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>]
54 [B<-verify_depth num>]
55 [B<-verify_email email>]
56 [B<-verify_hostname hostname>]
58 [B<-verify_name name>]
92 [B<-cipher cipherlist>]
94 [B<-starttls protocol>]
95 [B<-xmpphost hostname>]
99 [B<-sess_out filename>]
100 [B<-sess_in filename>]
102 [B<-serverinfo types>]
105 [B<-nextprotoneg protocols>]
108 [B<-keylogfile file>]
109 [B<-early_data file>]
113 The B<s_client> command implements a generic SSL/TLS client which connects
114 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
119 In addition to the options below the B<s_client> utility also supports the
120 common and client only options documented in the
121 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
128 Print out a usage message.
130 =item B<-connect host:port>
132 This specifies the host and optional port to connect to. If not specified
133 then an attempt is made to connect to the local host on port 4433.
135 =item B<-proxy host:port>
137 When used with the B<-connect> flag, the program uses the host and port
138 specified with this flag and issues an HTTP CONNECT command to connect
139 to the desired server.
143 Connect over the specified Unix-domain socket.
153 =item B<-servername name>
155 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
157 =item B<-cert certname>
159 The certificate to use, if one is requested by the server. The default is
160 not to use a certificate.
162 =item B<-certform format>
164 The certificate format to use: DER or PEM. PEM is the default.
166 =item B<-key keyfile>
168 The private key to use. If not specified then the certificate file will
171 =item B<-keyform format>
173 The private format to use: DER or PEM. PEM is the default.
177 the private key password source. For more information about the format of B<arg>
178 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
180 =item B<-verify depth>
182 The verify depth to use. This specifies the maximum length of the
183 server certificate chain and turns on server certificate verification.
184 Currently the verify operation continues after errors so all the problems
185 with a certificate chain can be seen. As a side effect the connection
186 will never fail due to a server certificate verify failure.
188 =item B<-verify_return_error>
190 Return verification errors instead of continuing. This will typically
191 abort the handshake with a fatal error.
193 =item B<-nameopt option>
195 option which determines how the subject or issuer names are displayed. The
196 B<option> argument can be a single option or multiple options separated by
197 commas. Alternatively the B<-nameopt> switch may be used more than once to
198 set multiple options. See the L<x509(1)> manual page for details.
200 =item B<-CApath directory>
202 The directory to use for server certificate verification. This directory
203 must be in "hash format", see B<verify> for more information. These are
204 also used when building the client certificate chain.
206 =item B<-CAfile file>
208 A file containing trusted certificates to use during server authentication
209 and to use when attempting to build the client certificate chain.
213 Do not load the trusted CA certificates from the default file location
217 Do not load the trusted CA certificates from the default directory location
219 =item B<-dane_tlsa_domain domain>
221 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
222 TLSA base domain which becomes the default SNI hint and the primary
223 reference identifier for hostname checks. This must be used in
224 combination with at least one instance of the B<-dane_tlsa_rrdata>
227 When DANE authentication succeeds, the diagnostic output will include
228 the lowest (closest to 0) depth at which a TLSA record authenticated
229 a chain certificate. When that TLSA record is a "2 1 0" trust
230 anchor public key that signed (rather than matched) the top-most
231 certificate of the chain, the result is reported as "TA public key
232 verified". Otherwise, either the TLSA record "matched TA certificate"
233 at a positive depth or else "matched EE certificate" at depth 0.
235 =item B<-dane_tlsa_rrdata rrdata>
237 Use one or more times to specify the RRDATA fields of the DANE TLSA
238 RRset associated with the target service. The B<rrdata> value is
239 specied in "presentation form", that is four whitespace separated
240 fields that specify the usage, selector, matching type and associated
241 data, with the last of these encoded in hexadecimal. Optional
242 whitespace is ignored in the associated data field. For example:
244 $ openssl s_client -brief -starttls smtp \
245 -connect smtp.example.com:25 \
246 -dane_tlsa_domain smtp.example.com \
247 -dane_tlsa_rrdata "2 1 1
248 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
249 -dane_tlsa_rrdata "2 1 1
250 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
253 Verified peername: smtp.example.com
254 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
257 =item B<-dane_ee_no_namechecks>
259 This disables server name checks when authenticating via DANE-EE(3) TLSA
261 For some applications, primarily web browsers, it is not safe to disable name
262 checks due to "unknown key share" attacks, in which a malicious server can
263 convince a client that a connection to a victim server is instead a secure
264 connection to the malicious server.
265 The malicious server may then be able to violate cross-origin scripting
267 Thus, despite the text of RFC7671, name checks are by default enabled for
268 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
270 In particular, SMTP and XMPP clients should set this option as SRV and MX
271 records already make it possible for a remote domain to redirect client
272 connections to any server of its choice, and in any case SMTP and XMPP clients
273 do not execute scripts downloaded from remote servers.
275 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
276 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
277 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
278 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
279 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
280 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
281 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
283 Set various certificate chain validation options. See the
284 L<verify(1)> manual page for details.
288 reconnects to the same server 5 times using the same session ID, this can
289 be used as a test that session caching is working.
293 display the whole server certificate chain: normally only the server
294 certificate itself is displayed.
298 print session information when the program exits. This will always attempt
299 to print out information even if the connection fails. Normally information
300 will only be printed out once if the connection succeeds. This option is useful
301 because the cipher in use may be renegotiated or the connection may fail
302 because a client certificate is required or is requested only after an
303 attempt is made to access a certain URL. Note: the output produced by this
304 option is not always accurate because a connection might never have been
309 prints out the SSL session states.
313 print extensive debugging information including a hex dump of all traffic.
317 show all protocol messages with hex dump.
321 show verbose trace output of protocol messages. OpenSSL needs to be compiled
322 with B<enable-ssl-trace> for this option to work.
326 file to send output of B<-msg> or B<-trace> to, default standard output.
330 tests non-blocking I/O
334 turns on non-blocking I/O
338 this option translated a line feed from the terminal into CR+LF as required
343 inhibit shutting down the connection when end of file is reached in the
348 inhibit printing of session and certificate information. This implicitly
349 turns on B<-ign_eof> as well.
353 shut down the connection when end of file is reached in the input.
354 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
356 =item B<-psk_identity identity>
358 Use the PSK identity B<identity> when using a PSK cipher suite.
362 Use the PSK key B<key> when using a PSK cipher suite. The key is
363 given as a hexadecimal number without leading 0x, for example -psk
366 =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>
368 These options require or disable the use of the specified SSL or TLS protocols.
369 By default B<s_client> will negotiate the highest mutually supported protocol
371 When a specific TLS version is required, only that version will be offered to
372 and accepted from the server.
374 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
376 These options make B<s_client> use DTLS protocols instead of TLS.
377 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
378 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
381 =item B<-fallback_scsv>
383 Send TLS_FALLBACK_SCSV in the ClientHello.
387 switch on asynchronous mode. Cryptographic operations will be performed
388 asynchronously. This will only have an effect if an asynchronous capable engine
389 is also used via the B<-engine> option. For test purposes the dummy async engine
390 (dasync) can be used (if available).
392 =item B<-split_send_frag int>
394 The size used to split data for encrypt pipelines. If more data is written in
395 one go than this value then it will be split into multiple pipelines, up to the
396 maximum number of pipelines defined by max_pipelines. This only has an effect if
397 a suitable ciphersuite has been negotiated, an engine that supports pipelining
398 has been loaded, and max_pipelines is greater than 1. See
399 L<SSL_CTX_set_split_send_fragment(3)> for further information.
401 =item B<-max_pipelines int>
403 The maximum number of encrypt/decrypt pipelines to be used. This will only have
404 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
405 engine) and a suitable ciphersuite has been negotiated. The default value is 1.
406 See L<SSL_CTX_set_max_pipelines(3)> for further information.
408 =item B<-read_buf int>
410 The default read buffer size to be used for connections. This will only have an
411 effect if the buffer size is larger than the size that would otherwise be used
412 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
413 further information).
417 there are several known bug in SSL and TLS implementations. Adding this
418 option enables various workarounds.
422 Enables support for SSL/TLS compression.
423 This option was introduced in OpenSSL 1.1.0.
424 TLS compression is not recommended and is off by default as of
429 Disables support for SSL/TLS compression.
430 TLS compression is not recommended and is off by default as of
435 only provide a brief summary of connection parameters instead of the
436 normal verbose output.
438 =item B<-cipher cipherlist>
440 this allows the cipher list sent by the client to be modified. Although
441 the server determines which cipher suite is used it should take the first
442 supported cipher in the list sent by the client. See the B<ciphers>
443 command for more information.
445 =item B<-starttls protocol>
447 send the protocol-specific message(s) to switch to TLS for communication.
448 B<protocol> is a keyword for the intended protocol. Currently, the only
449 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
450 "irc", "postgres", "lmtp", "nntp", "sieve" and "ldap".
452 =item B<-xmpphost hostname>
454 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
455 specifies the host for the "to" attribute of the stream element.
456 If this option is not specified, then the host specified with "-connect"
459 =item B<-tlsextdebug>
461 print out a hex dump of any TLS extensions received from the server.
465 disable RFC4507bis session ticket support.
467 =item B<-sess_out filename>
469 output SSL session to B<filename>
471 =item B<-sess_in sess.pem>
473 load SSL session from B<filename>. The client will attempt to resume a
474 connection from this session.
478 specifying an engine (by its unique B<id> string) will cause B<s_client>
479 to attempt to obtain a functional reference to the specified engine,
480 thus initialising it if needed. The engine will then be set as the default
481 for all available algorithms.
483 =item B<-rand file(s)>
485 a file or files containing random data used to seed the random number
486 generator, or an EGD socket (see L<RAND_egd(3)>).
487 Multiple files can be specified separated by an OS-dependent character.
488 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
491 =item B<-serverinfo types>
493 a list of comma-separated TLS Extension Types (numbers between 0 and
494 65535). Each type will be sent as an empty ClientHello TLS Extension.
495 The server's response (if any) will be encoded and displayed as a PEM
500 sends a certificate status request to the server (OCSP stapling). The server
501 response (if any) is printed out.
503 =item B<-alpn protocols>, B<-nextprotoneg protocols>
505 these flags enable the
506 Enable the Application-Layer Protocol Negotiation or Next Protocol
507 Negotiation extension, respectively. ALPN is the IETF standard and
509 The B<protocols> list is a
510 comma-separated protocol names that the client should advertise
511 support for. The list should contain most wanted protocols first.
512 Protocol names are printable ASCII strings, for example "http/1.1" or
514 Empty list of protocols is treated specially and will cause the client to
515 advertise support for the TLS extension but disconnect just after
516 receiving ServerHello with a list of server supported protocols.
520 Use one of these two options to control whether Certificate Transparency (CT)
521 is enabled (B<-ct>) or disabled (B<-noct>).
522 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
523 the server and reported at handshake completion.
525 Enabling CT also enables OCSP stapling, as this is one possible delivery method
530 A file containing a list of known Certificate Transparency logs. See
531 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
533 =item B<-keylogfile file>
535 Appends TLS secrets to the specified keylog file such that external programs
536 (like Wireshark) can decrypt TLS connections.
538 =item B<-early_data file>
540 Reads the contents of the specified file and attempts to send it as early data
541 to the server. This will only work with resumed sessions that support early
542 data and when the server accepts the early data.
546 =head1 CONNECTED COMMANDS
548 If a connection is established with an SSL server then any data received
549 from the server is displayed and any key presses will be sent to the
550 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
551 have been given), the session will be renegotiated if the line begins with an
552 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
553 connection will be closed down.
557 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
560 openssl s_client -connect servername:443
562 would typically be used (https uses port 443). If the connection succeeds
563 then an HTTP command can be given such as "GET /" to retrieve a web page.
565 If the handshake fails then there are several possible causes, if it is
566 nothing obvious like no client certificate then the B<-bugs>,
567 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
568 in case it is a buggy server. In particular you should play with these
569 options B<before> submitting a bug report to an OpenSSL mailing list.
571 A frequent problem when attempting to get client certificates working
572 is that a web client complains it has no certificates or gives an empty
573 list to choose from. This is normally because the server is not sending
574 the clients certificate authority in its "acceptable CA list" when it
575 requests a certificate. By using B<s_client> the CA list can be viewed
576 and checked. However some servers only request client authentication
577 after a specific URL is requested. To obtain the list in this case it
578 is necessary to use the B<-prexit> option and send an HTTP request
579 for an appropriate page.
581 If a certificate is specified on the command line using the B<-cert>
582 option it will not be used unless the server specifically requests
583 a client certificate. Therefor merely including a client certificate
584 on the command line is no guarantee that the certificate works.
586 If there are problems verifying a server certificate then the
587 B<-showcerts> option can be used to show the whole chain.
589 The B<s_client> utility is a test tool and is designed to continue the
590 handshake after any certificate verification errors. As a result it will
591 accept any certificate chain (trusted or not) sent by the peer. None test
592 applications should B<not> do this as it makes them vulnerable to a MITM
593 attack. This behaviour can be changed by with the B<-verify_return_error>
594 option: any verify errors are then returned aborting the handshake.
598 Because this program has a lot of options and also because some of the
599 techniques used are rather old, the C source of B<s_client> is rather hard to
600 read and not a model of how things should be done.
601 A typical SSL client program would be much simpler.
603 The B<-prexit> option is a bit of a hack. We should really report
604 information whenever a session is renegotiated.
609 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
613 The -no_alt_chains options was first added to OpenSSL 1.1.0.
617 Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
619 Licensed under the OpenSSL license (the "License"). You may not use
620 this file except in compliance with the License. You can obtain a copy
621 in the file LICENSE in the source distribution or at
622 L<https://www.openssl.org/source/license.html>.