1SSL_CTX_SET_VERIFY(3ossl) OpenSSL SSL_CTX_SET_VERIFY(3ossl)
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 various SSL/TLS parameters for
10 peer certificate verification
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 In client mode verify_callback may also call the
45 SSL_set_retry_verify(3) function on the SSL object set in the
46 x509_store_ctx ex data (see SSL_get_ex_data_X509_STORE_CTX_idx(3)) and
47 return 1. This would be typically done in case the certificate
48 verification was not yet able to succeed. This makes the handshake
49 suspend and return control to the calling application with
50 SSL_ERROR_WANT_RETRY_VERIFY. The application can for instance fetch
51 further certificates or cert status information needed for the
52 verification. Calling SSL_connect(3) again resumes the connection
53 attempt by retrying the server certificate verification step. This
54 process may even be repeated if need be. Note that the handshake may
55 still be aborted if a subsequent invocation of the callback (e.g., at a
56 lower depth, or for a separate error condition) returns 0.
57 SSL_CTX_set_verify_depth() sets the maximum depth for the certificate
59 chain verification that shall be allowed for ctx.
60 SSL_set_verify_depth() sets the maximum depth for the certificate chain
62 verification that shall be allowed for ssl.
63 SSL_CTX_set_post_handshake_auth() and SSL_set_post_handshake_auth()
65 enable the Post-Handshake Authentication extension to be added to the
66 ClientHello such that post-handshake authentication can be requested by
67 the server. If val is 0 then the extension is not sent, otherwise it
68 is. By default the extension is not sent. A certificate callback will
69 need to be set via SSL_CTX_set_client_cert_cb() if no certificate is
70 provided at initialization.
71 SSL_verify_client_post_handshake() causes a CertificateRequest message
73 to be sent by a server on the given ssl connection. The SSL_VERIFY_PEER
74 flag must be set; the SSL_VERIFY_POST_HANDSHAKE flag is optional.
75
77 The verification of certificates can be controlled by a set of
78 logically or'ed mode flags:
79 SSL_VERIFY_NONE
81 Server mode: the server will not send a client certificate request
82 to the client, so the client will not send a certificate.
83 Client mode: if not using an anonymous cipher (by default
85 disabled), the server will send a certificate which will be
86 checked. The result of the certificate verification process can be
87 checked after the TLS/SSL handshake using the
88 SSL_get_verify_result(3) function. The handshake will be continued
89 regardless of the verification result.
90 SSL_VERIFY_PEER
92 Server mode: the server sends a client certificate request to the
93 client. The certificate returned (if any) is checked. If the
94 verification process fails, the TLS/SSL handshake is immediately
95 terminated with an alert message containing the reason for the
96 verification failure. The behaviour can be controlled by the
97 additional SSL_VERIFY_FAIL_IF_NO_PEER_CERT, SSL_VERIFY_CLIENT_ONCE
98 and SSL_VERIFY_POST_HANDSHAKE flags.
99 Client mode: the server certificate is verified. If the
101 verification process fails, the TLS/SSL handshake is immediately
102 terminated with an alert message containing the reason for the
103 verification failure. If no server certificate is sent, because an
104 anonymous cipher is used, SSL_VERIFY_PEER is ignored.
105 SSL_VERIFY_FAIL_IF_NO_PEER_CERT
107 Server mode: if the client did not return a certificate, the
108 TLS/SSL handshake is immediately terminated with a "handshake
109 failure" alert. This flag must be used together with
110 SSL_VERIFY_PEER.
111 Client mode: ignored (see BUGS)
113 SSL_VERIFY_CLIENT_ONCE
115 Server mode: only request a client certificate once during the
116 connection. Do not ask for a client certificate again during
117 renegotiation or post-authentication if a certificate was requested
118 during the initial handshake. This flag must be used together with
119 SSL_VERIFY_PEER.
120 Client mode: ignored (see BUGS)
122 SSL_VERIFY_POST_HANDSHAKE
124 Server mode: the server will not send a client certificate request
125 during the initial handshake, but will send the request via
126 SSL_verify_client_post_handshake(). This allows the SSL_CTX or SSL
127 to be configured for post-handshake peer verification before the
128 handshake occurs. This flag must be used together with
129 SSL_VERIFY_PEER. TLSv1.3 only; no effect on pre-TLSv1.3
130 connections.
131 Client mode: ignored (see BUGS)
133 If the mode is SSL_VERIFY_NONE none of the other flags may be set.
135 The actual verification procedure is performed either using the built-
137 in verification procedure or using another application provided
138 verification function set with SSL_CTX_set_cert_verify_callback(3).
139 The following descriptions apply in the case of the built-in procedure.
140 An application provided procedure also has access to the verify depth
141 information and the verify_callback() function, but the way this
142 information is used may be different.
143 SSL_CTX_set_verify_depth() and SSL_set_verify_depth() set a limit on
145 the number of certificates between the end-entity and trust-anchor
146 certificates. Neither the end-entity nor the trust-anchor certificates
147 count against depth. If the certificate chain needed to reach a trusted
148 issuer is longer than depth+2, X509_V_ERR_CERT_CHAIN_TOO_LONG will be
149 issued. The depth count is "level 0:peer certificate", "level 1: CA
150 certificate", "level 2: higher level CA certificate", and so on.
151 Setting the maximum depth to 2 allows the levels 0, 1, 2 and 3 (0 being
152 the end-entity and 3 the trust-anchor). The default depth limit is
153 100, allowing for the peer certificate, at most 100 intermediate CA
154 certificates and a final trust anchor certificate.
155 The verify_callback function is used to control the behaviour when the
157 SSL_VERIFY_PEER flag is set. It must be supplied by the application and
158 receives two arguments: preverify_ok indicates, whether the
159 verification of the certificate in question was passed (preverify_ok=1)
160 or not (preverify_ok=0). x509_ctx is a pointer to the complete context
161 used for the certificate chain verification.
162 The certificate chain is checked starting with the deepest nesting
164 level (the root CA certificate) and worked upward to the peer's
165 certificate. At each level signatures and issuer attributes are
166 checked. Whenever a verification error is found, the error number is
167 stored in x509_ctx and verify_callback is called with preverify_ok=0.
168 By applying X509_CTX_store_* functions verify_callback can locate the
169 certificate in question and perform additional steps (see EXAMPLES). If
170 no error is found for a certificate, verify_callback is called with
171 preverify_ok=1 before advancing to the next level.
172 The return value of verify_callback controls the strategy of the
174 further verification process. If verify_callback returns 0, the
175 verification process is immediately stopped with "verification failed"
176 state. If SSL_VERIFY_PEER is set, a verification failure alert is sent
177 to the peer and the TLS/SSL handshake is terminated. If verify_callback
178 returns 1, the verification process is continued. If verify_callback
179 always returns 1, the TLS/SSL handshake will not be terminated with
180 respect to verification failures and the connection will be
181 established. The calling process can however retrieve the error code of
182 the last verification error using SSL_get_verify_result(3) or by
183 maintaining its own error storage managed by verify_callback.
184 If no verify_callback is specified, the default callback will be used.
186 Its return value is identical to preverify_ok, so that any verification
187 failure will lead to a termination of the TLS/SSL handshake with an
188 alert message, if SSL_VERIFY_PEER is set.
189 After calling SSL_set_post_handshake_auth(), the client will need to
191 add a certificate or certificate callback to its configuration before
192 it can successfully authenticate. This must be called before
193 SSL_connect().
194 SSL_verify_client_post_handshake() requires that verify flags have been
196 previously set, and that a client sent the post-handshake
197 authentication extension. When the client returns a certificate the
198 verify callback will be invoked. A write operation must take place for
199 the Certificate Request to be sent to the client, this can be done with
200 SSL_do_handshake() or SSL_write_ex(). Only one certificate request may
201 be outstanding at any time.
202 When post-handshake authentication occurs, a refreshed NewSessionTicket
204 message is sent to the client.
205
207 In client mode, it is not checked whether the SSL_VERIFY_PEER flag is
208 set, but whether any flags other than SSL_VERIFY_NONE are set. This can
209 lead to unexpected behaviour if SSL_VERIFY_PEER and other flags are not
210 used as required.
211
213 The SSL*_set_verify*() functions do not provide diagnostic information.
214 The SSL_verify_client_post_handshake() function returns 1 if the
216 request succeeded, and 0 if the request failed. The error stack can be
217 examined to determine the failure reason.
218
220 The following code sequence realizes an example verify_callback
221 function that will always continue the TLS/SSL handshake regardless of
222 verification failure, if wished. The callback realizes a verification
223 depth limit with more informational output.
224 All verification errors are printed; information about the certificate
226 chain is printed on request. The example is realized for a server that
227 does allow but not require client certificates.
228 The example makes use of the ex_data technique to store application
230 data into/retrieve application data from the SSL structure (see
231 CRYPTO_get_ex_new_index(3), SSL_get_ex_data_X509_STORE_CTX_idx(3)).
232 ...
234 typedef struct {
235 int verbose_mode;
236 int verify_depth;
237 int always_continue;
238 } mydata_t;
239 int mydata_index;
240 ...
242 static int verify_callback(int preverify_ok, X509_STORE_CTX *ctx)
243 {
244 char buf[256];
245 X509 *err_cert;
246 int err, depth;
247 SSL *ssl;
248 mydata_t *mydata;
249 err_cert = X509_STORE_CTX_get_current_cert(ctx);
251 err = X509_STORE_CTX_get_error(ctx);
252 depth = X509_STORE_CTX_get_error_depth(ctx);
253 /*
255 * Retrieve the pointer to the SSL of the connection currently treated
256 * and the application specific data stored into the SSL object.
257 */
258 ssl = X509_STORE_CTX_get_ex_data(ctx, SSL_get_ex_data_X509_STORE_CTX_idx());
259 mydata = SSL_get_ex_data(ssl, mydata_index);
260 X509_NAME_oneline(X509_get_subject_name(err_cert), buf, 256);
262 /*
264 * Catch a too long certificate chain. The depth limit set using
265 * SSL_CTX_set_verify_depth() is by purpose set to "limit+1" so
266 * that whenever the "depth>verify_depth" condition is met, we
267 * have violated the limit and want to log this error condition.
268 * We must do it here, because the CHAIN_TOO_LONG error would not
269 * be found explicitly; only errors introduced by cutting off the
270 * additional certificates would be logged.
271 */
272 if (depth > mydata->verify_depth) {
273 preverify_ok = 0;
274 err = X509_V_ERR_CERT_CHAIN_TOO_LONG;
275 X509_STORE_CTX_set_error(ctx, err);
276 }
277 if (!preverify_ok) {
278 printf("verify error:num=%d:%s:depth=%d:%s\n", err,
279 X509_verify_cert_error_string(err), depth, buf);
280 } else if (mydata->verbose_mode) {
281 printf("depth=%d:%s\n", depth, buf);
282 }
283 /*
285 * At this point, err contains the last verification error. We can use
286 * it for something special
287 */
288 if (!preverify_ok && (err == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT)) {
289 X509_NAME_oneline(X509_get_issuer_name(err_cert), buf, 256);
290 printf("issuer= %s\n", buf);
291 }
292 if (mydata->always_continue)
294 return 1;
295 else
296 return preverify_ok;
297 }
298 ...
299 mydata_t mydata;
301 ...
303 mydata_index = SSL_get_ex_new_index(0, "mydata index", NULL, NULL, NULL);
304 ...
306 SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER | SSL_VERIFY_CLIENT_ONCE,
307 verify_callback);
308 /*
310 * Let the verify_callback catch the verify_depth error so that we get
311 * an appropriate error in the logfile.
312 */
313 SSL_CTX_set_verify_depth(verify_depth + 1);
314 /*
316 * Set up the SSL specific data into "mydata" and store it into th SSL
317 * structure.
318 */
319 mydata.verify_depth = verify_depth; ...
320 SSL_set_ex_data(ssl, mydata_index, &mydata);
321 ...
323 SSL_accept(ssl); /* check of success left out for clarity */
324 if (peer = SSL_get_peer_certificate(ssl)) {
325 if (SSL_get_verify_result(ssl) == X509_V_OK) {
326 /* The client sent a certificate which verified OK */
327 }
328 }
329
331 ssl(7), SSL_new(3), SSL_CTX_get_verify_mode(3),
332 SSL_get_verify_result(3), SSL_CTX_load_verify_locations(3),
333 SSL_get_peer_certificate(3), SSL_CTX_set_cert_verify_callback(3),
334 SSL_get_ex_data_X509_STORE_CTX_idx(3), SSL_CTX_set_client_cert_cb(3),
335 CRYPTO_get_ex_new_index(3)
336
338 The SSL_VERIFY_POST_HANDSHAKE option, and the
339 SSL_verify_client_post_handshake() and SSL_set_post_handshake_auth()
340 functions were added in OpenSSL 1.1.1.
341
343 Copyright 2000-2022 The OpenSSL Project Authors. All Rights Reserved.
344 Licensed under the Apache License 2.0 (the "License"). You may not use
346 this file except in compliance with the License. You can obtain a copy
347 in the file LICENSE in the source distribution or at
348 <https://www.openssl.org/source/license.html>.
3493.1.1 2023-08-31 SSL_CTX_SET_VERIFY(3ossl)