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129 .\" ========================================================================
130 .\"
131 .IX Title "SSL_CTX_set_verify 3"
132 .TH SSL_CTX_set_verify 3 "2009-07-23" "0.9.8k" "OpenSSL"
133 .SH "NAME"
134 SSL_CTX_set_verify, SSL_set_verify, SSL_CTX_set_verify_depth, SSL_set_verify_depth \- set peer certificate verification parameters
135 .SH "SYNOPSIS"
136 .IX Header "SYNOPSIS"
137 .Vb 1
138 \& #include <openssl/ssl.h>
139 .Ve
140 .PP
141 .Vb 6
142 \& void SSL_CTX_set_verify(SSL_CTX *ctx, int mode,
143 \& int (*verify_callback)(int, X509_STORE_CTX *));
144 \& void SSL_set_verify(SSL *s, int mode,
145 \& int (*verify_callback)(int, X509_STORE_CTX *));
146 \& void SSL_CTX_set_verify_depth(SSL_CTX *ctx,int depth);
147 \& void SSL_set_verify_depth(SSL *s, int depth);
148 .Ve
149 .PP
150 .Vb 1
151 \& int verify_callback(int preverify_ok, X509_STORE_CTX *x509_ctx);
152 .Ve
153 .SH "DESCRIPTION"
154 .IX Header "DESCRIPTION"
155 \&\fISSL_CTX_set_verify()\fR sets the verification flags for \fBctx\fR to be \fBmode\fR and
156 specifies the \fBverify_callback\fR function to be used. If no callback function
157 shall be specified, the \s-1NULL\s0 pointer can be used for \fBverify_callback\fR.
158 .PP
159 \&\fISSL_set_verify()\fR sets the verification flags for \fBssl\fR to be \fBmode\fR and
160 specifies the \fBverify_callback\fR function to be used. If no callback function
161 shall be specified, the \s-1NULL\s0 pointer can be used for \fBverify_callback\fR. In
162 this case last \fBverify_callback\fR set specifically for this \fBssl\fR remains. If
163 no special \fBcallback\fR was set before, the default callback for the underlying
164 \&\fBctx\fR is used, that was valid at the time \fBssl\fR was created with
165 \&\fISSL_new\fR\|(3).
166 .PP
167 \&\fISSL_CTX_set_verify_depth()\fR sets the maximum \fBdepth\fR for the certificate chain
168 verification that shall be allowed for \fBctx\fR. (See the \s-1BUGS\s0 section.)
169 .PP
170 \&\fISSL_set_verify_depth()\fR sets the maximum \fBdepth\fR for the certificate chain
171 verification that shall be allowed for \fBssl\fR. (See the \s-1BUGS\s0 section.)
172 .SH "NOTES"
173 .IX Header "NOTES"
174 The verification of certificates can be controlled by a set of logically
175 or'ed \fBmode\fR flags:
176 .IP "\s-1SSL_VERIFY_NONE\s0" 4
177 .IX Item "SSL_VERIFY_NONE"
178 \&\fBServer mode:\fR the server will not send a client certificate request to the
179 client, so the client will not send a certificate.
180 .Sp
181 \&\fBClient mode:\fR if not using an anonymous cipher (by default disabled), the
182 server will send a certificate which will be checked. The result of the
183 certificate verification process can be checked after the \s-1TLS/SSL\s0 handshake
184 using the \fISSL_get_verify_result\fR\|(3) function.
185 The handshake will be continued regardless of the verification result.
186 .IP "\s-1SSL_VERIFY_PEER\s0" 4
187 .IX Item "SSL_VERIFY_PEER"
188 \&\fBServer mode:\fR the server sends a client certificate request to the client.
189 The certificate returned (if any) is checked. If the verification process
190 fails, the \s-1TLS/SSL\s0 handshake is
191 immediately terminated with an alert message containing the reason for
192 the verification failure.
193 The behaviour can be controlled by the additional
194 \&\s-1SSL_VERIFY_FAIL_IF_NO_PEER_CERT\s0 and \s-1SSL_VERIFY_CLIENT_ONCE\s0 flags.
195 .Sp
196 \&\fBClient mode:\fR the server certificate is verified. If the verification process
197 fails, the \s-1TLS/SSL\s0 handshake is
198 immediately terminated with an alert message containing the reason for
199 the verification failure. If no server certificate is sent, because an
200 anonymous cipher is used, \s-1SSL_VERIFY_PEER\s0 is ignored.
201 .IP "\s-1SSL_VERIFY_FAIL_IF_NO_PEER_CERT\s0" 4
202 .IX Item "SSL_VERIFY_FAIL_IF_NO_PEER_CERT"
203 \&\fBServer mode:\fR if the client did not return a certificate, the \s-1TLS/SSL\s0
204 handshake is immediately terminated with a \*(L"handshake failure\*(R" alert.
205 This flag must be used together with \s-1SSL_VERIFY_PEER\s0.
206 .Sp
207 \&\fBClient mode:\fR ignored
208 .IP "\s-1SSL_VERIFY_CLIENT_ONCE\s0" 4
209 .IX Item "SSL_VERIFY_CLIENT_ONCE"
210 \&\fBServer mode:\fR only request a client certificate on the initial \s-1TLS/SSL\s0
211 handshake. Do not ask for a client certificate again in case of a
212 renegotiation. This flag must be used together with \s-1SSL_VERIFY_PEER\s0.
213 .Sp
214 \&\fBClient mode:\fR ignored
215 .PP
216 Exactly one of the \fBmode\fR flags \s-1SSL_VERIFY_NONE\s0 and \s-1SSL_VERIFY_PEER\s0 must be
217 set at any time.
218 .PP
219 The actual verification procedure is performed either using the built-in
220 verification procedure or using another application provided verification
221 function set with
222 \&\fISSL_CTX_set_cert_verify_callback\fR\|(3).
223 The following descriptions apply in the case of the built-in procedure. An
224 application provided procedure also has access to the verify depth information
225 and the \fIverify_callback()\fR function, but the way this information is used
226 may be different.
227 .PP
228 \&\fISSL_CTX_set_verify_depth()\fR and \fISSL_set_verify_depth()\fR set the limit up
229 to which depth certificates in a chain are used during the verification
230 procedure. If the certificate chain is longer than allowed, the certificates
231 above the limit are ignored. Error messages are generated as if these
232 certificates would not be present, most likely a
233 X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY will be issued.
234 The depth count is \*(L"level 0:peer certificate\*(R", \*(L"level 1: \s-1CA\s0 certificate\*(R",
235 \&\*(L"level 2: higher level \s-1CA\s0 certificate\*(R", and so on. Setting the maximum
236 depth to 2 allows the levels 0, 1, and 2. The default depth limit is 9,
237 allowing for the peer certificate and additional 9 \s-1CA\s0 certificates.
238 .PP
239 The \fBverify_callback\fR function is used to control the behaviour when the
240 \&\s-1SSL_VERIFY_PEER\s0 flag is set. It must be supplied by the application and
241 receives two arguments: \fBpreverify_ok\fR indicates, whether the verification of
242 the certificate in question was passed (preverify_ok=1) or not
243 (preverify_ok=0). \fBx509_ctx\fR is a pointer to the complete context used
244 for the certificate chain verification.
245 .PP
246 The certificate chain is checked starting with the deepest nesting level
247 (the root \s-1CA\s0 certificate) and worked upward to the peer's certificate.
248 At each level signatures and issuer attributes are checked. Whenever
249 a verification error is found, the error number is stored in \fBx509_ctx\fR
250 and \fBverify_callback\fR is called with \fBpreverify_ok\fR=0. By applying
251 X509_CTX_store_* functions \fBverify_callback\fR can locate the certificate
252 in question and perform additional steps (see \s-1EXAMPLES\s0). If no error is
253 found for a certificate, \fBverify_callback\fR is called with \fBpreverify_ok\fR=1
254 before advancing to the next level.
255 .PP
256 The return value of \fBverify_callback\fR controls the strategy of the further
257 verification process. If \fBverify_callback\fR returns 0, the verification
258 process is immediately stopped with \*(L"verification failed\*(R" state. If
259 \&\s-1SSL_VERIFY_PEER\s0 is set, a verification failure alert is sent to the peer and
260 the \s-1TLS/SSL\s0 handshake is terminated. If \fBverify_callback\fR returns 1,
261 the verification process is continued. If \fBverify_callback\fR always returns
262 1, the \s-1TLS/SSL\s0 handshake will not be terminated with respect to verification
263 failures and the connection will be established. The calling process can
264 however retrieve the error code of the last verification error using
265 \&\fISSL_get_verify_result\fR\|(3) or by maintaining its
266 own error storage managed by \fBverify_callback\fR.
267 .PP
268 If no \fBverify_callback\fR is specified, the default callback will be used.
269 Its return value is identical to \fBpreverify_ok\fR, so that any verification
270 failure will lead to a termination of the \s-1TLS/SSL\s0 handshake with an
271 alert message, if \s-1SSL_VERIFY_PEER\s0 is set.
272 .SH "BUGS"
273 .IX Header "BUGS"
274 In client mode, it is not checked whether the \s-1SSL_VERIFY_PEER\s0 flag
275 is set, but whether \s-1SSL_VERIFY_NONE\s0 is not set. This can lead to
276 unexpected behaviour, if the \s-1SSL_VERIFY_PEER\s0 and \s-1SSL_VERIFY_NONE\s0 are not
277 used as required (exactly one must be set at any time).
278 .PP
279 The certificate verification depth set with SSL[_CTX]\fI_verify_depth()\fR
280 stops the verification at a certain depth. The error message produced
281 will be that of an incomplete certificate chain and not
282 X509_V_ERR_CERT_CHAIN_TOO_LONG as may be expected.
283 .SH "RETURN VALUES"
284 .IX Header "RETURN VALUES"
285 The SSL*_set_verify*() functions do not provide diagnostic information.
286 .SH "EXAMPLES"
287 .IX Header "EXAMPLES"
288 The following code sequence realizes an example \fBverify_callback\fR function
289 that will always continue the \s-1TLS/SSL\s0 handshake regardless of verification
290 failure, if wished. The callback realizes a verification depth limit with
291 more informational output.
292 .PP
293 All verification errors are printed, informations about the certificate chain
294 are printed on request.
295 The example is realized for a server that does allow but not require client
296 certificates.
297 .PP
298 The example makes use of the ex_data technique to store application data
299 into/retrieve application data from the \s-1SSL\s0 structure
300 (see \fISSL_get_ex_new_index\fR\|(3),
301 \&\fISSL_get_ex_data_X509_STORE_CTX_idx\fR\|(3)).
302 .PP
303 .Vb 15
304 \& ...
305 \& typedef struct {
306 \& int verbose_mode;
307 \& int verify_depth;
308 \& int always_continue;
309 \& } mydata_t;
310 \& int mydata_index;
311 \& ...
312 \& static int verify_callback(int preverify_ok, X509_STORE_CTX *ctx)
313 \& {
314 \& char buf[256];
315 \& X509 *err_cert;
316 \& int err, depth;
317 \& SSL *ssl;
318 \& mydata_t *mydata;
319 .Ve
320 .PP
321 .Vb 3
322 \& err_cert = X509_STORE_CTX_get_current_cert(ctx);
323 \& err = X509_STORE_CTX_get_error(ctx);
324 \& depth = X509_STORE_CTX_get_error_depth(ctx);
325 .Ve
326 .PP
327 .Vb 6
328 \& /*
329 \& * Retrieve the pointer to the SSL of the connection currently treated
330 \& * and the application specific data stored into the SSL object.
331 \& */
332 \& ssl = X509_STORE_CTX_get_ex_data(ctx, SSL_get_ex_data_X509_STORE_CTX_idx());
333 \& mydata = SSL_get_ex_data(ssl, mydata_index);
334 .Ve
335 .PP
336 .Vb 1
337 \& X509_NAME_oneline(X509_get_subject_name(err_cert), buf, 256);
338 .Ve
339 .PP
340 .Vb 22
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 .Ve
364 .PP
365 .Vb 9
366 \& /*
367 \& * At this point, err contains the last verification error. We can use
368 \& * it for something special
369 \& */
370 \& if (!preverify_ok && (err == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT))
371 \& {
372 \& X509_NAME_oneline(X509_get_issuer_name(ctx->current_cert), buf, 256);
373 \& printf("issuer= %s\en", buf);
374 \& }
375 .Ve
376 .PP
377 .Vb 6
378 \& if (mydata->always_continue)
379 \& return 1;
380 \& else
381 \& return preverify_ok;
382 \& }
383 \& ...
384 .Ve
385 .PP
386 .Vb 1
387 \& mydata_t mydata;
388 .Ve
389 .PP
390 .Vb 2
391 \& ...
392 \& mydata_index = SSL_get_ex_new_index(0, "mydata index", NULL, NULL, NULL);
393 .Ve
394 .PP
395 .Vb 3
396 \& ...
397 \& SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER|SSL_VERIFY_CLIENT_ONCE,
398 \& verify_callback);
399 .Ve
400 .PP
401 .Vb 5
402 \& /*
403 \& * Let the verify_callback catch the verify_depth error so that we get
404 \& * an appropriate error in the logfile.
405 \& */
406 \& SSL_CTX_set_verify_depth(verify_depth + 1);
407 .Ve
408 .PP
409 .Vb 6
410 \& /*
411 \& * Set up the SSL specific data into "mydata" and store it into th SSL
412 \& * structure.
413 \& */
414 \& mydata.verify_depth = verify_depth; ...
415 \& SSL_set_ex_data(ssl, mydata_index, &mydata);
416 .Ve
417 .PP
418 .Vb 9
419 \& ...
420 \& SSL_accept(ssl); /* check of success left out for clarity */
421 \& if (peer = SSL_get_peer_certificate(ssl))
422 \& {
423 \& if (SSL_get_verify_result(ssl) == X509_V_OK)
424 \& {
425 \& /* The client sent a certificate which verified OK */
426 \& }
427 \& }
428 .Ve
429 .SH "SEE ALSO"
430 .IX Header "SEE ALSO"
431 \&\fIssl\fR\|(3), \fISSL_new\fR\|(3),
432 \&\fISSL_CTX_get_verify_mode\fR\|(3),
433 \&\fISSL_get_verify_result\fR\|(3),
434 \&\fISSL_CTX_load_verify_locations\fR\|(3),
435 \&\fISSL_get_peer_certificate\fR\|(3),
436 \&\fISSL_CTX_set_cert_verify_callback\fR\|(3),
437 \&\fISSL_get_ex_data_X509_STORE_CTX_idx\fR\|(3),
438 \&\fISSL_get_ex_new_index\fR\|(3)