6 s_client - SSL/TLS client program
10 B<openssl> B<s_client>
12 [B<-connect host:port>]
16 [B<-verify_return_error>]
18 [B<-certform DER|PEM>]
22 [B<-CApath directory>]
26 [B<-dane_tlsa_domain domain>]
27 [B<-dane_tlsa_rrdata rrdata>]
28 [B<-attime timestamp>]
48 [B<-verify_depth num>]
49 [B<-verify_email email>]
50 [B<-verify_hostname hostname>]
52 [B<-verify_name name>]
76 [B<-cipher cipherlist>]
78 [B<-starttls protocol>]
79 [B<-xmpphost hostname>]
83 [B<-sess_out filename>]
84 [B<-sess_in filename>]
86 [B<-serverinfo types>]
88 [B<-nextprotoneg protocols>]
92 The B<s_client> command implements a generic SSL/TLS client which connects
93 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
98 In addition to the options below the B<s_client> utility also supports the
99 common and client only options documented in the
100 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
107 Print out a usage message.
109 =item B<-connect host:port>
111 This specifies the host and optional port to connect to. If not specified
112 then an attempt is made to connect to the local host on port 4433.
114 =item B<-proxy host:port>
116 When used with the B<-connect> flag, the program uses the host and port
117 specified with this flag and issues an HTTP CONNECT command to connect
118 to the desired server.
120 =item B<-servername name>
122 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
124 =item B<-cert certname>
126 The certificate to use, if one is requested by the server. The default is
127 not to use a certificate.
129 =item B<-certform format>
131 The certificate format to use: DER or PEM. PEM is the default.
133 =item B<-key keyfile>
135 The private key to use. If not specified then the certificate file will
138 =item B<-keyform format>
140 The private format to use: DER or PEM. PEM is the default.
144 the private key password source. For more information about the format of B<arg>
145 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
147 =item B<-verify depth>
149 The verify depth to use. This specifies the maximum length of the
150 server certificate chain and turns on server certificate verification.
151 Currently the verify operation continues after errors so all the problems
152 with a certificate chain can be seen. As a side effect the connection
153 will never fail due to a server certificate verify failure.
155 =item B<-verify_return_error>
157 Return verification errors instead of continuing. This will typically
158 abort the handshake with a fatal error.
160 =item B<-CApath directory>
162 The directory to use for server certificate verification. This directory
163 must be in "hash format", see B<verify> for more information. These are
164 also used when building the client certificate chain.
166 =item B<-CAfile file>
168 A file containing trusted certificates to use during server authentication
169 and to use when attempting to build the client certificate chain.
173 Do not load the trusted CA certificates from the default file location
177 Do not load the trusted CA certificates from the default directory location
179 =item B<-dane_tlsa_domain domain>
181 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
182 TLSA base domain which becomes the default SNI hint and the primary
183 reference identifier for hostname checks. This must be used in
184 combination with at least one instance of the B<-dane_tlsa_rrdata>
187 When DANE authentication succeeds, the diagnostic output will include
188 the lowest (closest to 0) depth at which a TLSA record authenticated
189 a chain certificate. When that TLSA record is a "2 1 0" trust
190 anchor public key that signed (rather than matched) the top-most
191 certificate of the chain, the result is reported as "TA public key
192 verified". Otherwise, either the TLSA record "matched TA certificate"
193 at a positive depth or else "matched EE certificate" at depth 0.
195 =item B<-dane_tlsa_rrdata rrdata>
197 Use one or more times to specify the RRDATA fields of the DANE TLSA
198 RRset associated with the target service. The B<rrdata> value is
199 specied in "presentation form", that is four whitespace separated
200 fields that specify the usage, selector, matching type and associated
201 data, with the last of these encoded in hexadecimal. Optional
202 whitespace is ignored in the associated data field. For example:
204 $ openssl s_client -brief -starttls smtp \
205 -connect smtp.example.com:25 \
206 -dane_tlsa_domain smtp.example.com \
207 -dane_tlsa_rrdata "2 1 1
208 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
209 -dane_tlsa_rrdata "2 1 1
210 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
213 Verified peername: smtp.example.com
214 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
217 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
218 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
219 B<-inhibit_map>, B<-no_alt_chains>, B<-partial_chain>, B<-policy>,
220 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
221 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
222 B<-verify_depth>, B<-verify_email>, B<-verify_hostname>, B<-verify_ip>,
223 B<-verify_name>, B<-x509_strict>
225 Set various certificate chain validation options. See the
226 L<verify(1)> manual page for details.
230 reconnects to the same server 5 times using the same session ID, this can
231 be used as a test that session caching is working.
235 display the whole server certificate chain: normally only the server
236 certificate itself is displayed.
240 print session information when the program exits. This will always attempt
241 to print out information even if the connection fails. Normally information
242 will only be printed out once if the connection succeeds. This option is useful
243 because the cipher in use may be renegotiated or the connection may fail
244 because a client certificate is required or is requested only after an
245 attempt is made to access a certain URL. Note: the output produced by this
246 option is not always accurate because a connection might never have been
251 prints out the SSL session states.
255 print extensive debugging information including a hex dump of all traffic.
259 show all protocol messages with hex dump.
263 show verbose trace output of protocol messages. OpenSSL needs to be compiled
264 with B<enable-ssl-trace> for this option to work.
268 file to send output of B<-msg> or B<-trace> to, default standard output.
272 tests non-blocking I/O
276 turns on non-blocking I/O
280 this option translated a line feed from the terminal into CR+LF as required
285 inhibit shutting down the connection when end of file is reached in the
290 inhibit printing of session and certificate information. This implicitly
291 turns on B<-ign_eof> as well.
295 shut down the connection when end of file is reached in the input.
296 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
298 =item B<-psk_identity identity>
300 Use the PSK identity B<identity> when using a PSK cipher suite.
304 Use the PSK key B<key> when using a PSK cipher suite. The key is
305 given as a hexadecimal number without leading 0x, for example -psk
308 =item B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>
310 these options disable the use of certain SSL or TLS protocols. By default
311 the initial handshake uses a method which should be compatible with all
312 servers and permit them to use SSL v3 or TLS as appropriate.
314 Unfortunately there are still ancient and broken servers in use which
315 cannot handle this technique and will fail to connect. Some servers only
316 work if TLS is turned off.
318 =item B<-fallback_scsv>
320 Send TLS_FALLBACK_SCSV in the ClientHello.
324 switch on asynchronous mode. Cryptographic operations will be performed
325 asynchronously. This will only have an effect if an asynchronous capable engine
326 is also used via the B<-engine> option. For test purposes the dummy async engine
327 (dasync) can be used (if available).
331 there are several known bug in SSL and TLS implementations. Adding this
332 option enables various workarounds.
336 Enables support for SSL/TLS compression.
337 This option was introduced in OpenSSL 1.1.0.
338 TLS compression is not recommended and is off by default as of
343 Disables support for SSL/TLS compression.
344 TLS compression is not recommended and is off by default as of
349 only provide a brief summary of connection parameters instead of the
350 normal verbose output.
352 =item B<-cipher cipherlist>
354 this allows the cipher list sent by the client to be modified. Although
355 the server determines which cipher suite is used it should take the first
356 supported cipher in the list sent by the client. See the B<ciphers>
357 command for more information.
359 =item B<-starttls protocol>
361 send the protocol-specific message(s) to switch to TLS for communication.
362 B<protocol> is a keyword for the intended protocol. Currently, the only
363 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
366 =item B<-xmpphost hostname>
368 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
369 specifies the host for the "to" attribute of the stream element.
370 If this option is not specified, then the host specified with "-connect"
373 =item B<-tlsextdebug>
375 print out a hex dump of any TLS extensions received from the server.
379 disable RFC4507bis session ticket support.
381 =item B<-sess_out filename>
383 output SSL session to B<filename>
385 =item B<-sess_in sess.pem>
387 load SSL session from B<filename>. The client will attempt to resume a
388 connection from this session.
392 specifying an engine (by its unique B<id> string) will cause B<s_client>
393 to attempt to obtain a functional reference to the specified engine,
394 thus initialising it if needed. The engine will then be set as the default
395 for all available algorithms.
397 =item B<-rand file(s)>
399 a file or files containing random data used to seed the random number
400 generator, or an EGD socket (see L<RAND_egd(3)>).
401 Multiple files can be specified separated by a OS-dependent character.
402 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
405 =item B<-serverinfo types>
407 a list of comma-separated TLS Extension Types (numbers between 0 and
408 65535). Each type will be sent as an empty ClientHello TLS Extension.
409 The server's response (if any) will be encoded and displayed as a PEM
414 sends a certificate status request to the server (OCSP stapling). The server
415 response (if any) is printed out.
417 =item B<-nextprotoneg protocols>
419 enable Next Protocol Negotiation TLS extension and provide a list of
420 comma-separated protocol names that the client should advertise
421 support for. The list should contain most wanted protocols first.
422 Protocol names are printable ASCII strings, for example "http/1.1" or
424 Empty list of protocols is treated specially and will cause the client to
425 advertise support for the TLS extension but disconnect just after
426 receiving ServerHello with a list of server supported protocols.
430 =head1 CONNECTED COMMANDS
432 If a connection is established with an SSL server then any data received
433 from the server is displayed and any key presses will be sent to the
434 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
435 have been given), the session will be renegotiated if the line begins with an
436 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
437 connection will be closed down.
441 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
444 openssl s_client -connect servername:443
446 would typically be used (https uses port 443). If the connection succeeds
447 then an HTTP command can be given such as "GET /" to retrieve a web page.
449 If the handshake fails then there are several possible causes, if it is
450 nothing obvious like no client certificate then the B<-bugs>,
451 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
452 in case it is a buggy server. In particular you should play with these
453 options B<before> submitting a bug report to an OpenSSL mailing list.
455 A frequent problem when attempting to get client certificates working
456 is that a web client complains it has no certificates or gives an empty
457 list to choose from. This is normally because the server is not sending
458 the clients certificate authority in its "acceptable CA list" when it
459 requests a certificate. By using B<s_client> the CA list can be viewed
460 and checked. However some servers only request client authentication
461 after a specific URL is requested. To obtain the list in this case it
462 is necessary to use the B<-prexit> option and send an HTTP request
463 for an appropriate page.
465 If a certificate is specified on the command line using the B<-cert>
466 option it will not be used unless the server specifically requests
467 a client certificate. Therefor merely including a client certificate
468 on the command line is no guarantee that the certificate works.
470 If there are problems verifying a server certificate then the
471 B<-showcerts> option can be used to show the whole chain.
473 The B<s_client> utility is a test tool and is designed to continue the
474 handshake after any certificate verification errors. As a result it will
475 accept any certificate chain (trusted or not) sent by the peer. None test
476 applications should B<not> do this as it makes them vulnerable to a MITM
477 attack. This behaviour can be changed by with the B<-verify_return_error>
478 option: any verify errors are then returned aborting the handshake.
482 Because this program has a lot of options and also because some of
483 the techniques used are rather old, the C source of s_client is rather
484 hard to read and not a model of how things should be done. A typical
485 SSL client program would be much simpler.
487 The B<-prexit> option is a bit of a hack. We should really report
488 information whenever a session is renegotiated.
492 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
496 The -no_alt_chains options was first added to OpenSSL 1.1.0.