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>]
88 [B<-cipher cipherlist>]
90 [B<-starttls protocol>]
91 [B<-xmpphost hostname>]
95 [B<-sess_out filename>]
96 [B<-sess_in filename>]
98 [B<-serverinfo types>]
101 [B<-nextprotoneg protocols>]
107 The B<s_client> command implements a generic SSL/TLS client which connects
108 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
113 In addition to the options below the B<s_client> utility also supports the
114 common and client only options documented in the
115 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
122 Print out a usage message.
124 =item B<-connect host:port>
126 This specifies the host and optional port to connect to. If not specified
127 then an attempt is made to connect to the local host on port 4433.
129 =item B<-proxy host:port>
131 When used with the B<-connect> flag, the program uses the host and port
132 specified with this flag and issues an HTTP CONNECT command to connect
133 to the desired server.
135 =item B<-servername name>
137 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
139 =item B<-cert certname>
141 The certificate to use, if one is requested by the server. The default is
142 not to use a certificate.
144 =item B<-certform format>
146 The certificate format to use: DER or PEM. PEM is the default.
148 =item B<-key keyfile>
150 The private key to use. If not specified then the certificate file will
153 =item B<-keyform format>
155 The private format to use: DER or PEM. PEM is the default.
159 the private key password source. For more information about the format of B<arg>
160 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
162 =item B<-verify depth>
164 The verify depth to use. This specifies the maximum length of the
165 server certificate chain and turns on server certificate verification.
166 Currently the verify operation continues after errors so all the problems
167 with a certificate chain can be seen. As a side effect the connection
168 will never fail due to a server certificate verify failure.
170 =item B<-verify_return_error>
172 Return verification errors instead of continuing. This will typically
173 abort the handshake with a fatal error.
175 =item B<-CApath directory>
177 The directory to use for server certificate verification. This directory
178 must be in "hash format", see B<verify> for more information. These are
179 also used when building the client certificate chain.
181 =item B<-CAfile file>
183 A file containing trusted certificates to use during server authentication
184 and to use when attempting to build the client certificate chain.
188 Do not load the trusted CA certificates from the default file location
192 Do not load the trusted CA certificates from the default directory location
194 =item B<-dane_tlsa_domain domain>
196 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
197 TLSA base domain which becomes the default SNI hint and the primary
198 reference identifier for hostname checks. This must be used in
199 combination with at least one instance of the B<-dane_tlsa_rrdata>
202 When DANE authentication succeeds, the diagnostic output will include
203 the lowest (closest to 0) depth at which a TLSA record authenticated
204 a chain certificate. When that TLSA record is a "2 1 0" trust
205 anchor public key that signed (rather than matched) the top-most
206 certificate of the chain, the result is reported as "TA public key
207 verified". Otherwise, either the TLSA record "matched TA certificate"
208 at a positive depth or else "matched EE certificate" at depth 0.
210 =item B<-dane_tlsa_rrdata rrdata>
212 Use one or more times to specify the RRDATA fields of the DANE TLSA
213 RRset associated with the target service. The B<rrdata> value is
214 specied in "presentation form", that is four whitespace separated
215 fields that specify the usage, selector, matching type and associated
216 data, with the last of these encoded in hexadecimal. Optional
217 whitespace is ignored in the associated data field. For example:
219 $ openssl s_client -brief -starttls smtp \
220 -connect smtp.example.com:25 \
221 -dane_tlsa_domain smtp.example.com \
222 -dane_tlsa_rrdata "2 1 1
223 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
224 -dane_tlsa_rrdata "2 1 1
225 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
228 Verified peername: smtp.example.com
229 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
232 =item B<-dane_ee_no_namechecks>
234 This disables server name checks when authenticating via DANE-EE(3) TLSA
236 For some applications, primarily web browsers, it is not safe to disable name
237 checks due to "unknown key share" attacks, in which a malicious server can
238 convince a client that a connection to a victim server is instead a secure
239 connection to the malicious server.
240 The malicious server may then be able to violate cross-origin scripting
242 Thus, despite the text of RFC7671, name checks are by default enabled for
243 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
245 In particular, SMTP and XMPP clients should set this option as SRV and MX
246 records already make it possible for a remote domain to redirect client
247 connections to any server of its choice, and in any case SMTP and XMPP clients
248 do not execute scripts downloaded from remote servers.
250 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
251 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
252 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
253 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
254 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
255 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
256 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
258 Set various certificate chain validation options. See the
259 L<verify(1)> manual page for details.
263 reconnects to the same server 5 times using the same session ID, this can
264 be used as a test that session caching is working.
268 display the whole server certificate chain: normally only the server
269 certificate itself is displayed.
273 print session information when the program exits. This will always attempt
274 to print out information even if the connection fails. Normally information
275 will only be printed out once if the connection succeeds. This option is useful
276 because the cipher in use may be renegotiated or the connection may fail
277 because a client certificate is required or is requested only after an
278 attempt is made to access a certain URL. Note: the output produced by this
279 option is not always accurate because a connection might never have been
284 prints out the SSL session states.
288 print extensive debugging information including a hex dump of all traffic.
292 show all protocol messages with hex dump.
296 show verbose trace output of protocol messages. OpenSSL needs to be compiled
297 with B<enable-ssl-trace> for this option to work.
301 file to send output of B<-msg> or B<-trace> to, default standard output.
305 tests non-blocking I/O
309 turns on non-blocking I/O
313 this option translated a line feed from the terminal into CR+LF as required
318 inhibit shutting down the connection when end of file is reached in the
323 inhibit printing of session and certificate information. This implicitly
324 turns on B<-ign_eof> as well.
328 shut down the connection when end of file is reached in the input.
329 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
331 =item B<-psk_identity identity>
333 Use the PSK identity B<identity> when using a PSK cipher suite.
337 Use the PSK key B<key> when using a PSK cipher suite. The key is
338 given as a hexadecimal number without leading 0x, for example -psk
341 =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>
343 These options require or disable the use of the specified SSL or TLS protocols.
344 By default B<s_client> will negotiate the highest mutually supported protocol
346 When a specific TLS version is required, only that version will be offered to
347 and accepted from the server.
349 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
351 These options make B<s_client> use DTLS protocols instead of TLS.
352 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
353 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
356 =item B<-fallback_scsv>
358 Send TLS_FALLBACK_SCSV in the ClientHello.
362 switch on asynchronous mode. Cryptographic operations will be performed
363 asynchronously. This will only have an effect if an asynchronous capable engine
364 is also used via the B<-engine> option. For test purposes the dummy async engine
365 (dasync) can be used (if available).
367 =item B<-split_send_frag int>
369 The size used to split data for encrypt pipelines. If more data is written in
370 one go than this value then it will be split into multiple pipelines, up to the
371 maximum number of pipelines defined by max_pipelines. This only has an effect if
372 a suitable ciphersuite has been negotiated, an engine that supports pipelining
373 has been loaded, and max_pipelines is greater than 1. See
374 L<SSL_CTX_set_split_send_fragment(3)> for further information.
376 =item B<-max_pipelines int>
378 The maximum number of encrypt/decrypt pipelines to be used. This will only have
379 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
380 engine) and a suitable ciphersuite has been negotiated. The default value is 1.
381 See L<SSL_CTX_set_max_pipelines(3)> for further information.
383 =item B<-read_buf int>
385 The default read buffer size to be used for connections. This will only have an
386 effect if the buffer size is larger than the size that would otherwise be used
387 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
388 further information).
392 there are several known bug in SSL and TLS implementations. Adding this
393 option enables various workarounds.
397 Enables support for SSL/TLS compression.
398 This option was introduced in OpenSSL 1.1.0.
399 TLS compression is not recommended and is off by default as of
404 Disables support for SSL/TLS compression.
405 TLS compression is not recommended and is off by default as of
410 only provide a brief summary of connection parameters instead of the
411 normal verbose output.
413 =item B<-cipher cipherlist>
415 this allows the cipher list sent by the client to be modified. Although
416 the server determines which cipher suite is used it should take the first
417 supported cipher in the list sent by the client. See the B<ciphers>
418 command for more information.
420 =item B<-starttls protocol>
422 send the protocol-specific message(s) to switch to TLS for communication.
423 B<protocol> is a keyword for the intended protocol. Currently, the only
424 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
425 "irc" and "postgres."
427 =item B<-xmpphost hostname>
429 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
430 specifies the host for the "to" attribute of the stream element.
431 If this option is not specified, then the host specified with "-connect"
434 =item B<-tlsextdebug>
436 print out a hex dump of any TLS extensions received from the server.
440 disable RFC4507bis session ticket support.
442 =item B<-sess_out filename>
444 output SSL session to B<filename>
446 =item B<-sess_in sess.pem>
448 load SSL session from B<filename>. The client will attempt to resume a
449 connection from this session.
453 specifying an engine (by its unique B<id> string) will cause B<s_client>
454 to attempt to obtain a functional reference to the specified engine,
455 thus initialising it if needed. The engine will then be set as the default
456 for all available algorithms.
458 =item B<-rand file(s)>
460 a file or files containing random data used to seed the random number
461 generator, or an EGD socket (see L<RAND_egd(3)>).
462 Multiple files can be specified separated by an OS-dependent character.
463 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
466 =item B<-serverinfo types>
468 a list of comma-separated TLS Extension Types (numbers between 0 and
469 65535). Each type will be sent as an empty ClientHello TLS Extension.
470 The server's response (if any) will be encoded and displayed as a PEM
475 sends a certificate status request to the server (OCSP stapling). The server
476 response (if any) is printed out.
478 =item B<-alpn protocols>, B<-nextprotoneg protocols>
480 these flags enable the
481 Enable the Application-Layer Protocol Negotiation or Next Protocol
482 Negotiation extension, respectively. ALPN is the IETF standard and
484 The B<protocols> list is a
485 comma-separated protocol names that the client should advertise
486 support for. The list should contain most wanted protocols first.
487 Protocol names are printable ASCII strings, for example "http/1.1" or
489 Empty list of protocols is treated specially and will cause the client to
490 advertise support for the TLS extension but disconnect just after
491 receiving ServerHello with a list of server supported protocols.
495 Use one of these two options to control whether Certificate Transparency (CT)
496 is enabled (B<-ct>) or disabled (B<-noct>).
497 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
498 the server and reported at handshake completion.
500 Enabling CT also enables OCSP stapling, as this is one possible delivery method
505 A file containing a list of known Certificate Transparency logs. See
506 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
510 =head1 CONNECTED COMMANDS
512 If a connection is established with an SSL server then any data received
513 from the server is displayed and any key presses will be sent to the
514 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
515 have been given), the session will be renegotiated if the line begins with an
516 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
517 connection will be closed down.
521 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
524 openssl s_client -connect servername:443
526 would typically be used (https uses port 443). If the connection succeeds
527 then an HTTP command can be given such as "GET /" to retrieve a web page.
529 If the handshake fails then there are several possible causes, if it is
530 nothing obvious like no client certificate then the B<-bugs>,
531 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
532 in case it is a buggy server. In particular you should play with these
533 options B<before> submitting a bug report to an OpenSSL mailing list.
535 A frequent problem when attempting to get client certificates working
536 is that a web client complains it has no certificates or gives an empty
537 list to choose from. This is normally because the server is not sending
538 the clients certificate authority in its "acceptable CA list" when it
539 requests a certificate. By using B<s_client> the CA list can be viewed
540 and checked. However some servers only request client authentication
541 after a specific URL is requested. To obtain the list in this case it
542 is necessary to use the B<-prexit> option and send an HTTP request
543 for an appropriate page.
545 If a certificate is specified on the command line using the B<-cert>
546 option it will not be used unless the server specifically requests
547 a client certificate. Therefor merely including a client certificate
548 on the command line is no guarantee that the certificate works.
550 If there are problems verifying a server certificate then the
551 B<-showcerts> option can be used to show the whole chain.
553 The B<s_client> utility is a test tool and is designed to continue the
554 handshake after any certificate verification errors. As a result it will
555 accept any certificate chain (trusted or not) sent by the peer. None test
556 applications should B<not> do this as it makes them vulnerable to a MITM
557 attack. This behaviour can be changed by with the B<-verify_return_error>
558 option: any verify errors are then returned aborting the handshake.
562 Because this program has a lot of options and also because some of the
563 techniques used are rather old, the C source of B<s_client> is rather hard to
564 read and not a model of how things should be done.
565 A typical SSL client program would be much simpler.
567 The B<-prexit> option is a bit of a hack. We should really report
568 information whenever a session is renegotiated.
573 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
577 The -no_alt_chains options was first added to OpenSSL 1.1.0.
581 Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
583 Licensed under the OpenSSL license (the "License"). You may not use
584 this file except in compliance with the License. You can obtain a copy
585 in the file LICENSE in the source distribution or at
586 L<https://www.openssl.org/source/license.html>.