6 s_client - SSL/TLS client program
10 B<openssl> B<s_client>
11 [B<-connect host:port>]
15 [B<-verify_return_error>]
17 [B<-certform DER|PEM>]
21 [B<-CApath directory>]
25 [B<-attime timestamp>]
46 [B<-verify_depth num>]
47 [B<-verify_email email>]
48 [B<-verify_hostname hostname>]
50 [B<-verify_name name>]
72 [B<-cipher cipherlist>]
74 [B<-starttls protocol>]
75 [B<-xmpphost hostname>]
79 [B<-sess_out filename>]
80 [B<-sess_in filename>]
82 [B<-serverinfo types>]
84 [B<-nextprotoneg protocols>]
88 The B<s_client> command implements a generic SSL/TLS client which connects
89 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
94 In addition to the options below the B<s_client> utility also supports the
95 common and client only options documented in the
96 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
101 =item B<-connect host:port>
103 This specifies the host and optional port to connect to. If not specified
104 then an attempt is made to connect to the local host on port 4433.
106 =item B<-proxy host:port>
108 When used with the B<-connect> flag, the program uses the host and port
109 specified with this flag and issues an HTTP CONNECT command to connect
110 to the desired server.
112 =item B<-servername name>
114 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
116 =item B<-cert certname>
118 The certificate to use, if one is requested by the server. The default is
119 not to use a certificate.
121 =item B<-certform format>
123 The certificate format to use: DER or PEM. PEM is the default.
125 =item B<-key keyfile>
127 The private key to use. If not specified then the certificate file will
130 =item B<-keyform format>
132 The private format to use: DER or PEM. PEM is the default.
136 the private key password source. For more information about the format of B<arg>
137 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
139 =item B<-verify depth>
141 The verify depth to use. This specifies the maximum length of the
142 server certificate chain and turns on server certificate verification.
143 Currently the verify operation continues after errors so all the problems
144 with a certificate chain can be seen. As a side effect the connection
145 will never fail due to a server certificate verify failure.
147 =item B<-verify_return_error>
149 Return verification errors instead of continuing. This will typically
150 abort the handshake with a fatal error.
152 =item B<-CApath directory>
154 The directory to use for server certificate verification. This directory
155 must be in "hash format", see B<verify> for more information. These are
156 also used when building the client certificate chain.
158 =item B<-CAfile file>
160 A file containing trusted certificates to use during server authentication
161 and to use when attempting to build the client certificate chain.
165 Do not load the trusted CA certificates from the default file location
169 Do not load the trusted CA certificates from the default directory location
171 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
172 B<explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
173 B<-inhibit_map>, B<-issuer_checks>, B<-partial_chain>, B<-policy>,
174 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
175 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-no_alt_chains>,
176 B<-use_deltas>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
177 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
179 Set various certificate chain validation options. See the
180 L<verify(1)> manual page for details.
184 reconnects to the same server 5 times using the same session ID, this can
185 be used as a test that session caching is working.
189 pauses 1 second between each read and write call.
193 display the whole server certificate chain: normally only the server
194 certificate itself is displayed.
198 print session information when the program exits. This will always attempt
199 to print out information even if the connection fails. Normally information
200 will only be printed out once if the connection succeeds. This option is useful
201 because the cipher in use may be renegotiated or the connection may fail
202 because a client certificate is required or is requested only after an
203 attempt is made to access a certain URL. Note: the output produced by this
204 option is not always accurate because a connection might never have been
209 prints out the SSL session states.
213 print extensive debugging information including a hex dump of all traffic.
217 show all protocol messages with hex dump.
221 show verbose trace output of protocol messages. OpenSSL needs to be compiled
222 with B<enable-ssl-trace> for this option to work.
226 file to send output of B<-msg> or B<-trace> to, default standard output.
230 tests non-blocking I/O
234 turns on non-blocking I/O
238 this option translated a line feed from the terminal into CR+LF as required
243 inhibit shutting down the connection when end of file is reached in the
248 inhibit printing of session and certificate information. This implicitly
249 turns on B<-ign_eof> as well.
253 shut down the connection when end of file is reached in the input.
254 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
256 =item B<-psk_identity identity>
258 Use the PSK identity B<identity> when using a PSK cipher suite.
262 Use the PSK key B<key> when using a PSK cipher suite. The key is
263 given as a hexadecimal number without leading 0x, for example -psk
266 =item B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>
268 these options disable the use of certain SSL or TLS protocols. By default
269 the initial handshake uses a method which should be compatible with all
270 servers and permit them to use SSL v3 or TLS as appropriate.
272 Unfortunately there are still ancient and broken servers in use which
273 cannot handle this technique and will fail to connect. Some servers only
274 work if TLS is turned off.
276 =item B<-fallback_scsv>
278 Send TLS_FALLBACK_SCSV in the ClientHello.
282 there are several known bug in SSL and TLS implementations. Adding this
283 option enables various workarounds.
287 only provide a brief summary of connection parameters instead of the
288 normal verbose output.
290 =item B<-cipher cipherlist>
292 this allows the cipher list sent by the client to be modified. Although
293 the server determines which cipher suite is used it should take the first
294 supported cipher in the list sent by the client. See the B<ciphers>
295 command for more information.
297 =item B<-starttls protocol>
299 send the protocol-specific message(s) to switch to TLS for communication.
300 B<protocol> is a keyword for the intended protocol. Currently, the only
301 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp",
304 =item B<-xmpphost hostname>
306 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
307 specifies the host for the "to" attribute of the stream element.
308 If this option is not specified, then the host specified with "-connect"
311 =item B<-tlsextdebug>
313 print out a hex dump of any TLS extensions received from the server.
317 disable RFC4507bis session ticket support.
319 =item B<-sess_out filename>
321 output SSL session to B<filename>
323 =item B<-sess_in sess.pem>
325 load SSL session from B<filename>. The client will attempt to resume a
326 connection from this session.
330 specifying an engine (by its unique B<id> string) will cause B<s_client>
331 to attempt to obtain a functional reference to the specified engine,
332 thus initialising it if needed. The engine will then be set as the default
333 for all available algorithms.
335 =item B<-rand file(s)>
337 a file or files containing random data used to seed the random number
338 generator, or an EGD socket (see L<RAND_egd(3)>).
339 Multiple files can be specified separated by a OS-dependent character.
340 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
343 =item B<-serverinfo types>
345 a list of comma-separated TLS Extension Types (numbers between 0 and
346 65535). Each type will be sent as an empty ClientHello TLS Extension.
347 The server's response (if any) will be encoded and displayed as a PEM
352 sends a certificate status request to the server (OCSP stapling). The server
353 response (if any) is printed out.
355 =item B<-nextprotoneg protocols>
357 enable Next Protocol Negotiation TLS extension and provide a list of
358 comma-separated protocol names that the client should advertise
359 support for. The list should contain most wanted protocols first.
360 Protocol names are printable ASCII strings, for example "http/1.1" or
362 Empty list of protocols is treated specially and will cause the client to
363 advertise support for the TLS extension but disconnect just after
364 receiving ServerHello with a list of server supported protocols.
368 =head1 CONNECTED COMMANDS
370 If a connection is established with an SSL server then any data received
371 from the server is displayed and any key presses will be sent to the
372 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
373 have been given), the session will be renegotiated if the line begins with an
374 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
375 connection will be closed down.
379 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
382 openssl s_client -connect servername:443
384 would typically be used (https uses port 443). If the connection succeeds
385 then an HTTP command can be given such as "GET /" to retrieve a web page.
387 If the handshake fails then there are several possible causes, if it is
388 nothing obvious like no client certificate then the B<-bugs>,
389 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
390 in case it is a buggy server. In particular you should play with these
391 options B<before> submitting a bug report to an OpenSSL mailing list.
393 A frequent problem when attempting to get client certificates working
394 is that a web client complains it has no certificates or gives an empty
395 list to choose from. This is normally because the server is not sending
396 the clients certificate authority in its "acceptable CA list" when it
397 requests a certificate. By using B<s_client> the CA list can be viewed
398 and checked. However some servers only request client authentication
399 after a specific URL is requested. To obtain the list in this case it
400 is necessary to use the B<-prexit> option and send an HTTP request
401 for an appropriate page.
403 If a certificate is specified on the command line using the B<-cert>
404 option it will not be used unless the server specifically requests
405 a client certificate. Therefor merely including a client certificate
406 on the command line is no guarantee that the certificate works.
408 If there are problems verifying a server certificate then the
409 B<-showcerts> option can be used to show the whole chain.
411 The B<s_client> utility is a test tool and is designed to continue the
412 handshake after any certificate verification errors. As a result it will
413 accept any certificate chain (trusted or not) sent by the peer. None test
414 applications should B<not> do this as it makes them vulnerable to a MITM
415 attack. This behaviour can be changed by with the B<-verify_return_error>
416 option: any verify errors are then returned aborting the handshake.
420 Because this program has a lot of options and also because some of
421 the techniques used are rather old, the C source of s_client is rather
422 hard to read and not a model of how things should be done. A typical
423 SSL client program would be much simpler.
425 The B<-prexit> option is a bit of a hack. We should really report
426 information whenever a session is renegotiated.
430 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
434 The -no_alt_chains options was first added to OpenSSL 1.1.0.