6 s_client - SSL/TLS client program
10 B<openssl> B<s_client>
11 [B<-connect host:port>]
14 [B<-verify_return_error>]
16 [B<-certform DER|PEM>]
20 [B<-CApath directory>]
23 [B<-attime timestamp>]
43 [B<-verify_depth num>]
44 [B<-verify_email email>]
45 [B<-verify_hostname hostname>]
47 [B<-verify_name name>]
71 [B<-cipher cipherlist>]
73 [B<-starttls protocol>]
74 [B<-xmpphost hostname>]
78 [B<-sess_out filename>]
79 [B<-sess_in filename>]
81 [B<-serverinfo types>]
83 [B<-nextprotoneg protocols>]
87 The B<s_client> command implements a generic SSL/TLS client which connects
88 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
93 In addition to the options below the B<s_client> utility also supports the
94 common and client only options documented in the
95 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
100 =item B<-connect host:port>
102 This specifies the host and optional port to connect to. If not specified
103 then an attempt is made to connect to the local host on port 4433.
105 =item B<-servername name>
107 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
109 =item B<-cert certname>
111 The certificate to use, if one is requested by the server. The default is
112 not to use a certificate.
114 =item B<-certform format>
116 The certificate format to use: DER or PEM. PEM is the default.
118 =item B<-key keyfile>
120 The private key to use. If not specified then the certificate file will
123 =item B<-keyform format>
125 The private format to use: DER or PEM. PEM is the default.
129 the private key password source. For more information about the format of B<arg>
130 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
132 =item B<-verify depth>
134 The verify depth to use. This specifies the maximum length of the
135 server certificate chain and turns on server certificate verification.
136 Currently the verify operation continues after errors so all the problems
137 with a certificate chain can be seen. As a side effect the connection
138 will never fail due to a server certificate verify failure.
140 =item B<-verify_return_error>
142 Return verification errors instead of continuing. This will typically
143 abort the handshake with a fatal error.
145 =item B<-CApath directory>
147 The directory to use for server certificate verification. This directory
148 must be in "hash format", see B<verify> for more information. These are
149 also used when building the client certificate chain.
151 =item B<-CAfile file>
153 A file containing trusted certificates to use during server authentication
154 and to use when attempting to build the client certificate chain.
156 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
157 B<explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
158 B<-inhibit_map>, B<-issuer_checks>, B<-partial_chain>, B<-policy>,
159 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
160 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
161 B<-verify_depth>, B<-verify_email>, B<-verify_hostname>, B<-verify_ip>,
162 B<-verify_name>, B<-x509_strict>
164 Set various certificate chain valiadition options. See the
165 L<B<verify>|verify(1)> manual page for details.
169 reconnects to the same server 5 times using the same session ID, this can
170 be used as a test that session caching is working.
174 pauses 1 second between each read and write call.
178 display the whole server certificate chain: normally only the server
179 certificate itself is displayed.
183 print session information when the program exits. This will always attempt
184 to print out information even if the connection fails. Normally information
185 will only be printed out once if the connection succeeds. This option is useful
186 because the cipher in use may be renegotiated or the connection may fail
187 because a client certificate is required or is requested only after an
188 attempt is made to access a certain URL. Note: the output produced by this
189 option is not always accurate because a connection might never have been
194 prints out the SSL session states.
198 print extensive debugging information including a hex dump of all traffic.
202 show all protocol messages with hex dump.
206 show verbose trace output of protocol messages. OpenSSL needs to be compiled
207 with B<enable-ssl-trace> for this option to work.
211 file to send output of B<-msg> or B<-trace> to, default standard output.
215 tests non-blocking I/O
219 turns on non-blocking I/O
223 this option translated a line feed from the terminal into CR+LF as required
228 inhibit shutting down the connection when end of file is reached in the
233 inhibit printing of session and certificate information. This implicitly
234 turns on B<-ign_eof> as well.
238 shut down the connection when end of file is reached in the input.
239 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
241 =item B<-psk_identity identity>
243 Use the PSK identity B<identity> when using a PSK cipher suite.
247 Use the PSK key B<key> when using a PSK cipher suite. The key is
248 given as a hexadecimal number without leading 0x, for example -psk
251 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>
253 these options disable the use of certain SSL or TLS protocols. By default
254 the initial handshake uses a method which should be compatible with all
255 servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
257 Unfortunately there are still ancient and broken servers in use which
258 cannot handle this technique and will fail to connect. Some servers only
259 work if TLS is turned off.
261 =item B<-fallback_scsv>
263 Send TLS_FALLBACK_SCSV in the ClientHello.
267 there are several known bug in SSL and TLS implementations. Adding this
268 option enables various workarounds.
272 only provide a brief summary of connection parameters instead of the
273 normal verbose output.
275 =item B<-cipher cipherlist>
277 this allows the cipher list sent by the client to be modified. Although
278 the server determines which cipher suite is used it should take the first
279 supported cipher in the list sent by the client. See the B<ciphers>
280 command for more information.
284 use the server's cipher preferences; only used for SSLV2.
286 =item B<-starttls protocol>
288 send the protocol-specific message(s) to switch to TLS for communication.
289 B<protocol> is a keyword for the intended protocol. Currently, the only
290 supported keywords are "smtp", "pop3", "imap", "ftp" and "xmpp".
292 =item B<-xmpphost hostname>
294 This option, when used with "-starttls xmpp", specifies the host for the
295 "to" attribute of the stream element.
296 If this option is not specified, then the host specified with "-connect"
299 =item B<-tlsextdebug>
301 print out a hex dump of any TLS extensions received from the server.
305 disable RFC4507bis session ticket support.
307 =item B<-sess_out filename>
309 output SSL session to B<filename>
311 =item B<-sess_in sess.pem>
313 load SSL session from B<filename>. The client will attempt to resume a
314 connection from this session.
318 specifying an engine (by its unique B<id> string) will cause B<s_client>
319 to attempt to obtain a functional reference to the specified engine,
320 thus initialising it if needed. The engine will then be set as the default
321 for all available algorithms.
323 =item B<-rand file(s)>
325 a file or files containing random data used to seed the random number
326 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
327 Multiple files can be specified separated by a OS-dependent character.
328 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
331 =item B<-serverinfo types>
333 a list of comma-separated TLS Extension Types (numbers between 0 and
334 65535). Each type will be sent as an empty ClientHello TLS Extension.
335 The server's response (if any) will be encoded and displayed as a PEM
340 sends a certificate status request to the server (OCSP stapling). The server
341 response (if any) is printed out.
343 =item B<-nextprotoneg protocols>
345 enable Next Protocol Negotiation TLS extension and provide a list of
346 comma-separated protocol names that the client should advertise
347 support for. The list should contain most wanted protocols first.
348 Protocol names are printable ASCII strings, for example "http/1.1" or
350 Empty list of protocols is treated specially and will cause the client to
351 advertise support for the TLS extension but disconnect just after
352 reciving ServerHello with a list of server supported protocols.
356 =head1 CONNECTED COMMANDS
358 If a connection is established with an SSL server then any data received
359 from the server is displayed and any key presses will be sent to the
360 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
361 have been given), the session will be renegotiated if the line begins with an
362 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
363 connection will be closed down.
367 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
370 openssl s_client -connect servername:443
372 would typically be used (https uses port 443). If the connection succeeds
373 then an HTTP command can be given such as "GET /" to retrieve a web page.
375 If the handshake fails then there are several possible causes, if it is
376 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
377 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried
378 in case it is a buggy server. In particular you should play with these
379 options B<before> submitting a bug report to an OpenSSL mailing list.
381 A frequent problem when attempting to get client certificates working
382 is that a web client complains it has no certificates or gives an empty
383 list to choose from. This is normally because the server is not sending
384 the clients certificate authority in its "acceptable CA list" when it
385 requests a certificate. By using B<s_client> the CA list can be viewed
386 and checked. However some servers only request client authentication
387 after a specific URL is requested. To obtain the list in this case it
388 is necessary to use the B<-prexit> option and send an HTTP request
389 for an appropriate page.
391 If a certificate is specified on the command line using the B<-cert>
392 option it will not be used unless the server specifically requests
393 a client certificate. Therefor merely including a client certificate
394 on the command line is no guarantee that the certificate works.
396 If there are problems verifying a server certificate then the
397 B<-showcerts> option can be used to show the whole chain.
399 Since the SSLv23 client hello cannot include compression methods or extensions
400 these will only be supported if its use is disabled, for example by using the
403 The B<s_client> utility is a test tool and is designed to continue the
404 handshake after any certificate verification errors. As a result it will
405 accept any certificate chain (trusted or not) sent by the peer. None test
406 applications should B<not> do this as it makes them vulnerable to a MITM
407 attack. This behaviour can be changed by with the B<-verify_return_error>
408 option: any verify errors are then returned aborting the handshake.
412 Because this program has a lot of options and also because some of
413 the techniques used are rather old, the C source of s_client is rather
414 hard to read and not a model of how things should be done. A typical
415 SSL client program would be much simpler.
417 The B<-prexit> option is a bit of a hack. We should really report
418 information whenever a session is renegotiated.
422 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>