL_verify_client_post_handshake() causes a CertificateRequest message
59 to be sent by a server on the given ssl connection. The SSL_VERIFY_PEER
60 flag must be set; the SSL_VERIFY_POST_HANDSHAKE flag is optional.
61
63 The verification of certificates can be controlled by a set of
64 logically or'ed mode flags:
65 SSL_VERIFY_NONE
67 Server mode: the server will not send a client certificate request
68 to the client, so the client will not send a certificate.
69 Client mode: if not using an anonymous cipher (by default
71 disabled), the server will send a certificate which will be
72 checked. The result of the certificate verification process can be
73 checked after the TLS/SSL handshake using the
74 SSL_get_verify_result(3) function. The handshake will be continued
75 regardless of the verification result.
76 SSL_VERIFY_PEER
78 Server mode: the server sends a client certificate request to the
79 client. The certificate returned (if any) is checked. If the
80 verification process fails, the TLS/SSL handshake is immediately
81 terminated with an alert message containing the reason for the
82 verification failure. The behaviour can be controlled by the
83 additional SSL_VERIFY_FAIL_IF_NO_PEER_CERT, SSL_VERIFY_CLIENT_ONCE
84 and SSL_VERIFY_POST_HANDSHAKE flags.
85 Client mode: the server certificate is verified. If the
87 verification process fails, the TLS/SSL handshake is immediately
88 terminated with an alert message containing the reason for the
89 verification failure. If no server certificate is sent, because an
90 anonymous cipher is used, SSL_VERIFY_PEER is ignored.
91 SSL_VERIFY_FAIL_IF_NO_PEER_CERT
93 Server mode: if the client did not return a certificate, the
94 TLS/SSL handshake is immediately terminated with a "handshake
95 failure" alert. This flag must be used together with
96 SSL_VERIFY_PEER.
97 Client mode: ignored (see BUGS)
99 SSL_VERIFY_CLIENT_ONCE
101 Server mode: only request a client certificate once during the
102 connection. Do not ask for a client certificate again during
103 renegotiation or post-authentication if a certificate was requested
104 during the initial handshake. This flag must be used together with
105 SSL_VERIFY_PEER.
106 Client mode: ignored (see BUGS)
108 SSL_VERIFY_POST_HANDSHAKE
110 Server mode: the server will not send a client certificate request
111 during the initial handshake, but will send the request via
112 SSL_verify_client_post_handshake(). This allows the SSL_CTX or SSL
113 to be configured for post-handshake peer verification before the
114 handshake occurs. This flag must be used together with
115 SSL_VERIFY_PEER. TLSv1.3 only; no effect on pre-TLSv1.3
116 connections.
117 Client mode: ignored (see BUGS)
119 If the mode is SSL_VERIFY_NONE none of the other flags may be set.
121 The actual verification procedure is performed either using the built-
123 in verification procedure or using another application provided
124 verification function set with SSL_CTX_set_cert_verify_callback(3).
125 The following descriptions apply in the case of the built-in procedure.
126 An application provided procedure also has access to the verify depth
127 information and the verify_callback() function, but the way this
128 information is used may be different.
129 SSL_CTX_set_verify_depth() and SSL_set_verify_depth() set a limit on
131 the number of certificates between the end-entity and trust-anchor
132 certificates. Neither the end-entity nor the trust-anchor certificates
133 count against depth. If the certificate chain needed to reach a trusted
134 issuer is longer than depth+2, X509_V_ERR_CERT_CHAIN_TOO_LONG will be
135 issued. The depth count is "level 0:peer certificate", "level 1: CA
136 certificate", "level 2: higher level CA certificate", and so on.
137 Setting the maximum depth to 2 allows the levels 0, 1, 2 and 3 (0 being
138 the end-entity and 3 the trust-anchor). The default depth limit is
139 100, allowing for the peer certificate, at most 100 intermediate CA
140 certificates and a final trust anchor certificate.
141 The verify_callback function is used to control the behaviour when the
143 SSL_VERIFY_PEER flag is set. It must be supplied by the application and
144 receives two arguments: preverify_ok indicates, whether the
145 verification of the certificate in question was passed (preverify_ok=1)
146 or not (preverify_ok=0). x509_ctx is a pointer to the complete context
147 used for the certificate chain verification.
148 The certificate chain is checked starting with the deepest nesting
150 level (the root CA certificate) and worked upward to the peer's
151 certificate. At each level signatures and issuer attributes are
152 checked. Whenever a verification error is found, the error number is
153 stored in x509_ctx and verify_callback is called with preverify_ok=0.
154 By applying X509_CTX_store_* functions verify_callback can locate the
155 certificate in question and perform additional steps (see EXAMPLES). If
156 no error is found for a certificate, verify_callback is called with
157 preverify_ok=1 before advancing to the next level.
158 The return value of verify_callback controls the strategy of the
160 further verification process. If verify_callback returns 0, the
161 verification process is immediately stopped with "verification failed"
162 state. If SSL_VERIFY_PEER is set, a verification failure alert is sent
163 to the peer and the TLS/SSL handshake is terminated. If verify_callback
164 returns 1, the verification process is continued. If verify_callback
165 always returns 1, the TLS/SSL handshake will not be terminated with
166 respect to verification failures and the connection will be
167 established. The calling process can however retrieve the error code of
168 the last verification error using SSL_get_verify_result(3) or by
169 maintaining its own error storage managed by verify_callback.
170 If no verify_callback is specified, the default callback will be used.
172 Its return value is identical to preverify_ok, so that any verification
173 failure will lead to a termination of the TLS/SSL handshake with an
174 alert message, if SSL_VERIFY_PEER is set.
175 After calling SSL_set_post_handshake_auth(), the client will need to
177 add a certificate or certificate callback to its configuration before
178 it can successfully authenticate. This must be called before
179 SSL_connect().
180 SSL_verify_client_post_handshake() requires that verify flags have been
182 previously set, and that a client sent the post-handshake
183 authentication extension. When the client returns a certificate the
184 verify callback will be invoked. A write operation must take place for
185 the Certificate Request to be sent to the client, this can be done with
186 SSL_do_handshake() or SSL_write_ex(). Only one certificate request may
187 be outstanding at any time.
188 When post-handshake authentication occurs, a refreshed NewSessionTicket
190 message is sent to the client.
191
193 In client mode, it is not checked whether the SSL_VERIFY_PEER flag is
194 set, but whether any flags other than SSL_VERIFY_NONE are set. This can
195 lead to unexpected behaviour if SSL_VERIFY_PEER and other flags are not
196 used as required.
197
199 The SSL*_set_verify*() functions do not provide diagnostic information.
200 The SSL_verify_client_post_handshake() function returns 1 if the
202 request succeeded, and 0 if the request failed. The error stack can be
203 examined to determine the failure reason.
204
206 The following code sequence realizes an example verify_callback
207 function that will always continue the TLS/SSL handshake regardless of
208 verification failure, if wished. The callback realizes a verification
209 depth limit with more informational output.
210 All verification errors are printed; information about the certificate
212 chain is printed on request. The example is realized for a server that
213 does allow but not require client certificates.
214 The example makes use of the ex_data technique to store application
216 data into/retrieve application data from the SSL structure (see
217 CRYPTO_get_ex_new_index(3), SSL_get_ex_data_X509_STORE_CTX_idx(3)).
218 ...
220 typedef struct {
221 int verbose_mode;
222 int verify_depth;
223 int always_continue;
224 } mydata_t;
225 int mydata_index;
226 ...
228 static int verify_callback(int preverify_ok, X509_STORE_CTX *ctx)
229 {
230 char buf[256];
231 X509 *err_cert;
232 int err, depth;
233 SSL *ssl;
234 mydata_t *mydata;
235 err_cert = X509_STORE_CTX_get_current_cert(ctx);
237 err = X509_STORE_CTX_get_error(ctx);
238 depth = X509_STORE_CTX_get_error_depth(ctx);
239 /*
241 * Retrieve the pointer to the SSL of the connection currently treated
242 * and the application specific data stored into the SSL object.
243 */
244 ssl = X509_STORE_CTX_get_ex_data(ctx, SSL_get_ex_data_X509_STORE_CTX_idx());
245 mydata = SSL_get_ex_data(ssl, mydata_index);
246 X509_NAME_oneline(X509_get_subject_name(err_cert), buf, 256);
248 /*
250 * Catch a too long certificate chain. The depth limit set using
251 * SSL_CTX_set_verify_depth() is by purpose set to "limit+1" so
252 * that whenever the "depth>verify_depth" condition is met, we
253 * have violated the limit and want to log this error condition.
254 * We must do it here, because the CHAIN_TOO_LONG error would not
255 * be found explicitly; only errors introduced by cutting off the
256 * additional certificates would be logged.
257 */
258 if (depth > mydata->verify_depth) {
259 preverify_ok = 0;
260 err = X509_V_ERR_CERT_CHAIN_TOO_LONG;
261 X509_STORE_CTX_set_error(ctx, err);
262 }
263 if (!preverify_ok) {
264 printf("verify error:num=%d:%s:depth=%d:%s\n", err,
265 X509_verify_cert_error_string(err), depth, buf);
266 } else if (mydata->verbose_mode) {
267 printf("depth=%d:%s\n", depth, buf);
268 }
269 /*
271 * At this point, err contains the last verification error. We can use
272 * it for something special
273 */
274 if (!preverify_ok && (err == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT)) {
275 X509_NAME_oneline(X509_get_issuer_name(err_cert), buf, 256);
276 printf("issuer= %s\n", buf);
277 }
278 if (mydata->always_continue)
280 return 1;
281 else
282 return preverify_ok;
283 }
284 ...
285 mydata_t mydata;
287 ...
289 mydata_index = SSL_get_ex_new_index(0, "mydata index", NULL, NULL, NULL);
290 ...
292 SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER | SSL_VERIFY_CLIENT_ONCE,
293 verify_callback);
294 /*
296 * Let the verify_callback catch the verify_depth error so that we get
297 * an appropriate error in the logfile.
298 */
299 SSL_CTX_set_verify_depth(verify_depth + 1);
300 /*
302 * Set up the SSL specific data into "mydata" and store it into th SSL
303 * structure.
304 */
305 mydata.verify_depth = verify_depth; ...
306 SSL_set_ex_data(ssl, mydata_index, &mydata);
307 ...
309 SSL_accept(ssl); /* check of success left out for clarity */
310 if (peer = SSL_get_peer_certificate(ssl)) {
311 if (SSL_get_verify_result(ssl) == X509_V_OK) {
312 /* The client sent a certificate which verified OK */
313 }
314 }
315
317 ssl(7), SSL_new(3), SSL_CTX_get_verify_mode(3),
318 SSL_get_verify_result(3), SSL_CTX_load_verify_locations(3),
319 SSL_get_peer_certificate(3), SSL_CTX_set_cert_verify_callback(3),
320 SSL_get_ex_data_X509_STORE_CTX_idx(3), SSL_CTX_set_client_cert_cb(3),
321 CRYPTO_get_ex_new_index(3)
322
324 The SSL_VERIFY_POST_HANDSHAKE option, and the
325 SSL_verify_client_post_handshake() and SSL_set_post_handshake_auth()
326 functions were added in OpenSSL 1.1.1.
327
329 Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
330 Licensed under the OpenSSL license (the "License"). You may not use
332 this file except in compliance with the License. You can obtain a copy
333 in the file LICENSE in the source distribution or at
334 <https://www.openssl.org/source/license.html>.
3351.1.1i 2021-01-26 SSL_CTX_SET_VERIFY(3)