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<-dane_tlsa_domain domain>]
26 [B<-dane_tlsa_rrdata rrdata>]
27 [B<-attime timestamp>]
48 [B<-verify_depth num>]
49 [B<-verify_email email>]
50 [B<-verify_hostname hostname>]
52 [B<-verify_name name>]
75 [B<-cipher cipherlist>]
77 [B<-starttls protocol>]
78 [B<-xmpphost hostname>]
82 [B<-sess_out filename>]
83 [B<-sess_in filename>]
85 [B<-serverinfo types>]
87 [B<-nextprotoneg protocols>]
91 The B<s_client> command implements a generic SSL/TLS client which connects
92 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
97 In addition to the options below the B<s_client> utility also supports the
98 common and client only options documented in the
99 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
104 =item B<-connect host:port>
106 This specifies the host and optional port to connect to. If not specified
107 then an attempt is made to connect to the local host on port 4433.
109 =item B<-proxy host:port>
111 When used with the B<-connect> flag, the program uses the host and port
112 specified with this flag and issues an HTTP CONNECT command to connect
113 to the desired server.
115 =item B<-servername name>
117 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
119 =item B<-cert certname>
121 The certificate to use, if one is requested by the server. The default is
122 not to use a certificate.
124 =item B<-certform format>
126 The certificate format to use: DER or PEM. PEM is the default.
128 =item B<-key keyfile>
130 The private key to use. If not specified then the certificate file will
133 =item B<-keyform format>
135 The private format to use: DER or PEM. PEM is the default.
139 the private key password source. For more information about the format of B<arg>
140 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
142 =item B<-verify depth>
144 The verify depth to use. This specifies the maximum length of the
145 server certificate chain and turns on server certificate verification.
146 Currently the verify operation continues after errors so all the problems
147 with a certificate chain can be seen. As a side effect the connection
148 will never fail due to a server certificate verify failure.
150 =item B<-verify_return_error>
152 Return verification errors instead of continuing. This will typically
153 abort the handshake with a fatal error.
155 =item B<-CApath directory>
157 The directory to use for server certificate verification. This directory
158 must be in "hash format", see B<verify> for more information. These are
159 also used when building the client certificate chain.
161 =item B<-CAfile file>
163 A file containing trusted certificates to use during server authentication
164 and to use when attempting to build the client certificate chain.
168 Do not load the trusted CA certificates from the default file location
172 Do not load the trusted CA certificates from the default directory location
174 =item B<-dane_tlsa_domain domain>
176 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
177 TLSA base domain which becomes the default SNI hint and the primary
178 reference identifier for hostname checks. This must be used in
179 combination with at least one instance of the B<-dane_tlsa_rrdata>
182 When DANE authentication succeeds, the diagnostic output will include
183 the lowest (closest to 0) depth at which a TLSA record authenticated
184 a chain certificate. When that TLSA record is a "2 1 0" trust
185 anchor public key that signed (rather than matched) the top-most
186 certificate of the chain, the result is reported as "TA public key
187 verified". Otherwise, either the TLSA record "matched TA certificate"
188 at a positive depth or else "matched EE certificate" at depth 0.
190 =item B<-dane_tlsa_rrdata rrdata>
192 Use one or more times to specify the RRDATA fields of the DANE TLSA
193 RRset associated with the target service. The B<rrdata> value is
194 specied in "presentation form", that is four whitespace separated
195 fields that specify the usage, selector, matching type and associated
196 data, with the last of these encoded in hexadecimal. Optional
197 whitespace is ignored in the associated data field. For example:
199 $ openssl s_client -starttls smtp -connect smtp.example.com:25 \
200 -dane_tlsa_domain smtp.example.com \
201 -dane_tlsa_rrdata "2 1 1
202 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
203 -dane_tlsa_rrdata "2 1 1
204 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
207 DANE TLSA 2 1 1 matched TA certificate at depth 1
208 Verified peername: smtp.example.com
210 Verify return code: 0 (ok)
213 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
214 B<explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
215 B<-inhibit_map>, B<-issuer_checks>, B<-partial_chain>, B<-policy>,
216 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
217 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-no_alt_chains>,
218 B<-use_deltas>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
219 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
221 Set various certificate chain validation options. See the
222 L<verify(1)> manual page for details.
226 reconnects to the same server 5 times using the same session ID, this can
227 be used as a test that session caching is working.
231 pauses 1 second between each read and write call.
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 only provide a brief summary of connection parameters instead of the
337 normal verbose output.
339 =item B<-cipher cipherlist>
341 this allows the cipher list sent by the client to be modified. Although
342 the server determines which cipher suite is used it should take the first
343 supported cipher in the list sent by the client. See the B<ciphers>
344 command for more information.
346 =item B<-starttls protocol>
348 send the protocol-specific message(s) to switch to TLS for communication.
349 B<protocol> is a keyword for the intended protocol. Currently, the only
350 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
353 =item B<-xmpphost hostname>
355 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
356 specifies the host for the "to" attribute of the stream element.
357 If this option is not specified, then the host specified with "-connect"
360 =item B<-tlsextdebug>
362 print out a hex dump of any TLS extensions received from the server.
366 disable RFC4507bis session ticket support.
368 =item B<-sess_out filename>
370 output SSL session to B<filename>
372 =item B<-sess_in sess.pem>
374 load SSL session from B<filename>. The client will attempt to resume a
375 connection from this session.
379 specifying an engine (by its unique B<id> string) will cause B<s_client>
380 to attempt to obtain a functional reference to the specified engine,
381 thus initialising it if needed. The engine will then be set as the default
382 for all available algorithms.
384 =item B<-rand file(s)>
386 a file or files containing random data used to seed the random number
387 generator, or an EGD socket (see L<RAND_egd(3)>).
388 Multiple files can be specified separated by a OS-dependent character.
389 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
392 =item B<-serverinfo types>
394 a list of comma-separated TLS Extension Types (numbers between 0 and
395 65535). Each type will be sent as an empty ClientHello TLS Extension.
396 The server's response (if any) will be encoded and displayed as a PEM
401 sends a certificate status request to the server (OCSP stapling). The server
402 response (if any) is printed out.
404 =item B<-nextprotoneg protocols>
406 enable Next Protocol Negotiation TLS extension and provide a list of
407 comma-separated protocol names that the client should advertise
408 support for. The list should contain most wanted protocols first.
409 Protocol names are printable ASCII strings, for example "http/1.1" or
411 Empty list of protocols is treated specially and will cause the client to
412 advertise support for the TLS extension but disconnect just after
413 receiving ServerHello with a list of server supported protocols.
417 =head1 CONNECTED COMMANDS
419 If a connection is established with an SSL server then any data received
420 from the server is displayed and any key presses will be sent to the
421 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
422 have been given), the session will be renegotiated if the line begins with an
423 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
424 connection will be closed down.
428 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
431 openssl s_client -connect servername:443
433 would typically be used (https uses port 443). If the connection succeeds
434 then an HTTP command can be given such as "GET /" to retrieve a web page.
436 If the handshake fails then there are several possible causes, if it is
437 nothing obvious like no client certificate then the B<-bugs>,
438 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
439 in case it is a buggy server. In particular you should play with these
440 options B<before> submitting a bug report to an OpenSSL mailing list.
442 A frequent problem when attempting to get client certificates working
443 is that a web client complains it has no certificates or gives an empty
444 list to choose from. This is normally because the server is not sending
445 the clients certificate authority in its "acceptable CA list" when it
446 requests a certificate. By using B<s_client> the CA list can be viewed
447 and checked. However some servers only request client authentication
448 after a specific URL is requested. To obtain the list in this case it
449 is necessary to use the B<-prexit> option and send an HTTP request
450 for an appropriate page.
452 If a certificate is specified on the command line using the B<-cert>
453 option it will not be used unless the server specifically requests
454 a client certificate. Therefor merely including a client certificate
455 on the command line is no guarantee that the certificate works.
457 If there are problems verifying a server certificate then the
458 B<-showcerts> option can be used to show the whole chain.
460 The B<s_client> utility is a test tool and is designed to continue the
461 handshake after any certificate verification errors. As a result it will
462 accept any certificate chain (trusted or not) sent by the peer. None test
463 applications should B<not> do this as it makes them vulnerable to a MITM
464 attack. This behaviour can be changed by with the B<-verify_return_error>
465 option: any verify errors are then returned aborting the handshake.
469 Because this program has a lot of options and also because some of
470 the techniques used are rather old, the C source of s_client is rather
471 hard to read and not a model of how things should be done. A typical
472 SSL client program would be much simpler.
474 The B<-prexit> option is a bit of a hack. We should really report
475 information whenever a session is renegotiated.
479 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
483 The -no_alt_chains options was first added to OpenSSL 1.1.0.