5 s_client - SSL/TLS client program
11 [B<-connect host:port>]
18 [B<-verify_return_error>]
20 [B<-certform DER|PEM>]
24 [B<-CApath directory>]
28 [B<-dane_tlsa_domain domain>]
29 [B<-dane_tlsa_rrdata rrdata>]
30 [B<-dane_ee_no_namechecks>]
31 [B<-attime timestamp>]
53 [B<-verify_depth num>]
54 [B<-verify_email email>]
55 [B<-verify_hostname hostname>]
57 [B<-verify_name name>]
91 [B<-cipher cipherlist>]
93 [B<-starttls protocol>]
94 [B<-xmpphost hostname>]
98 [B<-sess_out filename>]
99 [B<-sess_in filename>]
101 [B<-serverinfo types>]
104 [B<-nextprotoneg protocols>]
110 The B<s_client> command implements a generic SSL/TLS client which connects
111 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
116 In addition to the options below the B<s_client> utility also supports the
117 common and client only options documented in the
118 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
125 Print out a usage message.
127 =item B<-connect host:port>
129 This specifies the host and optional port to connect to. If not specified
130 then an attempt is made to connect to the local host on port 4433.
132 =item B<-proxy host:port>
134 When used with the B<-connect> flag, the program uses the host and port
135 specified with this flag and issues an HTTP CONNECT command to connect
136 to the desired server.
140 Connect over the specified Unix-domain socket.
150 =item B<-servername name>
152 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
154 =item B<-cert certname>
156 The certificate to use, if one is requested by the server. The default is
157 not to use a certificate.
159 =item B<-certform format>
161 The certificate format to use: DER or PEM. PEM is the default.
163 =item B<-key keyfile>
165 The private key to use. If not specified then the certificate file will
168 =item B<-keyform format>
170 The private format to use: DER or PEM. PEM is the default.
174 the private key password source. For more information about the format of B<arg>
175 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
177 =item B<-verify depth>
179 The verify depth to use. This specifies the maximum length of the
180 server certificate chain and turns on server certificate verification.
181 Currently the verify operation continues after errors so all the problems
182 with a certificate chain can be seen. As a side effect the connection
183 will never fail due to a server certificate verify failure.
185 =item B<-verify_return_error>
187 Return verification errors instead of continuing. This will typically
188 abort the handshake with a fatal error.
190 =item B<-CApath directory>
192 The directory to use for server certificate verification. This directory
193 must be in "hash format", see B<verify> for more information. These are
194 also used when building the client certificate chain.
196 =item B<-CAfile file>
198 A file containing trusted certificates to use during server authentication
199 and to use when attempting to build the client certificate chain.
203 Do not load the trusted CA certificates from the default file location
207 Do not load the trusted CA certificates from the default directory location
209 =item B<-dane_tlsa_domain domain>
211 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
212 TLSA base domain which becomes the default SNI hint and the primary
213 reference identifier for hostname checks. This must be used in
214 combination with at least one instance of the B<-dane_tlsa_rrdata>
217 When DANE authentication succeeds, the diagnostic output will include
218 the lowest (closest to 0) depth at which a TLSA record authenticated
219 a chain certificate. When that TLSA record is a "2 1 0" trust
220 anchor public key that signed (rather than matched) the top-most
221 certificate of the chain, the result is reported as "TA public key
222 verified". Otherwise, either the TLSA record "matched TA certificate"
223 at a positive depth or else "matched EE certificate" at depth 0.
225 =item B<-dane_tlsa_rrdata rrdata>
227 Use one or more times to specify the RRDATA fields of the DANE TLSA
228 RRset associated with the target service. The B<rrdata> value is
229 specied in "presentation form", that is four whitespace separated
230 fields that specify the usage, selector, matching type and associated
231 data, with the last of these encoded in hexadecimal. Optional
232 whitespace is ignored in the associated data field. For example:
234 $ openssl s_client -brief -starttls smtp \
235 -connect smtp.example.com:25 \
236 -dane_tlsa_domain smtp.example.com \
237 -dane_tlsa_rrdata "2 1 1
238 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
239 -dane_tlsa_rrdata "2 1 1
240 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
243 Verified peername: smtp.example.com
244 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
247 =item B<-dane_ee_no_namechecks>
249 This disables server name checks when authenticating via DANE-EE(3) TLSA
251 For some applications, primarily web browsers, it is not safe to disable name
252 checks due to "unknown key share" attacks, in which a malicious server can
253 convince a client that a connection to a victim server is instead a secure
254 connection to the malicious server.
255 The malicious server may then be able to violate cross-origin scripting
257 Thus, despite the text of RFC7671, name checks are by default enabled for
258 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
260 In particular, SMTP and XMPP clients should set this option as SRV and MX
261 records already make it possible for a remote domain to redirect client
262 connections to any server of its choice, and in any case SMTP and XMPP clients
263 do not execute scripts downloaded from remote servers.
265 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
266 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
267 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
268 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
269 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
270 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
271 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
273 Set various certificate chain validation options. See the
274 L<verify(1)> manual page for details.
278 reconnects to the same server 5 times using the same session ID, this can
279 be used as a test that session caching is working.
283 display the whole server certificate chain: normally only the server
284 certificate itself is displayed.
288 print session information when the program exits. This will always attempt
289 to print out information even if the connection fails. Normally information
290 will only be printed out once if the connection succeeds. This option is useful
291 because the cipher in use may be renegotiated or the connection may fail
292 because a client certificate is required or is requested only after an
293 attempt is made to access a certain URL. Note: the output produced by this
294 option is not always accurate because a connection might never have been
299 prints out the SSL session states.
303 print extensive debugging information including a hex dump of all traffic.
307 show all protocol messages with hex dump.
311 show verbose trace output of protocol messages. OpenSSL needs to be compiled
312 with B<enable-ssl-trace> for this option to work.
316 file to send output of B<-msg> or B<-trace> to, default standard output.
320 tests non-blocking I/O
324 turns on non-blocking I/O
328 this option translated a line feed from the terminal into CR+LF as required
333 inhibit shutting down the connection when end of file is reached in the
338 inhibit printing of session and certificate information. This implicitly
339 turns on B<-ign_eof> as well.
343 shut down the connection when end of file is reached in the input.
344 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
346 =item B<-psk_identity identity>
348 Use the PSK identity B<identity> when using a PSK cipher suite.
352 Use the PSK key B<key> when using a PSK cipher suite. The key is
353 given as a hexadecimal number without leading 0x, for example -psk
356 =item B<-ssl3>, B<-tls1>, B<-tls1_1>, B<-tls1_2>, B<-tls1_3>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>, B<-no_tls1_3>
358 These options require or disable the use of the specified SSL or TLS protocols.
359 By default B<s_client> will negotiate the highest mutually supported protocol
361 When a specific TLS version is required, only that version will be offered to
362 and accepted from the server.
364 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
366 These options make B<s_client> use DTLS protocols instead of TLS.
367 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
368 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
371 =item B<-fallback_scsv>
373 Send TLS_FALLBACK_SCSV in the ClientHello.
377 switch on asynchronous mode. Cryptographic operations will be performed
378 asynchronously. This will only have an effect if an asynchronous capable engine
379 is also used via the B<-engine> option. For test purposes the dummy async engine
380 (dasync) can be used (if available).
382 =item B<-split_send_frag int>
384 The size used to split data for encrypt pipelines. If more data is written in
385 one go than this value then it will be split into multiple pipelines, up to the
386 maximum number of pipelines defined by max_pipelines. This only has an effect if
387 a suitable ciphersuite has been negotiated, an engine that supports pipelining
388 has been loaded, and max_pipelines is greater than 1. See
389 L<SSL_CTX_set_split_send_fragment(3)> for further information.
391 =item B<-max_pipelines int>
393 The maximum number of encrypt/decrypt pipelines to be used. This will only have
394 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
395 engine) and a suitable ciphersuite has been negotiated. The default value is 1.
396 See L<SSL_CTX_set_max_pipelines(3)> for further information.
398 =item B<-read_buf int>
400 The default read buffer size to be used for connections. This will only have an
401 effect if the buffer size is larger than the size that would otherwise be used
402 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
403 further information).
407 there are several known bug in SSL and TLS implementations. Adding this
408 option enables various workarounds.
412 Enables support for SSL/TLS compression.
413 This option was introduced in OpenSSL 1.1.0.
414 TLS compression is not recommended and is off by default as of
419 Disables support for SSL/TLS compression.
420 TLS compression is not recommended and is off by default as of
425 only provide a brief summary of connection parameters instead of the
426 normal verbose output.
428 =item B<-cipher cipherlist>
430 this allows the cipher list sent by the client to be modified. Although
431 the server determines which cipher suite is used it should take the first
432 supported cipher in the list sent by the client. See the B<ciphers>
433 command for more information.
435 =item B<-starttls protocol>
437 send the protocol-specific message(s) to switch to TLS for communication.
438 B<protocol> is a keyword for the intended protocol. Currently, the only
439 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
440 "irc", "postgres", "lmtp" and "nntp".
442 =item B<-xmpphost hostname>
444 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
445 specifies the host for the "to" attribute of the stream element.
446 If this option is not specified, then the host specified with "-connect"
449 =item B<-tlsextdebug>
451 print out a hex dump of any TLS extensions received from the server.
455 disable RFC4507bis session ticket support.
457 =item B<-sess_out filename>
459 output SSL session to B<filename>
461 =item B<-sess_in sess.pem>
463 load SSL session from B<filename>. The client will attempt to resume a
464 connection from this session.
468 specifying an engine (by its unique B<id> string) will cause B<s_client>
469 to attempt to obtain a functional reference to the specified engine,
470 thus initialising it if needed. The engine will then be set as the default
471 for all available algorithms.
473 =item B<-rand file(s)>
475 a file or files containing random data used to seed the random number
476 generator, or an EGD socket (see L<RAND_egd(3)>).
477 Multiple files can be specified separated by an OS-dependent character.
478 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
481 =item B<-serverinfo types>
483 a list of comma-separated TLS Extension Types (numbers between 0 and
484 65535). Each type will be sent as an empty ClientHello TLS Extension.
485 The server's response (if any) will be encoded and displayed as a PEM
490 sends a certificate status request to the server (OCSP stapling). The server
491 response (if any) is printed out.
493 =item B<-alpn protocols>, B<-nextprotoneg protocols>
495 these flags enable the
496 Enable the Application-Layer Protocol Negotiation or Next Protocol
497 Negotiation extension, respectively. ALPN is the IETF standard and
499 The B<protocols> list is a
500 comma-separated protocol names that the client should advertise
501 support for. The list should contain most wanted protocols first.
502 Protocol names are printable ASCII strings, for example "http/1.1" or
504 Empty list of protocols is treated specially and will cause the client to
505 advertise support for the TLS extension but disconnect just after
506 receiving ServerHello with a list of server supported protocols.
510 Use one of these two options to control whether Certificate Transparency (CT)
511 is enabled (B<-ct>) or disabled (B<-noct>).
512 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
513 the server and reported at handshake completion.
515 Enabling CT also enables OCSP stapling, as this is one possible delivery method
520 A file containing a list of known Certificate Transparency logs. See
521 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
523 =item B<-keylogfile path>
525 Appends TLS secrets to the specified keylog file such that external programs
526 (like Wireshark) can decrypt TLS connections.
530 =head1 CONNECTED COMMANDS
532 If a connection is established with an SSL server then any data received
533 from the server is displayed and any key presses will be sent to the
534 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
535 have been given), the session will be renegotiated if the line begins with an
536 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
537 connection will be closed down.
541 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
544 openssl s_client -connect servername:443
546 would typically be used (https uses port 443). If the connection succeeds
547 then an HTTP command can be given such as "GET /" to retrieve a web page.
549 If the handshake fails then there are several possible causes, if it is
550 nothing obvious like no client certificate then the B<-bugs>,
551 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
552 in case it is a buggy server. In particular you should play with these
553 options B<before> submitting a bug report to an OpenSSL mailing list.
555 A frequent problem when attempting to get client certificates working
556 is that a web client complains it has no certificates or gives an empty
557 list to choose from. This is normally because the server is not sending
558 the clients certificate authority in its "acceptable CA list" when it
559 requests a certificate. By using B<s_client> the CA list can be viewed
560 and checked. However some servers only request client authentication
561 after a specific URL is requested. To obtain the list in this case it
562 is necessary to use the B<-prexit> option and send an HTTP request
563 for an appropriate page.
565 If a certificate is specified on the command line using the B<-cert>
566 option it will not be used unless the server specifically requests
567 a client certificate. Therefor merely including a client certificate
568 on the command line is no guarantee that the certificate works.
570 If there are problems verifying a server certificate then the
571 B<-showcerts> option can be used to show the whole chain.
573 The B<s_client> utility is a test tool and is designed to continue the
574 handshake after any certificate verification errors. As a result it will
575 accept any certificate chain (trusted or not) sent by the peer. None test
576 applications should B<not> do this as it makes them vulnerable to a MITM
577 attack. This behaviour can be changed by with the B<-verify_return_error>
578 option: any verify errors are then returned aborting the handshake.
582 Because this program has a lot of options and also because some of the
583 techniques used are rather old, the C source of B<s_client> is rather hard to
584 read and not a model of how things should be done.
585 A typical SSL client program would be much simpler.
587 The B<-prexit> option is a bit of a hack. We should really report
588 information whenever a session is renegotiated.
593 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
597 The -no_alt_chains options was first added to OpenSSL 1.1.0.
601 Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
603 Licensed under the OpenSSL license (the "License"). You may not use
604 this file except in compliance with the License. You can obtain a copy
605 in the file LICENSE in the source distribution or at
606 L<https://www.openssl.org/source/license.html>.