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>]
81 [B<-cipher cipherlist>]
83 [B<-starttls protocol>]
84 [B<-xmpphost hostname>]
88 [B<-sess_out filename>]
89 [B<-sess_in filename>]
91 [B<-serverinfo types>]
93 [B<-nextprotoneg protocols>]
94 [B<-noct|requestct|requirect>]
99 The B<s_client> command implements a generic SSL/TLS client which connects
100 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
105 In addition to the options below the B<s_client> utility also supports the
106 common and client only options documented in the
107 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
114 Print out a usage message.
116 =item B<-connect host:port>
118 This specifies the host and optional port to connect to. If not specified
119 then an attempt is made to connect to the local host on port 4433.
121 =item B<-proxy host:port>
123 When used with the B<-connect> flag, the program uses the host and port
124 specified with this flag and issues an HTTP CONNECT command to connect
125 to the desired server.
127 =item B<-servername name>
129 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
131 =item B<-cert certname>
133 The certificate to use, if one is requested by the server. The default is
134 not to use a certificate.
136 =item B<-certform format>
138 The certificate format to use: DER or PEM. PEM is the default.
140 =item B<-key keyfile>
142 The private key to use. If not specified then the certificate file will
145 =item B<-keyform format>
147 The private format to use: DER or PEM. PEM is the default.
151 the private key password source. For more information about the format of B<arg>
152 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
154 =item B<-verify depth>
156 The verify depth to use. This specifies the maximum length of the
157 server certificate chain and turns on server certificate verification.
158 Currently the verify operation continues after errors so all the problems
159 with a certificate chain can be seen. As a side effect the connection
160 will never fail due to a server certificate verify failure.
162 =item B<-verify_return_error>
164 Return verification errors instead of continuing. This will typically
165 abort the handshake with a fatal error.
167 =item B<-CApath directory>
169 The directory to use for server certificate verification. This directory
170 must be in "hash format", see B<verify> for more information. These are
171 also used when building the client certificate chain.
173 =item B<-CAfile file>
175 A file containing trusted certificates to use during server authentication
176 and to use when attempting to build the client certificate chain.
180 Do not load the trusted CA certificates from the default file location
184 Do not load the trusted CA certificates from the default directory location
186 =item B<-dane_tlsa_domain domain>
188 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
189 TLSA base domain which becomes the default SNI hint and the primary
190 reference identifier for hostname checks. This must be used in
191 combination with at least one instance of the B<-dane_tlsa_rrdata>
194 When DANE authentication succeeds, the diagnostic output will include
195 the lowest (closest to 0) depth at which a TLSA record authenticated
196 a chain certificate. When that TLSA record is a "2 1 0" trust
197 anchor public key that signed (rather than matched) the top-most
198 certificate of the chain, the result is reported as "TA public key
199 verified". Otherwise, either the TLSA record "matched TA certificate"
200 at a positive depth or else "matched EE certificate" at depth 0.
202 =item B<-dane_tlsa_rrdata rrdata>
204 Use one or more times to specify the RRDATA fields of the DANE TLSA
205 RRset associated with the target service. The B<rrdata> value is
206 specied in "presentation form", that is four whitespace separated
207 fields that specify the usage, selector, matching type and associated
208 data, with the last of these encoded in hexadecimal. Optional
209 whitespace is ignored in the associated data field. For example:
211 $ openssl s_client -brief -starttls smtp \
212 -connect smtp.example.com:25 \
213 -dane_tlsa_domain smtp.example.com \
214 -dane_tlsa_rrdata "2 1 1
215 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
216 -dane_tlsa_rrdata "2 1 1
217 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
220 Verified peername: smtp.example.com
221 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
224 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
225 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
226 B<-inhibit_map>, B<-no_alt_chains>, B<-partial_chain>, B<-policy>,
227 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
228 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
229 B<-verify_depth>, B<-verify_email>, B<-verify_hostname>, B<-verify_ip>,
230 B<-verify_name>, B<-x509_strict>
232 Set various certificate chain validation options. See the
233 L<verify(1)> manual page for details.
237 reconnects to the same server 5 times using the same session ID, this can
238 be used as a test that session caching is working.
242 display the whole server certificate chain: normally only the server
243 certificate itself is displayed.
247 print session information when the program exits. This will always attempt
248 to print out information even if the connection fails. Normally information
249 will only be printed out once if the connection succeeds. This option is useful
250 because the cipher in use may be renegotiated or the connection may fail
251 because a client certificate is required or is requested only after an
252 attempt is made to access a certain URL. Note: the output produced by this
253 option is not always accurate because a connection might never have been
258 prints out the SSL session states.
262 print extensive debugging information including a hex dump of all traffic.
266 show all protocol messages with hex dump.
270 show verbose trace output of protocol messages. OpenSSL needs to be compiled
271 with B<enable-ssl-trace> for this option to work.
275 file to send output of B<-msg> or B<-trace> to, default standard output.
279 tests non-blocking I/O
283 turns on non-blocking I/O
287 this option translated a line feed from the terminal into CR+LF as required
292 inhibit shutting down the connection when end of file is reached in the
297 inhibit printing of session and certificate information. This implicitly
298 turns on B<-ign_eof> as well.
302 shut down the connection when end of file is reached in the input.
303 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
305 =item B<-psk_identity identity>
307 Use the PSK identity B<identity> when using a PSK cipher suite.
311 Use the PSK key B<key> when using a PSK cipher suite. The key is
312 given as a hexadecimal number without leading 0x, for example -psk
315 =item B<-ssl3>, B<-tls1>, B<-tls1_1>, B<-tls1_2>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>
317 These options require or disable the use of the specified SSL or TLS protocols.
318 By default B<s_client> will negotiate the highest mutually supported protocol
320 When a specific TLS version is required, only that version will be offered to
321 and accepted from the server.
323 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
325 These options make B<s_client> use DTLS protocols instead of TLS.
326 With B<-dtls>, B<s_client> will negotiate any supported DTLS protcol version,
327 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
330 =item B<-fallback_scsv>
332 Send TLS_FALLBACK_SCSV in the ClientHello.
336 switch on asynchronous mode. Cryptographic operations will be performed
337 asynchronously. This will only have an effect if an asynchronous capable engine
338 is also used via the B<-engine> option. For test purposes the dummy async engine
339 (dasync) can be used (if available).
343 there are several known bug in SSL and TLS implementations. Adding this
344 option enables various workarounds.
348 Enables support for SSL/TLS compression.
349 This option was introduced in OpenSSL 1.1.0.
350 TLS compression is not recommended and is off by default as of
355 Disables support for SSL/TLS compression.
356 TLS compression is not recommended and is off by default as of
361 only provide a brief summary of connection parameters instead of the
362 normal verbose output.
364 =item B<-cipher cipherlist>
366 this allows the cipher list sent by the client to be modified. Although
367 the server determines which cipher suite is used it should take the first
368 supported cipher in the list sent by the client. See the B<ciphers>
369 command for more information.
371 =item B<-starttls protocol>
373 send the protocol-specific message(s) to switch to TLS for communication.
374 B<protocol> is a keyword for the intended protocol. Currently, the only
375 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
378 =item B<-xmpphost hostname>
380 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
381 specifies the host for the "to" attribute of the stream element.
382 If this option is not specified, then the host specified with "-connect"
385 =item B<-tlsextdebug>
387 print out a hex dump of any TLS extensions received from the server.
391 disable RFC4507bis session ticket support.
393 =item B<-sess_out filename>
395 output SSL session to B<filename>
397 =item B<-sess_in sess.pem>
399 load SSL session from B<filename>. The client will attempt to resume a
400 connection from this session.
404 specifying an engine (by its unique B<id> string) will cause B<s_client>
405 to attempt to obtain a functional reference to the specified engine,
406 thus initialising it if needed. The engine will then be set as the default
407 for all available algorithms.
409 =item B<-rand file(s)>
411 a file or files containing random data used to seed the random number
412 generator, or an EGD socket (see L<RAND_egd(3)>).
413 Multiple files can be specified separated by a OS-dependent character.
414 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
417 =item B<-serverinfo types>
419 a list of comma-separated TLS Extension Types (numbers between 0 and
420 65535). Each type will be sent as an empty ClientHello TLS Extension.
421 The server's response (if any) will be encoded and displayed as a PEM
426 sends a certificate status request to the server (OCSP stapling). The server
427 response (if any) is printed out.
429 =item B<-nextprotoneg protocols>
431 enable Next Protocol Negotiation TLS extension and provide a list of
432 comma-separated protocol names that the client should advertise
433 support for. The list should contain most wanted protocols first.
434 Protocol names are printable ASCII strings, for example "http/1.1" or
436 Empty list of protocols is treated specially and will cause the client to
437 advertise support for the TLS extension but disconnect just after
438 receiving ServerHello with a list of server supported protocols.
440 =item B<-noct|requestct|requirect>
442 Use one of these three options to control whether Certificate Transparency (CT)
443 is disabled (-noct), enabled but not enforced (-requestct), or enabled and
444 enforced (-requirect). If CT is enabled, signed certificate timestamps (SCTs)
445 will be requested from the server and invalid SCTs will cause the connection to
446 be aborted. If CT is enforced, at least one valid SCT from a recognised CT log
447 (see B<-ctlogfile>) will be required or the connection will be aborted.
449 Enabling CT also enables OCSP stapling, as this is one possible delivery method
454 A file containing a list of known Certificate Transparency logs. See
455 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
459 =head1 CONNECTED COMMANDS
461 If a connection is established with an SSL server then any data received
462 from the server is displayed and any key presses will be sent to the
463 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
464 have been given), the session will be renegotiated if the line begins with an
465 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
466 connection will be closed down.
470 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
473 openssl s_client -connect servername:443
475 would typically be used (https uses port 443). If the connection succeeds
476 then an HTTP command can be given such as "GET /" to retrieve a web page.
478 If the handshake fails then there are several possible causes, if it is
479 nothing obvious like no client certificate then the B<-bugs>,
480 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
481 in case it is a buggy server. In particular you should play with these
482 options B<before> submitting a bug report to an OpenSSL mailing list.
484 A frequent problem when attempting to get client certificates working
485 is that a web client complains it has no certificates or gives an empty
486 list to choose from. This is normally because the server is not sending
487 the clients certificate authority in its "acceptable CA list" when it
488 requests a certificate. By using B<s_client> the CA list can be viewed
489 and checked. However some servers only request client authentication
490 after a specific URL is requested. To obtain the list in this case it
491 is necessary to use the B<-prexit> option and send an HTTP request
492 for an appropriate page.
494 If a certificate is specified on the command line using the B<-cert>
495 option it will not be used unless the server specifically requests
496 a client certificate. Therefor merely including a client certificate
497 on the command line is no guarantee that the certificate works.
499 If there are problems verifying a server certificate then the
500 B<-showcerts> option can be used to show the whole chain.
502 The B<s_client> utility is a test tool and is designed to continue the
503 handshake after any certificate verification errors. As a result it will
504 accept any certificate chain (trusted or not) sent by the peer. None test
505 applications should B<not> do this as it makes them vulnerable to a MITM
506 attack. This behaviour can be changed by with the B<-verify_return_error>
507 option: any verify errors are then returned aborting the handshake.
511 Because this program has a lot of options and also because some of the
512 techniques used are rather old, the C source of B<s_client> is rather hard to
513 read and not a model of how things should be done.
514 A typical SSL client program would be much simpler.
516 The B<-prexit> option is a bit of a hack. We should really report
517 information whenever a session is renegotiated.
521 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
525 The -no_alt_chains options was first added to OpenSSL 1.1.0.