5 s_client - SSL/TLS client program
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<-dane_ee_no_namechecks>]
28 [B<-attime timestamp>]
50 [B<-verify_depth num>]
51 [B<-verify_email email>]
52 [B<-verify_hostname hostname>]
54 [B<-verify_name name>]
86 [B<-cipher cipherlist>]
88 [B<-starttls protocol>]
89 [B<-xmpphost hostname>]
93 [B<-sess_out filename>]
94 [B<-sess_in filename>]
96 [B<-serverinfo types>]
98 [B<-nextprotoneg protocols>]
104 The B<s_client> command implements a generic SSL/TLS client which connects
105 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
110 In addition to the options below the B<s_client> utility also supports the
111 common and client only options documented in the
112 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
119 Print out a usage message.
121 =item B<-connect host:port>
123 This specifies the host and optional port to connect to. If not specified
124 then an attempt is made to connect to the local host on port 4433.
126 =item B<-proxy host:port>
128 When used with the B<-connect> flag, the program uses the host and port
129 specified with this flag and issues an HTTP CONNECT command to connect
130 to the desired server.
132 =item B<-servername name>
134 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
136 =item B<-cert certname>
138 The certificate to use, if one is requested by the server. The default is
139 not to use a certificate.
141 =item B<-certform format>
143 The certificate format to use: DER or PEM. PEM is the default.
145 =item B<-key keyfile>
147 The private key to use. If not specified then the certificate file will
150 =item B<-keyform format>
152 The private format to use: DER or PEM. PEM is the default.
156 the private key password source. For more information about the format of B<arg>
157 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
159 =item B<-verify depth>
161 The verify depth to use. This specifies the maximum length of the
162 server certificate chain and turns on server certificate verification.
163 Currently the verify operation continues after errors so all the problems
164 with a certificate chain can be seen. As a side effect the connection
165 will never fail due to a server certificate verify failure.
167 =item B<-verify_return_error>
169 Return verification errors instead of continuing. This will typically
170 abort the handshake with a fatal error.
172 =item B<-CApath directory>
174 The directory to use for server certificate verification. This directory
175 must be in "hash format", see B<verify> for more information. These are
176 also used when building the client certificate chain.
178 =item B<-CAfile file>
180 A file containing trusted certificates to use during server authentication
181 and to use when attempting to build the client certificate chain.
185 Do not load the trusted CA certificates from the default file location
189 Do not load the trusted CA certificates from the default directory location
191 =item B<-dane_tlsa_domain domain>
193 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
194 TLSA base domain which becomes the default SNI hint and the primary
195 reference identifier for hostname checks. This must be used in
196 combination with at least one instance of the B<-dane_tlsa_rrdata>
199 When DANE authentication succeeds, the diagnostic output will include
200 the lowest (closest to 0) depth at which a TLSA record authenticated
201 a chain certificate. When that TLSA record is a "2 1 0" trust
202 anchor public key that signed (rather than matched) the top-most
203 certificate of the chain, the result is reported as "TA public key
204 verified". Otherwise, either the TLSA record "matched TA certificate"
205 at a positive depth or else "matched EE certificate" at depth 0.
207 =item B<-dane_tlsa_rrdata rrdata>
209 Use one or more times to specify the RRDATA fields of the DANE TLSA
210 RRset associated with the target service. The B<rrdata> value is
211 specied in "presentation form", that is four whitespace separated
212 fields that specify the usage, selector, matching type and associated
213 data, with the last of these encoded in hexadecimal. Optional
214 whitespace is ignored in the associated data field. For example:
216 $ openssl s_client -brief -starttls smtp \
217 -connect smtp.example.com:25 \
218 -dane_tlsa_domain smtp.example.com \
219 -dane_tlsa_rrdata "2 1 1
220 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
221 -dane_tlsa_rrdata "2 1 1
222 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
225 Verified peername: smtp.example.com
226 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
229 =item B<-dane_ee_no_namechecks>
231 This disables server name checks when authenticating via DANE-EE(3) TLSA
233 For some applications, primarily web browsers, it is not safe to disable name
234 checks due to "unknown key share" attacks, in which a malicious server can
235 convince a client that a connection to a victim server is instead a secure
236 connection to the malicious server.
237 The malicious server may then be able to violate cross-origin scripting
239 Thus, despite the text of RFC7671, name checks are by default enabled for
240 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
242 In particular, SMTP and XMPP clients should set this option as SRV and MX
243 records already make it possible for a remote domain to redirect client
244 connections to any server of its choice, and in any case SMTP and XMPP clients
245 do not execute scripts downloaded from remote servers.
247 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
248 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
249 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
250 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
251 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
252 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
253 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
255 Set various certificate chain validation options. See the
256 L<verify(1)> manual page for details.
260 reconnects to the same server 5 times using the same session ID, this can
261 be used as a test that session caching is working.
265 display the whole server certificate chain: normally only the server
266 certificate itself is displayed.
270 print session information when the program exits. This will always attempt
271 to print out information even if the connection fails. Normally information
272 will only be printed out once if the connection succeeds. This option is useful
273 because the cipher in use may be renegotiated or the connection may fail
274 because a client certificate is required or is requested only after an
275 attempt is made to access a certain URL. Note: the output produced by this
276 option is not always accurate because a connection might never have been
281 prints out the SSL session states.
285 print extensive debugging information including a hex dump of all traffic.
289 show all protocol messages with hex dump.
293 show verbose trace output of protocol messages. OpenSSL needs to be compiled
294 with B<enable-ssl-trace> for this option to work.
298 file to send output of B<-msg> or B<-trace> to, default standard output.
302 tests non-blocking I/O
306 turns on non-blocking I/O
310 this option translated a line feed from the terminal into CR+LF as required
315 inhibit shutting down the connection when end of file is reached in the
320 inhibit printing of session and certificate information. This implicitly
321 turns on B<-ign_eof> as well.
325 shut down the connection when end of file is reached in the input.
326 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
328 =item B<-psk_identity identity>
330 Use the PSK identity B<identity> when using a PSK cipher suite.
334 Use the PSK key B<key> when using a PSK cipher suite. The key is
335 given as a hexadecimal number without leading 0x, for example -psk
338 =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>
340 These options require or disable the use of the specified SSL or TLS protocols.
341 By default B<s_client> will negotiate the highest mutually supported protocol
343 When a specific TLS version is required, only that version will be offered to
344 and accepted from the server.
346 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
348 These options make B<s_client> use DTLS protocols instead of TLS.
349 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
350 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
353 =item B<-fallback_scsv>
355 Send TLS_FALLBACK_SCSV in the ClientHello.
359 switch on asynchronous mode. Cryptographic operations will be performed
360 asynchronously. This will only have an effect if an asynchronous capable engine
361 is also used via the B<-engine> option. For test purposes the dummy async engine
362 (dasync) can be used (if available).
364 =item B<-split_send_frag int>
366 The size used to split data for encrypt pipelines. If more data is written in
367 one go than this value then it will be split into multiple pipelines, up to the
368 maximum number of pipelines defined by max_pipelines. This only has an effect if
369 a suitable ciphersuite has been negotiated, an engine that supports pipelining
370 has been loaded, and max_pipelines is greater than 1. See
371 L<SSL_CTX_set_split_send_fragment(3)> for further information.
373 =item B<-max_pipelines int>
375 The maximum number of encrypt/decrypt pipelines to be used. This will only have
376 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
377 engine) and a suitable ciphersuite has been negotiated. The default value is 1.
378 See L<SSL_CTX_set_max_pipelines(3)> for further information.
380 =item B<-read_buf int>
382 The default read buffer size to be used for connections. This will only have an
383 effect if the buffer size is larger than the size that would otherwise be used
384 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
385 further information).
389 there are several known bug in SSL and TLS implementations. Adding this
390 option enables various workarounds.
394 Enables support for SSL/TLS compression.
395 This option was introduced in OpenSSL 1.1.0.
396 TLS compression is not recommended and is off by default as of
401 Disables support for SSL/TLS compression.
402 TLS compression is not recommended and is off by default as of
407 only provide a brief summary of connection parameters instead of the
408 normal verbose output.
410 =item B<-cipher cipherlist>
412 this allows the cipher list sent by the client to be modified. Although
413 the server determines which cipher suite is used it should take the first
414 supported cipher in the list sent by the client. See the B<ciphers>
415 command for more information.
417 =item B<-starttls protocol>
419 send the protocol-specific message(s) to switch to TLS for communication.
420 B<protocol> is a keyword for the intended protocol. Currently, the only
421 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
424 =item B<-xmpphost hostname>
426 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
427 specifies the host for the "to" attribute of the stream element.
428 If this option is not specified, then the host specified with "-connect"
431 =item B<-tlsextdebug>
433 print out a hex dump of any TLS extensions received from the server.
437 disable RFC4507bis session ticket support.
439 =item B<-sess_out filename>
441 output SSL session to B<filename>
443 =item B<-sess_in sess.pem>
445 load SSL session from B<filename>. The client will attempt to resume a
446 connection from this session.
450 specifying an engine (by its unique B<id> string) will cause B<s_client>
451 to attempt to obtain a functional reference to the specified engine,
452 thus initialising it if needed. The engine will then be set as the default
453 for all available algorithms.
455 =item B<-rand file(s)>
457 a file or files containing random data used to seed the random number
458 generator, or an EGD socket (see L<RAND_egd(3)>).
459 Multiple files can be specified separated by an OS-dependent character.
460 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
463 =item B<-serverinfo types>
465 a list of comma-separated TLS Extension Types (numbers between 0 and
466 65535). Each type will be sent as an empty ClientHello TLS Extension.
467 The server's response (if any) will be encoded and displayed as a PEM
472 sends a certificate status request to the server (OCSP stapling). The server
473 response (if any) is printed out.
475 =item B<-nextprotoneg protocols>
477 enable Next Protocol Negotiation TLS extension and provide a list of
478 comma-separated protocol names that the client should advertise
479 support for. The list should contain most wanted protocols first.
480 Protocol names are printable ASCII strings, for example "http/1.1" or
482 Empty list of protocols is treated specially and will cause the client to
483 advertise support for the TLS extension but disconnect just after
484 receiving ServerHello with a list of server supported protocols.
488 Use one of these two options to control whether Certificate Transparency (CT)
489 is enabled (B<-ct>) or disabled (B<-noct>).
490 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
491 the server and reported at handshake completion.
493 Enabling CT also enables OCSP stapling, as this is one possible delivery method
498 A file containing a list of known Certificate Transparency logs. See
499 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
503 =head1 CONNECTED COMMANDS
505 If a connection is established with an SSL server then any data received
506 from the server is displayed and any key presses will be sent to the
507 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
508 have been given), the session will be renegotiated if the line begins with an
509 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
510 connection will be closed down.
514 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
517 openssl s_client -connect servername:443
519 would typically be used (https uses port 443). If the connection succeeds
520 then an HTTP command can be given such as "GET /" to retrieve a web page.
522 If the handshake fails then there are several possible causes, if it is
523 nothing obvious like no client certificate then the B<-bugs>,
524 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
525 in case it is a buggy server. In particular you should play with these
526 options B<before> submitting a bug report to an OpenSSL mailing list.
528 A frequent problem when attempting to get client certificates working
529 is that a web client complains it has no certificates or gives an empty
530 list to choose from. This is normally because the server is not sending
531 the clients certificate authority in its "acceptable CA list" when it
532 requests a certificate. By using B<s_client> the CA list can be viewed
533 and checked. However some servers only request client authentication
534 after a specific URL is requested. To obtain the list in this case it
535 is necessary to use the B<-prexit> option and send an HTTP request
536 for an appropriate page.
538 If a certificate is specified on the command line using the B<-cert>
539 option it will not be used unless the server specifically requests
540 a client certificate. Therefor merely including a client certificate
541 on the command line is no guarantee that the certificate works.
543 If there are problems verifying a server certificate then the
544 B<-showcerts> option can be used to show the whole chain.
546 The B<s_client> utility is a test tool and is designed to continue the
547 handshake after any certificate verification errors. As a result it will
548 accept any certificate chain (trusted or not) sent by the peer. None test
549 applications should B<not> do this as it makes them vulnerable to a MITM
550 attack. This behaviour can be changed by with the B<-verify_return_error>
551 option: any verify errors are then returned aborting the handshake.
555 Because this program has a lot of options and also because some of the
556 techniques used are rather old, the C source of B<s_client> is rather hard to
557 read and not a model of how things should be done.
558 A typical SSL client program would be much simpler.
560 The B<-prexit> option is a bit of a hack. We should really report
561 information whenever a session is renegotiated.
565 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
569 The -no_alt_chains options was first added to OpenSSL 1.1.0.
573 Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
575 Licensed under the OpenSSL license (the "License"). You may not use
576 this file except in compliance with the License. You can obtain a copy
577 in the file LICENSE in the source distribution or at
578 L<https://www.openssl.org/source/license.html>.