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>]
69 [B<-cipher cipherlist>]
71 [B<-starttls protocol>]
72 [B<-xmpphost hostname>]
76 [B<-sess_out filename>]
77 [B<-sess_in filename>]
79 [B<-serverinfo types>]
81 [B<-nextprotoneg protocols>]
85 The B<s_client> command implements a generic SSL/TLS client which connects
86 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
91 In addition to the options below the B<s_client> utility also supports the
92 common and client only options documented in the
93 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
98 =item B<-connect host:port>
100 This specifies the host and optional port to connect to. If not specified
101 then an attempt is made to connect to the local host on port 4433.
103 =item B<-servername name>
105 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
107 =item B<-cert certname>
109 The certificate to use, if one is requested by the server. The default is
110 not to use a certificate.
112 =item B<-certform format>
114 The certificate format to use: DER or PEM. PEM is the default.
116 =item B<-key keyfile>
118 The private key to use. If not specified then the certificate file will
121 =item B<-keyform format>
123 The private format to use: DER or PEM. PEM is the default.
127 the private key password source. For more information about the format of B<arg>
128 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
130 =item B<-verify depth>
132 The verify depth to use. This specifies the maximum length of the
133 server certificate chain and turns on server certificate verification.
134 Currently the verify operation continues after errors so all the problems
135 with a certificate chain can be seen. As a side effect the connection
136 will never fail due to a server certificate verify failure.
138 =item B<-verify_return_error>
140 Return verification errors instead of continuing. This will typically
141 abort the handshake with a fatal error.
143 =item B<-CApath directory>
145 The directory to use for server certificate verification. This directory
146 must be in "hash format", see B<verify> for more information. These are
147 also used when building the client certificate chain.
149 =item B<-CAfile file>
151 A file containing trusted certificates to use during server authentication
152 and to use when attempting to build the client certificate chain.
154 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
155 B<explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
156 B<-inhibit_map>, B<-issuer_checks>, B<-partial_chain>, B<-policy>,
157 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
158 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
159 B<-verify_depth>, B<-verify_email>, B<-verify_hostname>, B<-verify_ip>,
160 B<-verify_name>, B<-x509_strict>
162 Set various certificate chain valiadition options. See the
163 L<B<verify>|verify(1)> manual page for details.
167 reconnects to the same server 5 times using the same session ID, this can
168 be used as a test that session caching is working.
172 pauses 1 second between each read and write call.
176 display the whole server certificate chain: normally only the server
177 certificate itself is displayed.
181 print session information when the program exits. This will always attempt
182 to print out information even if the connection fails. Normally information
183 will only be printed out once if the connection succeeds. This option is useful
184 because the cipher in use may be renegotiated or the connection may fail
185 because a client certificate is required or is requested only after an
186 attempt is made to access a certain URL. Note: the output produced by this
187 option is not always accurate because a connection might never have been
192 prints out the SSL session states.
196 print extensive debugging information including a hex dump of all traffic.
200 show all protocol messages with hex dump.
204 show verbose trace output of protocol messages. OpenSSL needs to be compiled
205 with B<enable-ssl-trace> for this option to work.
209 file to send output of B<-msg> or B<-trace> to, default standard output.
213 tests non-blocking I/O
217 turns on non-blocking I/O
221 this option translated a line feed from the terminal into CR+LF as required
226 inhibit shutting down the connection when end of file is reached in the
231 inhibit printing of session and certificate information. This implicitly
232 turns on B<-ign_eof> as well.
236 shut down the connection when end of file is reached in the input.
237 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
239 =item B<-psk_identity identity>
241 Use the PSK identity B<identity> when using a PSK cipher suite.
245 Use the PSK key B<key> when using a PSK cipher suite. The key is
246 given as a hexadecimal number without leading 0x, for example -psk
249 =item B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>
251 these options disable the use of certain SSL or TLS protocols. By default
252 the initial handshake uses a method which should be compatible with all
253 servers and permit them to use SSL v3 or TLS as appropriate.
255 Unfortunately there are still ancient and broken servers in use which
256 cannot handle this technique and will fail to connect. Some servers only
257 work if TLS is turned off.
259 =item B<-fallback_scsv>
261 Send TLS_FALLBACK_SCSV in the ClientHello.
265 there are several known bug in SSL and TLS implementations. Adding this
266 option enables various workarounds.
270 only provide a brief summary of connection parameters instead of the
271 normal verbose output.
273 =item B<-cipher cipherlist>
275 this allows the cipher list sent by the client to be modified. Although
276 the server determines which cipher suite is used it should take the first
277 supported cipher in the list sent by the client. See the B<ciphers>
278 command for more information.
280 =item B<-starttls protocol>
282 send the protocol-specific message(s) to switch to TLS for communication.
283 B<protocol> is a keyword for the intended protocol. Currently, the only
284 supported keywords are "smtp", "pop3", "imap", "ftp" and "xmpp".
286 =item B<-xmpphost hostname>
288 This option, when used with "-starttls xmpp", specifies the host for the
289 "to" attribute of the stream element.
290 If this option is not specified, then the host specified with "-connect"
293 =item B<-tlsextdebug>
295 print out a hex dump of any TLS extensions received from the server.
299 disable RFC4507bis session ticket support.
301 =item B<-sess_out filename>
303 output SSL session to B<filename>
305 =item B<-sess_in sess.pem>
307 load SSL session from B<filename>. The client will attempt to resume a
308 connection from this session.
312 specifying an engine (by its unique B<id> string) will cause B<s_client>
313 to attempt to obtain a functional reference to the specified engine,
314 thus initialising it if needed. The engine will then be set as the default
315 for all available algorithms.
317 =item B<-rand file(s)>
319 a file or files containing random data used to seed the random number
320 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
321 Multiple files can be specified separated by a OS-dependent character.
322 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
325 =item B<-serverinfo types>
327 a list of comma-separated TLS Extension Types (numbers between 0 and
328 65535). Each type will be sent as an empty ClientHello TLS Extension.
329 The server's response (if any) will be encoded and displayed as a PEM
334 sends a certificate status request to the server (OCSP stapling). The server
335 response (if any) is printed out.
337 =item B<-nextprotoneg protocols>
339 enable Next Protocol Negotiation TLS extension and provide a list of
340 comma-separated protocol names that the client should advertise
341 support for. The list should contain most wanted protocols first.
342 Protocol names are printable ASCII strings, for example "http/1.1" or
344 Empty list of protocols is treated specially and will cause the client to
345 advertise support for the TLS extension but disconnect just after
346 reciving ServerHello with a list of server supported protocols.
350 =head1 CONNECTED COMMANDS
352 If a connection is established with an SSL server then any data received
353 from the server is displayed and any key presses will be sent to the
354 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
355 have been given), the session will be renegotiated if the line begins with an
356 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
357 connection will be closed down.
361 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
364 openssl s_client -connect servername:443
366 would typically be used (https uses port 443). If the connection succeeds
367 then an HTTP command can be given such as "GET /" to retrieve a web page.
369 If the handshake fails then there are several possible causes, if it is
370 nothing obvious like no client certificate then the B<-bugs>,
371 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
372 in case it is a buggy server. In particular you should play with these
373 options B<before> submitting a bug report to an OpenSSL mailing list.
375 A frequent problem when attempting to get client certificates working
376 is that a web client complains it has no certificates or gives an empty
377 list to choose from. This is normally because the server is not sending
378 the clients certificate authority in its "acceptable CA list" when it
379 requests a certificate. By using B<s_client> the CA list can be viewed
380 and checked. However some servers only request client authentication
381 after a specific URL is requested. To obtain the list in this case it
382 is necessary to use the B<-prexit> option and send an HTTP request
383 for an appropriate page.
385 If a certificate is specified on the command line using the B<-cert>
386 option it will not be used unless the server specifically requests
387 a client certificate. Therefor merely including a client certificate
388 on the command line is no guarantee that the certificate works.
390 If there are problems verifying a server certificate then the
391 B<-showcerts> option can be used to show the whole chain.
393 The B<s_client> utility is a test tool and is designed to continue the
394 handshake after any certificate verification errors. As a result it will
395 accept any certificate chain (trusted or not) sent by the peer. None test
396 applications should B<not> do this as it makes them vulnerable to a MITM
397 attack. This behaviour can be changed by with the B<-verify_return_error>
398 option: any verify errors are then returned aborting the handshake.
402 Because this program has a lot of options and also because some of
403 the techniques used are rather old, the C source of s_client is rather
404 hard to read and not a model of how things should be done. A typical
405 SSL client program would be much simpler.
407 The B<-prexit> option is a bit of a hack. We should really report
408 information whenever a session is renegotiated.
412 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>