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>]
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>
105 =item B<-connect host:port>
107 This specifies the host and optional port to connect to. If not specified
108 then an attempt is made to connect to the local host on port 4433.
110 =item B<-proxy host:port>
112 When used with the B<-connect> flag, the program uses the host and port
113 specified with this flag and issues an HTTP CONNECT command to connect
114 to the desired server.
116 =item B<-servername name>
118 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
120 =item B<-cert certname>
122 The certificate to use, if one is requested by the server. The default is
123 not to use a certificate.
125 =item B<-certform format>
127 The certificate format to use: DER or PEM. PEM is the default.
129 =item B<-key keyfile>
131 The private key to use. If not specified then the certificate file will
134 =item B<-keyform format>
136 The private format to use: DER or PEM. PEM is the default.
140 the private key password source. For more information about the format of B<arg>
141 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
143 =item B<-verify depth>
145 The verify depth to use. This specifies the maximum length of the
146 server certificate chain and turns on server certificate verification.
147 Currently the verify operation continues after errors so all the problems
148 with a certificate chain can be seen. As a side effect the connection
149 will never fail due to a server certificate verify failure.
151 =item B<-verify_return_error>
153 Return verification errors instead of continuing. This will typically
154 abort the handshake with a fatal error.
156 =item B<-CApath directory>
158 The directory to use for server certificate verification. This directory
159 must be in "hash format", see B<verify> for more information. These are
160 also used when building the client certificate chain.
162 =item B<-CAfile file>
164 A file containing trusted certificates to use during server authentication
165 and to use when attempting to build the client certificate chain.
169 Do not load the trusted CA certificates from the default file location
173 Do not load the trusted CA certificates from the default directory location
175 =item B<-dane_tlsa_domain domain>
177 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
178 TLSA base domain which becomes the default SNI hint and the primary
179 reference identifier for hostname checks. This must be used in
180 combination with at least one instance of the B<-dane_tlsa_rrdata>
183 When DANE authentication succeeds, the diagnostic output will include
184 the lowest (closest to 0) depth at which a TLSA record authenticated
185 a chain certificate. When that TLSA record is a "2 1 0" trust
186 anchor public key that signed (rather than matched) the top-most
187 certificate of the chain, the result is reported as "TA public key
188 verified". Otherwise, either the TLSA record "matched TA certificate"
189 at a positive depth or else "matched EE certificate" at depth 0.
191 =item B<-dane_tlsa_rrdata rrdata>
193 Use one or more times to specify the RRDATA fields of the DANE TLSA
194 RRset associated with the target service. The B<rrdata> value is
195 specied in "presentation form", that is four whitespace separated
196 fields that specify the usage, selector, matching type and associated
197 data, with the last of these encoded in hexadecimal. Optional
198 whitespace is ignored in the associated data field. For example:
200 $ openssl s_client -starttls smtp -connect smtp.example.com:25 \
201 -dane_tlsa_domain smtp.example.com \
202 -dane_tlsa_rrdata "2 1 1
203 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
204 -dane_tlsa_rrdata "2 1 1
205 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
208 DANE TLSA 2 1 1 matched TA certificate at depth 1
209 Verified peername: smtp.example.com
211 Verify return code: 0 (ok)
214 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
215 B<explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
216 B<-inhibit_map>, B<-issuer_checks>, B<-partial_chain>, B<-policy>,
217 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
218 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-no_alt_chains>,
219 B<-use_deltas>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
220 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
222 Set various certificate chain validation options. See the
223 L<verify(1)> manual page for details.
227 reconnects to the same server 5 times using the same session ID, this can
228 be used as a test that session caching is working.
232 display the whole server certificate chain: normally only the server
233 certificate itself is displayed.
237 print session information when the program exits. This will always attempt
238 to print out information even if the connection fails. Normally information
239 will only be printed out once if the connection succeeds. This option is useful
240 because the cipher in use may be renegotiated or the connection may fail
241 because a client certificate is required or is requested only after an
242 attempt is made to access a certain URL. Note: the output produced by this
243 option is not always accurate because a connection might never have been
248 prints out the SSL session states.
252 print extensive debugging information including a hex dump of all traffic.
256 show all protocol messages with hex dump.
260 show verbose trace output of protocol messages. OpenSSL needs to be compiled
261 with B<enable-ssl-trace> for this option to work.
265 file to send output of B<-msg> or B<-trace> to, default standard output.
269 tests non-blocking I/O
273 turns on non-blocking I/O
277 this option translated a line feed from the terminal into CR+LF as required
282 inhibit shutting down the connection when end of file is reached in the
287 inhibit printing of session and certificate information. This implicitly
288 turns on B<-ign_eof> as well.
292 shut down the connection when end of file is reached in the input.
293 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
295 =item B<-psk_identity identity>
297 Use the PSK identity B<identity> when using a PSK cipher suite.
301 Use the PSK key B<key> when using a PSK cipher suite. The key is
302 given as a hexadecimal number without leading 0x, for example -psk
305 =item B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>
307 these options disable the use of certain SSL or TLS protocols. By default
308 the initial handshake uses a method which should be compatible with all
309 servers and permit them to use SSL v3 or TLS as appropriate.
311 Unfortunately there are still ancient and broken servers in use which
312 cannot handle this technique and will fail to connect. Some servers only
313 work if TLS is turned off.
315 =item B<-fallback_scsv>
317 Send TLS_FALLBACK_SCSV in the ClientHello.
321 switch on asynchronous mode. Cryptographic operations will be performed
322 asynchronously. This will only have an effect if an asynchronous capable engine
323 is also used via the B<-engine> option. For test purposes the dummy async engine
324 (dasync) can be used (if available).
328 there are several known bug in SSL and TLS implementations. Adding this
329 option enables various workarounds.
333 Enables support for SSL/TLS compression.
334 This option was introduced in OpenSSL 1.1.0.
335 TLS compression is not recommended and is off by default as of
340 Disables support for SSL/TLS compression.
341 TLS compression is not recommended and is off by default as of
346 only provide a brief summary of connection parameters instead of the
347 normal verbose output.
349 =item B<-cipher cipherlist>
351 this allows the cipher list sent by the client to be modified. Although
352 the server determines which cipher suite is used it should take the first
353 supported cipher in the list sent by the client. See the B<ciphers>
354 command for more information.
356 =item B<-starttls protocol>
358 send the protocol-specific message(s) to switch to TLS for communication.
359 B<protocol> is a keyword for the intended protocol. Currently, the only
360 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
363 =item B<-xmpphost hostname>
365 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
366 specifies the host for the "to" attribute of the stream element.
367 If this option is not specified, then the host specified with "-connect"
370 =item B<-tlsextdebug>
372 print out a hex dump of any TLS extensions received from the server.
376 disable RFC4507bis session ticket support.
378 =item B<-sess_out filename>
380 output SSL session to B<filename>
382 =item B<-sess_in sess.pem>
384 load SSL session from B<filename>. The client will attempt to resume a
385 connection from this session.
389 specifying an engine (by its unique B<id> string) will cause B<s_client>
390 to attempt to obtain a functional reference to the specified engine,
391 thus initialising it if needed. The engine will then be set as the default
392 for all available algorithms.
394 =item B<-rand file(s)>
396 a file or files containing random data used to seed the random number
397 generator, or an EGD socket (see L<RAND_egd(3)>).
398 Multiple files can be specified separated by a OS-dependent character.
399 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
402 =item B<-serverinfo types>
404 a list of comma-separated TLS Extension Types (numbers between 0 and
405 65535). Each type will be sent as an empty ClientHello TLS Extension.
406 The server's response (if any) will be encoded and displayed as a PEM
411 sends a certificate status request to the server (OCSP stapling). The server
412 response (if any) is printed out.
414 =item B<-nextprotoneg protocols>
416 enable Next Protocol Negotiation TLS extension and provide a list of
417 comma-separated protocol names that the client should advertise
418 support for. The list should contain most wanted protocols first.
419 Protocol names are printable ASCII strings, for example "http/1.1" or
421 Empty list of protocols is treated specially and will cause the client to
422 advertise support for the TLS extension but disconnect just after
423 receiving ServerHello with a list of server supported protocols.
427 =head1 CONNECTED COMMANDS
429 If a connection is established with an SSL server then any data received
430 from the server is displayed and any key presses will be sent to the
431 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
432 have been given), the session will be renegotiated if the line begins with an
433 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
434 connection will be closed down.
438 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
441 openssl s_client -connect servername:443
443 would typically be used (https uses port 443). If the connection succeeds
444 then an HTTP command can be given such as "GET /" to retrieve a web page.
446 If the handshake fails then there are several possible causes, if it is
447 nothing obvious like no client certificate then the B<-bugs>,
448 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
449 in case it is a buggy server. In particular you should play with these
450 options B<before> submitting a bug report to an OpenSSL mailing list.
452 A frequent problem when attempting to get client certificates working
453 is that a web client complains it has no certificates or gives an empty
454 list to choose from. This is normally because the server is not sending
455 the clients certificate authority in its "acceptable CA list" when it
456 requests a certificate. By using B<s_client> the CA list can be viewed
457 and checked. However some servers only request client authentication
458 after a specific URL is requested. To obtain the list in this case it
459 is necessary to use the B<-prexit> option and send an HTTP request
460 for an appropriate page.
462 If a certificate is specified on the command line using the B<-cert>
463 option it will not be used unless the server specifically requests
464 a client certificate. Therefor merely including a client certificate
465 on the command line is no guarantee that the certificate works.
467 If there are problems verifying a server certificate then the
468 B<-showcerts> option can be used to show the whole chain.
470 The B<s_client> utility is a test tool and is designed to continue the
471 handshake after any certificate verification errors. As a result it will
472 accept any certificate chain (trusted or not) sent by the peer. None test
473 applications should B<not> do this as it makes them vulnerable to a MITM
474 attack. This behaviour can be changed by with the B<-verify_return_error>
475 option: any verify errors are then returned aborting the handshake.
479 Because this program has a lot of options and also because some of
480 the techniques used are rather old, the C source of s_client is rather
481 hard to read and not a model of how things should be done. A typical
482 SSL client program would be much simpler.
484 The B<-prexit> option is a bit of a hack. We should really report
485 information whenever a session is renegotiated.
489 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
493 The -no_alt_chains options was first added to OpenSSL 1.1.0.