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>]
73 [B<-cipher cipherlist>]
75 [B<-starttls protocol>]
76 [B<-xmpphost hostname>]
80 [B<-sess_out filename>]
81 [B<-sess_in filename>]
83 [B<-serverinfo types>]
85 [B<-nextprotoneg protocols>]
89 The B<s_client> command implements a generic SSL/TLS client which connects
90 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
95 In addition to the options below the B<s_client> utility also supports the
96 common and client only options documented in the
97 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
102 =item B<-connect host:port>
104 This specifies the host and optional port to connect to. If not specified
105 then an attempt is made to connect to the local host on port 4433.
107 =item B<-proxy host:port>
109 When used with the B<-connect> flag, the program uses the host and port
110 specified with this flag and issues an HTTP CONNECT command to connect
111 to the desired server.
113 =item B<-servername name>
115 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
117 =item B<-cert certname>
119 The certificate to use, if one is requested by the server. The default is
120 not to use a certificate.
122 =item B<-certform format>
124 The certificate format to use: DER or PEM. PEM is the default.
126 =item B<-key keyfile>
128 The private key to use. If not specified then the certificate file will
131 =item B<-keyform format>
133 The private format to use: DER or PEM. PEM is the default.
137 the private key password source. For more information about the format of B<arg>
138 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
140 =item B<-verify depth>
142 The verify depth to use. This specifies the maximum length of the
143 server certificate chain and turns on server certificate verification.
144 Currently the verify operation continues after errors so all the problems
145 with a certificate chain can be seen. As a side effect the connection
146 will never fail due to a server certificate verify failure.
148 =item B<-verify_return_error>
150 Return verification errors instead of continuing. This will typically
151 abort the handshake with a fatal error.
153 =item B<-CApath directory>
155 The directory to use for server certificate verification. This directory
156 must be in "hash format", see B<verify> for more information. These are
157 also used when building the client certificate chain.
159 =item B<-CAfile file>
161 A file containing trusted certificates to use during server authentication
162 and to use when attempting to build the client certificate chain.
166 Do not load the trusted CA certificates from the default file location
170 Do not load the trusted CA certificates from the default directory location
172 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
173 B<explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
174 B<-inhibit_map>, B<-issuer_checks>, B<-partial_chain>, B<-policy>,
175 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
176 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-no_alt_chains>,
177 B<-use_deltas>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
178 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
180 Set various certificate chain validation options. See the
181 L<verify(1)> manual page for details.
185 reconnects to the same server 5 times using the same session ID, this can
186 be used as a test that session caching is working.
190 pauses 1 second between each read and write call.
194 display the whole server certificate chain: normally only the server
195 certificate itself is displayed.
199 print session information when the program exits. This will always attempt
200 to print out information even if the connection fails. Normally information
201 will only be printed out once if the connection succeeds. This option is useful
202 because the cipher in use may be renegotiated or the connection may fail
203 because a client certificate is required or is requested only after an
204 attempt is made to access a certain URL. Note: the output produced by this
205 option is not always accurate because a connection might never have been
210 prints out the SSL session states.
214 print extensive debugging information including a hex dump of all traffic.
218 show all protocol messages with hex dump.
222 show verbose trace output of protocol messages. OpenSSL needs to be compiled
223 with B<enable-ssl-trace> for this option to work.
227 file to send output of B<-msg> or B<-trace> to, default standard output.
231 tests non-blocking I/O
235 turns on non-blocking I/O
239 this option translated a line feed from the terminal into CR+LF as required
244 inhibit shutting down the connection when end of file is reached in the
249 inhibit printing of session and certificate information. This implicitly
250 turns on B<-ign_eof> as well.
254 shut down the connection when end of file is reached in the input.
255 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
257 =item B<-psk_identity identity>
259 Use the PSK identity B<identity> when using a PSK cipher suite.
263 Use the PSK key B<key> when using a PSK cipher suite. The key is
264 given as a hexadecimal number without leading 0x, for example -psk
267 =item B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>
269 these options disable the use of certain SSL or TLS protocols. By default
270 the initial handshake uses a method which should be compatible with all
271 servers and permit them to use SSL v3 or TLS as appropriate.
273 Unfortunately there are still ancient and broken servers in use which
274 cannot handle this technique and will fail to connect. Some servers only
275 work if TLS is turned off.
277 =item B<-fallback_scsv>
279 Send TLS_FALLBACK_SCSV in the ClientHello.
283 switch on asynchronous mode. Cryptographic operations will be performed
284 asynchronously. This will only have an effect if an asynchronous capable engine
285 is also used via the B<-engine> option. For test purposes the dummy async engine
286 (dasync) can be used (if available).
290 there are several known bug in SSL and TLS implementations. Adding this
291 option enables various workarounds.
295 only provide a brief summary of connection parameters instead of the
296 normal verbose output.
298 =item B<-cipher cipherlist>
300 this allows the cipher list sent by the client to be modified. Although
301 the server determines which cipher suite is used it should take the first
302 supported cipher in the list sent by the client. See the B<ciphers>
303 command for more information.
305 =item B<-starttls protocol>
307 send the protocol-specific message(s) to switch to TLS for communication.
308 B<protocol> is a keyword for the intended protocol. Currently, the only
309 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
312 =item B<-xmpphost hostname>
314 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
315 specifies the host for the "to" attribute of the stream element.
316 If this option is not specified, then the host specified with "-connect"
319 =item B<-tlsextdebug>
321 print out a hex dump of any TLS extensions received from the server.
325 disable RFC4507bis session ticket support.
327 =item B<-sess_out filename>
329 output SSL session to B<filename>
331 =item B<-sess_in sess.pem>
333 load SSL session from B<filename>. The client will attempt to resume a
334 connection from this session.
338 specifying an engine (by its unique B<id> string) will cause B<s_client>
339 to attempt to obtain a functional reference to the specified engine,
340 thus initialising it if needed. The engine will then be set as the default
341 for all available algorithms.
343 =item B<-rand file(s)>
345 a file or files containing random data used to seed the random number
346 generator, or an EGD socket (see L<RAND_egd(3)>).
347 Multiple files can be specified separated by a OS-dependent character.
348 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
351 =item B<-serverinfo types>
353 a list of comma-separated TLS Extension Types (numbers between 0 and
354 65535). Each type will be sent as an empty ClientHello TLS Extension.
355 The server's response (if any) will be encoded and displayed as a PEM
360 sends a certificate status request to the server (OCSP stapling). The server
361 response (if any) is printed out.
363 =item B<-nextprotoneg protocols>
365 enable Next Protocol Negotiation TLS extension and provide a list of
366 comma-separated protocol names that the client should advertise
367 support for. The list should contain most wanted protocols first.
368 Protocol names are printable ASCII strings, for example "http/1.1" or
370 Empty list of protocols is treated specially and will cause the client to
371 advertise support for the TLS extension but disconnect just after
372 receiving ServerHello with a list of server supported protocols.
376 =head1 CONNECTED COMMANDS
378 If a connection is established with an SSL server then any data received
379 from the server is displayed and any key presses will be sent to the
380 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
381 have been given), the session will be renegotiated if the line begins with an
382 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
383 connection will be closed down.
387 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
390 openssl s_client -connect servername:443
392 would typically be used (https uses port 443). If the connection succeeds
393 then an HTTP command can be given such as "GET /" to retrieve a web page.
395 If the handshake fails then there are several possible causes, if it is
396 nothing obvious like no client certificate then the B<-bugs>,
397 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
398 in case it is a buggy server. In particular you should play with these
399 options B<before> submitting a bug report to an OpenSSL mailing list.
401 A frequent problem when attempting to get client certificates working
402 is that a web client complains it has no certificates or gives an empty
403 list to choose from. This is normally because the server is not sending
404 the clients certificate authority in its "acceptable CA list" when it
405 requests a certificate. By using B<s_client> the CA list can be viewed
406 and checked. However some servers only request client authentication
407 after a specific URL is requested. To obtain the list in this case it
408 is necessary to use the B<-prexit> option and send an HTTP request
409 for an appropriate page.
411 If a certificate is specified on the command line using the B<-cert>
412 option it will not be used unless the server specifically requests
413 a client certificate. Therefor merely including a client certificate
414 on the command line is no guarantee that the certificate works.
416 If there are problems verifying a server certificate then the
417 B<-showcerts> option can be used to show the whole chain.
419 The B<s_client> utility is a test tool and is designed to continue the
420 handshake after any certificate verification errors. As a result it will
421 accept any certificate chain (trusted or not) sent by the peer. None test
422 applications should B<not> do this as it makes them vulnerable to a MITM
423 attack. This behaviour can be changed by with the B<-verify_return_error>
424 option: any verify errors are then returned aborting the handshake.
428 Because this program has a lot of options and also because some of
429 the techniques used are rather old, the C source of s_client is rather
430 hard to read and not a model of how things should be done. A typical
431 SSL client program would be much simpler.
433 The B<-prexit> option is a bit of a hack. We should really report
434 information whenever a session is renegotiated.
438 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
442 The -no_alt_chains options was first added to OpenSSL 1.1.0.