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>]
97 The B<s_client> command implements a generic SSL/TLS client which connects
98 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
103 In addition to the options below the B<s_client> utility also supports the
104 common and client only options documented in the
105 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
112 Print out a usage message.
114 =item B<-connect host:port>
116 This specifies the host and optional port to connect to. If not specified
117 then an attempt is made to connect to the local host on port 4433.
119 =item B<-proxy host:port>
121 When used with the B<-connect> flag, the program uses the host and port
122 specified with this flag and issues an HTTP CONNECT command to connect
123 to the desired server.
125 =item B<-servername name>
127 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
129 =item B<-cert certname>
131 The certificate to use, if one is requested by the server. The default is
132 not to use a certificate.
134 =item B<-certform format>
136 The certificate format to use: DER or PEM. PEM is the default.
138 =item B<-key keyfile>
140 The private key to use. If not specified then the certificate file will
143 =item B<-keyform format>
145 The private format to use: DER or PEM. PEM is the default.
149 the private key password source. For more information about the format of B<arg>
150 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
152 =item B<-verify depth>
154 The verify depth to use. This specifies the maximum length of the
155 server certificate chain and turns on server certificate verification.
156 Currently the verify operation continues after errors so all the problems
157 with a certificate chain can be seen. As a side effect the connection
158 will never fail due to a server certificate verify failure.
160 =item B<-verify_return_error>
162 Return verification errors instead of continuing. This will typically
163 abort the handshake with a fatal error.
165 =item B<-CApath directory>
167 The directory to use for server certificate verification. This directory
168 must be in "hash format", see B<verify> for more information. These are
169 also used when building the client certificate chain.
171 =item B<-CAfile file>
173 A file containing trusted certificates to use during server authentication
174 and to use when attempting to build the client certificate chain.
178 Do not load the trusted CA certificates from the default file location
182 Do not load the trusted CA certificates from the default directory location
184 =item B<-dane_tlsa_domain domain>
186 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
187 TLSA base domain which becomes the default SNI hint and the primary
188 reference identifier for hostname checks. This must be used in
189 combination with at least one instance of the B<-dane_tlsa_rrdata>
192 When DANE authentication succeeds, the diagnostic output will include
193 the lowest (closest to 0) depth at which a TLSA record authenticated
194 a chain certificate. When that TLSA record is a "2 1 0" trust
195 anchor public key that signed (rather than matched) the top-most
196 certificate of the chain, the result is reported as "TA public key
197 verified". Otherwise, either the TLSA record "matched TA certificate"
198 at a positive depth or else "matched EE certificate" at depth 0.
200 =item B<-dane_tlsa_rrdata rrdata>
202 Use one or more times to specify the RRDATA fields of the DANE TLSA
203 RRset associated with the target service. The B<rrdata> value is
204 specied in "presentation form", that is four whitespace separated
205 fields that specify the usage, selector, matching type and associated
206 data, with the last of these encoded in hexadecimal. Optional
207 whitespace is ignored in the associated data field. For example:
209 $ openssl s_client -brief -starttls smtp \
210 -connect smtp.example.com:25 \
211 -dane_tlsa_domain smtp.example.com \
212 -dane_tlsa_rrdata "2 1 1
213 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
214 -dane_tlsa_rrdata "2 1 1
215 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
218 Verified peername: smtp.example.com
219 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
222 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
223 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
224 B<-inhibit_map>, B<-no_alt_chains>, B<-partial_chain>, B<-policy>,
225 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
226 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
227 B<-verify_depth>, B<-verify_email>, B<-verify_hostname>, B<-verify_ip>,
228 B<-verify_name>, B<-x509_strict>
230 Set various certificate chain validation options. See the
231 L<verify(1)> manual page for details.
235 reconnects to the same server 5 times using the same session ID, this can
236 be used as a test that session caching is working.
240 display the whole server certificate chain: normally only the server
241 certificate itself is displayed.
245 print session information when the program exits. This will always attempt
246 to print out information even if the connection fails. Normally information
247 will only be printed out once if the connection succeeds. This option is useful
248 because the cipher in use may be renegotiated or the connection may fail
249 because a client certificate is required or is requested only after an
250 attempt is made to access a certain URL. Note: the output produced by this
251 option is not always accurate because a connection might never have been
256 prints out the SSL session states.
260 print extensive debugging information including a hex dump of all traffic.
264 show all protocol messages with hex dump.
268 show verbose trace output of protocol messages. OpenSSL needs to be compiled
269 with B<enable-ssl-trace> for this option to work.
273 file to send output of B<-msg> or B<-trace> to, default standard output.
277 tests non-blocking I/O
281 turns on non-blocking I/O
285 this option translated a line feed from the terminal into CR+LF as required
290 inhibit shutting down the connection when end of file is reached in the
295 inhibit printing of session and certificate information. This implicitly
296 turns on B<-ign_eof> as well.
300 shut down the connection when end of file is reached in the input.
301 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
303 =item B<-psk_identity identity>
305 Use the PSK identity B<identity> when using a PSK cipher suite.
309 Use the PSK key B<key> when using a PSK cipher suite. The key is
310 given as a hexadecimal number without leading 0x, for example -psk
313 =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>
315 These options require or disable the use of the specified SSL or TLS protocols.
316 By default B<s_client> will negotiate the highest mutually supported protocol
318 When a specific TLS version is required, only that version will be offered to
319 and accepted from the server.
321 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
323 These options make B<s_client> use DTLS protocols instead of TLS.
324 With B<-dtls>, B<s_client> will negotiate any supported DTLS protcol version,
325 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
328 =item B<-fallback_scsv>
330 Send TLS_FALLBACK_SCSV in the ClientHello.
334 switch on asynchronous mode. Cryptographic operations will be performed
335 asynchronously. This will only have an effect if an asynchronous capable engine
336 is also used via the B<-engine> option. For test purposes the dummy async engine
337 (dasync) can be used (if available).
341 there are several known bug in SSL and TLS implementations. Adding this
342 option enables various workarounds.
346 Enables support for SSL/TLS compression.
347 This option was introduced in OpenSSL 1.1.0.
348 TLS compression is not recommended and is off by default as of
353 Disables support for SSL/TLS compression.
354 TLS compression is not recommended and is off by default as of
359 only provide a brief summary of connection parameters instead of the
360 normal verbose output.
362 =item B<-cipher cipherlist>
364 this allows the cipher list sent by the client to be modified. Although
365 the server determines which cipher suite is used it should take the first
366 supported cipher in the list sent by the client. See the B<ciphers>
367 command for more information.
369 =item B<-starttls protocol>
371 send the protocol-specific message(s) to switch to TLS for communication.
372 B<protocol> is a keyword for the intended protocol. Currently, the only
373 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
376 =item B<-xmpphost hostname>
378 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
379 specifies the host for the "to" attribute of the stream element.
380 If this option is not specified, then the host specified with "-connect"
383 =item B<-tlsextdebug>
385 print out a hex dump of any TLS extensions received from the server.
389 disable RFC4507bis session ticket support.
391 =item B<-sess_out filename>
393 output SSL session to B<filename>
395 =item B<-sess_in sess.pem>
397 load SSL session from B<filename>. The client will attempt to resume a
398 connection from this session.
402 specifying an engine (by its unique B<id> string) will cause B<s_client>
403 to attempt to obtain a functional reference to the specified engine,
404 thus initialising it if needed. The engine will then be set as the default
405 for all available algorithms.
407 =item B<-rand file(s)>
409 a file or files containing random data used to seed the random number
410 generator, or an EGD socket (see L<RAND_egd(3)>).
411 Multiple files can be specified separated by a OS-dependent character.
412 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
415 =item B<-serverinfo types>
417 a list of comma-separated TLS Extension Types (numbers between 0 and
418 65535). Each type will be sent as an empty ClientHello TLS Extension.
419 The server's response (if any) will be encoded and displayed as a PEM
424 sends a certificate status request to the server (OCSP stapling). The server
425 response (if any) is printed out.
427 =item B<-nextprotoneg protocols>
429 enable Next Protocol Negotiation TLS extension and provide a list of
430 comma-separated protocol names that the client should advertise
431 support for. The list should contain most wanted protocols first.
432 Protocol names are printable ASCII strings, for example "http/1.1" or
434 Empty list of protocols is treated specially and will cause the client to
435 advertise support for the TLS extension but disconnect just after
436 receiving ServerHello with a list of server supported protocols.
440 =head1 CONNECTED COMMANDS
442 If a connection is established with an SSL server then any data received
443 from the server is displayed and any key presses will be sent to the
444 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
445 have been given), the session will be renegotiated if the line begins with an
446 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
447 connection will be closed down.
451 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
454 openssl s_client -connect servername:443
456 would typically be used (https uses port 443). If the connection succeeds
457 then an HTTP command can be given such as "GET /" to retrieve a web page.
459 If the handshake fails then there are several possible causes, if it is
460 nothing obvious like no client certificate then the B<-bugs>,
461 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
462 in case it is a buggy server. In particular you should play with these
463 options B<before> submitting a bug report to an OpenSSL mailing list.
465 A frequent problem when attempting to get client certificates working
466 is that a web client complains it has no certificates or gives an empty
467 list to choose from. This is normally because the server is not sending
468 the clients certificate authority in its "acceptable CA list" when it
469 requests a certificate. By using B<s_client> the CA list can be viewed
470 and checked. However some servers only request client authentication
471 after a specific URL is requested. To obtain the list in this case it
472 is necessary to use the B<-prexit> option and send an HTTP request
473 for an appropriate page.
475 If a certificate is specified on the command line using the B<-cert>
476 option it will not be used unless the server specifically requests
477 a client certificate. Therefor merely including a client certificate
478 on the command line is no guarantee that the certificate works.
480 If there are problems verifying a server certificate then the
481 B<-showcerts> option can be used to show the whole chain.
483 The B<s_client> utility is a test tool and is designed to continue the
484 handshake after any certificate verification errors. As a result it will
485 accept any certificate chain (trusted or not) sent by the peer. None test
486 applications should B<not> do this as it makes them vulnerable to a MITM
487 attack. This behaviour can be changed by with the B<-verify_return_error>
488 option: any verify errors are then returned aborting the handshake.
492 Because this program has a lot of options and also because some of the
493 techniques used are rather old, the C source of B<s_client> is rather hard to
494 read and not a model of how things should be done.
495 A typical SSL client program would be much simpler.
497 The B<-prexit> option is a bit of a hack. We should really report
498 information whenever a session is renegotiated.
502 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
506 The -no_alt_chains options was first added to OpenSSL 1.1.0.