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133 .\" ========================================================================
134 .\"
135 .IX Title "S_CLIENT 1"
136 .TH S_CLIENT 1 "2016-05-03" "1.0.2h" "OpenSSL"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
138 .\" way too many mistakes in technical documents.
139 .if n .ad l
140 .nh
141 .SH "NAME"
142 s_client \- SSL/TLS client program
143 .SH "SYNOPSIS"
144 .IX Header "SYNOPSIS"
145 \&\fBopenssl\fR \fBs_client\fR
146 [\fB\-connect host:port\fR]
147 [\fB\-servername name\fR]
148 [\fB\-verify depth\fR]
149 [\fB\-verify_return_error\fR]
150 [\fB\-cert filename\fR]
151 [\fB\-certform DER|PEM\fR]
152 [\fB\-key filename\fR]
153 [\fB\-keyform DER|PEM\fR]
154 [\fB\-pass arg\fR]
155 [\fB\-CApath directory\fR]
156 [\fB\-CAfile filename\fR]
157 [\fB\-no_alt_chains\fR]
158 [\fB\-reconnect\fR]
159 [\fB\-pause\fR]
160 [\fB\-showcerts\fR]
161 [\fB\-debug\fR]
162 [\fB\-msg\fR]
163 [\fB\-nbio_test\fR]
164 [\fB\-state\fR]
165 [\fB\-nbio\fR]
166 [\fB\-crlf\fR]
167 [\fB\-ign_eof\fR]
168 [\fB\-no_ign_eof\fR]
169 [\fB\-quiet\fR]
170 [\fB\-ssl2\fR]
171 [\fB\-ssl3\fR]
172 [\fB\-tls1\fR]
173 [\fB\-no_ssl2\fR]
174 [\fB\-no_ssl3\fR]
175 [\fB\-no_tls1\fR]
176 [\fB\-no_tls1_1\fR]
177 [\fB\-no_tls1_2\fR]
178 [\fB\-fallback_scsv\fR]
179 [\fB\-bugs\fR]
180 [\fB\-cipher cipherlist\fR]
181 [\fB\-serverpref\fR]
182 [\fB\-starttls protocol\fR]
183 [\fB\-engine id\fR]
184 [\fB\-tlsextdebug\fR]
185 [\fB\-no_ticket\fR]
186 [\fB\-sess_out filename\fR]
187 [\fB\-sess_in filename\fR]
188 [\fB\-rand file(s)\fR]
189 [\fB\-serverinfo types\fR]
190 [\fB\-status\fR]
191 [\fB\-nextprotoneg protocols\fR]
192 .SH "DESCRIPTION"
193 .IX Header "DESCRIPTION"
194 The \fBs_client\fR command implements a generic \s-1SSL/TLS\s0 client which connects
195 to a remote host using \s-1SSL/TLS.\s0 It is a \fIvery\fR useful diagnostic tool for
196 \&\s-1SSL\s0 servers.
197 .SH "OPTIONS"
198 .IX Header "OPTIONS"
199 .IP "\fB\-connect host:port\fR" 4
200 .IX Item "-connect host:port"
201 This specifies the host and optional port to connect to. If not specified
202 then an attempt is made to connect to the local host on port 4433.
203 .IP "\fB\-servername name\fR" 4
204 .IX Item "-servername name"
205 Set the \s-1TLS SNI \s0(Server Name Indication) extension in the ClientHello message.
206 .IP "\fB\-cert certname\fR" 4
207 .IX Item "-cert certname"
208 The certificate to use, if one is requested by the server. The default is
209 not to use a certificate.
210 .IP "\fB\-certform format\fR" 4
211 .IX Item "-certform format"
212 The certificate format to use: \s-1DER\s0 or \s-1PEM. PEM\s0 is the default.
213 .IP "\fB\-key keyfile\fR" 4
214 .IX Item "-key keyfile"
215 The private key to use. If not specified then the certificate file will
216 be used.
217 .IP "\fB\-keyform format\fR" 4
218 .IX Item "-keyform format"
219 The private format to use: \s-1DER\s0 or \s-1PEM. PEM\s0 is the default.
220 .IP "\fB\-pass arg\fR" 4
221 .IX Item "-pass arg"
222 the private key password source. For more information about the format of \fBarg\fR
223 see the \fB\s-1PASS PHRASE ARGUMENTS\s0\fR section in \fIopenssl\fR\|(1).
224 .IP "\fB\-verify depth\fR" 4
225 .IX Item "-verify depth"
226 The verify depth to use. This specifies the maximum length of the
227 server certificate chain and turns on server certificate verification.
228 Currently the verify operation continues after errors so all the problems
229 with a certificate chain can be seen. As a side effect the connection
230 will never fail due to a server certificate verify failure.
231 .IP "\fB\-verify_return_error\fR" 4
232 .IX Item "-verify_return_error"
233 Return verification errors instead of continuing. This will typically
234 abort the handshake with a fatal error.
235 .IP "\fB\-CApath directory\fR" 4
236 .IX Item "-CApath directory"
237 The directory to use for server certificate verification. This directory
238 must be in \*(L"hash format\*(R", see \fBverify\fR for more information. These are
239 also used when building the client certificate chain.
240 .IP "\fB\-CAfile file\fR" 4
241 .IX Item "-CAfile file"
242 A file containing trusted certificates to use during server authentication
243 and to use when attempting to build the client certificate chain.
244 .IP "\fB\-purpose, \-ignore_critical, \-issuer_checks, \-crl_check, \-crl_check_all, \-policy_check, \-extended_crl, \-x509_strict, \-policy \-check_ss_sig \-no_alt_chains\fR" 4
245 .IX Item "-purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all, -policy_check, -extended_crl, -x509_strict, -policy -check_ss_sig -no_alt_chains"
246 Set various certificate chain valiadition option. See the
247 \&\fBverify\fR manual page for details.
248 .IP "\fB\-reconnect\fR" 4
249 .IX Item "-reconnect"
250 reconnects to the same server 5 times using the same session \s-1ID,\s0 this can
251 be used as a test that session caching is working.
252 .IP "\fB\-pause\fR" 4
253 .IX Item "-pause"
254 pauses 1 second between each read and write call.
255 .IP "\fB\-showcerts\fR" 4
256 .IX Item "-showcerts"
257 display the whole server certificate chain: normally only the server
258 certificate itself is displayed.
259 .IP "\fB\-prexit\fR" 4
260 .IX Item "-prexit"
261 print session information when the program exits. This will always attempt
262 to print out information even if the connection fails. Normally information
263 will only be printed out once if the connection succeeds. This option is useful
264 because the cipher in use may be renegotiated or the connection may fail
265 because a client certificate is required or is requested only after an
266 attempt is made to access a certain \s-1URL.\s0 Note: the output produced by this
267 option is not always accurate because a connection might never have been
268 established.
269 .IP "\fB\-state\fR" 4
270 .IX Item "-state"
271 prints out the \s-1SSL\s0 session states.
272 .IP "\fB\-debug\fR" 4
273 .IX Item "-debug"
274 print extensive debugging information including a hex dump of all traffic.
275 .IP "\fB\-msg\fR" 4
276 .IX Item "-msg"
277 show all protocol messages with hex dump.
278 .IP "\fB\-nbio_test\fR" 4
279 .IX Item "-nbio_test"
280 tests non-blocking I/O
281 .IP "\fB\-nbio\fR" 4
282 .IX Item "-nbio"
283 turns on non-blocking I/O
284 .IP "\fB\-crlf\fR" 4
285 .IX Item "-crlf"
286 this option translated a line feed from the terminal into \s-1CR+LF\s0 as required
287 by some servers.
288 .IP "\fB\-ign_eof\fR" 4
289 .IX Item "-ign_eof"
290 inhibit shutting down the connection when end of file is reached in the
291 input.
292 .IP "\fB\-quiet\fR" 4
293 .IX Item "-quiet"
294 inhibit printing of session and certificate information. This implicitly
295 turns on \fB\-ign_eof\fR as well.
296 .IP "\fB\-no_ign_eof\fR" 4
297 .IX Item "-no_ign_eof"
298 shut down the connection when end of file is reached in the input.
299 Can be used to override the implicit \fB\-ign_eof\fR after \fB\-quiet\fR.
300 .IP "\fB\-psk_identity identity\fR" 4
301 .IX Item "-psk_identity identity"
302 Use the \s-1PSK\s0 identity \fBidentity\fR when using a \s-1PSK\s0 cipher suite.
303 .IP "\fB\-psk key\fR" 4
304 .IX Item "-psk key"
305 Use the \s-1PSK\s0 key \fBkey\fR when using a \s-1PSK\s0 cipher suite. The key is
306 given as a hexadecimal number without leading 0x, for example \-psk
307 1a2b3c4d.
308 .IP "\fB\-ssl2\fR, \fB\-ssl3\fR, \fB\-tls1\fR, \fB\-tls1_1\fR, \fB\-tls1_2\fR, \fB\-no_ssl2\fR, \fB\-no_ssl3\fR, \fB\-no_tls1\fR, \fB\-no_tls1_1\fR, \fB\-no_tls1_2\fR" 4
309 .IX Item "-ssl2, -ssl3, -tls1, -tls1_1, -tls1_2, -no_ssl2, -no_ssl3, -no_tls1, -no_tls1_1, -no_tls1_2"
310 These options require or disable the use of the specified \s-1SSL\s0 or \s-1TLS\s0 protocols.
311 By default the initial handshake uses a \fIversion-flexible\fR method which will
312 negotiate the highest mutually supported protocol version.
313 .IP "\fB\-fallback_scsv\fR" 4
314 .IX Item "-fallback_scsv"
315 Send \s-1TLS_FALLBACK_SCSV\s0 in the ClientHello.
316 .IP "\fB\-bugs\fR" 4
317 .IX Item "-bugs"
318 there are several known bug in \s-1SSL\s0 and \s-1TLS\s0 implementations. Adding this
319 option enables various workarounds.
320 .IP "\fB\-cipher cipherlist\fR" 4
321 .IX Item "-cipher cipherlist"
322 this allows the cipher list sent by the client to be modified. Although
323 the server determines which cipher suite is used it should take the first
324 supported cipher in the list sent by the client. See the \fBciphers\fR
325 command for more information.
326 .IP "\fB\-serverpref\fR" 4
327 .IX Item "-serverpref"
328 use the server's cipher preferences; only used for \s-1SSLV2.\s0
329 .IP "\fB\-starttls protocol\fR" 4
330 .IX Item "-starttls protocol"
331 send the protocol-specific message(s) to switch to \s-1TLS\s0 for communication.
332 \&\fBprotocol\fR is a keyword for the intended protocol. Currently, the only
333 supported keywords are \*(L"smtp\*(R", \*(L"pop3\*(R", \*(L"imap\*(R", and \*(L"ftp\*(R".
334 .IP "\fB\-tlsextdebug\fR" 4
335 .IX Item "-tlsextdebug"
336 print out a hex dump of any \s-1TLS\s0 extensions received from the server.
337 .IP "\fB\-no_ticket\fR" 4
338 .IX Item "-no_ticket"
339 disable RFC4507bis session ticket support.
340 .IP "\fB\-sess_out filename\fR" 4
341 .IX Item "-sess_out filename"
342 output \s-1SSL\s0 session to \fBfilename\fR
343 .IP "\fB\-sess_in sess.pem\fR" 4
344 .IX Item "-sess_in sess.pem"
345 load \s-1SSL\s0 session from \fBfilename\fR. The client will attempt to resume a
346 connection from this session.
347 .IP "\fB\-engine id\fR" 4
348 .IX Item "-engine id"
349 specifying an engine (by its unique \fBid\fR string) will cause \fBs_client\fR
350 to attempt to obtain a functional reference to the specified engine,
351 thus initialising it if needed. The engine will then be set as the default
352 for all available algorithms.
353 .IP "\fB\-rand file(s)\fR" 4
354 .IX Item "-rand file(s)"
355 a file or files containing random data used to seed the random number
356 generator, or an \s-1EGD\s0 socket (see \fIRAND_egd\fR\|(3)).
357 Multiple files can be specified separated by a OS-dependent character.
358 The separator is \fB;\fR for MS-Windows, \fB,\fR for OpenVMS, and \fB:\fR for
359 all others.
360 .IP "\fB\-serverinfo types\fR" 4
361 .IX Item "-serverinfo types"
362 a list of comma-separated \s-1TLS\s0 Extension Types (numbers between 0 and
363 65535). Each type will be sent as an empty ClientHello \s-1TLS\s0 Extension.
364 The server's response (if any) will be encoded and displayed as a \s-1PEM\s0
365 file.
366 .IP "\fB\-status\fR" 4
367 .IX Item "-status"
368 sends a certificate status request to the server (\s-1OCSP\s0 stapling). The server
369 response (if any) is printed out.
370 .IP "\fB\-nextprotoneg protocols\fR" 4
371 .IX Item "-nextprotoneg protocols"
372 enable Next Protocol Negotiation \s-1TLS\s0 extension and provide a list of
373 comma-separated protocol names that the client should advertise
374 support for. The list should contain most wanted protocols first.
375 Protocol names are printable \s-1ASCII\s0 strings, for example \*(L"http/1.1\*(R" or
376 \&\*(L"spdy/3\*(R".
377 Empty list of protocols is treated specially and will cause the client to
378 advertise support for the \s-1TLS\s0 extension but disconnect just after
379 reciving ServerHello with a list of server supported protocols.
380 .SH "CONNECTED COMMANDS"
381 .IX Header "CONNECTED COMMANDS"
382 If a connection is established with an \s-1SSL\s0 server then any data received
383 from the server is displayed and any key presses will be sent to the
384 server. When used interactively (which means neither \fB\-quiet\fR nor \fB\-ign_eof\fR
385 have been given), the session will be renegotiated if the line begins with an
386 \&\fBR\fR, and if the line begins with a \fBQ\fR or if end of file is reached, the
387 connection will be closed down.
388 .SH "NOTES"
389 .IX Header "NOTES"
390 \&\fBs_client\fR can be used to debug \s-1SSL\s0 servers. To connect to an \s-1SSL HTTP\s0
391 server the command:
392 .PP
393 .Vb 1
394 \& openssl s_client \-connect servername:443
395 .Ve
396 .PP
397 would typically be used (https uses port 443). If the connection succeeds
398 then an \s-1HTTP\s0 command can be given such as \*(L"\s-1GET /\*(R"\s0 to retrieve a web page.
399 .PP
400 If the handshake fails then there are several possible causes, if it is
401 nothing obvious like no client certificate then the \fB\-bugs\fR, \fB\-ssl2\fR,
402 \&\fB\-ssl3\fR, \fB\-tls1\fR, \fB\-no_ssl2\fR, \fB\-no_ssl3\fR, \fB\-no_tls1\fR options can be tried
403 in case it is a buggy server. In particular you should play with these
404 options \fBbefore\fR submitting a bug report to an OpenSSL mailing list.
405 .PP
406 A frequent problem when attempting to get client certificates working
407 is that a web client complains it has no certificates or gives an empty
408 list to choose from. This is normally because the server is not sending
409 the clients certificate authority in its \*(L"acceptable \s-1CA\s0 list\*(R" when it
410 requests a certificate. By using \fBs_client\fR the \s-1CA\s0 list can be viewed
411 and checked. However some servers only request client authentication
412 after a specific \s-1URL\s0 is requested. To obtain the list in this case it
413 is necessary to use the \fB\-prexit\fR option and send an \s-1HTTP\s0 request
414 for an appropriate page.
415 .PP
416 If a certificate is specified on the command line using the \fB\-cert\fR
417 option it will not be used unless the server specifically requests
418 a client certificate. Therefor merely including a client certificate
419 on the command line is no guarantee that the certificate works.
420 .PP
421 If there are problems verifying a server certificate then the
422 \&\fB\-showcerts\fR option can be used to show the whole chain.
423 .PP
424 Since the SSLv23 client hello cannot include compression methods or extensions
425 these will only be supported if its use is disabled, for example by using the
426 \&\fB\-no_sslv2\fR option.
427 .PP
428 The \fBs_client\fR utility is a test tool and is designed to continue the
429 handshake after any certificate verification errors. As a result it will
430 accept any certificate chain (trusted or not) sent by the peer. None test
431 applications should \fBnot\fR do this as it makes them vulnerable to a \s-1MITM\s0
432 attack. This behaviour can be changed by with the \fB\-verify_return_error\fR
433 option: any verify errors are then returned aborting the handshake.
434 .SH "BUGS"
435 .IX Header "BUGS"
436 Because this program has a lot of options and also because some of
437 the techniques used are rather old, the C source of s_client is rather
438 hard to read and not a model of how things should be done. A typical
439 \&\s-1SSL\s0 client program would be much simpler.
440 .PP
441 The \fB\-prexit\fR option is a bit of a hack. We should really report
442 information whenever a session is renegotiated.
443 .SH "SEE ALSO"
444 .IX Header "SEE ALSO"
445 \&\fIsess_id\fR\|(1), \fIs_server\fR\|(1), \fIciphers\fR\|(1)
446 .SH "HISTORY"
447 .IX Header "HISTORY"
448 The \-no_alt_chains options was first added to OpenSSL 1.0.2b.