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>]
82 The B<s_client> command implements a generic SSL/TLS client which connects
83 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
88 In addition to the options below the B<s_client> utility also supports the
89 common and client only options documented in the
90 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
95 =item B<-connect host:port>
97 This specifies the host and optional port to connect to. If not specified
98 then an attempt is made to connect to the local host on port 4433.
100 =item B<-servername name>
102 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
104 =item B<-cert certname>
106 The certificate to use, if one is requested by the server. The default is
107 not to use a certificate.
109 =item B<-certform format>
111 The certificate format to use: DER or PEM. PEM is the default.
113 =item B<-key keyfile>
115 The private key to use. If not specified then the certificate file will
118 =item B<-keyform format>
120 The private format to use: DER or PEM. PEM is the default.
124 the private key password source. For more information about the format of B<arg>
125 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
127 =item B<-verify depth>
129 The verify depth to use. This specifies the maximum length of the
130 server certificate chain and turns on server certificate verification.
131 Currently the verify operation continues after errors so all the problems
132 with a certificate chain can be seen. As a side effect the connection
133 will never fail due to a server certificate verify failure.
135 =item B<-verify_return_error>
137 Return verification errors instead of continuing. This will typically
138 abort the handshake with a fatal error.
140 =item B<-CApath directory>
142 The directory to use for server certificate verification. This directory
143 must be in "hash format", see B<verify> for more information. These are
144 also used when building the client certificate chain.
146 =item B<-CAfile file>
148 A file containing trusted certificates to use during server authentication
149 and to use when attempting to build the client certificate chain.
151 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
152 B<explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
153 B<-inhibit_map>, B<-issuer_checks>, B<-partial_chain>, B<-policy>,
154 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
155 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
156 B<-verify_depth>, B<-verify_email>, B<-verify_hostname>, B<-verify_ip>,
157 B<-verify_name>, B<-x509_strict>
159 Set various certificate chain valiadition options. See the
160 L<B<verify>|verify(1)> manual page for details.
164 reconnects to the same server 5 times using the same session ID, this can
165 be used as a test that session caching is working.
169 pauses 1 second between each read and write call.
173 display the whole server certificate chain: normally only the server
174 certificate itself is displayed.
178 print session information when the program exits. This will always attempt
179 to print out information even if the connection fails. Normally information
180 will only be printed out once if the connection succeeds. This option is useful
181 because the cipher in use may be renegotiated or the connection may fail
182 because a client certificate is required or is requested only after an
183 attempt is made to access a certain URL. Note: the output produced by this
184 option is not always accurate because a connection might never have been
189 prints out the SSL session states.
193 print extensive debugging information including a hex dump of all traffic.
197 show all protocol messages with hex dump.
201 show verbose trace output of protocol messages. OpenSSL needs to be compiled
202 with B<enable-ssl-trace> for this option to work.
206 file to send output of B<-msg> or B<-trace> to, default standard output.
210 tests non-blocking I/O
214 turns on non-blocking I/O
218 this option translated a line feed from the terminal into CR+LF as required
223 inhibit shutting down the connection when end of file is reached in the
228 inhibit printing of session and certificate information. This implicitly
229 turns on B<-ign_eof> as well.
233 shut down the connection when end of file is reached in the input.
234 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
236 =item B<-psk_identity identity>
238 Use the PSK identity B<identity> when using a PSK cipher suite.
242 Use the PSK key B<key> when using a PSK cipher suite. The key is
243 given as a hexadecimal number without leading 0x, for example -psk
246 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>
248 these options disable the use of certain SSL or TLS protocols. By default
249 the initial handshake uses a method which should be compatible with all
250 servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
252 Unfortunately there are a lot of ancient and broken servers in use which
253 cannot handle this technique and will fail to connect. Some servers only
254 work if TLS is turned off with the B<-no_tls> option others will only
255 support SSL v2 and may need the B<-ssl2> option.
259 there are several known bug in SSL and TLS implementations. Adding this
260 option enables various workarounds.
264 only provide a brief summary of connection parameters instead of the
265 normal verbose output.
267 =item B<-cipher cipherlist>
269 this allows the cipher list sent by the client to be modified. Although
270 the server determines which cipher suite is used it should take the first
271 supported cipher in the list sent by the client. See the B<ciphers>
272 command for more information.
276 use the server's cipher preferences; only used for SSLV2.
278 =item B<-starttls protocol>
280 send the protocol-specific message(s) to switch to TLS for communication.
281 B<protocol> is a keyword for the intended protocol. Currently, the only
282 supported keywords are "smtp", "pop3", "imap", "ftp" and "xmpp".
284 =item B<-xmpphost hostname>
286 This option, when used with "-starttls xmpp", specifies the host for the
287 "to" attribute of the stream element.
288 If this option is not specified, then the host specified with "-connect"
291 =item B<-tlsextdebug>
293 print out a hex dump of any TLS extensions received from the server.
297 disable RFC4507bis session ticket support.
299 =item B<-sess_out filename>
301 output SSL session to B<filename>
303 =item B<-sess_in sess.pem>
305 load SSL session from B<filename>. The client will attempt to resume a
306 connection from this session.
310 specifying an engine (by its unique B<id> string) will cause B<s_client>
311 to attempt to obtain a functional reference to the specified engine,
312 thus initialising it if needed. The engine will then be set as the default
313 for all available algorithms.
315 =item B<-rand file(s)>
317 a file or files containing random data used to seed the random number
318 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
319 Multiple files can be specified separated by a OS-dependent character.
320 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
323 =item B<-serverinfo types>
325 a list of comma-separated TLS Extension Types (numbers between 0 and
326 65535). Each type will be sent as an empty ClientHello TLS Extension.
327 The server's response (if any) will be encoded and displayed as a PEM
332 =head1 CONNECTED COMMANDS
334 If a connection is established with an SSL server then any data received
335 from the server is displayed and any key presses will be sent to the
336 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
337 have been given), the session will be renegotiated if the line begins with an
338 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
339 connection will be closed down.
343 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
346 openssl s_client -connect servername:443
348 would typically be used (https uses port 443). If the connection succeeds
349 then an HTTP command can be given such as "GET /" to retrieve a web page.
351 If the handshake fails then there are several possible causes, if it is
352 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
353 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried
354 in case it is a buggy server. In particular you should play with these
355 options B<before> submitting a bug report to an OpenSSL mailing list.
357 A frequent problem when attempting to get client certificates working
358 is that a web client complains it has no certificates or gives an empty
359 list to choose from. This is normally because the server is not sending
360 the clients certificate authority in its "acceptable CA list" when it
361 requests a certificate. By using B<s_client> the CA list can be viewed
362 and checked. However some servers only request client authentication
363 after a specific URL is requested. To obtain the list in this case it
364 is necessary to use the B<-prexit> option and send an HTTP request
365 for an appropriate page.
367 If a certificate is specified on the command line using the B<-cert>
368 option it will not be used unless the server specifically requests
369 a client certificate. Therefor merely including a client certificate
370 on the command line is no guarantee that the certificate works.
372 If there are problems verifying a server certificate then the
373 B<-showcerts> option can be used to show the whole chain.
375 Since the SSLv23 client hello cannot include compression methods or extensions
376 these will only be supported if its use is disabled, for example by using the
379 The B<s_client> utility is a test tool and is designed to continue the
380 handshake after any certificate verification errors. As a result it will
381 accept any certificate chain (trusted or not) sent by the peer. None test
382 applications should B<not> do this as it makes them vulnerable to a MITM
383 attack. This behaviour can be changed by with the B<-verify_return_error>
384 option: any verify errors are then returned aborting the handshake.
388 Because this program has a lot of options and also because some of
389 the techniques used are rather old, the C source of s_client is rather
390 hard to read and not a model of how things should be done. A typical
391 SSL client program would be much simpler.
393 The B<-prexit> option is a bit of a hack. We should really report
394 information whenever a session is renegotiated.
398 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>