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>]
23 [B<-attime timestamp>]
44 [B<-verify_depth num>]
45 [B<-verify_email email>]
46 [B<-verify_hostname hostname>]
48 [B<-verify_name name>]
70 [B<-cipher cipherlist>]
72 [B<-starttls protocol>]
73 [B<-xmpphost hostname>]
77 [B<-sess_out filename>]
78 [B<-sess_in filename>]
80 [B<-serverinfo types>]
82 [B<-nextprotoneg protocols>]
86 The B<s_client> command implements a generic SSL/TLS client which connects
87 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
92 In addition to the options below the B<s_client> utility also supports the
93 common and client only options documented in the
94 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
99 =item B<-connect host:port>
101 This specifies the host and optional port to connect to. If not specified
102 then an attempt is made to connect to the local host on port 4433.
104 =item B<-proxy host:port>
106 When used with the B<-connect> flag, the program uses the host and port
107 specified with this flag and issues an HTTP CONNECT command to connect
108 to the desired server.
110 =item B<-servername name>
112 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
114 =item B<-cert certname>
116 The certificate to use, if one is requested by the server. The default is
117 not to use a certificate.
119 =item B<-certform format>
121 The certificate format to use: DER or PEM. PEM is the default.
123 =item B<-key keyfile>
125 The private key to use. If not specified then the certificate file will
128 =item B<-keyform format>
130 The private format to use: DER or PEM. PEM is the default.
134 the private key password source. For more information about the format of B<arg>
135 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
137 =item B<-verify depth>
139 The verify depth to use. This specifies the maximum length of the
140 server certificate chain and turns on server certificate verification.
141 Currently the verify operation continues after errors so all the problems
142 with a certificate chain can be seen. As a side effect the connection
143 will never fail due to a server certificate verify failure.
145 =item B<-verify_return_error>
147 Return verification errors instead of continuing. This will typically
148 abort the handshake with a fatal error.
150 =item B<-CApath directory>
152 The directory to use for server certificate verification. This directory
153 must be in "hash format", see B<verify> for more information. These are
154 also used when building the client certificate chain.
156 =item B<-CAfile file>
158 A file containing trusted certificates to use during server authentication
159 and to use when attempting to build the client certificate chain.
161 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
162 B<explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
163 B<-inhibit_map>, B<-issuer_checks>, B<-partial_chain>, B<-policy>,
164 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
165 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-no_alt_chains>,
166 B<-use_deltas>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
167 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
169 Set various certificate chain validation options. See the
170 L<B<verify>|verify(1)> manual page for details.
174 reconnects to the same server 5 times using the same session ID, this can
175 be used as a test that session caching is working.
179 pauses 1 second between each read and write call.
183 display the whole server certificate chain: normally only the server
184 certificate itself is displayed.
188 print session information when the program exits. This will always attempt
189 to print out information even if the connection fails. Normally information
190 will only be printed out once if the connection succeeds. This option is useful
191 because the cipher in use may be renegotiated or the connection may fail
192 because a client certificate is required or is requested only after an
193 attempt is made to access a certain URL. Note: the output produced by this
194 option is not always accurate because a connection might never have been
199 prints out the SSL session states.
203 print extensive debugging information including a hex dump of all traffic.
207 show all protocol messages with hex dump.
211 show verbose trace output of protocol messages. OpenSSL needs to be compiled
212 with B<enable-ssl-trace> for this option to work.
216 file to send output of B<-msg> or B<-trace> to, default standard output.
220 tests non-blocking I/O
224 turns on non-blocking I/O
228 this option translated a line feed from the terminal into CR+LF as required
233 inhibit shutting down the connection when end of file is reached in the
238 inhibit printing of session and certificate information. This implicitly
239 turns on B<-ign_eof> as well.
243 shut down the connection when end of file is reached in the input.
244 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
246 =item B<-psk_identity identity>
248 Use the PSK identity B<identity> when using a PSK cipher suite.
252 Use the PSK key B<key> when using a PSK cipher suite. The key is
253 given as a hexadecimal number without leading 0x, for example -psk
256 =item B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>
258 these options disable the use of certain SSL or TLS protocols. By default
259 the initial handshake uses a method which should be compatible with all
260 servers and permit them to use SSL v3 or TLS as appropriate.
262 Unfortunately there are still ancient and broken servers in use which
263 cannot handle this technique and will fail to connect. Some servers only
264 work if TLS is turned off.
266 =item B<-fallback_scsv>
268 Send TLS_FALLBACK_SCSV in the ClientHello.
272 there are several known bug in SSL and TLS implementations. Adding this
273 option enables various workarounds.
277 only provide a brief summary of connection parameters instead of the
278 normal verbose output.
280 =item B<-cipher cipherlist>
282 this allows the cipher list sent by the client to be modified. Although
283 the server determines which cipher suite is used it should take the first
284 supported cipher in the list sent by the client. See the B<ciphers>
285 command for more information.
287 =item B<-starttls protocol>
289 send the protocol-specific message(s) to switch to TLS for communication.
290 B<protocol> is a keyword for the intended protocol. Currently, the only
291 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp",
294 =item B<-xmpphost hostname>
296 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
297 specifies the host for the "to" attribute of the stream element.
298 If this option is not specified, then the host specified with "-connect"
301 =item B<-tlsextdebug>
303 print out a hex dump of any TLS extensions received from the server.
307 disable RFC4507bis session ticket support.
309 =item B<-sess_out filename>
311 output SSL session to B<filename>
313 =item B<-sess_in sess.pem>
315 load SSL session from B<filename>. The client will attempt to resume a
316 connection from this session.
320 specifying an engine (by its unique B<id> string) will cause B<s_client>
321 to attempt to obtain a functional reference to the specified engine,
322 thus initialising it if needed. The engine will then be set as the default
323 for all available algorithms.
325 =item B<-rand file(s)>
327 a file or files containing random data used to seed the random number
328 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
329 Multiple files can be specified separated by a OS-dependent character.
330 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
333 =item B<-serverinfo types>
335 a list of comma-separated TLS Extension Types (numbers between 0 and
336 65535). Each type will be sent as an empty ClientHello TLS Extension.
337 The server's response (if any) will be encoded and displayed as a PEM
342 sends a certificate status request to the server (OCSP stapling). The server
343 response (if any) is printed out.
345 =item B<-nextprotoneg protocols>
347 enable Next Protocol Negotiation TLS extension and provide a list of
348 comma-separated protocol names that the client should advertise
349 support for. The list should contain most wanted protocols first.
350 Protocol names are printable ASCII strings, for example "http/1.1" or
352 Empty list of protocols is treated specially and will cause the client to
353 advertise support for the TLS extension but disconnect just after
354 receiving ServerHello with a list of server supported protocols.
358 =head1 CONNECTED COMMANDS
360 If a connection is established with an SSL server then any data received
361 from the server is displayed and any key presses will be sent to the
362 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
363 have been given), the session will be renegotiated if the line begins with an
364 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
365 connection will be closed down.
369 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
372 openssl s_client -connect servername:443
374 would typically be used (https uses port 443). If the connection succeeds
375 then an HTTP command can be given such as "GET /" to retrieve a web page.
377 If the handshake fails then there are several possible causes, if it is
378 nothing obvious like no client certificate then the B<-bugs>,
379 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
380 in case it is a buggy server. In particular you should play with these
381 options B<before> submitting a bug report to an OpenSSL mailing list.
383 A frequent problem when attempting to get client certificates working
384 is that a web client complains it has no certificates or gives an empty
385 list to choose from. This is normally because the server is not sending
386 the clients certificate authority in its "acceptable CA list" when it
387 requests a certificate. By using B<s_client> the CA list can be viewed
388 and checked. However some servers only request client authentication
389 after a specific URL is requested. To obtain the list in this case it
390 is necessary to use the B<-prexit> option and send an HTTP request
391 for an appropriate page.
393 If a certificate is specified on the command line using the B<-cert>
394 option it will not be used unless the server specifically requests
395 a client certificate. Therefor merely including a client certificate
396 on the command line is no guarantee that the certificate works.
398 If there are problems verifying a server certificate then the
399 B<-showcerts> option can be used to show the whole chain.
401 The B<s_client> utility is a test tool and is designed to continue the
402 handshake after any certificate verification errors. As a result it will
403 accept any certificate chain (trusted or not) sent by the peer. None test
404 applications should B<not> do this as it makes them vulnerable to a MITM
405 attack. This behaviour can be changed by with the B<-verify_return_error>
406 option: any verify errors are then returned aborting the handshake.
410 Because this program has a lot of options and also because some of
411 the techniques used are rather old, the C source of s_client is rather
412 hard to read and not a model of how things should be done. A typical
413 SSL client program would be much simpler.
415 The B<-prexit> option is a bit of a hack. We should really report
416 information whenever a session is renegotiated.
420 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>
424 The -no_alt_chains options was first added to OpenSSL 1.1.0.