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135 .\" ========================================================================
136 .\"
137 .IX Title "SSL_CTX_set_verify 3"
138 .TH SSL_CTX_set_verify 3 "2014-08-10" "1.0.1n" "OpenSSL"
139 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
140 .\" way too many mistakes in technical documents.
141 .if n .ad l
142 .nh
143 .SH "NAME"
144 SSL_CTX_set_verify, SSL_set_verify, SSL_CTX_set_verify_depth, SSL_set_verify_depth \- set peer certificate verification parameters
145 .SH "LIBRARY"
146 libcrypto, -lcrypto
147 .SH "SYNOPSIS"
148 .IX Header "SYNOPSIS"
149 .Vb 1
150 \& #include <openssl/ssl.h>
151 \&
152 \& void SSL_CTX_set_verify(SSL_CTX *ctx, int mode,
153 \& int (*verify_callback)(int, X509_STORE_CTX *));
154 \& void SSL_set_verify(SSL *s, int mode,
155 \& int (*verify_callback)(int, X509_STORE_CTX *));
156 \& void SSL_CTX_set_verify_depth(SSL_CTX *ctx,int depth);
157 \& void SSL_set_verify_depth(SSL *s, int depth);
158 \&
159 \& int verify_callback(int preverify_ok, X509_STORE_CTX *x509_ctx);
160 .Ve
161 .SH "DESCRIPTION"
162 .IX Header "DESCRIPTION"
163 \&\fISSL_CTX_set_verify()\fR sets the verification flags for \fBctx\fR to be \fBmode\fR and
164 specifies the \fBverify_callback\fR function to be used. If no callback function
165 shall be specified, the \s-1NULL\s0 pointer can be used for \fBverify_callback\fR.
166 .PP
167 \&\fISSL_set_verify()\fR sets the verification flags for \fBssl\fR to be \fBmode\fR and
168 specifies the \fBverify_callback\fR function to be used. If no callback function
169 shall be specified, the \s-1NULL\s0 pointer can be used for \fBverify_callback\fR. In
170 this case last \fBverify_callback\fR set specifically for this \fBssl\fR remains. If
171 no special \fBcallback\fR was set before, the default callback for the underlying
172 \&\fBctx\fR is used, that was valid at the time \fBssl\fR was created with
173 \&\fISSL_new\fR\|(3).
174 .PP
175 \&\fISSL_CTX_set_verify_depth()\fR sets the maximum \fBdepth\fR for the certificate chain
176 verification that shall be allowed for \fBctx\fR. (See the \s-1BUGS\s0 section.)
177 .PP
178 \&\fISSL_set_verify_depth()\fR sets the maximum \fBdepth\fR for the certificate chain
179 verification that shall be allowed for \fBssl\fR. (See the \s-1BUGS\s0 section.)
180 .SH "NOTES"
181 .IX Header "NOTES"
182 The verification of certificates can be controlled by a set of logically
183 or'ed \fBmode\fR flags:
184 .IP "\s-1SSL_VERIFY_NONE\s0" 4
185 .IX Item "SSL_VERIFY_NONE"
186 \&\fBServer mode:\fR the server will not send a client certificate request to the
187 client, so the client will not send a certificate.
188 .Sp
189 \&\fBClient mode:\fR if not using an anonymous cipher (by default disabled), the
190 server will send a certificate which will be checked. The result of the
191 certificate verification process can be checked after the \s-1TLS/SSL\s0 handshake
192 using the \fISSL_get_verify_result\fR\|(3) function.
193 The handshake will be continued regardless of the verification result.
194 .IP "\s-1SSL_VERIFY_PEER\s0" 4
195 .IX Item "SSL_VERIFY_PEER"
196 \&\fBServer mode:\fR the server sends a client certificate request to the client.
197 The certificate returned (if any) is checked. If the verification process
198 fails, the \s-1TLS/SSL\s0 handshake is
199 immediately terminated with an alert message containing the reason for
200 the verification failure.
201 The behaviour can be controlled by the additional
202 \&\s-1SSL_VERIFY_FAIL_IF_NO_PEER_CERT\s0 and \s-1SSL_VERIFY_CLIENT_ONCE\s0 flags.
203 .Sp
204 \&\fBClient mode:\fR the server certificate is verified. If the verification process
205 fails, the \s-1TLS/SSL\s0 handshake is
206 immediately terminated with an alert message containing the reason for
207 the verification failure. If no server certificate is sent, because an
208 anonymous cipher is used, \s-1SSL_VERIFY_PEER\s0 is ignored.
209 .IP "\s-1SSL_VERIFY_FAIL_IF_NO_PEER_CERT\s0" 4
210 .IX Item "SSL_VERIFY_FAIL_IF_NO_PEER_CERT"
211 \&\fBServer mode:\fR if the client did not return a certificate, the \s-1TLS/SSL\s0
212 handshake is immediately terminated with a \*(L"handshake failure\*(R" alert.
213 This flag must be used together with \s-1SSL_VERIFY_PEER.\s0
214 .Sp
215 \&\fBClient mode:\fR ignored
216 .IP "\s-1SSL_VERIFY_CLIENT_ONCE\s0" 4
217 .IX Item "SSL_VERIFY_CLIENT_ONCE"
218 \&\fBServer mode:\fR only request a client certificate on the initial \s-1TLS/SSL\s0
219 handshake. Do not ask for a client certificate again in case of a
220 renegotiation. This flag must be used together with \s-1SSL_VERIFY_PEER.\s0
221 .Sp
222 \&\fBClient mode:\fR ignored
223 .PP
224 Exactly one of the \fBmode\fR flags \s-1SSL_VERIFY_NONE\s0 and \s-1SSL_VERIFY_PEER\s0 must be
225 set at any time.
226 .PP
227 The actual verification procedure is performed either using the built-in
228 verification procedure or using another application provided verification
229 function set with
230 \&\fISSL_CTX_set_cert_verify_callback\fR\|(3).
231 The following descriptions apply in the case of the built-in procedure. An
232 application provided procedure also has access to the verify depth information
233 and the \fIverify_callback()\fR function, but the way this information is used
234 may be different.
235 .PP
236 \&\fISSL_CTX_set_verify_depth()\fR and \fISSL_set_verify_depth()\fR set the limit up
237 to which depth certificates in a chain are used during the verification
238 procedure. If the certificate chain is longer than allowed, the certificates
239 above the limit are ignored. Error messages are generated as if these
240 certificates would not be present, most likely a
241 X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY will be issued.
242 The depth count is \*(L"level 0:peer certificate\*(R", \*(L"level 1: \s-1CA\s0 certificate\*(R",
243 \&\*(L"level 2: higher level \s-1CA\s0 certificate\*(R", and so on. Setting the maximum
244 depth to 2 allows the levels 0, 1, and 2. The default depth limit is 100,
245 allowing for the peer certificate and additional 100 \s-1CA\s0 certificates.
246 .PP
247 The \fBverify_callback\fR function is used to control the behaviour when the
248 \&\s-1SSL_VERIFY_PEER\s0 flag is set. It must be supplied by the application and
249 receives two arguments: \fBpreverify_ok\fR indicates, whether the verification of
250 the certificate in question was passed (preverify_ok=1) or not
251 (preverify_ok=0). \fBx509_ctx\fR is a pointer to the complete context used
252 for the certificate chain verification.
253 .PP
254 The certificate chain is checked starting with the deepest nesting level
255 (the root \s-1CA\s0 certificate) and worked upward to the peer's certificate.
256 At each level signatures and issuer attributes are checked. Whenever
257 a verification error is found, the error number is stored in \fBx509_ctx\fR
258 and \fBverify_callback\fR is called with \fBpreverify_ok\fR=0. By applying
259 X509_CTX_store_* functions \fBverify_callback\fR can locate the certificate
260 in question and perform additional steps (see \s-1EXAMPLES\s0). If no error is
261 found for a certificate, \fBverify_callback\fR is called with \fBpreverify_ok\fR=1
262 before advancing to the next level.
263 .PP
264 The return value of \fBverify_callback\fR controls the strategy of the further
265 verification process. If \fBverify_callback\fR returns 0, the verification
266 process is immediately stopped with \*(L"verification failed\*(R" state. If
267 \&\s-1SSL_VERIFY_PEER\s0 is set, a verification failure alert is sent to the peer and
268 the \s-1TLS/SSL\s0 handshake is terminated. If \fBverify_callback\fR returns 1,
269 the verification process is continued. If \fBverify_callback\fR always returns
270 1, the \s-1TLS/SSL\s0 handshake will not be terminated with respect to verification
271 failures and the connection will be established. The calling process can
272 however retrieve the error code of the last verification error using
273 \&\fISSL_get_verify_result\fR\|(3) or by maintaining its
274 own error storage managed by \fBverify_callback\fR.
275 .PP
276 If no \fBverify_callback\fR is specified, the default callback will be used.
277 Its return value is identical to \fBpreverify_ok\fR, so that any verification
278 failure will lead to a termination of the \s-1TLS/SSL\s0 handshake with an
279 alert message, if \s-1SSL_VERIFY_PEER\s0 is set.
280 .SH "BUGS"
281 .IX Header "BUGS"
282 In client mode, it is not checked whether the \s-1SSL_VERIFY_PEER\s0 flag
283 is set, but whether \s-1SSL_VERIFY_NONE\s0 is not set. This can lead to
284 unexpected behaviour, if the \s-1SSL_VERIFY_PEER\s0 and \s-1SSL_VERIFY_NONE\s0 are not
285 used as required (exactly one must be set at any time).
286 .PP
287 The certificate verification depth set with SSL[_CTX]\fI_verify_depth()\fR
288 stops the verification at a certain depth. The error message produced
289 will be that of an incomplete certificate chain and not
290 X509_V_ERR_CERT_CHAIN_TOO_LONG as may be expected.
291 .SH "RETURN VALUES"
292 .IX Header "RETURN VALUES"
293 The SSL*_set_verify*() functions do not provide diagnostic information.
294 .SH "EXAMPLES"
295 .IX Header "EXAMPLES"
296 The following code sequence realizes an example \fBverify_callback\fR function
297 that will always continue the \s-1TLS/SSL\s0 handshake regardless of verification
298 failure, if wished. The callback realizes a verification depth limit with
299 more informational output.
300 .PP
301 All verification errors are printed; information about the certificate chain
302 is printed on request.
303 The example is realized for a server that does allow but not require client
304 certificates.
305 .PP
306 The example makes use of the ex_data technique to store application data
307 into/retrieve application data from the \s-1SSL\s0 structure
308 (see \fISSL_get_ex_new_index\fR\|(3),
309 \&\fISSL_get_ex_data_X509_STORE_CTX_idx\fR\|(3)).
310 .PP
311 .Vb 10
312 \& ...
313 \& typedef struct {
314 \& int verbose_mode;
315 \& int verify_depth;
316 \& int always_continue;
317 \& } mydata_t;
318 \& int mydata_index;
319 \& ...
320 \& static int verify_callback(int preverify_ok, X509_STORE_CTX *ctx)
321 \& {
322 \& char buf[256];
323 \& X509 *err_cert;
324 \& int err, depth;
325 \& SSL *ssl;
326 \& mydata_t *mydata;
327 \&
328 \& err_cert = X509_STORE_CTX_get_current_cert(ctx);
329 \& err = X509_STORE_CTX_get_error(ctx);
330 \& depth = X509_STORE_CTX_get_error_depth(ctx);
331 \&
332 \& /*
333 \& * Retrieve the pointer to the SSL of the connection currently treated
334 \& * and the application specific data stored into the SSL object.
335 \& */
336 \& ssl = X509_STORE_CTX_get_ex_data(ctx, SSL_get_ex_data_X509_STORE_CTX_idx());
337 \& mydata = SSL_get_ex_data(ssl, mydata_index);
338 \&
339 \& X509_NAME_oneline(X509_get_subject_name(err_cert), buf, 256);
340 \&
341 \& /*
342 \& * Catch a too long certificate chain. The depth limit set using
343 \& * SSL_CTX_set_verify_depth() is by purpose set to "limit+1" so
344 \& * that whenever the "depth>verify_depth" condition is met, we
345 \& * have violated the limit and want to log this error condition.
346 \& * We must do it here, because the CHAIN_TOO_LONG error would not
347 \& * be found explicitly; only errors introduced by cutting off the
348 \& * additional certificates would be logged.
349 \& */
350 \& if (depth > mydata\->verify_depth) {
351 \& preverify_ok = 0;
352 \& err = X509_V_ERR_CERT_CHAIN_TOO_LONG;
353 \& X509_STORE_CTX_set_error(ctx, err);
354 \& }
355 \& if (!preverify_ok) {
356 \& printf("verify error:num=%d:%s:depth=%d:%s\en", err,
357 \& X509_verify_cert_error_string(err), depth, buf);
358 \& }
359 \& else if (mydata\->verbose_mode)
360 \& {
361 \& printf("depth=%d:%s\en", depth, buf);
362 \& }
363 \&
364 \& /*
365 \& * At this point, err contains the last verification error. We can use
366 \& * it for something special
367 \& */
368 \& if (!preverify_ok && (err == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT))
369 \& {
370 \& X509_NAME_oneline(X509_get_issuer_name(ctx\->current_cert), buf, 256);
371 \& printf("issuer= %s\en", buf);
372 \& }
373 \&
374 \& if (mydata\->always_continue)
375 \& return 1;
376 \& else
377 \& return preverify_ok;
378 \& }
379 \& ...
380 \&
381 \& mydata_t mydata;
382 \&
383 \& ...
384 \& mydata_index = SSL_get_ex_new_index(0, "mydata index", NULL, NULL, NULL);
385 \&
386 \& ...
387 \& SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER|SSL_VERIFY_CLIENT_ONCE,
388 \& verify_callback);
389 \&
390 \& /*
391 \& * Let the verify_callback catch the verify_depth error so that we get
392 \& * an appropriate error in the logfile.
393 \& */
394 \& SSL_CTX_set_verify_depth(verify_depth + 1);
395 \&
396 \& /*
397 \& * Set up the SSL specific data into "mydata" and store it into th SSL
398 \& * structure.
399 \& */
400 \& mydata.verify_depth = verify_depth; ...
401 \& SSL_set_ex_data(ssl, mydata_index, &mydata);
402 \&
403 \& ...
404 \& SSL_accept(ssl); /* check of success left out for clarity */
405 \& if (peer = SSL_get_peer_certificate(ssl))
406 \& {
407 \& if (SSL_get_verify_result(ssl) == X509_V_OK)
408 \& {
409 \& /* The client sent a certificate which verified OK */
410 \& }
411 \& }
412 .Ve
413 .SH "SEE ALSO"
414 .IX Header "SEE ALSO"
415 \&\fIssl\fR\|(3), \fISSL_new\fR\|(3),
416 \&\fISSL_CTX_get_verify_mode\fR\|(3),
417 \&\fISSL_get_verify_result\fR\|(3),
418 \&\fISSL_CTX_load_verify_locations\fR\|(3),
419 \&\fISSL_get_peer_certificate\fR\|(3),
420 \&\fISSL_CTX_set_cert_verify_callback\fR\|(3),
421 \&\fISSL_get_ex_data_X509_STORE_CTX_idx\fR\|(3),
422 \&\fISSL_get_ex_new_index\fR\|(3)