5 s_client - SSL/TLS client program
11 [B<-connect host:port>]
19 [B<-verify_return_error>]
21 [B<-certform DER|PEM>]
25 [B<-CApath directory>]
29 [B<-requestCAfile filename>]
30 [B<-dane_tlsa_domain domain>]
31 [B<-dane_tlsa_rrdata rrdata>]
32 [B<-dane_ee_no_namechecks>]
33 [B<-attime timestamp>]
56 [B<-verify_depth num>]
57 [B<-verify_email email>]
58 [B<-verify_hostname hostname>]
60 [B<-verify_name name>]
96 [B<-allow_no_dhe_kex>]
97 [B<-sigalgs sigalglist>]
98 [B<-curves curvelist>]
99 [B<-cipher cipherlist>]
101 [B<-starttls protocol>]
102 [B<-xmpphost hostname>]
107 [B<-sess_out filename>]
108 [B<-sess_in filename>]
111 [B<-serverinfo types>]
114 [B<-nextprotoneg protocols>]
118 [B<-keylogfile file>]
119 [B<-early_data file>]
124 The B<s_client> command implements a generic SSL/TLS client which connects
125 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
130 In addition to the options below the B<s_client> utility also supports the
131 common and client only options documented in the
132 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
139 Print out a usage message.
141 =item B<-connect host:port>
143 This specifies the host and optional port to connect to. It is possible to
144 select the host and port using the optional target positional argument instead.
145 If neither this nor the target positonal argument are specified then an attempt
146 is made to connect to the local host on port 4433.
148 =item B<-proxy host:port>
150 When used with the B<-connect> flag, the program uses the host and port
151 specified with this flag and issues an HTTP CONNECT command to connect
152 to the desired server.
156 Connect over the specified Unix-domain socket.
166 =item B<-servername name>
168 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
169 the given value. If both this option and the B<-noservername> are not given, the
170 TLS SNI extension is still set to the hostname provided to the B<-connect> option,
171 or "localhost" if B<-connect> has not been supplied. This is default since OpenSSL
174 Even though SNI name should normally be a DNS name and not an IP address, this
175 option will not make the distinction when parsing B<-connect> and will send
176 IP address if one passed.
178 =item B<-noservername>
180 Suppresses sending of the SNI (Server Name Indication) extension in the
181 ClientHello message. Cannot be used in conjunction with the B<-servername> or
182 <-dane_tlsa_domain> options.
184 =item B<-cert certname>
186 The certificate to use, if one is requested by the server. The default is
187 not to use a certificate.
189 =item B<-certform format>
191 The certificate format to use: DER or PEM. PEM is the default.
193 =item B<-key keyfile>
195 The private key to use. If not specified then the certificate file will
198 =item B<-keyform format>
200 The private format to use: DER or PEM. PEM is the default.
204 the private key password source. For more information about the format of B<arg>
205 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
207 =item B<-verify depth>
209 The verify depth to use. This specifies the maximum length of the
210 server certificate chain and turns on server certificate verification.
211 Currently the verify operation continues after errors so all the problems
212 with a certificate chain can be seen. As a side effect the connection
213 will never fail due to a server certificate verify failure.
215 =item B<-verify_return_error>
217 Return verification errors instead of continuing. This will typically
218 abort the handshake with a fatal error.
220 =item B<-nameopt option>
222 Option which determines how the subject or issuer names are displayed. The
223 B<option> argument can be a single option or multiple options separated by
224 commas. Alternatively the B<-nameopt> switch may be used more than once to
225 set multiple options. See the L<x509(1)> manual page for details.
227 =item B<-CApath directory>
229 The directory to use for server certificate verification. This directory
230 must be in "hash format", see B<verify> for more information. These are
231 also used when building the client certificate chain.
233 =item B<-CAfile file>
235 A file containing trusted certificates to use during server authentication
236 and to use when attempting to build the client certificate chain.
240 Do not load the trusted CA certificates from the default file location
244 Do not load the trusted CA certificates from the default directory location
246 =item B<-requestCAfile file>
248 A file containing a list of certificates whose subject names will be sent
249 to the server in the B<certificate_authorities> extension. Only supported
252 =item B<-dane_tlsa_domain domain>
254 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
255 TLSA base domain which becomes the default SNI hint and the primary
256 reference identifier for hostname checks. This must be used in
257 combination with at least one instance of the B<-dane_tlsa_rrdata>
260 When DANE authentication succeeds, the diagnostic output will include
261 the lowest (closest to 0) depth at which a TLSA record authenticated
262 a chain certificate. When that TLSA record is a "2 1 0" trust
263 anchor public key that signed (rather than matched) the top-most
264 certificate of the chain, the result is reported as "TA public key
265 verified". Otherwise, either the TLSA record "matched TA certificate"
266 at a positive depth or else "matched EE certificate" at depth 0.
268 =item B<-dane_tlsa_rrdata rrdata>
270 Use one or more times to specify the RRDATA fields of the DANE TLSA
271 RRset associated with the target service. The B<rrdata> value is
272 specied in "presentation form", that is four whitespace separated
273 fields that specify the usage, selector, matching type and associated
274 data, with the last of these encoded in hexadecimal. Optional
275 whitespace is ignored in the associated data field. For example:
277 $ openssl s_client -brief -starttls smtp \
278 -connect smtp.example.com:25 \
279 -dane_tlsa_domain smtp.example.com \
280 -dane_tlsa_rrdata "2 1 1
281 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
282 -dane_tlsa_rrdata "2 1 1
283 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
286 Verified peername: smtp.example.com
287 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
290 =item B<-dane_ee_no_namechecks>
292 This disables server name checks when authenticating via DANE-EE(3) TLSA
294 For some applications, primarily web browsers, it is not safe to disable name
295 checks due to "unknown key share" attacks, in which a malicious server can
296 convince a client that a connection to a victim server is instead a secure
297 connection to the malicious server.
298 The malicious server may then be able to violate cross-origin scripting
300 Thus, despite the text of RFC7671, name checks are by default enabled for
301 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
303 In particular, SMTP and XMPP clients should set this option as SRV and MX
304 records already make it possible for a remote domain to redirect client
305 connections to any server of its choice, and in any case SMTP and XMPP clients
306 do not execute scripts downloaded from remote servers.
308 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
309 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
310 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
311 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
312 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
313 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
314 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
316 Set various certificate chain validation options. See the
317 L<verify(1)> manual page for details.
321 Reconnects to the same server 5 times using the same session ID, this can
322 be used as a test that session caching is working.
326 Display the whole server certificate chain: normally only the server
327 certificate itself is displayed.
331 Print session information when the program exits. This will always attempt
332 to print out information even if the connection fails. Normally information
333 will only be printed out once if the connection succeeds. This option is useful
334 because the cipher in use may be renegotiated or the connection may fail
335 because a client certificate is required or is requested only after an
336 attempt is made to access a certain URL. Note: the output produced by this
337 option is not always accurate because a connection might never have been
342 Prints out the SSL session states.
346 Print extensive debugging information including a hex dump of all traffic.
350 Show all protocol messages with hex dump.
354 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
355 with B<enable-ssl-trace> for this option to work.
359 File to send output of B<-msg> or B<-trace> to, default standard output.
363 Tests non-blocking I/O
367 Turns on non-blocking I/O
371 This option translated a line feed from the terminal into CR+LF as required
376 Inhibit shutting down the connection when end of file is reached in the
381 Inhibit printing of session and certificate information. This implicitly
382 turns on B<-ign_eof> as well.
386 Shut down the connection when end of file is reached in the input.
387 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
389 =item B<-psk_identity identity>
391 Use the PSK identity B<identity> when using a PSK cipher suite.
392 The default value is "Client_identity" (without the quotes).
396 Use the PSK key B<key> when using a PSK cipher suite. The key is
397 given as a hexadecimal number without leading 0x, for example -psk
399 This option must be provided in order to use a PSK cipher.
401 =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>
403 These options require or disable the use of the specified SSL or TLS protocols.
404 By default B<s_client> will negotiate the highest mutually supported protocol
406 When a specific TLS version is required, only that version will be offered to
407 and accepted from the server.
409 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
411 These options make B<s_client> use DTLS protocols instead of TLS.
412 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
413 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
418 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
419 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
420 available where OpenSSL has support for SCTP enabled.
422 =item B<-fallback_scsv>
424 Send TLS_FALLBACK_SCSV in the ClientHello.
428 Switch on asynchronous mode. Cryptographic operations will be performed
429 asynchronously. This will only have an effect if an asynchronous capable engine
430 is also used via the B<-engine> option. For test purposes the dummy async engine
431 (dasync) can be used (if available).
433 =item B<-max_send_frag int>
435 The maximum size of data fragment to send.
436 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
438 =item B<-split_send_frag int>
440 The size used to split data for encrypt pipelines. If more data is written in
441 one go than this value then it will be split into multiple pipelines, up to the
442 maximum number of pipelines defined by max_pipelines. This only has an effect if
443 a suitable cipher suite has been negotiated, an engine that supports pipelining
444 has been loaded, and max_pipelines is greater than 1. See
445 L<SSL_CTX_set_split_send_fragment(3)> for further information.
447 =item B<-max_pipelines int>
449 The maximum number of encrypt/decrypt pipelines to be used. This will only have
450 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
451 engine) and a suitable cipher suite has been negotiated. The default value is 1.
452 See L<SSL_CTX_set_max_pipelines(3)> for further information.
454 =item B<-read_buf int>
456 The default read buffer size to be used for connections. This will only have an
457 effect if the buffer size is larger than the size that would otherwise be used
458 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
459 further information).
463 There are several known bug in SSL and TLS implementations. Adding this
464 option enables various workarounds.
468 Enables support for SSL/TLS compression.
469 This option was introduced in OpenSSL 1.1.0.
470 TLS compression is not recommended and is off by default as of
475 Disables support for SSL/TLS compression.
476 TLS compression is not recommended and is off by default as of
481 Only provide a brief summary of connection parameters instead of the
482 normal verbose output.
484 =item B<-sigalgs sigalglist>
486 Specifies the list of signature algorithms that are sent by the client.
487 The server selects one entry in the list based on its preferences.
488 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
490 =item B<-curves curvelist>
492 Specifies the list of supported curves to be sent by the client. The curve is
493 is ultimately selected by the server. For a list of all curves, use:
495 $ openssl ecparam -list_curves
497 =item B<-cipher cipherlist>
499 This allows the cipher list sent by the client to be modified. Although
500 the server determines which cipher suite is used it should take the first
501 supported cipher in the list sent by the client. See the B<ciphers>
502 command for more information.
504 =item B<-starttls protocol>
506 Send the protocol-specific message(s) to switch to TLS for communication.
507 B<protocol> is a keyword for the intended protocol. Currently, the only
508 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
509 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
511 =item B<-xmpphost hostname>
513 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
514 specifies the host for the "to" attribute of the stream element.
515 If this option is not specified, then the host specified with "-connect"
518 This option is an alias of the B<-name> option for "xmpp" and "xmpp-server".
520 =item B<-name hostname>
522 This option is used to specify hostname information for various protocols
523 used with B<-starttls> option. Currently only "xmpp", "xmpp-server",
524 "smtp" and "lmtp" can utilize this B<-name> option.
526 If this option is used with "-starttls xmpp" or "-starttls xmpp-server",
527 if specifies the host for the "to" attribute of the stream element. If this
528 option is not specified, then the host specified with "-connect" will be used.
530 If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies
531 the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If
532 this option is not specified, then "mail.example.com" will be used.
534 =item B<-tlsextdebug>
536 Print out a hex dump of any TLS extensions received from the server.
540 Disable RFC4507bis session ticket support.
542 =item B<-sess_out filename>
544 Output SSL session to B<filename>.
546 =item B<-sess_in sess.pem>
548 Load SSL session from B<filename>. The client will attempt to resume a
549 connection from this session.
553 Specifying an engine (by its unique B<id> string) will cause B<s_client>
554 to attempt to obtain a functional reference to the specified engine,
555 thus initialising it if needed. The engine will then be set as the default
556 for all available algorithms.
558 =item B<-rand file...>
560 A file or files containing random data used to seed the random number
562 Multiple files can be specified separated by an OS-dependent character.
563 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
566 =item [B<-writerand file>]
568 Writes random data to the specified I<file> upon exit.
569 This can be used with a subsequent B<-rand> flag.
571 =item B<-serverinfo types>
573 A list of comma-separated TLS Extension Types (numbers between 0 and
574 65535). Each type will be sent as an empty ClientHello TLS Extension.
575 The server's response (if any) will be encoded and displayed as a PEM
580 Sends a certificate status request to the server (OCSP stapling). The server
581 response (if any) is printed out.
583 =item B<-alpn protocols>, B<-nextprotoneg protocols>
585 These flags enable the Enable the Application-Layer Protocol Negotiation
586 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
587 IETF standard and replaces NPN.
588 The B<protocols> list is a comma-separated list of protocol names that
589 the client should advertise support for. The list should contain the most
590 desirable protocols first. Protocol names are printable ASCII strings,
591 for example "http/1.1" or "spdy/3".
592 An empty list of protocols is treated specially and will cause the
593 client to advertise support for the TLS extension but disconnect just
594 after receiving ServerHello with a list of server supported protocols.
595 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
597 =item B<-ct>, B<-noct>
599 Use one of these two options to control whether Certificate Transparency (CT)
600 is enabled (B<-ct>) or disabled (B<-noct>).
601 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
602 the server and reported at handshake completion.
604 Enabling CT also enables OCSP stapling, as this is one possible delivery method
609 A file containing a list of known Certificate Transparency logs. See
610 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
612 =item B<-keylogfile file>
614 Appends TLS secrets to the specified keylog file such that external programs
615 (like Wireshark) can decrypt TLS connections.
617 =item B<-early_data file>
619 Reads the contents of the specified file and attempts to send it as early data
620 to the server. This will only work with resumed sessions that support early
621 data and when the server accepts the early data.
625 Rather than providing B<-connect>, the target hostname and optional port may
626 be provided as a single positional argument after all options. If neither this
627 nor B<-connect> are provided, falls back to attempting to connect to localhost
632 =head1 CONNECTED COMMANDS
634 If a connection is established with an SSL server then any data received
635 from the server is displayed and any key presses will be sent to the
636 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
637 have been given), the session will be renegotiated if the line begins with an
638 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
639 connection will be closed down.
643 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
646 openssl s_client -connect servername:443
648 would typically be used (https uses port 443). If the connection succeeds
649 then an HTTP command can be given such as "GET /" to retrieve a web page.
651 If the handshake fails then there are several possible causes, if it is
652 nothing obvious like no client certificate then the B<-bugs>,
653 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
654 in case it is a buggy server. In particular you should play with these
655 options B<before> submitting a bug report to an OpenSSL mailing list.
657 A frequent problem when attempting to get client certificates working
658 is that a web client complains it has no certificates or gives an empty
659 list to choose from. This is normally because the server is not sending
660 the clients certificate authority in its "acceptable CA list" when it
661 requests a certificate. By using B<s_client> the CA list can be viewed
662 and checked. However some servers only request client authentication
663 after a specific URL is requested. To obtain the list in this case it
664 is necessary to use the B<-prexit> option and send an HTTP request
665 for an appropriate page.
667 If a certificate is specified on the command line using the B<-cert>
668 option it will not be used unless the server specifically requests
669 a client certificate. Therefor merely including a client certificate
670 on the command line is no guarantee that the certificate works.
672 If there are problems verifying a server certificate then the
673 B<-showcerts> option can be used to show the whole chain.
675 The B<s_client> utility is a test tool and is designed to continue the
676 handshake after any certificate verification errors. As a result it will
677 accept any certificate chain (trusted or not) sent by the peer. None test
678 applications should B<not> do this as it makes them vulnerable to a MITM
679 attack. This behaviour can be changed by with the B<-verify_return_error>
680 option: any verify errors are then returned aborting the handshake.
684 Because this program has a lot of options and also because some of the
685 techniques used are rather old, the C source of B<s_client> is rather hard to
686 read and not a model of how things should be done.
687 A typical SSL client program would be much simpler.
689 The B<-prexit> option is a bit of a hack. We should really report
690 information whenever a session is renegotiated.
694 L<SSL_CONF_cmd(3)>, L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>,
695 L<SSL_CTX_set_max_send_fragment(3)>, L<SSL_CTX_set_split_send_fragment(3)>
696 L<SSL_CTX_set_max_pipelines(3)>
700 The B<-no_alt_chains> option was first added to OpenSSL 1.1.0.
701 The B<-name> option was added in OpenSSL 1.1.1.
705 Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
707 Licensed under the OpenSSL license (the "License"). You may not use
708 this file except in compliance with the License. You can obtain a copy
709 in the file LICENSE in the source distribution or at
710 L<https://www.openssl.org/source/license.html>.