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>]
68 [B<-cipher cipherlist>]
70 [B<-starttls protocol>]
71 [B<-xmpphost hostname>]
75 [B<-sess_out filename>]
76 [B<-sess_in filename>]
78 [B<-serverinfo types>]
83 The B<s_client> command implements a generic SSL/TLS client which connects
84 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
89 In addition to the options below the B<s_client> utility also supports the
90 common and client only options documented in the
91 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
96 =item B<-connect host:port>
98 This specifies the host and optional port to connect to. If not specified
99 then an attempt is made to connect to the local host on port 4433.
101 =item B<-servername name>
103 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
105 =item B<-cert certname>
107 The certificate to use, if one is requested by the server. The default is
108 not to use a certificate.
110 =item B<-certform format>
112 The certificate format to use: DER or PEM. PEM is the default.
114 =item B<-key keyfile>
116 The private key to use. If not specified then the certificate file will
119 =item B<-keyform format>
121 The private format to use: DER or PEM. PEM is the default.
125 the private key password source. For more information about the format of B<arg>
126 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
128 =item B<-verify depth>
130 The verify depth to use. This specifies the maximum length of the
131 server certificate chain and turns on server certificate verification.
132 Currently the verify operation continues after errors so all the problems
133 with a certificate chain can be seen. As a side effect the connection
134 will never fail due to a server certificate verify failure.
136 =item B<-verify_return_error>
138 Return verification errors instead of continuing. This will typically
139 abort the handshake with a fatal error.
141 =item B<-CApath directory>
143 The directory to use for server certificate verification. This directory
144 must be in "hash format", see B<verify> for more information. These are
145 also used when building the client certificate chain.
147 =item B<-CAfile file>
149 A file containing trusted certificates to use during server authentication
150 and to use when attempting to build the client certificate chain.
152 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
153 B<explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
154 B<-inhibit_map>, B<-issuer_checks>, B<-partial_chain>, B<-policy>,
155 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
156 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
157 B<-verify_depth>, B<-verify_email>, B<-verify_hostname>, B<-verify_ip>,
158 B<-verify_name>, B<-x509_strict>
160 Set various certificate chain valiadition options. See the
161 L<B<verify>|verify(1)> manual page for details.
165 reconnects to the same server 5 times using the same session ID, this can
166 be used as a test that session caching is working.
170 pauses 1 second between each read and write call.
174 display the whole server certificate chain: normally only the server
175 certificate itself is displayed.
179 print session information when the program exits. This will always attempt
180 to print out information even if the connection fails. Normally information
181 will only be printed out once if the connection succeeds. This option is useful
182 because the cipher in use may be renegotiated or the connection may fail
183 because a client certificate is required or is requested only after an
184 attempt is made to access a certain URL. Note: the output produced by this
185 option is not always accurate because a connection might never have been
190 prints out the SSL session states.
194 print extensive debugging information including a hex dump of all traffic.
198 show all protocol messages with hex dump.
202 show verbose trace output of protocol messages. OpenSSL needs to be compiled
203 with B<enable-ssl-trace> for this option to work.
207 file to send output of B<-msg> or B<-trace> to, default standard output.
211 tests non-blocking I/O
215 turns on non-blocking I/O
219 this option translated a line feed from the terminal into CR+LF as required
224 inhibit shutting down the connection when end of file is reached in the
229 inhibit printing of session and certificate information. This implicitly
230 turns on B<-ign_eof> as well.
234 shut down the connection when end of file is reached in the input.
235 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
237 =item B<-psk_identity identity>
239 Use the PSK identity B<identity> when using a PSK cipher suite.
243 Use the PSK key B<key> when using a PSK cipher suite. The key is
244 given as a hexadecimal number without leading 0x, for example -psk
247 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>
249 these options disable the use of certain SSL or TLS protocols. By default
250 the initial handshake uses a method which should be compatible with all
251 servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
253 Unfortunately there are a lot of ancient and broken servers in use which
254 cannot handle this technique and will fail to connect. Some servers only
255 work if TLS is turned off with the B<-no_tls> option others will only
256 support SSL v2 and may need the B<-ssl2> option.
260 there are several known bug in SSL and TLS implementations. Adding this
261 option enables various workarounds.
265 only provide a brief summary of connection parameters instead of the
266 normal verbose output.
268 =item B<-cipher cipherlist>
270 this allows the cipher list sent by the client to be modified. Although
271 the server determines which cipher suite is used it should take the first
272 supported cipher in the list sent by the client. See the B<ciphers>
273 command for more information.
277 use the server's cipher preferences; only used for SSLV2.
279 =item B<-starttls protocol>
281 send the protocol-specific message(s) to switch to TLS for communication.
282 B<protocol> is a keyword for the intended protocol. Currently, the only
283 supported keywords are "smtp", "pop3", "imap", "ftp" and "xmpp".
285 =item B<-xmpphost hostname>
287 This option, when used with "-starttls xmpp", specifies the host for the
288 "to" attribute of the stream element.
289 If this option is not specified, then the host specified with "-connect"
292 =item B<-tlsextdebug>
294 print out a hex dump of any TLS extensions received from the server.
298 disable RFC4507bis session ticket support.
300 =item B<-sess_out filename>
302 output SSL session to B<filename>
304 =item B<-sess_in sess.pem>
306 load SSL session from B<filename>. The client will attempt to resume a
307 connection from this session.
311 specifying an engine (by its unique B<id> string) will cause B<s_client>
312 to attempt to obtain a functional reference to the specified engine,
313 thus initialising it if needed. The engine will then be set as the default
314 for all available algorithms.
316 =item B<-rand file(s)>
318 a file or files containing random data used to seed the random number
319 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
320 Multiple files can be specified separated by a OS-dependent character.
321 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
324 =item B<-serverinfo types>
326 a list of comma-separated TLS Extension Types (numbers between 0 and
327 65535). Each type will be sent as an empty ClientHello TLS Extension.
328 The server's response (if any) will be encoded and displayed as a PEM
333 sends a certificate status request to the server (OCSP stapling). The server
334 response (if any) is printed out.
338 =head1 CONNECTED COMMANDS
340 If a connection is established with an SSL server then any data received
341 from the server is displayed and any key presses will be sent to the
342 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
343 have been given), the session will be renegotiated if the line begins with an
344 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
345 connection will be closed down.
349 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
352 openssl s_client -connect servername:443
354 would typically be used (https uses port 443). If the connection succeeds
355 then an HTTP command can be given such as "GET /" to retrieve a web page.
357 If the handshake fails then there are several possible causes, if it is
358 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
359 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried
360 in case it is a buggy server. In particular you should play with these
361 options B<before> submitting a bug report to an OpenSSL mailing list.
363 A frequent problem when attempting to get client certificates working
364 is that a web client complains it has no certificates or gives an empty
365 list to choose from. This is normally because the server is not sending
366 the clients certificate authority in its "acceptable CA list" when it
367 requests a certificate. By using B<s_client> the CA list can be viewed
368 and checked. However some servers only request client authentication
369 after a specific URL is requested. To obtain the list in this case it
370 is necessary to use the B<-prexit> option and send an HTTP request
371 for an appropriate page.
373 If a certificate is specified on the command line using the B<-cert>
374 option it will not be used unless the server specifically requests
375 a client certificate. Therefor merely including a client certificate
376 on the command line is no guarantee that the certificate works.
378 If there are problems verifying a server certificate then the
379 B<-showcerts> option can be used to show the whole chain.
381 Since the SSLv23 client hello cannot include compression methods or extensions
382 these will only be supported if its use is disabled, for example by using the
385 The B<s_client> utility is a test tool and is designed to continue the
386 handshake after any certificate verification errors. As a result it will
387 accept any certificate chain (trusted or not) sent by the peer. None test
388 applications should B<not> do this as it makes them vulnerable to a MITM
389 attack. This behaviour can be changed by with the B<-verify_return_error>
390 option: any verify errors are then returned aborting the handshake.
394 Because this program has a lot of options and also because some of
395 the techniques used are rather old, the C source of s_client is rather
396 hard to read and not a model of how things should be done. A typical
397 SSL client program would be much simpler.
399 The B<-prexit> option is a bit of a hack. We should really report
400 information whenever a session is renegotiated.
404 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>